variation of chemical composition in australasian tektites ... · oxide ratio plots, were used to...

Meteoritics amp Planetary Science 41 Nr 1 107ndash123 (2006)Abstract available online at httpmeteoriticsorg

107 copy The Meteoritical Society 2006 Printed in USA

Variation of chemical composition in Australasian tektites from different localities in Vietnam

Kassa AMARE and Christian KOEBERL

Department of Geological Sciences University of Vienna Althanstrasse 14 A-1090 Vienna AustriaCorresponding author E-mail christiankoeberlunivieacat

(Received 05 October 2004 revision accepted 06 August 2005)

AbstractndashOne hundred and thirteen Australasian tektites from Vietnam (Hanoi Vinh Dalat andSaigon areas) were analyzed for their major and trace element contents The tektites are either ofsplash form or Muong Nong-type The splash-form tektites have SiO2 contents ranging from 697 to768 wt whereas Muong Nong-type tektites which are considerably larger than splash-formtektites and have a blocky and chunky appearance have slightly higher silica contents in the range of74ndash81 wt Major-element relationships such as FeO versus major oxides Na2O versus K2O andoxide ratio plots were used to distinguish the different groups of the tektites In addition correlationcoefficients have been calculated for each tektite group of this study Many chemical similarities arenoted between Hanoi and Vinh tektites from the north of Vietnam except that the Hanoi tektitescontain higher contents of CaO than Vinh the higher content of CaO might be due to some carbonateparent material Both Dalat and Saigon tektites have nearly similar composition whereas the bulkchemistries of the tektites from Hanoi and Vinh appear different from those of Saigon and DalatThere are differences especially in the lower CaO and Na2O and higher MgO FeO for the tektites ofDalat and Saigon in comparison to that of Hanoi tektites Furthermore the Dalat and Saigon tektitesshow enrichments by factors of 3 and 2 for the Ni and Cr contents respectively compared to those ofHanoi and Vinh The difference in chemistry between the North Vietnam tektites (Hanoi Vinh) to thatof South Vietnam tektites (Saigon Dalat) of this study indicate that the parent material washeterogeneous and possibly mixing between different source rocks took place

Muong Nong-type tektites are enriched in the volatile elements such as Br Zn As and Sbcompared to the average splash-form tektites of this study The chemical compositions of the averagesplash-form and Muong Nong-type tektites of this study closely resemble published data for averagesplash-form and Muong Nong-type indochinites indicating that they have the same source The traceelement ratios BaRb (27) ThU (52) ThSc (13) ThSm (22) and the rare earth element (REE)abundances of this study show close similarities to those of average upper continental crust

INTRODUCTION

Tektites are natural glasses that are millimeter- tocentimeter-sized and occur in four major geographicallyextended strewn fields (eg Barnes 1963 1964 1990 Chao1963) North American ~35 Ma old (Storzer and Wagner1971 Glass et al 1985 1995) Central European (moldavites)144 Ma old (Staudacher et al 1982 Laurenzi et al 2003)Ivory Coast 107 Ma old (Koeberl et al 1997) andAustralasian 08 Ma old (Izett and Obradovich 1992) Despitesome earlier hypotheses regarding their origin (OrsquoKeefe1976 1994) most workers now agree that the bulk of thephysical and chemical data on tektites is consistent with their

formation by impact melting of terrestrial rocks (probablysediments) caused by the hypervelocity impact of an asteroidor cometary nucleus (eg Glass 1990 Koeberl 1986 19901992 1994 Blum et al 1992) The chemical and isotopiccomposition of tektites is similar to that of the uppercontinental crust (eg Taylor 1973 Koeberl 1986 1994)Tektite glasses are not only found on land but microtektitesalso occur in deep-sea sediments in three of the four strewnfields (eg Glass 1969 1990 Koeberl and Glass 1988)where they are important to define the extent of the strewnfields to constrain the stratigraphic age of tektites and toprovide evidence for the possible location of the sourcecraters Apart from the microtektites tektites (on land) occur

108 K Amare and C Koeberl

in three main forms 1) normal or splash-form tektites 2)aerodynamically shaped tektites and 3) Muong Nong-type(layered) tektites The aerodynamic ablation results frompartial re-melting of the tektite glasses and is known mainlyfrom the Australasian strewn fields primarily as flanged-button australites The shape of the splash-form tektites(spheres droplets tear drops dumbbells etc) is not formedaerodynamically but results mostly from the solidification ofrotating solids (Koeberl 1990 Elkins-Tanton et al 2003)Muong Nong-type tektites named after a type locality in Laos(Lacroix 1935) are usually considerably larger than normaltektites and have chunky and blocky appearance Mostcontain more vesicles are more heterogeneous on amillimeter scale and have higher volatile element contents

than the splash-form tektites (eg Koeberl 1992 Schnetzler1992) They are mostly found in Indochina in the countries ofLaos Vietnam Thailand Cambodia and adjacent areas ofChina The purpose of the present paper is to provide precisemajor and trace element analyses of a large tektite samplesuite to determine the regional variation in the chemicalcomposition to compare their chemical variation with otherAustralasian tektites and to provide further constraints on thenature of their precursor rocks This is the first time such alarge trace element data set was determined for a large samplesuite from a subset of the Australasian strewn field

SAMPLES AND ANALYTICAL METHODS

Tektites were collected from different localities inVietnam (areas near Hanoi Vinh Dalat and Saigon) asshown in Fig 1 Our samples range from only a fewmillimeters to about 4 cm in diameter and belong mostly tothe splash-form variety except three samples from Dalat twofrom Vinh and one from Saigon which are of Muong Nong-type We analyzed 113 tektite samples from differentlocalities of Vietnam these are from a collection given toC Koeberl by the late E Izokh (Novosibirsk) which is nowat the University of Vienna Department of GeologicalSciences The weights of the tektites are in the range between02 to 30 g for the Hanoi and Vinh area tektites except onesample from Hanoi having 54 g and tektites from Dalatweigh 04 to 35 g the Muong Nong-type tektites ranged inweight from 172 to 683 g The samples were split andfragments for analysis were carefully crushed into chips (20to 60 mg) and then rinsed with clean acetone and distilledwater and dried Only clean fragments were analyzed Thetektites were analyzed for their major and trace elementcontents First the trace elements were analyzed byinstrumental neutron activation analysis (INAA) at theDepartment of Geological Science University of ViennaAbout 20 to 60 mg of each sample and about 100 mg ofinternational rock standards were used for irradiation Detailson analytical techniques standards instrumentationcorrection procedures as well as data on precision andaccuracy of our method are described by Koeberl (1993)Specific uncertainties for the elements reported here usingour current INAA procedure are given in Son and Koeberl(2005) (their Table 3)

