noble gases in muong nong-type tektites and their implications · noble gases in muong nong-type...

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Meteoritics & Planetary Science 38, Nr 5, 747–758 (2003) Abstract available online at http://meteoritics.org 747 © Meteoritical Society, 2003. Printed in USA. Noble gases in Muong Nong-type tektites and their implications Sayaka MIZOTE, 1 Takuya MATSUMOTO, 1 Jun-ichi MATSUDA, 1* and Christian KOEBERL 2 1 Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560–0043, Japan 2 Department of Geological Sciences, University of Vienna, Althanstrasse 14, A–1090 Vienna, Austria * Corresponding author. E-mail: [email protected] (Received 25 June 2002; revision accepted 16 June 2003) Abstract–We have measured the elemental abundances and isotopic compositions of noble gases in Muong Nong-type tektites from the Australasian strewn field by crushing and by total fusion of the samples. We found that the abundances of the heavy noble gases are significantly enriched in Muong Nong-type tektites compared to those in normal splash-form tektites from the same strewn field. Neon enrichments were also observed in the Muong Nong-type tektites, but the Ne/Ar ratios were lower than those in splash-form tektites because of the higher Ar contents in the former. The absolute concentrations of the heavy noble gases in Muong Nong-type tektites are similar to those in impact glasses. The isotopic ratios of the noble gases in Muong Nong-type tektites are mostly identical to those in air, except for the presence of radiogenic 40 Ar. The obtained K-Ar ages for Muong Nong-type tektites were about 0.7 Myr, similar to ages of other Australasian tektites. The crushing experiments suggest that the noble gases in the Muong Nong-type tektites reside mostly in vesicles, although Xe was largely affected by adsorbed atmosphere after crushing. We used the partial pressure of the heavy noble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong-type tektites. Likely, Muong Nong-type tektites solidified at the altitude (between the surface and a maximum height of 8–30 km) lower than that for splash-form tektites. INTRODUCTION Tektites are a group of natural glasses occurring in 4 different strewn fields (North American, Central European, Ivory Coast, and Australasian strewn fields) on the Earth. Numerous geochemical and isotopic studies have confirmed the terrestrial impact origin of the tektites (e.g., Taylor 1973; King 1977; Koeberl 1986, 1990, 1994; Glass 1990; Montanari and Koeberl 2000). Although tektites and impact glasses have both been produced by impact melting of terrestrial surface rocks, differences between tektites and impact glasses exist (e.g., impact glasses are found directly at a crater, while tektites are distal ejecta that occur in a strewn field away from the source crater). Tektites can be divided into 3 groups. The first and second groups are splash-form tektites and aerodynamically shaped tektites. The third group is called Muong Nong-type tektites after the area in Laos from where they were first described by Lacroix (1935). Muong Nong-type tektites (also called “layered tektites”) differ in their appearance from other tektites by having irregular, blocky shapes, layered structures, and by their larger sizes (e.g., Glass 1990; Wasson 1991; Koeberl 1992, 1994). Muong Nong-type tektites are mostly found in the Indochina part of the Australasian strewn field, although, some of them have also been recovered from the Central European and North American strewn fields (e.g., Meisel et al. 1989; Glass et al. 1990, 1995). Chemically, Muong Nong-type tektites are enriched in volatile elements (e.g., Cl, Br, Zn, Cu, Pb) relative to splash-form and aerodynamically shaped tektites (e.g., Müller and Gentner 1973; Wasson 1991; Koeberl 1992). In addition to this compositional feature, petrographic evidence indicates a lower temperature origin for Muong Nong-type tektites than for other tektites (Glass and Barlow 1979; Barnes 1989; Koeberl 1992; Glass et al. 1995). However, uncertainty still exists regarding the formation mechanism of this particular type of tektite and its relation to the other tektite groups found in the Australasian strewn field. Being chemically inert and volatile, noble gases in tektites and impact glasses provide valuable information about the conditions of their formation (e.g., Matsuda et al. 1993). Matsuda et al. (1989) measured noble gas contents in Darwin impact glasses and found significant enrichments of neon compared to air. Neon enrichments have been recorded from silica-rich glasses, such as tektites (Hennecke et al. 1975; Matsubara and Matsuda 1991; Matsuda et al. 1993; 1996; Palma et al. 1997), impact glasses (Matsuda et al. 1989; Matsubara et al. 1991), and obsidians (Matsuda et al. 1989;

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Page 1: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

Meteoritics amp Planetary Science 38 Nr 5 747ndash758 (2003)Abstract available online at httpmeteoriticsorg

747 copy Meteoritical Society 2003 Printed in USA

Noble gases in Muong Nong-type tektites and their implications

Sayaka MIZOTE1 Takuya MATSUMOTO1 Jun-ichi MATSUDA1 and Christian KOEBERL2

1Department of Earth and Space Science Graduate School of Science Osaka University Toyonaka Osaka 560ndash0043 Japan2Department of Geological Sciences University of Vienna Althanstrasse 14 Andash1090 Vienna Austria

Corresponding author E-mail matsudaesssciosaka-uacjp

(Received 25 June 2002 revision accepted 16 June 2003)

AbstractndashWe have measured the elemental abundances and isotopic compositions of noble gases inMuong Nong-type tektites from the Australasian strewn field by crushing and by total fusion of thesamples We found that the abundances of the heavy noble gases are significantly enriched in MuongNong-type tektites compared to those in normal splash-form tektites from the same strewn field Neonenrichments were also observed in the Muong Nong-type tektites but the NeAr ratios were lowerthan those in splash-form tektites because of the higher Ar contents in the former The absoluteconcentrations of the heavy noble gases in Muong Nong-type tektites are similar to those in impactglasses The isotopic ratios of the noble gases in Muong Nong-type tektites are mostly identical tothose in air except for the presence of radiogenic 40Ar The obtained K-Ar ages for Muong Nong-typetektites were about 07 Myr similar to ages of other Australasian tektites The crushing experimentssuggest that the noble gases in the Muong Nong-type tektites reside mostly in vesicles although Xewas largely affected by adsorbed atmosphere after crushing We used the partial pressure of the heavynoble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong-typetektites Likely Muong Nong-type tektites solidified at the altitude (between the surface and amaximum height of 8ndash30 km) lower than that for splash-form tektites

INTRODUCTION

Tektites are a group of natural glasses occurring in 4different strewn fields (North American Central EuropeanIvory Coast and Australasian strewn fields) on the EarthNumerous geochemical and isotopic studies have confirmedthe terrestrial impact origin of the tektites (eg Taylor 1973King 1977 Koeberl 1986 1990 1994 Glass 1990Montanari and Koeberl 2000) Although tektites and impactglasses have both been produced by impact melting ofterrestrial surface rocks differences between tektites andimpact glasses exist (eg impact glasses are found directly ata crater while tektites are distal ejecta that occur in a strewnfield away from the source crater)

Tektites can be divided into 3 groups The first andsecond groups are splash-form tektites and aerodynamicallyshaped tektites The third group is called Muong Nong-typetektites after the area in Laos from where they were firstdescribed by Lacroix (1935) Muong Nong-type tektites (alsocalled ldquolayered tektitesrdquo) differ in their appearance from othertektites by having irregular blocky shapes layered structuresand by their larger sizes (eg Glass 1990 Wasson 1991Koeberl 1992 1994) Muong Nong-type tektites are mostlyfound in the Indochina part of the Australasian strewn field

although some of them have also been recovered from theCentral European and North American strewn fields (egMeisel et al 1989 Glass et al 1990 1995) ChemicallyMuong Nong-type tektites are enriched in volatile elements(eg Cl Br Zn Cu Pb) relative to splash-form andaerodynamically shaped tektites (eg Muumlller and Gentner1973 Wasson 1991 Koeberl 1992) In addition to thiscompositional feature petrographic evidence indicates alower temperature origin for Muong Nong-type tektites thanfor other tektites (Glass and Barlow 1979 Barnes 1989Koeberl 1992 Glass et al 1995) However uncertainty stillexists regarding the formation mechanism of this particulartype of tektite and its relation to the other tektite groups foundin the Australasian strewn field

Being chemically inert and volatile noble gases intektites and impact glasses provide valuable informationabout the conditions of their formation (eg Matsuda et al1993) Matsuda et al (1989) measured noble gas contents inDarwin impact glasses and found significant enrichments ofneon compared to air Neon enrichments have been recordedfrom silica-rich glasses such as tektites (Hennecke et al1975 Matsubara and Matsuda 1991 Matsuda et al 19931996 Palma et al 1997) impact glasses (Matsuda et al 1989Matsubara et al 1991) and obsidians (Matsuda et al 1989

748 S Mizote et al

Miura and Nagao 1991) A laboratory study clearlydemonstrated that these neon enrichments are due to the fasterdiffusion of neon compared with the heavier noble gases inglasses after solidification (Matsubara and Matsuda 1995)Neon concentrations in these glasses are rather uniformreflecting neon saturation in silica-rich glasses irrespective oftheir types In contrast there is a systematic difference in theconcentration of the heavier noble gases between tektites andimpact glassesmdashheavy noble gases are depleted in tektitescompared to impact glasses and can be used as tracers to inferthe height during their solidification (Matsuda et al 1993)Later Palma et al (1997) reported that Xe concentrations inNorth American tektites were similar to those of impactglasses and that Kr concentrations in these tektites werebetween those in impact glasses and tektites from otherstrewn fields

So far our knowledge on noble gases in the MuongNong-type tektites is based on a limited data set only 4samples had been analyzed by heating gas extraction(Jessberger and Gentner 1972 Murty 1997) Here we presentthe first comprehensive noble gas survey of Muong Nong-type tektites based on 16 total analyses Because tektites havevesicles in which noble gases are likely to be trapped weextracted the noble gases not only by heating but also bycrushing to better understand the formation processes oftektites from their noble gas abundance and isotopic ratiosMuong Nong-type tektites are of particular interest because1) they are compositionally different from splash-formtektites and 2) they are found only in a limited region in theAustralasian strewn field without an identified sourcecrater(s) Based on the new data we discuss the formation ofMuong Nong-type tektites and their relation to the splash-form Australasian tektites

SAMPLES AND ANALYSES

We analyzed a well-documented suite of Muong Nong-type tektites from Ubon Ratchatani in East Thailand (7samples) near the border of Laos and one sample (MN X-103) from southern Laos Detailed descriptions and chemicalcompositions for those and related samples were given inprevious papers (Glass and Koeberl 1989 Blum et al 1992Koeberl 1992 Beran and Koeberl 1997)

To avoid (known) heterogeneities in the vesiclepopulation samples were coarsely crushed and fragmentswith sizes between 118 to 170 mm were selected Thesamples were subsequently washed in an ultrasonic bath withdistilled water acetone and ethanol for 30 min each Afterdrying overnight in an oven at ~100degC about 03 g of thecrushed samples were loaded into stainless-steel samplecontainers in the crusher with 6 holders (Matsumoto et al2001) To determine the procedural blank levels at least 1container was loaded without a sample

Details of gas handling and purification as well as massspectrometry by the VG5400 noble gas mass spectrometer

are described in our previous publications (Wada andMatsuda 1998 Matsumoto et al 2001) Sensitivity andisotope discrimination of the mass spectrometer werecalibrated by analyzing known amounts of air aliquots (NeAr Kr and Xe) and the synthetic mixture of 3He and 4He(HESJ Standard 3He4He = (2888 plusmn 0014) acute 10-5 Matsudaet al 2002)

After the blank analysis each sample was crushed in avacuum by being hit by the piston for about 1000 strokesand the elemental concentrations and isotopic ratios of noblegases were measured The crushed samples were taken outof the vacuum line and were sieved under atmosphericpressure The grains with sizes lt150 mm were regarded asthose that release gases from vesicles and we normalized theelemental concentrations of the noble gases to the mass ofthe grains having sizes lt150 mm (samples and data labeledldquoCrushingrdquo in Tables 1ndash4) These crushed grains were againplaced in the vacuum line and were subsequently heated toanalyze the noble gases in the glass matrix (samples and datalabeled ldquoHeatingrdquo) Note that thin section observationrevealed the presence of vesicles lt150 mm thus theconcentrations of the noble gases measured by melting thegrains lt150 mm should be regarded as the upper limit ofgases trapped in glass matrix

Typical crusher blank levels were 30 10-10 34 10-1127 acute 10-11 12 acute 10-12 and 12 acute 10-14 cm3 STP for 4He20Ne 36Ar 84Kr and 130Xe respectively The hot blanks for4He 20Ne 36Ar 84Kr and 130Xe were 13 acute 10-8 19 acute 10-1029 acute 10-10 95 10-12 and 27 10-13 cm3 STP respectivelyIn many cases the helium fraction released during the samplerun was similar to the blank level Typically the crusher blankcontributed only a few percent of the sample value for theheavy noble gases Thus blank corrections with isotopicallyatmospheric compositions were applied to all results obtainedby crushing extraction The hot blank contribution wasslightly higher and was in many cases about 10 of thesample fraction Blank corrections were applied to allsamples unless the corrections exceeded 30 in which casewe only reported the uncorrected result of elementalabundance as an upper limit

