Meteorite studies:Terrestrial and extraterrestrial

applications, 1991

MICHAEL E. LIPSCHUTZ

Department of ChemistryPurdue University

West Lafayette, Indiana 47907

Since 1969, recovery teams from Japan, the United States,and most recently, a consortium of European countries haverecovered about 14,400 meteorite fragments from Antarctica.These derive from an estimated 3,600 ± 1,800 distinct impactson the ice sheet, a number at least comparable to recoveriesfrom the rest of the Earth over all time. Less than 1,000 of theantarctic samples have had more than cursory examination,and only a very few have been studied in great detail. Never-theless, sufficient information is available to demonstrate thatthe antarctic meteorite population differs significantly in manyways from nonantarctic falls, as proposed originally by Den-nison, Lingner, and Lipschutz (1986). As part of a group of 10papers (summarized by Koeberl and Cassidy 1991) studyingthis topic, Lipschutz and Samuels (1991) examined previouslypublished trace-element data for ordinary, i.e., H (or high-iron)and L (or low-iron) groups of chondrites by standard and newlydeveloped multivariate statistical techniques. Lipschutz andSamuels (1991) demonstrated the significance of the composi-tional difference for each group of antarctic and nonantarcticmeteorites beyond any reasonable doubt. They argued that thecause was a preterrestrial difference in average chondritic ther-mal history, the conclusion also reached by the summary ofKoeberl and Cassidy (1991).

Petrochemical data obtained by Sack, Azeredo, and Lip-schutz (1991) using electron probe microanalysis indicate thattwo antarctic olivine-rich diogenites from the howardite-eucrite-diogenite (HED) association of achondritic meteorites,provide the key to understanding the formation of the HEDparent body-4 Vesta or some other rare V-type asteroid. Theseancient basaltic mantle samples indicate an origin by partialmelting and apparently eliminate the possibility for significantfractional crystallization during formation and evolution of theparent body.

Most of the research carried out by my group to date hasinvolved radiochemical neutron activation analysis and atomicabsorption spectroscopy to determine part-per-million to part-per-trillion levels of 12 to 15 trace elements in each samplestudied. These elements are important because of their chal-cophile, lithophile, and siderophile geochemistry and espe-cially because most are labile (i.e., highly responsive to thermalprocesses), a state that usually accompanies geochemical orcosmochemical fractionation. Hence, in their absolute contentsand relative abundance trends, these elements can record var-ious fractionation events, both preterrestrial and terrestrial,during residence in and/or on the ice sheet. During the pastyear, the results of radiochemical neutron activation analysisstudies of antarctic and nonantarctic eucrites (Paul and Lip-schutz 1990a; cf., Lipschutz 1991a) and four antarctic carbona-ceous chondrites (Paul and Lipschutz 1990b) have been pub-lished. As noted by Lipschutz (1991a), the results of Paul andLipschutz (1990b) are of such interest as to warrant studies of

additional antarctic carbonaceous chondrites. Data for 39 ofthese meteorites are now in hand and indicate that the geneticpicture previously developed from studies of nonantarctic sam-ples is seriously flawed. In particular, observations that labileelement contents were quantized (indicating a two-componentmixing model), have given way to an essentially continuouscompositional distribution (indicating that carbonaceous chon-drites are random samples of matter hydrated preterrestriallyto different extents). Further, these results (to be presented atthe 54th Annual Meteoritical Society Meeting)—like those forall antarctic lunar meteorites studied to date (Lindstrom et al.,1991a, 1991b)—demonstrate the absence of any identifiable al-teration due to weathering during the meteorites' residence inAntarctica. If any meteorites would be expected to exhibit sucheffects, these should. Hence, compositions of antarctic meteo-rites yield unique genetic information and are changing, in afundamental way, our previous view of bodies in the inner solarsystem (Lipschutz 1991b). Information about the nature of theMoon deduced from lunar meteorites is sometimes at variancewith that obtained from Apollo samples. Whether this reflectsa biased population of lunar meteorites or of sampling duringthe Apollo missions remains to be determined (Lindstrom etal., 1991a, 1991b).

An analytical capability new to our research group is accel-erator mass spectrometry and during the past year we contin-ued (Lipschutz 1991a) to develop an accelerator mass spectrom-etry facility at Purdue University, primarily to measure thecosmogenic radionuclides shown in the table. We have pro-gressed according to schedule and our first results, for chlorine-36 in samples of the crater-forming Canyon Diablo meteorite,are in hand (Elmore et al., in preparation). This dedicated fa-cility is intended to become a national accelerator mass spec-trometry facility for the earth and planetary science commu-nities. If progress remains on schedule, within 1 year we planto be serving the communities' needs for tracer and datingstudies of meteorites and terrestrial antarctic (and nonantarctic)rock and ice samples.

Cosmogenic radionuclides

Half-lifeIsotope (in millions of years)

Beryllium-10 1.6Aluminum-26 0.74Chlorine-36 0.30Calcium-41 0.10Iodine-129 16

This research was supported in part by National ScienceFoundation grants DPP 87-15853 and EAR 89-16667 and Na-tional Aeronautics and Space Administration grant NAG 9-48.

References

Dennison, J.E., D.W. Lingner, and M.E. Lipschutz. 1986. Antarctic andnon-Antarctic meteorites form different populations. Nature, 319,390-393.

56 ANTARCTIC JOURNAL

Elmore, D., F.A. Rickey, P.C. Simms, M.E. Lipschutz, K.A. Mueller,and T.E. Miller. In preparation. PRIME Lab: A dedicated AMS facilityat Purdue University. In A. Long (Ed.), Proceedings of the FourteenthInternational Radiocarbon Conference, 20-24 May 1991, Tucson, Arizona,Center for the Study of Environmental Radioisotopes, University ofArizona.