After a cooling period of 6 months the irradiated tektitefragments were used for electron microprobe analysis todetermine the major element contents Polished sections wereanalyzed using a four-spectrometer Cameca SX-100microprobe at the Department of Geological SciencesUniversity of Vienna at 20 keV accelerating voltage 20 nAcurrent and 1 microm beam diameter Natural and syntheticstandards were used for calibration and the PAP correction(Pouchou and Pichoir 1991) was applied to the data Typicaluncertainties are about 1 to 2 rel

Fig 1 Schematic map of Vietnam and the neighboring countries ofIndochina Tektites analyzed in the present study were collected byE Izokh (deceased formerly Academy of Sciences of the USSRNovosibirsk) in the 1970s from locations near the locations markedwith stars Precise finding coordinates are not available

Variation of chemical composition in Australasian tektites from different localities in Vietnam 109

RESULTS

Major Element Composition

The major and trace element composition of the 113tektite samples as well as averages and standard deviationsare presented in Table 1 (available online at httpmeteoriticsorgOnline20Supplementshtm) The averagemajor oxide compositions of this study (Tables 1 and 2) areconsistent with average indochinite data (given in Table 3)All tektite samples analyzed have silica contents rangingbetween 70 and 81 wt with an average of 736 wt (Tables1 and 2) The data show an inverse relationship between thecontent of SiO2 and that of the oxides of Al Ti Fe and Mgsome of these correlations are shown in Fig 2 A stronginverse relationship is apparent between SiO2 versus TiO2Al2O3 and FeO (Fig 2) Both Na and K abundances scattermore widely than those of other oxides (Figs 2 and 3)Commonly the individual analyzed specimens show slightvariations in chemical composition between each other Thisvariation as indicated by the standard deviation (Table 1) isdifferent for each of the localities Some of the majorelements such as MgO (216 wt) CaO (207 wt) andNa2O (118 wt) show large deviations from their averagecontents which may reflect a chemically inhomogeneoussource rock The contents of the oxides of Ca and Mg in oursample suite are quite variable and span a wide range AsFig 2 illustrates these elements define two somewhatdifferent groups a high-Ca group extending to 35 wt withsmall variation in Mg content and a high-Mg groupextending to 35 wt with comparatively smaller variation inCa There are also related differences in the iron contentThese variations significantly exceed analytical uncertaintiesAs expected the splash-form tektites are more homogeneousin composition with silica contents ranging from 70 to76 wt whereas the Muong Nong-type tektites have highersilica contents from 74 to 81 wt (Table 2)

To minimize the overlap among the major element datafor different groups of tektites plots of FeO versus majoroxides have been used (Figs 3andashe) From these plotsdifferences between the sample locations are observed forFeO versus Na2O FeO versus CaO and FeO versus K2O ForFeO versus Al2O3 and FeO versus MgO (Figs 3a and 3b) nodifferences are obvious between the Hanoi and Vinh groupsor between the Saigon and Dalat groups The Hanoi and Vinhsamples have higher contents of CaO and lower FeO contentsand higher FeO and lower alkali contents than the Dalat andSaigon tektites (Figs 3cndashe) In addition there is a reasonablecorrelation between the FeO and the Al2O3 and MgO contents(Figs 3a and b) but poor correlations with CaO and Na2O(Figs 3c and 3e) On the other hand the Na2O versus K2Oplot shows no distinction between the different locations(Fig 3f) Figure 4 shows oxide ratio plots for the Vietnamsplash-form and Muong Nong-type tektites the ratios plotted

are those that seemed to show the best separation between thegroups In these diagrams (Figs 4andashd) the distinction betweenthe two groups (Hanoi + Vinh and Dalat + Saigon) is evenmore clearly expressed than in Fig 3 The Muong Nong-typetektites show a wide compositional range but seem to fitbetter to the Hanoi + Vinh group Here within the geographicgroups there is higher variation in the CaOTiO2 ratio Thehigh-Ca Hanoi (18ndash301 wt) and high-Ca Vinh tektites(163ndash276 wt) show large variations of their CaTiO2ratios whereas the high-Mg (18ndash34) and FeO (44ndash55 wt) tektites (Dalat and Saigon) are concentrated at theleft-bottom side of the diagram with less spread than theHanoi and Vinh tektites Figure 5 shows the comparison ofmajor and trace element compositions for the average splash-form tektites of the different locations of this study comparedto each other Based on major element data there is a goodcorrelation between tektites from the Hanoi and Vinh areas onthe one hand (Fig 5a) and among the Dalat and Saigon areatektites on the other (Fig 5b) this is also expressed in traceelement data (Figs 5cndashd) On the other hand largerdifferences exist if the other groups are plotted against eachother

Trace Element Composition

Trace elements can be used to infer similarities anddifferences between tektites from a certain strewn field andsource rocks (eg Koeberl 1986 1990) Results of traceelement contents for our sample suite are also given inTables 1 and 2 Figure 6 shows the correlation for traceelement abundances between the average data of our study(both splash-form and Muong Nong-type tektites) versus theliterature data for average indochinites Muong Nong-typetektites and the upper continental crust The average Vietnamtektites have somewhat higher contents in Zn and U andslightly higher Co contents compared to average indochinites(Fig 6a) Abundances are also within a factor of two or so ofthat of the average continental crust (Fig 6c) whereas MuongNong-type tektites show more variability (Figs 6b and 6d)Further comparisons between Muong Nong-type tektites andsplash-form tektites both from Vietnam (our study) areshown in Fig 7 Major element compositions are very similar(Fig 7a) but there are some differences in the trace elementcompositions between the two types (Fig 7b)