RESULTS

The elemental and isotopic compositions of the noblegases extracted from the Muong Nong-type tektites arereported in Tables 1ndash4

Elemental Abundance

To compare the elemental abundance patterns of theMuong Nong-type tektites to those of air fractionation factors(F[m]) are shown in Fig 1 The fractionation factor is definedby the equation

(1)F m( ) Xm

Ar36curren( )sample X

mAr

36curren( )curren air=

Noble gases in Muong Nong-type tektites 749

where mX represents a noble gas isotope of mass ldquomrdquo Heliumdata are not included because of their low abundances(possibly due to diffusive loss after tektite formation and inthe vacuum of the extraction system) As shown in Figs 1aand 1b the samples have F(20) values well above unityindicating a neon enrichment relative to argon No systematicdifference exists in the degrees of neon enrichment in thecrushing and heating experiments Interestingly the observedF(20) values in Muong Nong-type tektites (26 to 37) aresignificantly lower than those of normal tektites (200 to 7130Matsubara and Matsuda 1991) In fact the range of F(20)values for Muong Nong-type tektites agrees well withpreviously reported values for impact glasses (Matsuda et al1989 Matsubara et al 1991) Note that the difference in theF(20) values is not due to differences in neon concentrationbetween Muong Nong-type tektites and normal tektites Asshown in Fig 2 both types of tektites have relatively uniform20Ne concentrations (~10-7 cm3 STPg) Matsubara andMatsuda (1995) concluded that neon in natural silica glasseshas completely exchanged with atmospheric neon by rapiddiffusion after their formation Thus a relatively uniformrange of neon concentrations in these glasses reflects thesaturation level that can be acquired by diffusive input

Therefore systematically smaller F(20) values in MuongNong-type tektites should reflect their relatively high argonconcentrations As shown in Fig 2 the range of 36Arconcentrations in Muong Nong-type tektites are at least 1order of magnitude larger than those in splash-form tektitesand agree well with concentrations reported for impactglasses

Values of F(84) and F(130) for gases released bycrushing are consistent with atmospheric composition Incontrast gases extracted by the heating of powdered samplesyielded F(130) values significantly higher than unityindicating that the released fraction is enriched in xenon withrespect to the atmospheric composition This is probably dueto the adsorption of xenon onto the surface of the powderedgrains because xenon is the most easily adsorbed of all thenoble gases (Matsubara and Matsuda 1995) The potential ofldquoirreversiblerdquo adsorption is reported by Niedermann andEugster (1992) However the effect of adsorption ofatmosphere is only shown in the heated samples Our resultsindicate that noble gases in the Muong Nong-type tektitevesicles cannot have originated from atmospheric gasesadsorbed on sediments that were released during the tektite-forming heating event This is because fractionation values of

Table 1 He and Ne concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 4He(10-9 cm3 STPg)

3He4He(10-6)

20Ne(10-8 cm3 STPg)

20Ne22Ne 21Ne22Ne

CrushingMN 8301 0135 g times1000 lt29 ndash 43 945 plusmn 016 00285 plusmn 00008MN 8307 0203 g times1000 29 ndash 72 984 plusmn 003 00298 plusmn 00006

ndash times2000 lt18 ndash 063 970 plusmn 011 00301 plusmn 00007ndash Total lt47 ndash 79 982 plusmn 003 00298 plusmn 00006

MN 8309 0150 g times1000 lt29 ndash 82 984 plusmn 010 00293 plusmn 00006MN 8310 0165 g times1000 lt41 ndash 39 975 plusmn 011 00290 plusmn 00006MN 8311 0128 g times1000 lt22 ndash 79 976 plusmn 011 00291 plusmn 00006MN 8317 0151 g times1000 34 ndash 11 974 plusmn 011 00288 plusmn 00006MN 8318 0155 g times900 29 ndash 11 100 plusmn 02 00289 plusmn 00009MN X-103 0223 g times1000 57 160 plusmn 030 18 995 plusmn 012 00294 plusmn 00006

HeatingMN 8301 0110 g 1800degC lt22 ndash 19 955 plusmn 017 00272 plusmn 00008MN 8307 0189 g 800degC 37 ndash 20 957 plusmn 016 00292 plusmn 00007

ndash 1200degC lt21 ndash lt0008 ndash ndashndash 1600degC lt11 ndash lt0011 ndash ndashndash 1800degC 11 ndash lt0013 ndash ndashndash Total lt80 ndash lt21 ndash ndash

MN 8309 0148 g 1800degC 15 ndash 20 971 plusmn 017 00312 plusmn 00008MN 8310 0135 g 1800degC lt20 ndash 23 969 plusmn 008 00288 plusmn 00004MN 8311 0128 g 1800degC lt18 ndash 24 951 plusmn 006 00290 plusmn 00002MN 8317 0121 g 1800degC lt21 ndash 31 955 plusmn 005 00288 plusmn 00002MN 8318 0144 g 1800degC lt17 ndash 21 948 plusmn 005 00281 plusmn 00003MN X-103 0181 g 1800degC lt13 ndash 028 983 plusmn 031 00296 plusmn 00010

Air ndash ndash ndash 14 ndash 980 00290aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

750 S Mizote et al

the heavy noble gases (Kr Xe) are almost unity (see Fig 1a)in contrast to patterns for adsorbed gases In the case ofadsorption the heavy noble gases are highly fractionated andF(84) and F(130) values are about 10 or more (eg Matsudaand Nagao 1986)

Isotopic Ratios

As shown in Tables 1ndash4 almost all isotopic ratios exceptthe 40Ar36Ar ratios are consistent with atmosphericcompositions within experimental uncertainties The 20Ne

22Ne and 21Ne22Ne ratios in the heated samples are slightlylower than the atmospheric values (Table 1) but the Ne ratiosin the crushed samples are almost identical to the atmosphericvalues The low Ne ratios in the heated samples may be due tothe mass fractionation effect with the gas release by priorcrushing Up to about 80 of the Ne was released bycrushing and the Ne isotopic ratios are identical toatmospheric values Thus we can regard that Ne in the wholesample originated mostly from the air

Such an occurrence of isotopically air-like noble gases isa common characteristic of glassy materials of terrestrial

Fig 1 Elemental abundance patterns of noble gases in Muong Nong-type tektites are plotted as the fractionation factor F(m) (see text forexplanation) relative to the atmospheric composition a) values obtained by the crushing method b) data from the heating method F(4) valuesare not shown as helium abundances are as low as the procedural blank levels The shaded area labeled ldquoTektitesrdquo shows the range of F(20)values (200 ndash7130) reported previously for splash-form tektites (Matsubara and Matsuda 1991)

Noble gases in Muong Nong-type tektites 751

impact origin (such as tektites and impact glasses) Previouswork on Muong Nong-type tektites also reported atmosphere-like isotopic compositions (Jessberger and Gentner 1972Murty 1997) As to the 40Ar36Ar ratios note that 40Ar36Arratios higher than the atmospheric ratio of 2955 were foundfor gases released by crushing suggesting that someradiogenic 40Ar is also released by crushing from glassmatrix This is often observed in crushing experiments (egMatsumoto et al 2002)

K-Ar ages

By using the observed radiogenic 40Ar in gases releasedby total fusion as well as the potassium content of eachsample (Koeberl 1992) calculating approximate K-Ar ages ofthe samples is possible The ages with uncertainties smallerthan 50 are 071 plusmn 034 Myr (MN 8309) 067 plusmn 014 Myr(MN 8311) 064 plusmn 014 Myr (MN 8317) and 073 plusmn 015 Myr(MN 8318) (other samples have significantly largeruncertainties due to low amounts of radiogenic 40Ar) Theobtained ages may give values lower than the real agesbecause some radiogenic 40Ar was released by crushingbefore fusion This may be the case for MN 8311 and MN8317 which yielded relatively shorter ages and is consistentwith 40Ar36Ar ratios greater than the atmospheric ratio at thecrushing However applying corrections to K-Ar ages forsuch a loss of radiogenic 40Ar by prior crushing is quitedifficult because the radiogenic 40Ar released by crushingcannot easily be expressed in units of cm3 STPg Note that

argon concentrations in Table 2 are calculated based on theassumption that the grains smaller than 150 mm had gasestrapped in vesicles of gt150 mm Likely the concentrations ofradiogenic 40Ar by crushing are overestimates because of thenormalization to small masses

At any rate we assume the effect of radiogenic 40Ar lossby crushing is negligible for correcting ages obtained fromheating of the lt150 mm fraction because the ages of ~07 Myragreed with each other within their 2 sigma errors and moreimportantly they agree with the reported Ar-Ar ages ofAustralasian tektites (077 plusmn 002 Myr Izett and Obradovich1992) and with fission track ages for Muong Nong-typeindochinitesmdashabout 07 Myr (Storzer and Wagner 1977Bigazzi and Michele 1996) implying that Muong Nong-typetektites are formed by a common event with other Australasiantektites Note also that the K-Ar ages reported here are only abyproduct of our analyses and are not the main goal

DISCUSSION

Noble Gas Distribution

Because we have analyzed the samples both by crushingand by total fusion we can estimate the fractions of noblegases dissolved in the glass and trapped in the vesiclesrespectively We regard the amounts of Ne Ar Kr and Xereleased by crushing to represent the noble gases trapped invesicles Gases released from samples with grain sizes of lt150mm were regarded to represent the concentrations in the matrix

Fig 2 Concentrations of 20Ne (closed diamond) and 36Ar (open circle) for tektites from 4 strewn fields (Hennecke et al 1975 Matsubara andMatsuda 1991 Matsuda et al 1993 Palma et al 1997) and impact glasses Darwin glass (Matsuda et al 1989) Libyan Desert glassZhamanshin glass and Aouelloul glass (Matsubara et al 1991) The neon concentrations in all samples are confined to a small range Theargon concentrations in Muong Nong-type tektites are close to those reported for impact glasses The arrows indicate upper limits

752 S Mizote et al

glass As shown in Fig 3 the present samples appear to haveroughly 70 to 85 of Ne Ar and Kr in their vesicles A largeramount of xenon seems to be dissolved in the glass comparedto other noble gases However we can estimate the Xe amountin glass from the atmospheric XeAr ratio and the observed Arabundance in the glass The abundances of xenon in glasswould be about 19 to 139 of the total amount observed in thepowdered samples as shown in Fig 1b The correctionindicates that about 80ndash85 of Xe resides in vesicles

Likely the observed noble gases from the powderedsamples are also released from small vesicles (lt150 mm) ratherthan from the glass matrix itself In this case the fraction of gasresiding in vesicles should be higher than the values above

Altitude of Closure and Noble Gases in Muong Nong-TypeTektites

Noble gases trapped in vesicles may record the ambientatmospheric pressure of the altitude at which the tektitessolidified First we attempt to estimate the volumes of thevesicles that were crushed to release gases in each samplewhich is necessary to estimate the internal noble gas pressuresin the vesicles Note that the volumes estimated from thin

sections might not be useful because of the heterogeneousdistribution of the vesicles and uncertainty relatingincomplete crushing of smaller vesicles ie we need todetermine the volume of the vesicles that were actuallycrushed in the experiment Thus we estimated an ldquoactualexperimental vesicle volumerdquo (ldquoeffectiverdquo vesicularity) usingthe neon contents as described below

The reason that neon concentrations in the presentsamples are useful to determine the samplersquos effectivevesicularity lies in the high diffusivity of neon in glassMatsubara and Matsuda (1995) showed experimentally thatneon can diffuse into 149ndash250 mm obsidian grains and that itsconcentration approached saturation at room temperature fortime scales of several tens of days which results inpreferential acquisition of neon compared to heavier noblegases Because K-Ar ages of these Muong Nong-type tektitesare about 07 Myr we can reasonably assume that the partialpressure of neon in the vesicles is in equilibrium with that ofair Thus we may estimate the effective vesicularity of thesamples from the following equation

(2)

Table 2 Ar concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 36Ar(10-9 cm3STPg)

38Ar36Ar 40Ar36Ar

CrushingMN 8301 0135 g times1000 76 01909 plusmn 00033 3110 plusmn 50MN 8307 0203 g times1000 59 01928 plusmn 00043 3019 plusmn 56

times2000 04 01896 plusmn 00030 3154 plusmn 68Total 63 01926 plusmn 00040 3027 plusmn 53

MN 8309 0150 g times1000 15 01881 plusmn 00012 2970 plusmn 32MN 8310 0165 g times1000 29 01868 plusmn 00013 2937 plusmn 32MN 8311 0128 g times1000 11 01889 plusmn 00020 3051 plusmn 36MN 8317 0151 g times1000 56 01888 plusmn 00025 3048 plusmn 46MN 8318 0155 g times900 79 01809 plusmn 00017 2823 plusmn 104MN X-103 0223 g times1000 70 01881 plusmn 00012 3074 plusmn 35