Koeberl, C., and W.A. Cassidy. 1991. Differences between Antarcticand non-Antarctic meteorites: An assessment. Geochimica et Cosmo-chitnica Acta, 55, 3-18.

Lindstrom, MM., D.W. Mittlefehldt, R.R. Martinez, M.E. Lipschutz,and M.-S. Wang. 1991a. Geochemistry of Yamato 82192, 86032 and793274 Lunar Meteorites. Proceedings of the NIPR Symposium on Ant-arctic Meteorites, 4, 12-32.

Lindstrom. M.M., S.J. Wentworth, R.R. Martinez, D.W. Mittlefehldt,D.S. McKay, M.-S. Wang, and M.E. Lipschutz. 1991b. Geochemistryand Petrology of the MacAlpine Hills Lunar Meteorites. Geochimicaet Cosmochimica Acta, 55, 3089-3103.

Lipschutz, M.E. 1991a. Meteorite studies: Terrestrial and extraterres-trial applications, 1990. Antarctic Journal of the U.S., 25(5), 49-50.

Lipschutz, M.E. 1991b. The impact of Antarctic meteorites on the con-ventional view of the inner solar system. Observatory, 111, 7-8.

Lipschutz, M.E., and S.M. Samuels. 1991. Ordinary chondrites: Mul-tivariate statistical analysis of trace element contents. Geochmnmica etCosmochimica Acta, 55, 19-47

Paul, R.L., and M.E. Lipschutz. 1990a. Chemical studies of differen-tiated meteorites—I. Labile trace elements in Antarctic and non-Antarctic eucrites. Geochimica et Cosmnochimica Acta, 54, 3185-3195.

Paul, R.L., and M.E. Lipschutz. 1990b. Consortium study of labile traceelements in some Antarctic carbonaceous chondrites: Antarctic andnon-Antarctic meteorite comparisons. In K. Yana (Ed.), Proceedingsof the NIPR Symposium on Antarctic Meteorites, 3, 80-95, 6-8 June 1989,Tokyo, Japan, National Institute of Polar Research.

Sack, R.O., W.J. Azeredo, and M.E. Lipschutz. 1991. Olivine diogen-ites: The mantle of the eucrite parent body. Geochimica et CosmochimicaActa, 55, 1111-1120.

Terrestrial agesof antarctic meteorites

K. NisHlizuMi

Department of ChemistryUniversity of California, San Diego

La Jolla, California 92093-0317

P. SHARMA and P.W. KuBIK*

Nuclear Structure Research LaboratoryUniversity of Rochester

Rochester New York 14627

We continue to study cosmogenic nuclides in antarctic me-teorites. Through our measurement program on cosmogenicnuclides in antarctic ice, Greenland ice, antarctic rocks, andantarctic meteorites, we hope to understand meteorite accu-mulation mechanisms as well as the history of both polar icesheets and climatic change. In addition, we are studying thehistory of antarctic meteorites and cosmic rays. Our probes aremainly the long-lived, cosmic-ray-produced radionuclides ber-ylium-lO, aluminum-26, clorine-36, calcium-41, manganese-53,and iodine-129. The major objective is to measure terrestrialages of meteorites based on chlorine-36 concentrations. Chlo-rine-36 was determined using the University of Rochester tan-dem accelerator. We, at the University of California, San Diego,have developed a new dating method; we measure in situ pro-duced berylium-10 and aluminum-26 in terrestrial quartz (Laland Arnold 1985). We have applied this technique to several

antarctic mountains and moraines to understand duration ofexposure above glaciers and erosion rates for the antarctic con-tinent (Nishiizumi et al. 1986; Nishiizumi et al. 1991). We havemeasured terrestrial ages of meteorites from 29 locations inAntarctica although only one or two meteorites were measuredat many sites. We found stony meteorites with ages greaterthan 200,000 years at seven locations (Allan Hills, DominionRange, Elephant Moraine, Lewis Cliff, MacAlpine Hills, PecoraEscarpment, and Thiel Mountain). Four iron meteorites(DRP7800I-9, 1LD83500, Lazarev, and Mount Wegener), whichwere found on bedrock or in moraines, are all old (0.26-5 mil-lion years).

The figure shows a histogram of terrestrial ages of Yamato,Allan Hills, and other antarctic meteorites. Pairs of meteoritesare shown as one object plotted at the average age. Althoughthe total amount of data is nearly double, the general trendremains the same as in the previous publication on this subject(Nishiizumi, Elmore, and Kubik 1989).

There are four interesting points.• Many of the Lewis Cliff meteorites are as old as the Allan

Hills (Main Icefield**) meteorites. Although we have meas-ured only nine Lewis Cliff meteorites, five out of nine ofthem have terrestrial ages greater than 200,000 years. Noclear correlation has been found between the terrestrial agesand the locations of Lewis Cliff meteorites. Very old andyoung meteorites were found on both the lower and upperice tongues of Lewis Cliff. Fireman (1988) measured the ageof one dust-containing ice sample from lower Lewis Cliff icetongue using a uranium-thorium dating method. The terres-trial ages of Lewis Cliff meteorites, which we have measured,are significantly longer than the age of this Lewis Cliff ice,25,000 years. If we accept the young age for the Lewis Cliffice, then we must conclude either that ice from Law Glaciermust have flowed continuously into the Lewis Cliff ice tongue

*Present address: Inst it ut für Mittelenergiephysik,Eidgenossische TechnischeHochschule, Hon ggerherg, Zürich,Switzerland.

**The designation "Main Icefield" is not an official name, but the fea-ture is a distinct geographic unit.

1991 REVIEW 57