Siderophile Trace ElementsThere is a good correlation in the abundance of Ni and Co

between Hanoi and Vinh tektites and between Dalat andSaigon tektites (Figs 5cndashf) The content of Cr is slightlydepleted in the Saigon tektites (128 ppm) compared to theDalat tektites (174 ppm) In terms of average siderophileelement contents there is a difference between the Hanoi-Vinhand Dalat-Saigon tektites eg the average Ni content of theHanoi and Vinh samples is 36 and 48 ppm respectively


Table 2 Major and trace element compositions for Muong Nong-type tektites collected from Vinh Dalat and Saigon areas Vietnam

12d (Vinh)

Tk18-c (Dalat)

Tk8-a (Saigon)

A55-c (Vinh)

A55-d (Vinh)

A64 (Dalat) Avg Std dev Range

Original weight (g) 120 094 020 683 449 459

SiO2 7430 8050 8085 7569 7766 7503 7734 282 7430minus8085TiO2 076 052 049 078 066 077 066 013 049minus078Al2O3 1250 857 892 1148 1024 1143 1052 156 857minus125FeO 463 325 311 407 343 395 374 058 311minus463MnO 009 012 009 005 007 006 008 003 005minus012MgO 235 140 122 180 151 181 168 040 122minus235CaO 185 201 172 157 174 168 176 015 157minus201Na2O 105 096 115 103 103 103 104 006 096minus115K2O 236 216 229 247 228 241 233 011 216minus247Total 9990 9950 9984 9894 9863 9819

Sc 103 112 141 118 951 108 113 158 951minus141Cr 153 801 100 926 752 806 969 290 752minus153Co 238 133 158 154 129 142 159 40 129minus238Ni 87 62 43 31 66 39 55 21 314minus868Zn 22 75 70 62 68 72 61 20 218minus749As 107 112 518 421 392 432 659 341 392minus112Br 26 25 10 09 19 11 17 08 085minus260Rb 122 119 142 116 968 109 117 150 968minus142Zr 287 292 307 414 361 354 336 494 287minus414Sb 156 117 096 064 062 067 094 037 062minus156Cs 688 718 939 832 798 731 784 093 688minus939Ba 315 297 315 349 302 335 319 198 297minus349La 384 406 451 430 405 422 416 232 384minus451Ce 807 751 876 822 796 841 816 423 751minus876Nd 431 361 365 363 359 327 368 34 327minus431Sm 658 651 752 703 592 680 673 054 592minus752Eu 147 122 134 127 139 141 135 009 122minus147Gd 596 528 570 549 611 511 561 039 511minus611Tb 098 100 112 098 101 089 100 007 089minus112Tm 061 047 050 057 051 054 053 005 047minus061Yb 377 326 345 346 289 344 338 029 289minus377Lu 059 052 053 056 052 054 054 003 052minus059Hf 827 766 772 109 107 113 943 171 766minus113Ta 146 128 138 148 131 149 140 009 128minus149W 81 91 10 45 67 29 54 31 10minus91Ir (ppb) lt18 lt36 lt04 lt35 lt18 lt16Au (ppb) 18 04 10 12 09 13 11 046 040minus18Th 161 153 170 162 133 158 156 126 133minus170U 318 354 280 322 233 236 291 049 233minus354

KU 6184 5077 6815 6379 8149 8512 6853 1285 5077minus8512ThU 506 432 607 503 571 669 548 085 432minus669LaTh 239 265 265 265 305 267 268 021 239minus305ZrHf 347 381 398 380 337 313 375 320 313minus398HfTa 566 598 559 736 817 758 575 111 559minus817LaNYbN 688 842 883 840 947 829 838 085 688minus947EuEu 072 064 063 062 071 073 067 005 062minus073N = chondrite-normalized (Taylor and McLennan 1985) major elements in wt trace elements in ppm except as noted all Fe given as FeO


whereas that of the Dalat and Saigon tektites is 159 and152 ppm respectively The NiCo ratio of the Dalat andSaigon samples is close to 8 but only 3 for the Hanoi andVinh tektites The average concentration of Ni for the splash-form tektites is 15 ppm and for the Muong Nong-type 64 ppmComparisons with crustal rocks are shown in Figs 6ndash8 Forexample the Cr and Co contents are similar to (Post-ArcheanAustralian Shale (PAAS) values (Fig 8)

Volatile Trace Elements Some of the volatile trace elements analyzed in this study

show great variability Trace element studies demonstratedthat the volatile elements such as Sb As Br and Zn haveconsiderably higher abundances in Muong Nong-type tektitesthan in splash-form tektites from the same strewn fields(Koeberl 1986 1992) Similarly the average Muong Nong-type tektites of this study shows enrichments for the Sb AsBr and Zn contents respectively compared to the averagesplash-form tektites (Figs 6b 6e and 6f)

Refractory Trace Elements Refractory elements show less variation between the

Table 3 Major and trace element compositions of the average Vietnamese tektites compared to average splash-form and Muong Nong-type indochinites the average upper continental crust and the Post-Archean Australian Shale

AvgAvgHanoi

AvgVinh

AvgDalat

AvgSaigon A B C D E

SiO2 7370 7322 7281 7326 7734 727 789 660 628TiO2 077 079 076 077 066 078 063 05 10Al2O3 1267 1292 1267 1251 1052 1337 102 152 189FeO 428 441 497 504 374 485 374 45 65MnO 009 009 010 010 008 008 001 008 011MgO 198 205 263 232 168 214 143 22 22CaO 228 207 181 157 176 198 121 42 13Na2O 112 124 108 126 104 105 092 39 12K2O 240 253 237 276 233 262 242 34 37Total 9929 9932 9920 9959 9915 9957 9946 1000 977