HeatingMN 8301 0110 g 1800degC 27 01869 plusmn 00012 3049 plusmn 124MN 8307 0189 g 800degC 063 01874 plusmn 00012 4125 plusmn 292

ndash 1200degC 039 ndash ndashndash 1600degC 029 ndash ndashndash 1800degC 036 ndash ndashndash Total 17 ndash ndash

MN 8309 0148 g 1800degC 23 01884 plusmn 00011 3215 plusmn 120MN 8310 0135 g 1800degC 46 01884 plusmn 00031 3049 plusmn 47MN 8311 0128 g 1800degC 39 01878 plusmn 00007 3102 plusmn 24MN 8317 0121 g 1800degC 23 01888 plusmn 00019 3197 plusmn 38MN 8318 0144 g 1800degC 20 01866 plusmn 00011 3234 plusmn 41MN X-103 0181 g 1800degC 14 01889 plusmn 00023 3335 plusmn 58

Air ndash ndash ndash 01880 2955aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

Vvesicle M CNe

20 PNe

20air( )

currenacute=

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 2: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

748 S Mizote et al

Miura and Nagao 1991) A laboratory study clearlydemonstrated that these neon enrichments are due to the fasterdiffusion of neon compared with the heavier noble gases inglasses after solidification (Matsubara and Matsuda 1995)Neon concentrations in these glasses are rather uniformreflecting neon saturation in silica-rich glasses irrespective oftheir types In contrast there is a systematic difference in theconcentration of the heavier noble gases between tektites andimpact glassesmdashheavy noble gases are depleted in tektitescompared to impact glasses and can be used as tracers to inferthe height during their solidification (Matsuda et al 1993)Later Palma et al (1997) reported that Xe concentrations inNorth American tektites were similar to those of impactglasses and that Kr concentrations in these tektites werebetween those in impact glasses and tektites from otherstrewn fields

So far our knowledge on noble gases in the MuongNong-type tektites is based on a limited data set only 4samples had been analyzed by heating gas extraction(Jessberger and Gentner 1972 Murty 1997) Here we presentthe first comprehensive noble gas survey of Muong Nong-type tektites based on 16 total analyses Because tektites havevesicles in which noble gases are likely to be trapped weextracted the noble gases not only by heating but also bycrushing to better understand the formation processes oftektites from their noble gas abundance and isotopic ratiosMuong Nong-type tektites are of particular interest because1) they are compositionally different from splash-formtektites and 2) they are found only in a limited region in theAustralasian strewn field without an identified sourcecrater(s) Based on the new data we discuss the formation ofMuong Nong-type tektites and their relation to the splash-form Australasian tektites

SAMPLES AND ANALYSES

We analyzed a well-documented suite of Muong Nong-type tektites from Ubon Ratchatani in East Thailand (7samples) near the border of Laos and one sample (MN X-103) from southern Laos Detailed descriptions and chemicalcompositions for those and related samples were given inprevious papers (Glass and Koeberl 1989 Blum et al 1992Koeberl 1992 Beran and Koeberl 1997)

To avoid (known) heterogeneities in the vesiclepopulation samples were coarsely crushed and fragmentswith sizes between 118 to 170 mm were selected Thesamples were subsequently washed in an ultrasonic bath withdistilled water acetone and ethanol for 30 min each Afterdrying overnight in an oven at ~100degC about 03 g of thecrushed samples were loaded into stainless-steel samplecontainers in the crusher with 6 holders (Matsumoto et al2001) To determine the procedural blank levels at least 1container was loaded without a sample

Details of gas handling and purification as well as massspectrometry by the VG5400 noble gas mass spectrometer

are described in our previous publications (Wada andMatsuda 1998 Matsumoto et al 2001) Sensitivity andisotope discrimination of the mass spectrometer werecalibrated by analyzing known amounts of air aliquots (NeAr Kr and Xe) and the synthetic mixture of 3He and 4He(HESJ Standard 3He4He = (2888 plusmn 0014) acute 10-5 Matsudaet al 2002)

After the blank analysis each sample was crushed in avacuum by being hit by the piston for about 1000 strokesand the elemental concentrations and isotopic ratios of noblegases were measured The crushed samples were taken outof the vacuum line and were sieved under atmosphericpressure The grains with sizes lt150 mm were regarded asthose that release gases from vesicles and we normalized theelemental concentrations of the noble gases to the mass ofthe grains having sizes lt150 mm (samples and data labeledldquoCrushingrdquo in Tables 1ndash4) These crushed grains were againplaced in the vacuum line and were subsequently heated toanalyze the noble gases in the glass matrix (samples and datalabeled ldquoHeatingrdquo) Note that thin section observationrevealed the presence of vesicles lt150 mm thus theconcentrations of the noble gases measured by melting thegrains lt150 mm should be regarded as the upper limit ofgases trapped in glass matrix

Typical crusher blank levels were 30 10-10 34 10-1127 acute 10-11 12 acute 10-12 and 12 acute 10-14 cm3 STP for 4He20Ne 36Ar 84Kr and 130Xe respectively The hot blanks for4He 20Ne 36Ar 84Kr and 130Xe were 13 acute 10-8 19 acute 10-1029 acute 10-10 95 10-12 and 27 10-13 cm3 STP respectivelyIn many cases the helium fraction released during the samplerun was similar to the blank level Typically the crusher blankcontributed only a few percent of the sample value for theheavy noble gases Thus blank corrections with isotopicallyatmospheric compositions were applied to all results obtainedby crushing extraction The hot blank contribution wasslightly higher and was in many cases about 10 of thesample fraction Blank corrections were applied to allsamples unless the corrections exceeded 30 in which casewe only reported the uncorrected result of elementalabundance as an upper limit

RESULTS

The elemental and isotopic compositions of the noblegases extracted from the Muong Nong-type tektites arereported in Tables 1ndash4

Elemental Abundance

To compare the elemental abundance patterns of theMuong Nong-type tektites to those of air fractionation factors(F[m]) are shown in Fig 1 The fractionation factor is definedby the equation

(1)F m( ) Xm

Ar36curren( )sample X

mAr

36curren( )curren air=

Noble gases in Muong Nong-type tektites 749

where mX represents a noble gas isotope of mass ldquomrdquo Heliumdata are not included because of their low abundances(possibly due to diffusive loss after tektite formation and inthe vacuum of the extraction system) As shown in Figs 1aand 1b the samples have F(20) values well above unityindicating a neon enrichment relative to argon No systematicdifference exists in the degrees of neon enrichment in thecrushing and heating experiments Interestingly the observedF(20) values in Muong Nong-type tektites (26 to 37) aresignificantly lower than those of normal tektites (200 to 7130Matsubara and Matsuda 1991) In fact the range of F(20)values for Muong Nong-type tektites agrees well withpreviously reported values for impact glasses (Matsuda et al1989 Matsubara et al 1991) Note that the difference in theF(20) values is not due to differences in neon concentrationbetween Muong Nong-type tektites and normal tektites Asshown in Fig 2 both types of tektites have relatively uniform20Ne concentrations (~10-7 cm3 STPg) Matsubara andMatsuda (1995) concluded that neon in natural silica glasseshas completely exchanged with atmospheric neon by rapiddiffusion after their formation Thus a relatively uniformrange of neon concentrations in these glasses reflects thesaturation level that can be acquired by diffusive input

Therefore systematically smaller F(20) values in MuongNong-type tektites should reflect their relatively high argonconcentrations As shown in Fig 2 the range of 36Arconcentrations in Muong Nong-type tektites are at least 1order of magnitude larger than those in splash-form tektitesand agree well with concentrations reported for impactglasses

Values of F(84) and F(130) for gases released bycrushing are consistent with atmospheric composition Incontrast gases extracted by the heating of powdered samplesyielded F(130) values significantly higher than unityindicating that the released fraction is enriched in xenon withrespect to the atmospheric composition This is probably dueto the adsorption of xenon onto the surface of the powderedgrains because xenon is the most easily adsorbed of all thenoble gases (Matsubara and Matsuda 1995) The potential ofldquoirreversiblerdquo adsorption is reported by Niedermann andEugster (1992) However the effect of adsorption ofatmosphere is only shown in the heated samples Our resultsindicate that noble gases in the Muong Nong-type tektitevesicles cannot have originated from atmospheric gasesadsorbed on sediments that were released during the tektite-forming heating event This is because fractionation values of

Table 1 He and Ne concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 4He(10-9 cm3 STPg)

3He4He(10-6)

20Ne(10-8 cm3 STPg)

20Ne22Ne 21Ne22Ne

CrushingMN 8301 0135 g times1000 lt29 ndash 43 945 plusmn 016 00285 plusmn 00008MN 8307 0203 g times1000 29 ndash 72 984 plusmn 003 00298 plusmn 00006

ndash times2000 lt18 ndash 063 970 plusmn 011 00301 plusmn 00007ndash Total lt47 ndash 79 982 plusmn 003 00298 plusmn 00006

MN 8309 0150 g times1000 lt29 ndash 82 984 plusmn 010 00293 plusmn 00006MN 8310 0165 g times1000 lt41 ndash 39 975 plusmn 011 00290 plusmn 00006MN 8311 0128 g times1000 lt22 ndash 79 976 plusmn 011 00291 plusmn 00006MN 8317 0151 g times1000 34 ndash 11 974 plusmn 011 00288 plusmn 00006MN 8318 0155 g times900 29 ndash 11 100 plusmn 02 00289 plusmn 00009MN X-103 0223 g times1000 57 160 plusmn 030 18 995 plusmn 012 00294 plusmn 00006

HeatingMN 8301 0110 g 1800degC lt22 ndash 19 955 plusmn 017 00272 plusmn 00008MN 8307 0189 g 800degC 37 ndash 20 957 plusmn 016 00292 plusmn 00007

ndash 1200degC lt21 ndash lt0008 ndash ndashndash 1600degC lt11 ndash lt0011 ndash ndashndash 1800degC 11 ndash lt0013 ndash ndashndash Total lt80 ndash lt21 ndash ndash

MN 8309 0148 g 1800degC 15 ndash 20 971 plusmn 017 00312 plusmn 00008MN 8310 0135 g 1800degC lt20 ndash 23 969 plusmn 008 00288 plusmn 00004MN 8311 0128 g 1800degC lt18 ndash 24 951 plusmn 006 00290 plusmn 00002MN 8317 0121 g 1800degC lt21 ndash 31 955 plusmn 005 00288 plusmn 00002MN 8318 0144 g 1800degC lt17 ndash 21 948 plusmn 005 00281 plusmn 00003MN X-103 0181 g 1800degC lt13 ndash 028 983 plusmn 031 00296 plusmn 00010

Air ndash ndash ndash 14 ndash 980 00290aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

750 S Mizote et al

the heavy noble gases (Kr Xe) are almost unity (see Fig 1a)in contrast to patterns for adsorbed gases In the case ofadsorption the heavy noble gases are highly fractionated andF(84) and F(130) values are about 10 or more (eg Matsudaand Nagao 1986)

Isotopic Ratios

As shown in Tables 1ndash4 almost all isotopic ratios exceptthe 40Ar36Ar ratios are consistent with atmosphericcompositions within experimental uncertainties The 20Ne

22Ne and 21Ne22Ne ratios in the heated samples are slightlylower than the atmospheric values (Table 1) but the Ne ratiosin the crushed samples are almost identical to the atmosphericvalues The low Ne ratios in the heated samples may be due tothe mass fractionation effect with the gas release by priorcrushing Up to about 80 of the Ne was released bycrushing and the Ne isotopic ratios are identical toatmospheric values Thus we can regard that Ne in the wholesample originated mostly from the air

Such an occurrence of isotopically air-like noble gases isa common characteristic of glassy materials of terrestrial

Fig 1 Elemental abundance patterns of noble gases in Muong Nong-type tektites are plotted as the fractionation factor F(m) (see text forexplanation) relative to the atmospheric composition a) values obtained by the crushing method b) data from the heating method F(4) valuesare not shown as helium abundances are as low as the procedural blank levels The shaded area labeled ldquoTektitesrdquo shows the range of F(20)values (200 ndash7130) reported previously for splash-form tektites (Matsubara and Matsuda 1991)

Noble gases in Muong Nong-type tektites 751

impact origin (such as tektites and impact glasses) Previouswork on Muong Nong-type tektites also reported atmosphere-like isotopic compositions (Jessberger and Gentner 1972Murty 1997) As to the 40Ar36Ar ratios note that 40Ar36Arratios higher than the atmospheric ratio of 2955 were foundfor gases released by crushing suggesting that someradiogenic 40Ar is also released by crushing from glassmatrix This is often observed in crushing experiments (egMatsumoto et al 2002)