Sc 113 116 115 113 113 105 77 11 16Cr 78 901 180 128 969 63 606 35 110Co 141 148 243 187 159 11 126 10 23Ni 38 48 173 152 546 19 49 20 55Zn 11 24 20 39 613 57 67 71 85As 069 117 124 295 659 09 475 15 ndashBr 08 08 09 10 17 02 41 ndash ndashRb 115 125 118 121 117 130 110 112 160Zr 287 306 285 310 336 252 280 190 210Sb 050 060 081 060 094 05 082 02 ndashCs 66 741 724 719 784 65 509 37 15Ba 319 339 332 320 319 360 341 550 650La 421 418 421 387 416 365 282 30 38Ce 816 818 809 789 816 731 607 64 80Nd 368 374 374 357 368 332 291 26 32Sm 707 678 705 661 673 66 485 45 56Eu 139 140 145 127 135 122 101 088 11Gd 57 575 570 544 561 524 43 38 47Tb 106 106 106 101 10 085 075 064 077Tm 056 058 059 053 053 nd 042 033 04Yb 361 382 355 353 339 29 271 22 28Lu 054 058 055 052 054 04 042 032 043Hf 794 776 778 782 943 695 813 58 5Ta 138 143 148 133 14 16 117 22 ndashW 207 641 339 142 538 029 102 20 27Ir (ppb) lt32 lt3 lt4 lt2 lt2 002 lt1 002 ndashAu (ppb) 08 12 08 05 11 2 21 18 ndashTh 150 149 153 147 156 140 111 107 146U 280 288 328 270 291 207 248 28 31A = average Muong Nongndashtype (this study) B = average splash-form thailandites (Koeberl 1992) C = average Muong Nong-type indochinites (Koeberl

1992) D = average upper continental crust (Taylor and McLennan 1985) E = average Post-Archean Australian Shale (Taylor and McLennan 1985) majorelements in wt trace elements in ppm except as noted


locations and types (Fig 8) Except for U and Sc the data forsplash-form and Muong Nong-type of this study resemblethose of average splash-form and Muong Nong-typeindochinites (Koeberl 1992) The contents of Rb Zr U andTh are slightly depleted in both splash-form and MuongNong-type tektites (this study) compared to PAAS (Fig 8)

DISCUSSION

Here we discuss the abundances distribution andvariation in chemical composition in the Vietnam tektites and

the nature of their precursor material using major and traceelement chemistry The major element chemistry of mosttektite classes is well known (eg Chao 1963 OrsquoKeefe 1963Barnes 1964 Chapman and Scheiber 1969) In particulartektites are characterized by high SiO2 contents (65ndash85 wt)and by high FeO and low alkali contents compared tovolcanic glasses such as obsidian (Koeberl 1990) About 530Australasian tektites from 205 localities were chemicallyanalyzed by Chapman and Scheiber (1969) among whichsignificant chemical variations were found (see below) Cluesto the source material of the Vietnam tektites are provided by

Fig 2 Harker diagrams of major oxide contents versus silica contents for splash-form and Muong Nong-type Vietnam tektites (this study)a) Al2O3 and FeO strong correlation b) MgO and CaO moderate correlation c) Na2O and K2O weak correlation


average abundances and relationships between individualcomponents (Table 4) Correlation coefficients (r) werecomputed for major and some trace elements for eachgeographic group A strong negative correlation is apparentbetween SiO2-TiO2 (r = minus093) SiO2-Al2O3 (r = minus091) andSiO2-FeO (r = minus098) in the Saigon and Dalat tektites southVietnam On the other hand calcium has a significant positivecorrelation with SiO2 contents in the Dalat and Saigontektites but a negative correlation in the Hanoi and Dalattektites Moreover the CaO content is positively correlatedwith the abundances of all major oxides but silica in the Hanoi

and Vinh samples but negatively correlated with Al2O3 TiO2FeO and MnO in the Dalat tektites Contents of TiO2 have asignificant positive correlation with Al2O3 (r = +099) andFeO (r = +095) in the Dalat and Saigon areas this is muchless pronounced for the Vinh and Hanoi samples The weakcorrelation of Mn (r = +025) with SiO2 in Dalat and Saigoncould be due to the mobility of manganese probably duringweathering processes (Taylor 1962) Differences exist forsome of the major oxides such as Mg Fe Ca Na and Albetween the various locations There is a positive correlationof MgO with CaO in the Hanoi area tektites (r = +056)

Fig 3 Plots of total Fe (as FeO) versus the other major elements for splash-form tektites from Vietnam tektites (this study) Regression linescalculated from the data are shown in the cases where the correlations are statistically meaningful


which is absent in the Dalat and Saigon samples Acorrelation of the CaO with MgO contents points to adolomite component because the ratio of CaOMgOespecially in samples from the Hanoi and Vinh areas isapproximately 13 which is close to the ratio in dolomite(139) (cf Engelhardt et al 1987) As mentioned above theFeO versus major oxide plots (Fig 3) show that there is adistinction between the Hanoi and Dalat tektites and anoverlap between the Hanoi-Vinh and the Saigon-Dalat areatektites The high FeO content in the South Vietnam tektites(Dalat and Saigon) compared to the North Vietnam tektitescould result from the incorporation of residual iron oxide tothe parent material during the formation of tektites Inaddition the oxide ratio plots (eg Al2O3MgO FeOMgONa2OMgO and K2OMgO Fig 4) distinguish clearlybetween the north (Hanoi-Vinh) and South (Dalat-Saigon)Vietnam tektites Trace element contents in the tektites fromthe various localities are best used in the form of ratios suchas BaRb ThSm KU and LaSc the values of whichsupport the derivation of tektites from terrestrial post-Archean upper crustal sediments (eg Taylor 1973 Koeberl

et al 1986 Koeberl 1994) see Table 3 and Figs 6ndash8 The RbCs ratio is lower than that commonly encountered in igneousrocks and this holds also true for KCs (cf Taylor 1962) Theupper crustal RbCs and KCs ratios of 30 and 5900respectively are close to the values for the Vietnamesetektites The average KU ratios range from about 4000 to12000 which is consistent with the range encountered incrustal rocks (Taylor and McLennan 1985) The average ThUratio of 50 for the splash-form and 51 for the Muong Nong-type tektites is somewhat higher than the average crustalvalue (35) Sedimentary rocks have higher ThU ratios thanigneous rocks (McLennan 1980) The high ThU ratios of oursamples indicate that sedimentary rocks played a major rolein the source materials of these tektites this is also indicatedby the KSc KRb RbSc The elements Co Ni Cr Zr andTh are assumed to have a low mobility during sedimentaryprocesses (Taylor and McLennan 1985) These elements aremainly transported in the terrigenous sedimentarycomponents and therefore reflect the composition of thesource materials The Cr Ni Co Zr Th and U contents arerelatively uniform for both splash-form and Muong Nong-