K-Ar ages

By using the observed radiogenic 40Ar in gases releasedby total fusion as well as the potassium content of eachsample (Koeberl 1992) calculating approximate K-Ar ages ofthe samples is possible The ages with uncertainties smallerthan 50 are 071 plusmn 034 Myr (MN 8309) 067 plusmn 014 Myr(MN 8311) 064 plusmn 014 Myr (MN 8317) and 073 plusmn 015 Myr(MN 8318) (other samples have significantly largeruncertainties due to low amounts of radiogenic 40Ar) Theobtained ages may give values lower than the real agesbecause some radiogenic 40Ar was released by crushingbefore fusion This may be the case for MN 8311 and MN8317 which yielded relatively shorter ages and is consistentwith 40Ar36Ar ratios greater than the atmospheric ratio at thecrushing However applying corrections to K-Ar ages forsuch a loss of radiogenic 40Ar by prior crushing is quitedifficult because the radiogenic 40Ar released by crushingcannot easily be expressed in units of cm3 STPg Note that

argon concentrations in Table 2 are calculated based on theassumption that the grains smaller than 150 mm had gasestrapped in vesicles of gt150 mm Likely the concentrations ofradiogenic 40Ar by crushing are overestimates because of thenormalization to small masses

At any rate we assume the effect of radiogenic 40Ar lossby crushing is negligible for correcting ages obtained fromheating of the lt150 mm fraction because the ages of ~07 Myragreed with each other within their 2 sigma errors and moreimportantly they agree with the reported Ar-Ar ages ofAustralasian tektites (077 plusmn 002 Myr Izett and Obradovich1992) and with fission track ages for Muong Nong-typeindochinitesmdashabout 07 Myr (Storzer and Wagner 1977Bigazzi and Michele 1996) implying that Muong Nong-typetektites are formed by a common event with other Australasiantektites Note also that the K-Ar ages reported here are only abyproduct of our analyses and are not the main goal

DISCUSSION

Noble Gas Distribution

Because we have analyzed the samples both by crushingand by total fusion we can estimate the fractions of noblegases dissolved in the glass and trapped in the vesiclesrespectively We regard the amounts of Ne Ar Kr and Xereleased by crushing to represent the noble gases trapped invesicles Gases released from samples with grain sizes of lt150mm were regarded to represent the concentrations in the matrix

Fig 2 Concentrations of 20Ne (closed diamond) and 36Ar (open circle) for tektites from 4 strewn fields (Hennecke et al 1975 Matsubara andMatsuda 1991 Matsuda et al 1993 Palma et al 1997) and impact glasses Darwin glass (Matsuda et al 1989) Libyan Desert glassZhamanshin glass and Aouelloul glass (Matsubara et al 1991) The neon concentrations in all samples are confined to a small range Theargon concentrations in Muong Nong-type tektites are close to those reported for impact glasses The arrows indicate upper limits

752 S Mizote et al

glass As shown in Fig 3 the present samples appear to haveroughly 70 to 85 of Ne Ar and Kr in their vesicles A largeramount of xenon seems to be dissolved in the glass comparedto other noble gases However we can estimate the Xe amountin glass from the atmospheric XeAr ratio and the observed Arabundance in the glass The abundances of xenon in glasswould be about 19 to 139 of the total amount observed in thepowdered samples as shown in Fig 1b The correctionindicates that about 80ndash85 of Xe resides in vesicles

Likely the observed noble gases from the powderedsamples are also released from small vesicles (lt150 mm) ratherthan from the glass matrix itself In this case the fraction of gasresiding in vesicles should be higher than the values above

Altitude of Closure and Noble Gases in Muong Nong-TypeTektites

Noble gases trapped in vesicles may record the ambientatmospheric pressure of the altitude at which the tektitessolidified First we attempt to estimate the volumes of thevesicles that were crushed to release gases in each samplewhich is necessary to estimate the internal noble gas pressuresin the vesicles Note that the volumes estimated from thin

sections might not be useful because of the heterogeneousdistribution of the vesicles and uncertainty relatingincomplete crushing of smaller vesicles ie we need todetermine the volume of the vesicles that were actuallycrushed in the experiment Thus we estimated an ldquoactualexperimental vesicle volumerdquo (ldquoeffectiverdquo vesicularity) usingthe neon contents as described below

The reason that neon concentrations in the presentsamples are useful to determine the samplersquos effectivevesicularity lies in the high diffusivity of neon in glassMatsubara and Matsuda (1995) showed experimentally thatneon can diffuse into 149ndash250 mm obsidian grains and that itsconcentration approached saturation at room temperature fortime scales of several tens of days which results inpreferential acquisition of neon compared to heavier noblegases Because K-Ar ages of these Muong Nong-type tektitesare about 07 Myr we can reasonably assume that the partialpressure of neon in the vesicles is in equilibrium with that ofair Thus we may estimate the effective vesicularity of thesamples from the following equation

(2)

Table 2 Ar concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 36Ar(10-9 cm3STPg)

38Ar36Ar 40Ar36Ar

CrushingMN 8301 0135 g times1000 76 01909 plusmn 00033 3110 plusmn 50MN 8307 0203 g times1000 59 01928 plusmn 00043 3019 plusmn 56

times2000 04 01896 plusmn 00030 3154 plusmn 68Total 63 01926 plusmn 00040 3027 plusmn 53

MN 8309 0150 g times1000 15 01881 plusmn 00012 2970 plusmn 32MN 8310 0165 g times1000 29 01868 plusmn 00013 2937 plusmn 32MN 8311 0128 g times1000 11 01889 plusmn 00020 3051 plusmn 36MN 8317 0151 g times1000 56 01888 plusmn 00025 3048 plusmn 46MN 8318 0155 g times900 79 01809 plusmn 00017 2823 plusmn 104MN X-103 0223 g times1000 70 01881 plusmn 00012 3074 plusmn 35

HeatingMN 8301 0110 g 1800degC 27 01869 plusmn 00012 3049 plusmn 124MN 8307 0189 g 800degC 063 01874 plusmn 00012 4125 plusmn 292

ndash 1200degC 039 ndash ndashndash 1600degC 029 ndash ndashndash 1800degC 036 ndash ndashndash Total 17 ndash ndash

MN 8309 0148 g 1800degC 23 01884 plusmn 00011 3215 plusmn 120MN 8310 0135 g 1800degC 46 01884 plusmn 00031 3049 plusmn 47MN 8311 0128 g 1800degC 39 01878 plusmn 00007 3102 plusmn 24MN 8317 0121 g 1800degC 23 01888 plusmn 00019 3197 plusmn 38MN 8318 0144 g 1800degC 20 01866 plusmn 00011 3234 plusmn 41MN X-103 0181 g 1800degC 14 01889 plusmn 00023 3335 plusmn 58

Air ndash ndash ndash 01880 2955aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

Vvesicle M CNe

20 PNe

20air( )

currenacute=

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 3: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

Noble gases in Muong Nong-type tektites 749

where mX represents a noble gas isotope of mass ldquomrdquo Heliumdata are not included because of their low abundances(possibly due to diffusive loss after tektite formation and inthe vacuum of the extraction system) As shown in Figs 1aand 1b the samples have F(20) values well above unityindicating a neon enrichment relative to argon No systematicdifference exists in the degrees of neon enrichment in thecrushing and heating experiments Interestingly the observedF(20) values in Muong Nong-type tektites (26 to 37) aresignificantly lower than those of normal tektites (200 to 7130Matsubara and Matsuda 1991) In fact the range of F(20)values for Muong Nong-type tektites agrees well withpreviously reported values for impact glasses (Matsuda et al1989 Matsubara et al 1991) Note that the difference in theF(20) values is not due to differences in neon concentrationbetween Muong Nong-type tektites and normal tektites Asshown in Fig 2 both types of tektites have relatively uniform20Ne concentrations (~10-7 cm3 STPg) Matsubara andMatsuda (1995) concluded that neon in natural silica glasseshas completely exchanged with atmospheric neon by rapiddiffusion after their formation Thus a relatively uniformrange of neon concentrations in these glasses reflects thesaturation level that can be acquired by diffusive input

Therefore systematically smaller F(20) values in MuongNong-type tektites should reflect their relatively high argonconcentrations As shown in Fig 2 the range of 36Arconcentrations in Muong Nong-type tektites are at least 1order of magnitude larger than those in splash-form tektitesand agree well with concentrations reported for impactglasses

Values of F(84) and F(130) for gases released bycrushing are consistent with atmospheric composition Incontrast gases extracted by the heating of powdered samplesyielded F(130) values significantly higher than unityindicating that the released fraction is enriched in xenon withrespect to the atmospheric composition This is probably dueto the adsorption of xenon onto the surface of the powderedgrains because xenon is the most easily adsorbed of all thenoble gases (Matsubara and Matsuda 1995) The potential ofldquoirreversiblerdquo adsorption is reported by Niedermann andEugster (1992) However the effect of adsorption ofatmosphere is only shown in the heated samples Our resultsindicate that noble gases in the Muong Nong-type tektitevesicles cannot have originated from atmospheric gasesadsorbed on sediments that were released during the tektite-forming heating event This is because fractionation values of

Table 1 He and Ne concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 4He(10-9 cm3 STPg)

3He4He(10-6)

20Ne(10-8 cm3 STPg)

20Ne22Ne 21Ne22Ne

CrushingMN 8301 0135 g times1000 lt29 ndash 43 945 plusmn 016 00285 plusmn 00008MN 8307 0203 g times1000 29 ndash 72 984 plusmn 003 00298 plusmn 00006

ndash times2000 lt18 ndash 063 970 plusmn 011 00301 plusmn 00007ndash Total lt47 ndash 79 982 plusmn 003 00298 plusmn 00006

MN 8309 0150 g times1000 lt29 ndash 82 984 plusmn 010 00293 plusmn 00006MN 8310 0165 g times1000 lt41 ndash 39 975 plusmn 011 00290 plusmn 00006MN 8311 0128 g times1000 lt22 ndash 79 976 plusmn 011 00291 plusmn 00006MN 8317 0151 g times1000 34 ndash 11 974 plusmn 011 00288 plusmn 00006MN 8318 0155 g times900 29 ndash 11 100 plusmn 02 00289 plusmn 00009MN X-103 0223 g times1000 57 160 plusmn 030 18 995 plusmn 012 00294 plusmn 00006

HeatingMN 8301 0110 g 1800degC lt22 ndash 19 955 plusmn 017 00272 plusmn 00008MN 8307 0189 g 800degC 37 ndash 20 957 plusmn 016 00292 plusmn 00007

ndash 1200degC lt21 ndash lt0008 ndash ndashndash 1600degC lt11 ndash lt0011 ndash ndashndash 1800degC 11 ndash lt0013 ndash ndashndash Total lt80 ndash lt21 ndash ndash

MN 8309 0148 g 1800degC 15 ndash 20 971 plusmn 017 00312 plusmn 00008MN 8310 0135 g 1800degC lt20 ndash 23 969 plusmn 008 00288 plusmn 00004MN 8311 0128 g 1800degC lt18 ndash 24 951 plusmn 006 00290 plusmn 00002MN 8317 0121 g 1800degC lt21 ndash 31 955 plusmn 005 00288 plusmn 00002MN 8318 0144 g 1800degC lt17 ndash 21 948 plusmn 005 00281 plusmn 00003MN X-103 0181 g 1800degC lt13 ndash 028 983 plusmn 031 00296 plusmn 00010

Air ndash ndash ndash 14 ndash 980 00290aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

750 S Mizote et al

the heavy noble gases (Kr Xe) are almost unity (see Fig 1a)in contrast to patterns for adsorbed gases In the case ofadsorption the heavy noble gases are highly fractionated andF(84) and F(130) values are about 10 or more (eg Matsudaand Nagao 1986)

Isotopic Ratios

As shown in Tables 1ndash4 almost all isotopic ratios exceptthe 40Ar36Ar ratios are consistent with atmosphericcompositions within experimental uncertainties The 20Ne

22Ne and 21Ne22Ne ratios in the heated samples are slightlylower than the atmospheric values (Table 1) but the Ne ratiosin the crushed samples are almost identical to the atmosphericvalues The low Ne ratios in the heated samples may be due tothe mass fractionation effect with the gas release by priorcrushing Up to about 80 of the Ne was released bycrushing and the Ne isotopic ratios are identical toatmospheric values Thus we can regard that Ne in the wholesample originated mostly from the air

Such an occurrence of isotopically air-like noble gases isa common characteristic of glassy materials of terrestrial

Fig 1 Elemental abundance patterns of noble gases in Muong Nong-type tektites are plotted as the fractionation factor F(m) (see text forexplanation) relative to the atmospheric composition a) values obtained by the crushing method b) data from the heating method F(4) valuesare not shown as helium abundances are as low as the procedural blank levels The shaded area labeled ldquoTektitesrdquo shows the range of F(20)values (200 ndash7130) reported previously for splash-form tektites (Matsubara and Matsuda 1991)

Noble gases in Muong Nong-type tektites 751

impact origin (such as tektites and impact glasses) Previouswork on Muong Nong-type tektites also reported atmosphere-like isotopic compositions (Jessberger and Gentner 1972Murty 1997) As to the 40Ar36Ar ratios note that 40Ar36Arratios higher than the atmospheric ratio of 2955 were foundfor gases released by crushing suggesting that someradiogenic 40Ar is also released by crushing from glassmatrix This is often observed in crushing experiments (egMatsumoto et al 2002)