Fig 4 Oxide ratio plots for Hanoi Vinh Dalat and Saigon tektites of this study The Hanoi-Vinh and Dalat-Saigon tektites define two clearlyseparated groups shown by regression lines


type of this study and similar (but not identical) to PAASvalues (Fig 8d) The lower contents of Ba Cs and Zn in thetektites could be due to the precursor rock which wasdepleted during sedimentation processes The elements ThU Ni Ba have higher abundance in Dalat and Saigon tektites(South Vietnam) while Zr Rb and Sc are more abundant inVinh and Hanoi tektites Rubidium shows highly significantnegative correlation (r = minus096) with silica in the Dalat

tektites and poor correlations in the Vinh and Hanoi samplesThe depletion of volatile elements (Fig 7b) in the splash-formtektites compared with that of Muong Nong-type tektites ofthis study is likely due to a temperature effect during theformation of tektites as was suggested earlier (eg Koeberl1992) Regional variations have already been described byTaylor (1962) and Taylor and Sachs (1964) who commentedon the decrease in the alkali element concentration in

Fig 5 A comparison of major and trace element compositions for the average splash-form tektites of this study a) average major oxides ofsplash-form Hanoi with average splash-form Vinh tektites b) average major oxides of splash-form Dalat versus average splash-form Saigontektites c) average trace elements of splash-form Hanoi versus average splash-form Vinh tektites d) average trace element splash-form Dalatversus average splash-form Saigon tektites e) average trace element splash-form Hanoi versus average splash-form Dalat tektites f) averagetrace element contents of splash-form Vinh versus average splash-form Saigon tektites


australites from west to east across Australia A similarvariation exists in our data set with variations in the contentsof a number of elements from North to South VietnamFurthermore Taylor (1962) suggested that tektites may be theresult of mixing or fusion between at least two materials suchas quartz-sandstone and shale our data confirm this as wellGeochemical studies of tektites have shown that their

compositions can be explained as melts of upper crustal targetrocks with a very small projectile contribution (ltlt 1) andpossibly loss of some elements by selective volatilization(eg Blum et al 1992 Koeberl and Shirey 1997 Barrat et al1997) No extraterrestrial component is evident from the datafor the Vietnam tektites as the contents of Ni and othersiderophile elements are within the range of sedimentary

Fig 6 A comparison of the average splash-form tektites (this study) and the average Muong Nongtype tektites of this study with (a) and (d)average splash-form indochinites (Koeberl 1992) (b) and (e) average Muong Nong-type indochinites (Koeberl 1992) (c) and (f) averageupper crust (Taylor and McLennan 1985)


precursor materials The REEs are particularly useful todetermine the source of tektites several authors (eg Taylorand McLennan 1979 Koeberl 1990 1992 Wasson 1991)have noted that the REE patterns of tektites are similar tothose of the upper crustal sedimentary rocks Figure 9 showsthe (very narrow) range of the chondrite-normalized REEpatterns for four major areas of Vietnam tektites compared tothe patterns of the Muong Nong-type and splash-formindochinites The REE patterns of the tektites are very similarto those of post-Archean upper continental crust rocks with

enriched LREE relatively flat HREE patterns and significantnegative Eu anomalies (average EuEu = 06ndash08) Otherelement ratios such as LaTh and ThSc are also inagreement with sedimentary values

COMPARISON OF VIETNAMESE AND OTHER AUSTRALASIAN TEKTITES

Chapman and Scheiber (1969) analyzed major andselected trace element abundances of about 530 Australasian

Fig 7 A comparison of major elements and selected trace elements of average splash-form tektites and Muong Nong-type tektites fromVietnam (this study) with (a) and (b) average splash-form (this study) versus average Muong Nong-type (this study) c) average major oxidesnormalized to average splash-form indochinites (data from Koeberl 1992) d) average major oxides versus average normalized Muong Nong-type indochinites (data from Koeberl 1992) e) average major oxides in Vietnam tektites normalized to average upper continental crust (datafrom Taylor and McLennan 1985)


Fig 8 A comparison of some selected trace elements of splash-form tektites (this study) with a) average Vietnam tektites normalized toaverage indochinites (data from Koeberl 1992) b) average Vietnam tektites normalized to Muong Nong-type indochinites (data from Koeberl1992) c) average 15 Vietnam tektites normalized to the upper crust (Taylor and McLennan 1985) d) average Vietnam tektites normalized toPAAS (Taylor and McLennan 1985)


Table 4 Linear correlation coefficients (r) between major element oxides and selected trace elements of data (a) Hanoi (b) Vinh (c) Dalat and (d) Saigon tektites

(a) SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr Co Ni Rb ZrSiO2 1TiO2 minus056 1Al2O3 minus084 067 1FeO minus086 053 093 1MnO minus029 minus012 026 034 1MgO minus075 069 080 073 015 1CaO minus062 006 045 053 048 054 1Na2O minus030 022 minus002 009 minus028 016 003 1K2O minus008 001 018 034 019 007 017 023 1Cr minus001 007 009 018 minus005 020 minus009 015 047 1Co 014 minus007 004 007 minus003 minus008 001 minus006 057 040 1Ni 007 013 002 004 minus035 021 minus013 019 025 053 058 1Zn minus032 014 042 040 029 019 042 minus011 035 minus013 044 minus004Rb minus011 minus008 028 035 047 006 030 minus029 059 007 061 007 1Zr 033 005 minus028 minus030 minus022 minus019 minus020 minus011 minus009 minus021 minus015 minus005 minus007 1