K-Ar ages

By using the observed radiogenic 40Ar in gases releasedby total fusion as well as the potassium content of eachsample (Koeberl 1992) calculating approximate K-Ar ages ofthe samples is possible The ages with uncertainties smallerthan 50 are 071 plusmn 034 Myr (MN 8309) 067 plusmn 014 Myr(MN 8311) 064 plusmn 014 Myr (MN 8317) and 073 plusmn 015 Myr(MN 8318) (other samples have significantly largeruncertainties due to low amounts of radiogenic 40Ar) Theobtained ages may give values lower than the real agesbecause some radiogenic 40Ar was released by crushingbefore fusion This may be the case for MN 8311 and MN8317 which yielded relatively shorter ages and is consistentwith 40Ar36Ar ratios greater than the atmospheric ratio at thecrushing However applying corrections to K-Ar ages forsuch a loss of radiogenic 40Ar by prior crushing is quitedifficult because the radiogenic 40Ar released by crushingcannot easily be expressed in units of cm3 STPg Note that

argon concentrations in Table 2 are calculated based on theassumption that the grains smaller than 150 mm had gasestrapped in vesicles of gt150 mm Likely the concentrations ofradiogenic 40Ar by crushing are overestimates because of thenormalization to small masses

At any rate we assume the effect of radiogenic 40Ar lossby crushing is negligible for correcting ages obtained fromheating of the lt150 mm fraction because the ages of ~07 Myragreed with each other within their 2 sigma errors and moreimportantly they agree with the reported Ar-Ar ages ofAustralasian tektites (077 plusmn 002 Myr Izett and Obradovich1992) and with fission track ages for Muong Nong-typeindochinitesmdashabout 07 Myr (Storzer and Wagner 1977Bigazzi and Michele 1996) implying that Muong Nong-typetektites are formed by a common event with other Australasiantektites Note also that the K-Ar ages reported here are only abyproduct of our analyses and are not the main goal

DISCUSSION

Noble Gas Distribution

Because we have analyzed the samples both by crushingand by total fusion we can estimate the fractions of noblegases dissolved in the glass and trapped in the vesiclesrespectively We regard the amounts of Ne Ar Kr and Xereleased by crushing to represent the noble gases trapped invesicles Gases released from samples with grain sizes of lt150mm were regarded to represent the concentrations in the matrix

Fig 2 Concentrations of 20Ne (closed diamond) and 36Ar (open circle) for tektites from 4 strewn fields (Hennecke et al 1975 Matsubara andMatsuda 1991 Matsuda et al 1993 Palma et al 1997) and impact glasses Darwin glass (Matsuda et al 1989) Libyan Desert glassZhamanshin glass and Aouelloul glass (Matsubara et al 1991) The neon concentrations in all samples are confined to a small range Theargon concentrations in Muong Nong-type tektites are close to those reported for impact glasses The arrows indicate upper limits

752 S Mizote et al

glass As shown in Fig 3 the present samples appear to haveroughly 70 to 85 of Ne Ar and Kr in their vesicles A largeramount of xenon seems to be dissolved in the glass comparedto other noble gases However we can estimate the Xe amountin glass from the atmospheric XeAr ratio and the observed Arabundance in the glass The abundances of xenon in glasswould be about 19 to 139 of the total amount observed in thepowdered samples as shown in Fig 1b The correctionindicates that about 80ndash85 of Xe resides in vesicles

Likely the observed noble gases from the powderedsamples are also released from small vesicles (lt150 mm) ratherthan from the glass matrix itself In this case the fraction of gasresiding in vesicles should be higher than the values above

Altitude of Closure and Noble Gases in Muong Nong-TypeTektites

Noble gases trapped in vesicles may record the ambientatmospheric pressure of the altitude at which the tektitessolidified First we attempt to estimate the volumes of thevesicles that were crushed to release gases in each samplewhich is necessary to estimate the internal noble gas pressuresin the vesicles Note that the volumes estimated from thin

sections might not be useful because of the heterogeneousdistribution of the vesicles and uncertainty relatingincomplete crushing of smaller vesicles ie we need todetermine the volume of the vesicles that were actuallycrushed in the experiment Thus we estimated an ldquoactualexperimental vesicle volumerdquo (ldquoeffectiverdquo vesicularity) usingthe neon contents as described below

The reason that neon concentrations in the presentsamples are useful to determine the samplersquos effectivevesicularity lies in the high diffusivity of neon in glassMatsubara and Matsuda (1995) showed experimentally thatneon can diffuse into 149ndash250 mm obsidian grains and that itsconcentration approached saturation at room temperature fortime scales of several tens of days which results inpreferential acquisition of neon compared to heavier noblegases Because K-Ar ages of these Muong Nong-type tektitesare about 07 Myr we can reasonably assume that the partialpressure of neon in the vesicles is in equilibrium with that ofair Thus we may estimate the effective vesicularity of thesamples from the following equation

(2)

Table 2 Ar concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 36Ar(10-9 cm3STPg)

38Ar36Ar 40Ar36Ar

CrushingMN 8301 0135 g times1000 76 01909 plusmn 00033 3110 plusmn 50MN 8307 0203 g times1000 59 01928 plusmn 00043 3019 plusmn 56

times2000 04 01896 plusmn 00030 3154 plusmn 68Total 63 01926 plusmn 00040 3027 plusmn 53

MN 8309 0150 g times1000 15 01881 plusmn 00012 2970 plusmn 32MN 8310 0165 g times1000 29 01868 plusmn 00013 2937 plusmn 32MN 8311 0128 g times1000 11 01889 plusmn 00020 3051 plusmn 36MN 8317 0151 g times1000 56 01888 plusmn 00025 3048 plusmn 46MN 8318 0155 g times900 79 01809 plusmn 00017 2823 plusmn 104MN X-103 0223 g times1000 70 01881 plusmn 00012 3074 plusmn 35

HeatingMN 8301 0110 g 1800degC 27 01869 plusmn 00012 3049 plusmn 124MN 8307 0189 g 800degC 063 01874 plusmn 00012 4125 plusmn 292

ndash 1200degC 039 ndash ndashndash 1600degC 029 ndash ndashndash 1800degC 036 ndash ndashndash Total 17 ndash ndash

MN 8309 0148 g 1800degC 23 01884 plusmn 00011 3215 plusmn 120MN 8310 0135 g 1800degC 46 01884 plusmn 00031 3049 plusmn 47MN 8311 0128 g 1800degC 39 01878 plusmn 00007 3102 plusmn 24MN 8317 0121 g 1800degC 23 01888 plusmn 00019 3197 plusmn 38MN 8318 0144 g 1800degC 20 01866 plusmn 00011 3234 plusmn 41MN X-103 0181 g 1800degC 14 01889 plusmn 00023 3335 plusmn 58

Air ndash ndash ndash 01880 2955aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

Vvesicle M CNe

20 PNe

20air( )

currenacute=

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 4: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

750 S Mizote et al

the heavy noble gases (Kr Xe) are almost unity (see Fig 1a)in contrast to patterns for adsorbed gases In the case ofadsorption the heavy noble gases are highly fractionated andF(84) and F(130) values are about 10 or more (eg Matsudaand Nagao 1986)

Isotopic Ratios

As shown in Tables 1ndash4 almost all isotopic ratios exceptthe 40Ar36Ar ratios are consistent with atmosphericcompositions within experimental uncertainties The 20Ne

22Ne and 21Ne22Ne ratios in the heated samples are slightlylower than the atmospheric values (Table 1) but the Ne ratiosin the crushed samples are almost identical to the atmosphericvalues The low Ne ratios in the heated samples may be due tothe mass fractionation effect with the gas release by priorcrushing Up to about 80 of the Ne was released bycrushing and the Ne isotopic ratios are identical toatmospheric values Thus we can regard that Ne in the wholesample originated mostly from the air

Such an occurrence of isotopically air-like noble gases isa common characteristic of glassy materials of terrestrial

Fig 1 Elemental abundance patterns of noble gases in Muong Nong-type tektites are plotted as the fractionation factor F(m) (see text forexplanation) relative to the atmospheric composition a) values obtained by the crushing method b) data from the heating method F(4) valuesare not shown as helium abundances are as low as the procedural blank levels The shaded area labeled ldquoTektitesrdquo shows the range of F(20)values (200 ndash7130) reported previously for splash-form tektites (Matsubara and Matsuda 1991)

Noble gases in Muong Nong-type tektites 751

impact origin (such as tektites and impact glasses) Previouswork on Muong Nong-type tektites also reported atmosphere-like isotopic compositions (Jessberger and Gentner 1972Murty 1997) As to the 40Ar36Ar ratios note that 40Ar36Arratios higher than the atmospheric ratio of 2955 were foundfor gases released by crushing suggesting that someradiogenic 40Ar is also released by crushing from glassmatrix This is often observed in crushing experiments (egMatsumoto et al 2002)

K-Ar ages

By using the observed radiogenic 40Ar in gases releasedby total fusion as well as the potassium content of eachsample (Koeberl 1992) calculating approximate K-Ar ages ofthe samples is possible The ages with uncertainties smallerthan 50 are 071 plusmn 034 Myr (MN 8309) 067 plusmn 014 Myr(MN 8311) 064 plusmn 014 Myr (MN 8317) and 073 plusmn 015 Myr(MN 8318) (other samples have significantly largeruncertainties due to low amounts of radiogenic 40Ar) Theobtained ages may give values lower than the real agesbecause some radiogenic 40Ar was released by crushingbefore fusion This may be the case for MN 8311 and MN8317 which yielded relatively shorter ages and is consistentwith 40Ar36Ar ratios greater than the atmospheric ratio at thecrushing However applying corrections to K-Ar ages forsuch a loss of radiogenic 40Ar by prior crushing is quitedifficult because the radiogenic 40Ar released by crushingcannot easily be expressed in units of cm3 STPg Note that

argon concentrations in Table 2 are calculated based on theassumption that the grains smaller than 150 mm had gasestrapped in vesicles of gt150 mm Likely the concentrations ofradiogenic 40Ar by crushing are overestimates because of thenormalization to small masses

At any rate we assume the effect of radiogenic 40Ar lossby crushing is negligible for correcting ages obtained fromheating of the lt150 mm fraction because the ages of ~07 Myragreed with each other within their 2 sigma errors and moreimportantly they agree with the reported Ar-Ar ages ofAustralasian tektites (077 plusmn 002 Myr Izett and Obradovich1992) and with fission track ages for Muong Nong-typeindochinitesmdashabout 07 Myr (Storzer and Wagner 1977Bigazzi and Michele 1996) implying that Muong Nong-typetektites are formed by a common event with other Australasiantektites Note also that the K-Ar ages reported here are only abyproduct of our analyses and are not the main goal

DISCUSSION

Noble Gas Distribution

Because we have analyzed the samples both by crushingand by total fusion we can estimate the fractions of noblegases dissolved in the glass and trapped in the vesiclesrespectively We regard the amounts of Ne Ar Kr and Xereleased by crushing to represent the noble gases trapped invesicles Gases released from samples with grain sizes of lt150mm were regarded to represent the concentrations in the matrix

Fig 2 Concentrations of 20Ne (closed diamond) and 36Ar (open circle) for tektites from 4 strewn fields (Hennecke et al 1975 Matsubara andMatsuda 1991 Matsuda et al 1993 Palma et al 1997) and impact glasses Darwin glass (Matsuda et al 1989) Libyan Desert glassZhamanshin glass and Aouelloul glass (Matsubara et al 1991) The neon concentrations in all samples are confined to a small range Theargon concentrations in Muong Nong-type tektites are close to those reported for impact glasses The arrows indicate upper limits

752 S Mizote et al

glass As shown in Fig 3 the present samples appear to haveroughly 70 to 85 of Ne Ar and Kr in their vesicles A largeramount of xenon seems to be dissolved in the glass comparedto other noble gases However we can estimate the Xe amountin glass from the atmospheric XeAr ratio and the observed Arabundance in the glass The abundances of xenon in glasswould be about 19 to 139 of the total amount observed in thepowdered samples as shown in Fig 1b The correctionindicates that about 80ndash85 of Xe resides in vesicles

Likely the observed noble gases from the powderedsamples are also released from small vesicles (lt150 mm) ratherthan from the glass matrix itself In this case the fraction of gasresiding in vesicles should be higher than the values above

Altitude of Closure and Noble Gases in Muong Nong-TypeTektites

Noble gases trapped in vesicles may record the ambientatmospheric pressure of the altitude at which the tektitessolidified First we attempt to estimate the volumes of thevesicles that were crushed to release gases in each samplewhich is necessary to estimate the internal noble gas pressuresin the vesicles Note that the volumes estimated from thin

sections might not be useful because of the heterogeneousdistribution of the vesicles and uncertainty relatingincomplete crushing of smaller vesicles ie we need todetermine the volume of the vesicles that were actuallycrushed in the experiment Thus we estimated an ldquoactualexperimental vesicle volumerdquo (ldquoeffectiverdquo vesicularity) usingthe neon contents as described below

The reason that neon concentrations in the presentsamples are useful to determine the samplersquos effectivevesicularity lies in the high diffusivity of neon in glassMatsubara and Matsuda (1995) showed experimentally thatneon can diffuse into 149ndash250 mm obsidian grains and that itsconcentration approached saturation at room temperature fortime scales of several tens of days which results inpreferential acquisition of neon compared to heavier noblegases Because K-Ar ages of these Muong Nong-type tektitesare about 07 Myr we can reasonably assume that the partialpressure of neon in the vesicles is in equilibrium with that ofair Thus we may estimate the effective vesicularity of thesamples from the following equation

(2)

Table 2 Ar concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 36Ar(10-9 cm3STPg)

38Ar36Ar 40Ar36Ar

CrushingMN 8301 0135 g times1000 76 01909 plusmn 00033 3110 plusmn 50MN 8307 0203 g times1000 59 01928 plusmn 00043 3019 plusmn 56

times2000 04 01896 plusmn 00030 3154 plusmn 68Total 63 01926 plusmn 00040 3027 plusmn 53

MN 8309 0150 g times1000 15 01881 plusmn 00012 2970 plusmn 32MN 8310 0165 g times1000 29 01868 plusmn 00013 2937 plusmn 32MN 8311 0128 g times1000 11 01889 plusmn 00020 3051 plusmn 36MN 8317 0151 g times1000 56 01888 plusmn 00025 3048 plusmn 46MN 8318 0155 g times900 79 01809 plusmn 00017 2823 plusmn 104MN X-103 0223 g times1000 70 01881 plusmn 00012 3074 plusmn 35

HeatingMN 8301 0110 g 1800degC 27 01869 plusmn 00012 3049 plusmn 124MN 8307 0189 g 800degC 063 01874 plusmn 00012 4125 plusmn 292

ndash 1200degC 039 ndash ndashndash 1600degC 029 ndash ndashndash 1800degC 036 ndash ndashndash Total 17 ndash ndash

MN 8309 0148 g 1800degC 23 01884 plusmn 00011 3215 plusmn 120MN 8310 0135 g 1800degC 46 01884 plusmn 00031 3049 plusmn 47MN 8311 0128 g 1800degC 39 01878 plusmn 00007 3102 plusmn 24MN 8317 0121 g 1800degC 23 01888 plusmn 00019 3197 plusmn 38MN 8318 0144 g 1800degC 20 01866 plusmn 00011 3234 plusmn 41MN X-103 0181 g 1800degC 14 01889 plusmn 00023 3335 plusmn 58

Air ndash ndash ndash 01880 2955aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

Vvesicle M CNe

20 PNe

20air( )

currenacute=

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 5: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

Noble gases in Muong Nong-type tektites 751

impact origin (such as tektites and impact glasses) Previouswork on Muong Nong-type tektites also reported atmosphere-like isotopic compositions (Jessberger and Gentner 1972Murty 1997) As to the 40Ar36Ar ratios note that 40Ar36Arratios higher than the atmospheric ratio of 2955 were foundfor gases released by crushing suggesting that someradiogenic 40Ar is also released by crushing from glassmatrix This is often observed in crushing experiments (egMatsumoto et al 2002)

K-Ar ages

By using the observed radiogenic 40Ar in gases releasedby total fusion as well as the potassium content of eachsample (Koeberl 1992) calculating approximate K-Ar ages ofthe samples is possible The ages with uncertainties smallerthan 50 are 071 plusmn 034 Myr (MN 8309) 067 plusmn 014 Myr(MN 8311) 064 plusmn 014 Myr (MN 8317) and 073 plusmn 015 Myr(MN 8318) (other samples have significantly largeruncertainties due to low amounts of radiogenic 40Ar) Theobtained ages may give values lower than the real agesbecause some radiogenic 40Ar was released by crushingbefore fusion This may be the case for MN 8311 and MN8317 which yielded relatively shorter ages and is consistentwith 40Ar36Ar ratios greater than the atmospheric ratio at thecrushing However applying corrections to K-Ar ages forsuch a loss of radiogenic 40Ar by prior crushing is quitedifficult because the radiogenic 40Ar released by crushingcannot easily be expressed in units of cm3 STPg Note that

argon concentrations in Table 2 are calculated based on theassumption that the grains smaller than 150 mm had gasestrapped in vesicles of gt150 mm Likely the concentrations ofradiogenic 40Ar by crushing are overestimates because of thenormalization to small masses

At any rate we assume the effect of radiogenic 40Ar lossby crushing is negligible for correcting ages obtained fromheating of the lt150 mm fraction because the ages of ~07 Myragreed with each other within their 2 sigma errors and moreimportantly they agree with the reported Ar-Ar ages ofAustralasian tektites (077 plusmn 002 Myr Izett and Obradovich1992) and with fission track ages for Muong Nong-typeindochinitesmdashabout 07 Myr (Storzer and Wagner 1977Bigazzi and Michele 1996) implying that Muong Nong-typetektites are formed by a common event with other Australasiantektites Note also that the K-Ar ages reported here are only abyproduct of our analyses and are not the main goal

DISCUSSION

Noble Gas Distribution

Because we have analyzed the samples both by crushingand by total fusion we can estimate the fractions of noblegases dissolved in the glass and trapped in the vesiclesrespectively We regard the amounts of Ne Ar Kr and Xereleased by crushing to represent the noble gases trapped invesicles Gases released from samples with grain sizes of lt150mm were regarded to represent the concentrations in the matrix

Fig 2 Concentrations of 20Ne (closed diamond) and 36Ar (open circle) for tektites from 4 strewn fields (Hennecke et al 1975 Matsubara andMatsuda 1991 Matsuda et al 1993 Palma et al 1997) and impact glasses Darwin glass (Matsuda et al 1989) Libyan Desert glassZhamanshin glass and Aouelloul glass (Matsubara et al 1991) The neon concentrations in all samples are confined to a small range Theargon concentrations in Muong Nong-type tektites are close to those reported for impact glasses The arrows indicate upper limits

752 S Mizote et al

glass As shown in Fig 3 the present samples appear to haveroughly 70 to 85 of Ne Ar and Kr in their vesicles A largeramount of xenon seems to be dissolved in the glass comparedto other noble gases However we can estimate the Xe amountin glass from the atmospheric XeAr ratio and the observed Arabundance in the glass The abundances of xenon in glasswould be about 19 to 139 of the total amount observed in thepowdered samples as shown in Fig 1b The correctionindicates that about 80ndash85 of Xe resides in vesicles

Likely the observed noble gases from the powderedsamples are also released from small vesicles (lt150 mm) ratherthan from the glass matrix itself In this case the fraction of gasresiding in vesicles should be higher than the values above

Altitude of Closure and Noble Gases in Muong Nong-TypeTektites

Noble gases trapped in vesicles may record the ambientatmospheric pressure of the altitude at which the tektitessolidified First we attempt to estimate the volumes of thevesicles that were crushed to release gases in each samplewhich is necessary to estimate the internal noble gas pressuresin the vesicles Note that the volumes estimated from thin

sections might not be useful because of the heterogeneousdistribution of the vesicles and uncertainty relatingincomplete crushing of smaller vesicles ie we need todetermine the volume of the vesicles that were actuallycrushed in the experiment Thus we estimated an ldquoactualexperimental vesicle volumerdquo (ldquoeffectiverdquo vesicularity) usingthe neon contents as described below

The reason that neon concentrations in the presentsamples are useful to determine the samplersquos effectivevesicularity lies in the high diffusivity of neon in glassMatsubara and Matsuda (1995) showed experimentally thatneon can diffuse into 149ndash250 mm obsidian grains and that itsconcentration approached saturation at room temperature fortime scales of several tens of days which results inpreferential acquisition of neon compared to heavier noblegases Because K-Ar ages of these Muong Nong-type tektitesare about 07 Myr we can reasonably assume that the partialpressure of neon in the vesicles is in equilibrium with that ofair Thus we may estimate the effective vesicularity of thesamples from the following equation

(2)

Table 2 Ar concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 36Ar(10-9 cm3STPg)

38Ar36Ar 40Ar36Ar

CrushingMN 8301 0135 g times1000 76 01909 plusmn 00033 3110 plusmn 50MN 8307 0203 g times1000 59 01928 plusmn 00043 3019 plusmn 56

times2000 04 01896 plusmn 00030 3154 plusmn 68Total 63 01926 plusmn 00040 3027 plusmn 53

MN 8309 0150 g times1000 15 01881 plusmn 00012 2970 plusmn 32MN 8310 0165 g times1000 29 01868 plusmn 00013 2937 plusmn 32MN 8311 0128 g times1000 11 01889 plusmn 00020 3051 plusmn 36MN 8317 0151 g times1000 56 01888 plusmn 00025 3048 plusmn 46MN 8318 0155 g times900 79 01809 plusmn 00017 2823 plusmn 104MN X-103 0223 g times1000 70 01881 plusmn 00012 3074 plusmn 35

HeatingMN 8301 0110 g 1800degC 27 01869 plusmn 00012 3049 plusmn 124MN 8307 0189 g 800degC 063 01874 plusmn 00012 4125 plusmn 292

ndash 1200degC 039 ndash ndashndash 1600degC 029 ndash ndashndash 1800degC 036 ndash ndashndash Total 17 ndash ndash

MN 8309 0148 g 1800degC 23 01884 plusmn 00011 3215 plusmn 120MN 8310 0135 g 1800degC 46 01884 plusmn 00031 3049 plusmn 47MN 8311 0128 g 1800degC 39 01878 plusmn 00007 3102 plusmn 24MN 8317 0121 g 1800degC 23 01888 plusmn 00019 3197 plusmn 38MN 8318 0144 g 1800degC 20 01866 plusmn 00011 3234 plusmn 41MN X-103 0181 g 1800degC 14 01889 plusmn 00023 3335 plusmn 58

Air ndash ndash ndash 01880 2955aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

Vvesicle M CNe

20 PNe

20air( )

currenacute=

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 6: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

752 S Mizote et al

glass As shown in Fig 3 the present samples appear to haveroughly 70 to 85 of Ne Ar and Kr in their vesicles A largeramount of xenon seems to be dissolved in the glass comparedto other noble gases However we can estimate the Xe amountin glass from the atmospheric XeAr ratio and the observed Arabundance in the glass The abundances of xenon in glasswould be about 19 to 139 of the total amount observed in thepowdered samples as shown in Fig 1b The correctionindicates that about 80ndash85 of Xe resides in vesicles

Likely the observed noble gases from the powderedsamples are also released from small vesicles (lt150 mm) ratherthan from the glass matrix itself In this case the fraction of gasresiding in vesicles should be higher than the values above

Altitude of Closure and Noble Gases in Muong Nong-TypeTektites

Noble gases trapped in vesicles may record the ambientatmospheric pressure of the altitude at which the tektitessolidified First we attempt to estimate the volumes of thevesicles that were crushed to release gases in each samplewhich is necessary to estimate the internal noble gas pressuresin the vesicles Note that the volumes estimated from thin

sections might not be useful because of the heterogeneousdistribution of the vesicles and uncertainty relatingincomplete crushing of smaller vesicles ie we need todetermine the volume of the vesicles that were actuallycrushed in the experiment Thus we estimated an ldquoactualexperimental vesicle volumerdquo (ldquoeffectiverdquo vesicularity) usingthe neon contents as described below

The reason that neon concentrations in the presentsamples are useful to determine the samplersquos effectivevesicularity lies in the high diffusivity of neon in glassMatsubara and Matsuda (1995) showed experimentally thatneon can diffuse into 149ndash250 mm obsidian grains and that itsconcentration approached saturation at room temperature fortime scales of several tens of days which results inpreferential acquisition of neon compared to heavier noblegases Because K-Ar ages of these Muong Nong-type tektitesare about 07 Myr we can reasonably assume that the partialpressure of neon in the vesicles is in equilibrium with that ofair Thus we may estimate the effective vesicularity of thesamples from the following equation

(2)

Table 2 Ar concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 36Ar(10-9 cm3STPg)

38Ar36Ar 40Ar36Ar

CrushingMN 8301 0135 g times1000 76 01909 plusmn 00033 3110 plusmn 50MN 8307 0203 g times1000 59 01928 plusmn 00043 3019 plusmn 56

times2000 04 01896 plusmn 00030 3154 plusmn 68Total 63 01926 plusmn 00040 3027 plusmn 53

MN 8309 0150 g times1000 15 01881 plusmn 00012 2970 plusmn 32MN 8310 0165 g times1000 29 01868 plusmn 00013 2937 plusmn 32MN 8311 0128 g times1000 11 01889 plusmn 00020 3051 plusmn 36MN 8317 0151 g times1000 56 01888 plusmn 00025 3048 plusmn 46MN 8318 0155 g times900 79 01809 plusmn 00017 2823 plusmn 104MN X-103 0223 g times1000 70 01881 plusmn 00012 3074 plusmn 35

HeatingMN 8301 0110 g 1800degC 27 01869 plusmn 00012 3049 plusmn 124MN 8307 0189 g 800degC 063 01874 plusmn 00012 4125 plusmn 292

ndash 1200degC 039 ndash ndashndash 1600degC 029 ndash ndashndash 1800degC 036 ndash ndashndash Total 17 ndash ndash