(b) SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr Co Ni Rb ZrSiO2 1TiO2 minus056 1Al2O3 minus084 056 1FeO minus076 018 047 1MnO minus024 001 034 027 1MgO minus060 002 027 095 022 1CaO minus071 039 087 038 031 026 1Na2O minus032 072 023 006 minus012 minus012 005 1K2O minus042 049 061 004 023 minus014 064 050 1Cr minus021 008 007 047 006 048 014 017 018 1Co minus032 022 026 052 019 047 021 032 024 083 1Ni minus019 013 008 053 003 054 007 012 003 090 084 1Zn 015 008 minus038 minus028 minus045 minus024 minus046 032 minus011 minus003 minus014 minus008Rb minus020 020 023 001 017 minus008 032 054 059 013 035 minus008 1Zr 002 021 minus012 minus017 minus024 minus018 minus009 030 004 029 013 021 005 1

(c ) SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr Co Ni Rb ZrSiO2 1TiO2 minus093 1Al2O3 minus091 094 1FeO minus081 074 076 1MnO 025 minus028 minus025 003 1MgO minus061 049 045 088 minus004 1CaO 009 minus019 minus032 minus027 minus044 006 1Na2O minus035 028 016 minus015 minus026 minus022 037 1K2O minus028 037 035 minus024 minus028 minus055 002 071 1Cr 003 minus017 minus022 018 002 042 040 minus009 minus051 1Co minus012 001 minus002 032 minus016 055 033 minus013 minus050 092 1Ni minus030 010 006 036 minus006 049 035 009 minus026 081 082 1Zn 014 001 004 minus039 003 minus057 minus012 017 055 minus078 minus078 minus067Rb minus015 004 006 minus006 minus050 001 041 035 022 037 054 056 1Zr 011 minus009 minus002 minus009 minus014 minus011 minus007 minus024 minus008 007 014 002 028 1


(d) SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Cr Co Ni Rb ZrSiO2 1TiO2 minus098 1Al2O3 minus096 099 1FeO minus098 095 092 1MnO minus034 035 027 026 1MgO minus078 072 065 086 034 1CaO 037 minus046 minus057 minus031 046 011 1Na2O minus072 061 053 071 007 051 minus014 1K2O minus073 075 078 062 002 017 minus074 059 1Cr minus052 048 041 063 046 090 038 021 minus018 1Co minus045 044 041 058 030 085 022 003 minus022 096 1Ni minus024 024 021 037 030 073 035 minus018 minus043 090 097 1Zn minus022 028 033 006 minus010 minus043 minus070 026 080 minus070 minus072 minus082Rb minus096 093 092 094 014 072 minus047 070 079 040 036 015 1Zr minus054 044 035 046 046 034 017 076 051 009 minus015 minus027 054 1

Fig 9 Chondrite-normalized REE distribution in the Vietnam tektites (this study) as compared with a) average splash-form Vietnam tektites(this study) splash-form indochinites (Koeberl 1992) Muong Nong-type indochinites (Koeberl 1992) and the upper crust (Taylor andMcLennan 1985) b) average splash-form Muong Nong-type (this study) average splash-form Hanoi Vinh Dalat and Saigon tektites (thisstudy) and PAAS (Taylor and McLennan 1985) Chondrite normalization factors from Taylor and McLennan (1985)

Table 4 Continued Linear correlation coefficients (r) between major element oxides and selected trace elements of data (a) Hanoi (b) Vinh (c) Dalat and (d) Saigon tektites


tektites from 205 localities and based on the major and sometrace element contents these authors have classified theAustralasian tektites into 14 groups Some of their moredistinct groups included high-Mg tektites high-Ca(philippinites and australites) high-NaK australites high-Cu B indochinites low-Ca high-Al philippinites normal(philippinites indochinites australites) and Dalat type Someof the compositions found in our study (Tables 1ndash3) aresimilar to those reported by Chapman and Scheiber (1969)The MgO-CaO plot shows an overlap between normalindochinites australites and philippinites and Dalat-typetektites of this study but the high Mg high Ca (philippinitesand australites) are distinctly higher in Mg (up to 85 wt)and Ca (up to 10 wt) compared to our samples with up to3 wt MgO and 35 wt CaO The Dalat and Saigon tektites

of our study are similar to the Dalat-type samples ofChapman and Scheiber (1969) whereas their high-Mg grouphas higher contents of Cr (400 ppm) than the Dalat andSaigon tektites of this study (200 ppm) The range ofvariability in some trace elements such as Ba Cr and Zrgiven by Chapman and Scheiber (1969) is higher than in thisstudy The chemical composition of splash-form and MuongNong-type tektites of this study is compared to that of otherindochinites in Tables 2 and 3 and Figs 5ndash8 The majorelements of the splash-form tektites for Hanoi Vinh Dalatand Saigon are similar in composition to the average splash-form indochinites Except for higher CaO and Na2O contentsthe Muong Nong-type Vietnam tektites have similar majorelement compositions to those of the Muong Nong-typeindochinites from Thailand (Koeberl 1992) Similarly the

Fig 10 Comparison of major elements and some selected trace elements of Vietnamese tektites (this study the first four symbols of thelegend) with data (all others) from Chapman and Scheiber (1969) a) Plots of MgO versus CaO b) plots of Ni versus Cr


average trace element abundance of this study and theaverage splash-form and Muong Nong-type indochinites areshown in Fig 6 Except for higher Zn and U contents thechemical composition of splash-form Vietnam tektitesresemble those of splash-form indochinites (Fig 6a) Alsoaside for higher Co Cr and W contents the chemicalcomposition of Muong Nong-type Vietnam tektites closelyresembles the average composition of Muong Nong-typeindochinites As Muong Nong-type tektites represent meltfrom lower parts of the target stratigraphy compared tosplash-form tektites (eg Koeberl 1992 Ma et al 2004) andhave not traveled very far from their source such a limitedrange in composition argues against derivation of theseglasses from many different local sources as advocated byWasson (1991) Instead a single source region is indicatedThe comparison between average continental crust andaverage splash-form and Muong Nong- type tektites of thisstudy is shown in Figs 6 and 7 and it is evident that thecorrelation is not good for some elements Also acomparison of trace element data between tektites of thisstudy and the average upper crust (Figs 6c and 6d) showsthat some trace element correlations do not correspond Thisindicates that the tektites are a mixture of different sourcerocks Chemical compositions alone will not allow todetermine the exact source rocks of the tektites this requiresisotopic studies