MN 8309 0148 g 1800degC 23 01884 plusmn 00011 3215 plusmn 120MN 8310 0135 g 1800degC 46 01884 plusmn 00031 3049 plusmn 47MN 8311 0128 g 1800degC 39 01878 plusmn 00007 3102 plusmn 24MN 8317 0121 g 1800degC 23 01888 plusmn 00019 3197 plusmn 38MN 8318 0144 g 1800degC 20 01866 plusmn 00011 3234 plusmn 41MN X-103 0181 g 1800degC 14 01889 plusmn 00023 3335 plusmn 58

Air ndash ndash ndash 01880 2955aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrations are

simply given as upper limits without blank correctionbWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

Vvesicle M CNe

20 PNe

20air( )

currenacute=

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 7: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

Noble gases in Muong Nong-type tektites 753

where Vvesicle is the volume of actually crushed vesicles M isthe weight of the crushed samples (in grams) C20Ne is theamount of 20Ne in 1 gram of crushed sample (in cm3 STPg)and P20Ne(air) is the partial pressure of 20Ne in atmosphere(165 acute 10-5 atm Ozima and Podosek 1983)

We applied this method for the estimation of thevesicularity to a moldavite with a large bubble for thissample the accurate bubble volume was measured with an X-ray computed tomography (CT) scanner (Matsuda et al 2000)The bubble volume estimated from the Ne concentration was013 cm3 and that obtained from the X-ray CT scanner was016 cm3

Using the estimated bubble volume we can calculate thepartial pressures of the heavy noble gases (Ar Kr and Xe) inthe vesicles As discussed above the heavier noble gases invesicles have atmospheric elemental composition while theNeAr NeKr and NeXe ratios are significantly larger thanair We found no indication of diffusive input of these heaviernoble gases into Muong Nong-type tektites thus we cansafely conclude that these gases preserve their partialpressures during solidification in glass Then similar toEquation 2 we can write

(3)

where P36Ar denotes the partial pressure of 36Ar in 1 atm of theair vesicles with their effective total volumes (Vvesicle)estimated from neon above Using the above two equationswe can calculate the P36Ar simply from the Ne and Arconcentrations in the sample (Table 5) If we assume thedensity of the sample the vesicularity (cm3cm3) can also becalculated The vesicularities obtained by the above methodare typically about 1 vol of the total sample (Table 5)

As listed in Table 5 the estimated partial pressures invesicles are from 86 acute 10-7 to 12 acute 10-5 atm these values arelower than the partial pressure of 36Ar in 1 atm of the air (= 314acute 10-5 atm) Note that concentrations of argon in the glass(measured in powdered samples by fusion) are much lowerthan those of normal sedimentary rocks (Matsubara et al1991) which are equilibrated with air at atmospheric pressureThus the tektite source rocks have lost their original noblegases during the first stages of tektite formation (Matsuda et al1993) Subsequent equilibration of atmospheric noble gaseswith the melt is unlikely as equilibrium solubility should resultin elemental fractionations favoring lighter noble gases in themelt reflecting larger values of Henryrsquos constant for the lighternoble gases (eg Lux 1987) In addition gases trapped invesicles are unlikely to be those exsolved from solidifyingmelts to form vesicles because no difference exists in the noblegas elemental ratios between glass and vesicles (KrAr)melt

Fig 3 Distribution of Ne (a) Ar (b) Kr (c) and Xe (d) in Muong Nong-type tektites between vesicles and glasses The left and right arrowsindicate the upper limits from the crushing and heating methods respectively Note that high Xe fraction in glass is due to the adsorption ofXe in atmosphere (see text)

Vvesicle M CAr

36 PAr

36currenacute=

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 8: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

754 S Mizote et al

and (XeAr)melt should be smaller than (KrAr)vesicle and (XeAr)vesicle by 30 and 70 respectively for a suggestedvesicularity of 1 Although an adsorption effect ofatmospheric Xe in the glass samples exists the fractions ofgases in bubble to glass remain the same for all noble gases ifthe correction for the atmospheric XeAr ratio is made for theglass samples The gases in the vesicles constitute about 70 to80 of the whole noble gas content of the tektites Thereforeincorporation andor occlusion of ambient argon at a highaltitude is our explanation for the low argon pressure in thetektite vesicles We suspect that although the formation ofvesicles in melts is facilitated by the exsolution of gases duringa decrease of the ambient temperature the gases in the vesicleswere rapidly equilibrated with the atmosphere at highaltitudes resulting in systematically lower argon partialpressure in the present samples than at sea level Note that theatmospheric pressure decreases exponentially with a scaleheight of 84 km (Matsuda et al 1993) Thus we calculated thealtitude where the partial pressure of 36Ar in the vesicles isidentical to that in the ambient air using the equation

(4)

where P36Ar0 is the partial pressure of 36Ar at the sea level(=314 acute 10-5 atm) Z is the altitude and H is the scale height(=84 km) The range of partial pressures of 36Ar estimated forthe present samples is equivalent to altitudes of 8 to 30 km(Table 5)

However the estimates of the vesicle volumes are basedon the assumption that the atmosphere at sea level had anatmospheric pressure of 1 during the tektite-forming eventbut the pressure of the atmosphere might have been lower than1 atmospheric pressure and the temperature should have beenmuch higher than during normal ambient conditions Thus theestimated partial pressures of Ar should be regarded as lowerlimits and the estimated altitudes as maximum values

Implications for the Formation of the Muong Nong-TypeTektites

As noted earlier the overall characteristics of the MuongNong-type tektites resemble those of impact glasses This isconfirmed by the heavy noble gas data shown in Fig 4 wherethe Kr and Xe concentrations are plotted against the Arconcentration The heavy noble gas data of Muong Nong-typetektite plot in the field also occupied by impact glasses The

Table 3 Kr concentrations and isotopic compositions in Muong Nong-type tektitesa

Sample Weightb Crushingc 84Kr (10- cm3 STPg)

78Kr84Kr(10-3)

80Kr84Kr(10-2)

82Kr84Kr 83Kr84Kr 86Kr84Kr

CrushingMN 8301 0135 g times1000 24 611 plusmn 033 393 plusmn 006 0201 plusmn 0002 0203 plusmn 0001 0306 plusmn 0002MN 8307 0203 g times1000 17 631 plusmn 031 398 plusmn 007 0197 plusmn 0005 0204 plusmn 0002 0305 plusmn 0002

ndash times2000 lt013 ndash ndash ndash ndash ndashndash Total lt18 ndash ndash ndash ndash ndash

MN 8309 0150 g times1000 32 601 plusmn 028 395 plusmn 004 0202 plusmn 0002 0201 plusmn 0001 0304 plusmn 0002MN 8310 0165 g times1000 64 598 plusmn 018 400 plusmn 004 0202 plusmn 0001 0201 plusmn 0001 0307 plusmn 0001MN 8311 0128 g times1000 29 585 plusmn 035 390 plusmn 004 0201 plusmn 0001 0201 plusmn 0001 0306 plusmn 0002MN 8317 0151 g times1000 16 603 plusmn 042 399 plusmn 005 0203 plusmn 0001 0203 plusmn 0002 0302 plusmn 0002MN 8318 0155 g times900 24 599 plusmn 027 392 plusmn 007 0200 plusmn 0002 0201 plusmn 0001 0309 plusmn 0002MN X-103 0223 g times1000 14 607 plusmn 031 395 plusmn 005 0203 plusmn 0002 0203 plusmn 0001 0310 plusmn 0002

HeatingMN 8301 0110 g 1800degC lt071 ndash ndash ndash ndash ndashMN 8307 0189 g 800degC 019 ndash 466 plusmn 006 0171 plusmn 0002 0199 plusmn 0002 0296 plusmn 0002

ndash 1200degC 0062 ndash 390 plusmn 045 0214 plusmn 0010 0212 plusmn 0009 0310 plusmn 0013ndash 1600degC 0083 ndash 385 plusmn 025 0212 plusmn 0008 0201 plusmn 0010 0306 plusmn 0011ndash 1800degC lt013 ndash ndash ndash ndash ndashndash Total lt046 ndash ndash ndash ndash ndash

MN 8309 0148 g 1800degC 070 ndash 398 plusmn 012 0204 plusmn 0003 0202 plusmn 0004 0307 plusmn 0005MN 8310 0135 g 1800degC 093 ndash 391 plusmn 007 0204 plusmn 0003 0204 plusmn 0001 0308 plusmn 0002MN 8311 0128 g 1800degC 083 ndash 386 plusmn 006 0200 plusmn 0002 0198 plusmn 0001 0307 plusmn 0003MN 8317 0121 g 1800degC 080 520 plusmn 031 387 plusmn 012 0210 plusmn 0002 0204 plusmn 0001 0305 plusmn 0004MN 8318 0144 g 1800degC 064 456 plusmn 035 401 plusmn 011 0205 plusmn 0002 0202 plusmn 0003 0310 plusmn 0002MN X-103 0181 g 1800degC 089 534 plusmn 016 391 plusmn 008 0202 plusmn 0002 0202 plusmn 0002 0306 plusmn 0002

Air ndash ndash ndash 609 396 0202 0201 0305aConcentrations of gases and isotopic ratios are corrected for procedural blank but when blank levels exceed 30 of the sample signals the concentrationsare simply given as upper limits without blank correction

bWeight of samples For the crushing extractions the weight is for the grains smaller than 150 mmcNumber of crushing strokes for the crushing extraction For the heating extractions the temperatures to which the sample were heated are given

PAr

36 PAr 0

36 Zndash Hcurren( )ln=

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 9: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

Noble gases in Muong Nong-type tektites 755T

able

4 X

e co

ncen

trat

ions

and

iso

topi

c co

mpo

siti

ons

in M

uong

Non

g-ty

pe t

ekti

tes

a

a Con

cent

ratio

ns o

f ga

ses

and

isot

opic

rat

ios

are

corr

ecte

d fo

r pr

oced

ural

bla

nk b

ut w

hen

blan

k le

vels

exc

eed

30

of

the

sam

ple

sign

als

the

conc

entr

atio

ns a

re s

impl

y gi

ven

as u

pper

lim

its w

ithou

t bl

ank

corr

ectio

n

Sam

ple

Wei

ghtb

bW

eigh

t of

sam

ples

Fo

r th

e cr

ushi

ng e

xtra

ctio

ns t

he w

eigh

t is

for

the

grai

ns s

mal

ler

than

150

mm

Cru

shin

gc

c Num

ber o

f cr

ushi

ng s

trok

es f

or th

e cr

ushi

ng e

xtra

ctio

n F

or th

e he

atin

g ex

trac

tions

the

tem

pera

ture

s to

whi

ch th

e sa

mpl

e w

ere

heat

ed a

re g

iven

130 X

e(1

0- c

m3

ST

Pg

)

124 X

e13

0 Xe

(10- 2

)

126 X

e13

0 Xe

(10- 2

)

128 X

e13

0 Xe

129 X

e13

0 Xe

131 X

e13

0 Xe

132 X

e13

0 Xe

134 X

e13

0 Xe

136 X

e13

0 Xe

Cru

shin

gM

N 8

301

013

5 g

times100

01

52

40 plusmn

04

12

01 plusmn

02

90

409

plusmn 0

022

577

plusmn 0

22

478

plusmn 0

13

658

plusmn 0

16

235

plusmn 0

06

189

plusmn 0

07

MN

830

70

203

gtimes

1000

093

ndash1

98 plusmn

03

60

356

plusmn 0

070

665

plusmn 0

10

512

plusmn 0

13

638

plusmn 0

14

268

plusmn 0

04

216

plusmn 0

03

ndashtimes

2000

lt0

11ndash

ndashndash

ndashndash

ndashndash

ndashndash

Tota

llt

10

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

150

gtimes

1000

17

ndashndash

039

5 plusmn

004

86

53 plusmn

00

95

29 plusmn

00

86

63 plusmn

00

72

58 plusmn

00

42

20 plusmn

00

3M

N 8

310

016

5 g

times100

03

02

17 plusmn

02

02

22 plusmn

01

70

477

plusmn 0

009

657

plusmn 0

09

526

plusmn 0

05

662

plusmn 0

08

255

plusmn 0

04

213

plusmn 0

03

MN

831

10

128

gtimes

1000

18

ndashndash

043

8 plusmn

002

56

43 plusmn

00

65

16 plusmn

00

66

60 plusmn

00

72

57 plusmn

00

42

14 plusmn

00

3M

N 8

317

015

1 g

times100

01

0ndash

ndash0

364

plusmn 0

054

644

plusmn 0

09

511

plusmn 0

07

643

plusmn 0

06

255

plusmn 0

06

216

plusmn 0

06

MN

831

80

155

gtimes

900

13

214

plusmn 0

35

214

plusmn 0

38

035

6 plusmn

006

46

58 plusmn

01

55

32 plusmn

01

36

68 plusmn

01

52

57 plusmn

00

52

17 plusmn

00

4M

N X

-103

022

3 g

times10

000

872

15 plusmn

04

50

395

plusmn 0

046

655

plusmn 0

07

530

plusmn 0

06

673

plusmn 0

08

262

plusmn 0

03

220

plusmn 0

04

Hea

ting

MN

830

10

110

g18

00degC

lt2

6ndash

ndashndash

ndashndash

ndashndash

ndashM

N 8

307

018

9 g

800deg

Clt

017

ndashndash

ndashndash

ndashndash

ndashndash

ndash12

00degC

lt0

15ndash

ndashndash

ndashndash

ndashndash

ndashndash

1600

degC0

15ndash

ndash0

591

plusmn 0

104

695

plusmn 0

99

638

plusmn 0

77

906

plusmn 1

18

302

plusmn 0

32

247

plusmn 0

20

ndash18

00degC

018

ndashndash

047

3 plusmn

003

06

54 plusmn

01

55

93 plusmn

05

08

02 plusmn

07

72

62 plusmn

01

02

33 plusmn

01

3ndash

Tota

llt

066

ndashndash

ndashndash

ndashndash

ndashndash

MN

830

90

148

g18

00degC

44

ndashndash

046

5 plusmn

000

96

41 plusmn

00

85

37 plusmn

01

57

30 plusmn

02

32

57 plusmn

00

62

16 plusmn

00

4M

N 8

310

013

5 g

1800

degC6

82

19 plusmn

00

82

16 plusmn

01

20

472

plusmn 0

007

653

plusmn 0

09

521

plusmn 0

04

662

plusmn 0

06

259

plusmn 0

03

216

plusmn 0

02

MN

831

10

128

g18

00degC

69

230

plusmn 0

05

206

plusmn 0

14

047

8 plusmn

000

76

58 plusmn

01

05

20 plusmn

00

56

59 plusmn

00

62

57 plusmn

00

42

18 plusmn

00

3M

N 8

317

012

1 g

1800

degC6

72

31 plusmn

00

91

71 plusmn

02

00

476

plusmn 0

008

652

plusmn 0

08

520

plusmn 0

04

660

plusmn 0

05

258

plusmn 0

03

216

plusmn 0

03

MN

831

80

144

g18

00degC

88

231

plusmn 0

09

172

plusmn 0

20

047

7 plusmn

000

66

58 plusmn

00

75

25 plusmn

00

36

67 plusmn

00

52

57 plusmn

00

32

17 plusmn

00

2M

N X

-103

018

1 g

1800

degC4

82

46 plusmn

00

51

69 plusmn

02

30

474

plusmn 0

007

658

plusmn 0

06

525

plusmn 0

03

665

plusmn 0

04

258

plusmn 0

03

219

plusmn 0

02

Air

ndashndash

ndash2

342

180

472

650

521

661

256

218

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 10: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

756 S Mizote et al

Kr and Ar data lie on the air line but Xe shows a slightenrichment compared to the atmospheric ratio as is alsoshown in Fig 1

Matsuda et al (1993) indicated that splash-form tektitesincorporated their nobles gases at pressures equivalent to 20ndash40 km altitude based on the assumption of simple

equilibrium solubility As these authors did not carry out thecrushing and heating experiments performed here theirvalues are based on the gas amounts released by total fusionFurthermore they used solubility data at 1350degC much lowerthan the formation temperature of tektites Thus their altitudevalues represent lower limits The altitude estimated from the

Fig 4 Concentrations of 84Kr (a) and 132Xe (b) plotted against 36Ar content in Muong Nong-type tektites splash-form tektites and impactglasses Impact glasses (open symbols) indicate Darwin glasses (open triangles Matsuda et al 1989) Aouelloul (open circles) Zhamanshin(open squares) and Libyan Desert glasses (open diamonds Matsubara et al 1991) Normal tektites (closed symbol) are from the Australasianstrewn fields thailandites (closed triangles Hennecke et al 1975 Matsuda et al 1993) indochinites from Vietnam (closed circles Matsubaraand Matsuda 1991 Matsuda et al 1993) and australites (closed triangles Matsubara and Matsuda 1991 Matsuda et al 1993) These data wereobtained by heating of bulk samples In the present work we plotted the total values for each sample as the data on Muong Nong-type tektites(closed diamonds) because we analyzed each Muong Nong-type tektite sample both by the crushing and the heating techniques The datawithout arrows are after blank correction if it was less than 30 of the value and those with arrows show data without blank correction (ieupper limits) A dashed line labeled as ldquoAirrdquo shows the ratio of noble gases in the terrestrial atmosphere

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 11: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

Noble gases in Muong Nong-type tektites 757

partial pressure of the noble gases in a large vesicle in aphillippinite was 40ndash50 km (Matsuda et al 1996) The valueof 8 to 30 km estimated for the Muong Nong-type tektites asthe maximum altitude in this study is lower than those forsplash form tektites in agreement with the occurrence ofMuong Nong-type tektites closer to the (inferred) sourcecrater The wide distribution of splash-form tektites and therather limited geographical distribution of the Muong Nong-type tektitesmdash106 km2 (Schnetzler 1992) are consistent withthe estimated lower heights Therefore the present noble gasresults are in agreement with the suggestion that Muong Nongtektites have formed at lower altitudes and closer to thesource crater than splash-form tektites

AcknowledgmentsndashWe would like to thank Dr Palma and ananonymous reviewer for their critical comments that helpedto improve the manuscript C Koeberl is supported by theAustrian Science Foundation project Y58-GEO

Editorial Handlingmdash Dr Michael Gaffey

REFERENCES

Barnes V E 1989 Origin of tektites Texas Journal of Science 415ndash33

Beran A and Koeberl C 1997 Water in tektites and impact glassesby FTIR spectrometry Meteoritics amp Planetary Science 32211ndash216

Bigazzi G and de Michele V 1996 New fission-track agedeterminations on impact glasses Meteoritics amp PlanetaryScience 31234ndash236

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Neodymium and strontium isotopic study of Australasiantektites New constraints on provenance and age of targetmaterials Geochimica et Cosmochimica Acta 56483ndash492

Glass B P 1990 Tektites and microtektites Key facts andinferences Tectonophysics 171393ndash404

Glass B P and Barlow R A 1979 Mineral inclusions in MuongNong-type indochinites Inplications concerning parent materialand process of formation Meteoritics 1455ndash67

Glass B P and Koeberl C 1989 Trace element study of high- and

low-refractive index Muong Nong-type tektites from IndochinaMeteoritics 24143ndash146

Glass B P Koeberl C Blum J D Senftle F Izett G A Evans BJ Thorpe A N Povenmire H and Strange R L 1995 AMuong Nong-type Georgia tektite Geochimica etCosmochimica Acta 594071ndash4082

Glass B P Wasson J T and Futrell D S 1990 A layered moldavitecontaining baddeleyite Proceedings 17th Lunar and PlanetaryScience Conference pp 415ndash420

Hennecke E W Manuel O K and Sabu D D 1975 Noble gases inThailand tektites Journal of Geophysical Research 802931ndash2934

Izett G A and Obradovich J D 1992 Laser-fusion 40Ar39Ar ages ofaustralasian tektites Lunar and Planetary Science 23593ndash594

Jessberger E and Gentner W 1972 Mass spectrometric analysis ofgas inclusions in Muong Nong glass and Libyan Desert glassEarth and Planetary Science Letters 14221ndash225

King E A 1977 The origin of tektites A brief review AmericanScientist 65212ndash218

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Sciences 14323ndash350

Koeberl C 1990 The geochemistry of tektites An overviewTectonophysics 171405ndash422

Koeberl C 1992 Geochemistry and origin of Muong Nong-typetektites Geochimica et Cosmochimica Acta 561033ndash1064

Koeberl C 1994 Tektites origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderGeological Society of America 293133ndash151

Lacroix A 1935 Les tectites sans formes figureacutee de lrsquoIndochineAcademie des Science Paris Comptes Rendus Serie B SciencesPhysiques 2002129ndash2132

Lux G 1987 The behaviour of noble gases in silicate liquidsSolution diffusion bubbles and surface effects withapplications to natural samples Geochimica et CosmochimicaActa 511549ndash1560

Matsubara K and Matsuda J 1991 Anomalous Ne enrichments intektites Meteoritics 26217ndash220

Matsubara K and Matsuda J 1995 Laboratory experiments on theNe enrichments in terrestrial natural glasses GeochemicalJournal 29 293ndash300

Matsubara K Matsuda J and Koeberl C 1991 Noble gases and K-Ar ages in Aouelloul Zhamanshin and Libyan Desert impactglasses Geochimica et Cosmochimica Acta 552951ndash2955

Matsuda J and Nagao K 1986 Noble gas abundances in deep-seasediment core from eastern equatrorial Pacific GeochemicalJournal 2071ndash80

Matsuda J Matsubara K Yajima H and Yamamoto K 1989Anomalous Ne enrichment in obsidians and Darwin glassDiffusion of noble gases in silica-rich glasses Geochimica etCosmochimica Acta 533025ndash3033

Matsuda J Matsubara K and Koeberl C 1993 Origin of tektitesConstraints from heavy noble gas concentrations Meteoritics 28586ndash589

Matsuda J Maruoka T Pinti D L and Koeberl C 1996 Noble gasstudy of a philippinite with an unusually large bubbleMeteoritics 31273ndash277

Matsuda J Matsumoto T Seta A Tsuchiyama A Nakashima Yand Yoneda S 2000 Noble gases in a large bubble in modaviteA comparison with phillippinite In International Conference onCatastrophic Events amp Mass Extinction Impact and Beyond LPIContribution No 1053 pp 135ndash136

Matsuda J Matsumoto T Sumino H Nagao K Yamamoto J

Table 5 Estimated vesicularities and closing altitudes of the samples

Sample

Vvesicle

(10-4 cm3)Vesicularitya

(cm3cm3)

P36Ar

(10-6 atm)Altitude(km)

MN 8301 36 060 29 20MN 8307 97 11 13 27MN 8309 75 12 31 20MN 8310 39 054 12 78MN 8311 62 11 24 22MN 8317 99 15 086 30MN 8318 10 15 12 28MN X-103 24 02 65 13

aVesicularities [cm3cm3] were calculated assuming a density of 23 gcm3Uncertainties in the determinations of Ar and Ne contents in the samplewould result in uncertainties of about plusmn1 km in the estimated altitudes

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109

Page 12: Noble gases in Muong Nong-type tektites and their implications · Noble gases in Muong Nong-type tektites 749 where mX represents a noble gas isotope of mass “ m.” Helium data

758 S Mizote et al

Kaneoka I Takahata N and Sano Y 2002 The recommended3He4He ratio of the new internal He standard HESJ (He Standardof Japan) Geochemical Journal 36191ndash195

Matsumoto T Chen Y and Matsuda J 2001 Concomitantoccurrence of primordial and recycled noble gases in the Earthrsquosmantle Earth and Planetary Science Letters 18535ndash47

Matsumoto T Seta A Matsuda J Takebe M Chen Y and Arai S2002 Helium in the Archean komatiites revisited Significantlyhigh 3He4He ratios revealed by fractional crushing gasextraction Earth and Planetary Science Letters 196213ndash225

Meisel T Koeberl C and Jedlicka J 1989 Geochemical studies ofMuong Nong-type indochinites and possible Muong Nong-typemoldavites Meteoritics 24303

Miura Y and Nagao K 1991 Noble gases in six GSJ igneous rocksamples Geochemical Journal 25163ndash171

Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord (Lecture notes in earth sciences Volume 93 BerlinSpringer 364 p

Murty S V S 1997 Noble gases and nitrogen in Muong Nongtektites Meteoritics amp Planetary Science 32687ndash691

Muumlller O and Gentner W 1973 Enrichment of volatile elements inMuong Nong-type tektites Clues to their formation historyMeteoritics 8414ndash415

Niedermann S and Eugster O 1992 Noble gases in lunaranorthositic rocks 60018 and 65315 Acquisition of terrestrialkrypton and xenon indicating an irreversible adsorption processGeochimica et Cosmochimica Acta 56493ndash509

Ozima M and Podosek F A 1983 Noble Gas GeochemistryCambridge Cambridge University Press 367 p

Palma R L Rao M N Rowe M W and Koeberl C 1997 Kryptonand xenon fractionation in North American tektites Meteoriticsamp Planetary Science 329ndash14

Storzer D and Wagner G A 1977 Fission track dating of meteoriteimpacts Meteoritics 12368

Schnetzler C C 1992 Mechanism of Muong Nong-type tektiteformation and speculation on the source of Australasian tektitesMeteoritics 27154ndash165

Taylor S R 1973 Tektites A post-Apollo view Earth ScienceReviews 9101ndash123

Wada N and Matsuda J 1998 A noble gas study of cubic diamondsfrom Zaire Constraints on their mantle source Geochimica etCosmochimica Acta 622335ndash2345

Wasson J T 1991 Layered tektitesmdashA multiple impact origin for theAustralasian tektites Earth and Planetary Science Letters 10295ndash109