SUMMARY AND CONCLUSIONS

The main target of this study was to determine the rangein chemical composition within tektites from a restricted sub-area of the Australasian strewn field and in particular toprovide a large data base for trace element contents Wemeasured the major and trace element contents of 113 tektitesfrom four different areas in Vietnam and draw the followingconclusions

1 Distinct chemical differences exist between the splash-form and Muong Nong-type tektites from Vietnam inagreement with observations made before for similarsamples from Thailand For example the splash-formtektites have lower silica contents (70ndash76 wt) andhigher average contents of MgO (17ndash31 wt ) andAl2O3 (111ndash147 wt) compared to the ranges for theMuong Nong-type tektites of 74ndash81 wt SiO2 14ndash24 wt MgO and 86ndash125 wt Al2O3 Also theMuong Nong-type tektites have higher contents of thevolatile elements than the splash-form tektites

2 The major and trace element of the splash-form andMuong Nong-type tektites of this study closelyresembles the compositions of the average splash-formand Muong Nong-type indochinites from other locationsin the strewn field This uniform chemical compositionclearly supports a similar and single source region for allthose tektite types

3 The tektites from the four regions in Vietnam can beseparated into two chemically distinct groups The Hanoiand Vinh tektites (north Vietnam) have similarabundances of major and trace elements on the otherhand Dalat and Saigon tektites (south Vietnam) also havesimilar values Tektites found in northern Vietnam havehigher contents of Na2O K2O and CaO whereas tektitesin the south have higher contents of MgO FeO Cr andNi In addition the South Vietnam tektites (Dalat andSaigon) are distinguished from those of north Vietnam(Hanoi and Vinh) by having higher MgCa and NiCoratios of 15 and 7 respectively compared to Hanoi andVinh tektites where these ratios are 09 and 26respectively The variation in some specific chemicalcharacteristics among the tektite groups in this study mostlikely reflects variation in the parent materialcomposition

4 The trace element ratios BaRb ThSm and ThSc andthe REE patterns of the tektites of Vietnam showsedimentary values and are similar to those of typicalpost Archean upper crustal rocks although there aresome differences to the average continental crust

AcknowledgmentsndashA PhD stipend from the AustrianAcademic Exchange service (OumlAD) to K A is gratefullyacknowledged C K is indebted to the late E Izokh(Novosibirsk) for the samples and for discussions Thelaboratory work was supported by the Austrian ScienceFoundation (to C K) We thank T Ntaflos (Univ of Vienna)for help with the electron microprobe analyses We aregrateful to P Claeys (Univ Brussels) and H Newsom (Univof New Mexico) for thorough and helpful reviews

Editorial HandlingmdashDr A J Timothy Jull

REFERENCES

Barnes V E 1963 Tektite strewn-fields In Tektites edited byOrsquoKeefe J A Chicago University of Chicago Press pp 25ndash50

Barnes V E 1964 Variation of petrographical and chemicalcharacteristics of indochinite tektites within their strewn fieldsGeochimica et Cosmochimica Acta 28893ndash913

Barnes V E 1990 Tektite research 1936ndash1990 Meteoritics 25149ndash159

Barrat J A Jahn B M Amose J Rocchia R Keller F Poupeau GR and Diemer E 1997 Geochemistry and origin of Libyanglasses Geochimica et Cosmochimica Acta 611953ndash1959

Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialGeochimica et Cosmochimica Acta 56483ndash492

Chao E C T 1963 The petrographic and chemical characteristics oftektites In Tektites edited by OrsquoKeefe J A Chicago Universityof Chicago Press pp 51ndash94

Chapman D R and Scheiber L C 1969 Chemical investigation ofAustralasian tektites Journal of Geophysical Research 746737ndash6776


Elkins-Tanton L T Aussillous P Bico J Queacutereacute D and Bush J WM 2003 A laboratory model of splash-form tektites Meteoriticsamp Planetary Science 381331ndash1340

Engelhardt W V Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443

Glass B P 1969 Chemical composition of Ivory Coast microtektitesGeochimica et Cosmochimica Acta 331135ndash1147

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

Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference Journal of Geophysical Research 90D175ndashD196

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

Izett G A and Obradovich JD 1992 Laser-fusion 40Ar39Ar ages ofAustralasian tektites (abstract) Lunar and Planetary Science 23593ndash594

Koeberl C 1986 Geochemistry of tektites and impact glassesAnnual Review of Earth and Planetary Science 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 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60

Koeberl C 1994 Tektite 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 Sharpton V L GSA SpecialPaper 293 Boulder Colorado Geological Society of Americapp 133ndash152

Koeberl C and Glass B P 1988 Chemical composition of NorthAmerican microtektites and tektite fragments from deep-sea drillcores and Barbados Connection to the North American strewnfield Meteoritics 21421ndash422

Koeberl C and Shirey SB 1997 Re-Os isotope systematic asdiagnostic tool for the study of impact craters and ejectaPalaeogeography Palaeoclimatology Palaeoecology 13225ndash46

Koeberl C Kluger F and Kiesl W 1986 Trace element correlationsas clues to the origin of tektites and impactites Chemie der Erde451ndash21

Koeberl C Bottomley R Glass B P and Storzer D 1997Geochemistry and age of Ivory Coast tektites and microtektitesGeochimica et Cosmochimica Acta 611745ndash1772

Lacroix A 1935 Les tektites sans formes figurees de lrsquoIndochineComptes Rendus Academie des Sciences Paris 2002129ndash2132

Laurenzi M A Bigazzi G and Balestrieri M L 2003 40Ar39Argeochronology of central European tektites (moldavites)Meteoritics amp Planetary Science 38887ndash893

Ma P Aggrey K Tonzola C Schnabel C de Nicola P Herzog GF Wasson J T Glass B P Brown L Tera F Middleton R andKlein J 2004 Beryllium-10 in Australasian tektites constraintson the location of the source crater Geochimica et CosmochimicaActa 683883ndash3896

McLennan S M and Taylor S R 1980 Th and U in sedimentaryrocks Crustal evolution and sedimentary recycling Nature 285621ndash624

OrsquoKeefe J A 1963 Tektites and their origin New York-AmsterdamElsevier 254 p

OrsquoKeefe J A 1994 The origin of tektites Meteoritics 2973ndash78Pouchou J and Pichoir F 1991 Quantitative analysis of

homogeneous or stratified microvolumes applying the modelldquoPAPrdquo In Electron probe quantitation edited by Heinrich KF J and Newbury D E New York Plenum Press pp 31ndash75

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

Son T H and Koeberl C 2005 Chemical variation within fragmentsof Australasian tektites Meteoritics amp Planetary Science 40807ndash818

Staudacher T Jessberger E K Dominik B Kirsten T andSchaeffer O A 1982 40Ar-39Ar ages of rocks and glasses fromthe Noumlrdlinger Ries and the temperature history of impactbreccias Journal of Geophysics 511ndash11

Storzer D and Wagner G A 1971 Fission-track ages of NorthAmerican tektites Earth and Planetary Science Letters 10435ndash440

Taylor S R 1962 Fusion of soil during meteorite impact and thechemical composition of tektites Nature 19532ndash33

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

Taylor S R and McLennan S M 1969 Genetic significance of thechemical composition of tektites A review Geochimica etCosmochimica Acta 331083ndash1100

Taylor S R and McLennan S M 1979 Chemical relationshipamong irghizites zhamanshinites Australasian tektites andHenbury impact glasses Geochimica et Cosmochimica Acta 431551ndash1565

Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 pp

Taylor S R and Sachs M 1964 Geochemical evidence for the originof australites Geochimica et Cosmochimica Acta 28235ndash264

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


in three main forms 1) normal or splash-form tektites 2)aerodynamically shaped tektites and 3) Muong Nong-type(layered) tektites The aerodynamic ablation results frompartial re-melting of the tektite glasses and is known mainlyfrom the Australasian strewn fields primarily as flanged-button australites The shape of the splash-form tektites(spheres droplets tear drops dumbbells etc) is not formedaerodynamically but results mostly from the solidification ofrotating solids (Koeberl 1990 Elkins-Tanton et al 2003)Muong Nong-type tektites named after a type locality in Laos(Lacroix 1935) are usually considerably larger than normaltektites and have chunky and blocky appearance Mostcontain more vesicles are more heterogeneous on amillimeter scale and have higher volatile element contents

than the splash-form tektites (eg Koeberl 1992 Schnetzler1992) They are mostly found in Indochina in the countries ofLaos Vietnam Thailand Cambodia and adjacent areas ofChina The purpose of the present paper is to provide precisemajor and trace element analyses of a large tektite samplesuite to determine the regional variation in the chemicalcomposition to compare their chemical variation with otherAustralasian tektites and to provide further constraints on thenature of their precursor rocks This is the first time such alarge trace element data set was determined for a large samplesuite from a subset of the Australasian strewn field

SAMPLES AND ANALYTICAL METHODS

Tektites were collected from different localities inVietnam (areas near Hanoi Vinh Dalat and Saigon) asshown in Fig 1 Our samples range from only a fewmillimeters to about 4 cm in diameter and belong mostly tothe splash-form variety except three samples from Dalat twofrom Vinh and one from Saigon which are of Muong Nong-type We analyzed 113 tektite samples from differentlocalities of Vietnam these are from a collection given toC Koeberl by the late E Izokh (Novosibirsk) which is nowat the University of Vienna Department of GeologicalSciences The weights of the tektites are in the range between02 to 30 g for the Hanoi and Vinh area tektites except onesample from Hanoi having 54 g and tektites from Dalatweigh 04 to 35 g the Muong Nong-type tektites ranged inweight from 172 to 683 g The samples were split andfragments for analysis were carefully crushed into chips (20to 60 mg) and then rinsed with clean acetone and distilledwater and dried Only clean fragments were analyzed Thetektites were analyzed for their major and trace elementcontents First the trace elements were analyzed byinstrumental neutron activation analysis (INAA) at theDepartment of Geological Science University of ViennaAbout 20 to 60 mg of each sample and about 100 mg ofinternational rock standards were used for irradiation Detailson analytical techniques standards instrumentationcorrection procedures as well as data on precision andaccuracy of our method are described by Koeberl (1993)Specific uncertainties for the elements reported here usingour current INAA procedure are given in Son and Koeberl(2005) (their Table 3)

After a cooling period of 6 months the irradiated tektitefragments were used for electron microprobe analysis todetermine the major element contents Polished sections wereanalyzed using a four-spectrometer Cameca SX-100microprobe at the Department of Geological SciencesUniversity of Vienna at 20 keV accelerating voltage 20 nAcurrent and 1 microm beam diameter Natural and syntheticstandards were used for calibration and the PAP correction(Pouchou and Pichoir 1991) was applied to the data Typicaluncertainties are about 1 to 2 rel

Fig 1 Schematic map of Vietnam and the neighboring countries ofIndochina Tektites analyzed in the present study were collected byE Izokh (deceased formerly Academy of Sciences of the USSRNovosibirsk) in the 1970s from locations near the locations markedwith stars Precise finding coordinates are not available


RESULTS











12d (Vinh)

Tk18-c (Dalat)

Tk8-a (Saigon)

A55-c (Vinh)

A55-d (Vinh)












AvgAvgHanoi

AvgVinh

AvgDalat

AvgSaigon A B C D E






DISCUSSION



















































REFERENCES












































RESULTS











12d (Vinh)

Tk18-c (Dalat)

Tk8-a (Saigon)

A55-c (Vinh)

A55-d (Vinh)












AvgAvgHanoi

AvgVinh

AvgDalat

AvgSaigon A B C D E






DISCUSSION



















































REFERENCES













































12d (Vinh)

Tk18-c (Dalat)

Tk8-a (Saigon)

A55-c (Vinh)

A55-d (Vinh)












AvgAvgHanoi

AvgVinh

AvgDalat

AvgSaigon A B C D E






DISCUSSION



















































REFERENCES

















































AvgAvgHanoi

AvgVinh

AvgDalat

AvgSaigon A B C D E






DISCUSSION



















































REFERENCES













































DISCUSSION



















































REFERENCES


























































































REFERENCES











































variation of chemical composition in australasian tektites ... · oxide ratio plots, were used to...

Documents