National Aeronautics and Space Administration grants NAG9-48 and 9-580 and NAGW-3396 and 3640; Department ofEnergy grant DE-FG07-80ER1 072SJ; and the W.M. KeckFoundation.

ReferencesDep, L., D. Elmore, M.E. Lipschutz, S. Vogt, F.M. Phillips, and M.

Zreda. 1994. Depth dependence of cosmogenic neutron-captureproduced 36G1 in a terrestrial rock. Nuclear Instruments andMethods in Physics Research, B92(1-4), 301-307.

Dodd, R.T., S.F. Wolf, and M.E. Lipschutz. 1993. An H chondritestream: Identification and confirmation. Journal of GeophysicalResearch-Planets, 98(8), 15105-15118.

Elmore, D., L. Dep, R. Flack, M.J. Hawksworth, D.L. Knies, E.S.Michiovich, T.E. Miller, K.A. Mueller, F.A. Rickey, P. Sharma, P.C.Simms, H.-J. Woo, M.E. Lipschutz, S. Vogt, M.-S. Wang, and M.C.Monaghan. 1994. The Purdue Rare Isotope Measurement Labo-ratory. Nuclear Instruments and Methods in Physics Research,B92(1-4), 65-68.

Hiroi, T., G.M. Pieters, M.E. Zolensky, and M.E. Lipschutz. 1993. Evi-dence of thermal metamorphism on C, G, B, and F asteroids. Sci-ence, 261(5124), 1016-1018.

Hiroi, T., G.M. Pieters, M.E. Zolensky, and M.E. Lipschutz. 1994.Possible thermal metamorphism on the C, G, B, F asteroidsdetected from their reflectance spectra in comparison with car-bonaceous chondrites. Proceedings of the NIPR Symposium onAntarctic Meteorites, 7, 230-243.

Knies, D.L., D. Elmore, P. Sharma, S. Vogt, R. Li, M.E. Lipschutz, G.Petty, J. Farrel, M.G. Monaghan, S. Fritz, and E. Agee. 1994. 7Be,10Be, and 36G1 in precipitation. Nuclear Instruments and Methodsin Physics Research, B92(1-4), 340-344.

Lipschutz, M.E. In press. Neutron activation analysis and accelera-tor mass spectrometer studies of extraterrestrial materials. Pro-ceedings of the Symposium on Applications of Nuclear Chemistry.

Lipschutz, M.E., S.F. Wolf, S. Vogt, E. Michlovich, M.M. Lindstrom, M.E.Zolensky, D.W. Mittlefehldt, C. Satterwhite, L. Schultz, T. Loeken, P.Scherer, R.T. Dodd, D.W.G. Sears, P.H. Benoit, J.F. Wacker, R.G.Burns, and D.S. Fisher. 1993. Consortium study of the unusual Hchondrite regolith breccia, Noblesville. Meteoritics, 28(4), 528-537.

Michiovich, E.S., S. Vogt, J. Masarik, R.C. Reedy, D. Elmore, and M.E.Lipschutz. 1994. 26M, 10Be, and 36C1 depth profiles in the Canyon

Diablo iron meteorite. Journal of Geophysical Research-Planets,99(11), 23187-23194.

Michlovich, E.S., S.F. Wolf, M.-S. Wang, S. Vogt, D. Elmore and M.E.Lipschutz. In press. Chemical studies of H chondrites—V. Tem-poral variations of sources. Journal of Geophysical Research-Planets, 100(3).

Olsen, E., A. Davis, R.S. Clarke, Jr., L. Schultz, H.W. Weber, R. Clay-ton, T. Mayeda, E. Jarosewich, P. Sylvester, L. Grossman, M.-S.Wang, M.E. Lipschutz, I.M. Steele, and I. Schwade. 1994. Watson:A new link in the HE iron chain. Meteoritics, 29(2), 200-213.

Petaev, M.I., L.D. Barsukova, M.E. Lipschutz, M.-S. Wang, A.A.Ariskin, R.N. Clayton, and T.K. Mayeda. 1994. The Divnoe Mete-orite: Petrology, chemistry, oxygen isotopes and origin. Meteorit-ics, 29(2), 182-199.

Sack, R.O., M.S. Ghiorso, M.-S. Wang, and M.E. Lipschutz. 1994.Igneous inclusions from ordinary chondrites: High temperatureresidues and shock melts. Journal of Geophysical Research-Plan-ets, 99(12), 26029-26044.

Sears, D.W.G., A.D. Morse, R. Hutchison, R.K. Guimon, L. Jie, G.M.O.'D. Alexander, P.H. Benoit, I. Wright, C. Pillinger, T. Xie, andM.E. Lipschutz. In press. Metamorphism and aqueous alterationin low petrographic type ordinary chondrites. Meteoritics.

Treiman, A.H., G.A. McKay, D.D. Bogard, M.-S. Wang, M.E. Lip-schutz, D.W. Mittlefehldt, L. Keller, M.M. Lindstrom and D. Gar-rison. 1994. Comparison of the LEW 88516 and ALH A77005Shergottites. Similar but distinct. Meteoritics, 29(5), 581-592.

Vogt, S., M.-S. Wang, and M.E. Lipschutz. 1994. Chemistry opera-tions at Purdue's Accelerator Mass Spectrometry Facility.Nuclear Instruments and Methods in Physics Research, B92(1-4),153-157.

Wang, M.-S., E.S. Michlovich, S. Vogt, and M.E. Lipschutz. 1994.Labile trace elements and cosmogenic radionuclides in chon-dritic hosts of three consortium igneous inclusions. Proceedingsof the NIPR Symposium on Antarctic Meteorites 7, 144-149.

Wolf, S.F., and M.E. Lipschutz. In press a. Chemical studies of Hchondrites—IV. New data and comparison of antarctic popula-tions. Journal of Geophysical Research-Planets, 100(3).

Wolf, S.F., and M.E. Lipschutz. In press b. Chemical studies of Hchondrites—VI. Antarctic/non-antarctic compositional differ-ences revisited. Journal of Geophysical Research-Planets, 100(3).

Wolf, S.F., and M.E. Lipschutz. In press c. Multivariate statisticaltechniques for trace element analysis. In M. Hyman and M.Rowe (Eds.), Advances in analytical geochemistry.

Compositional studies of new groups of chondritic meteoritesALAN E. RUBIN and GREGORY W. KALLEMEYN, Institute of Geophysics and Planetary Physics, University of California,

LosAngeles, California 90024-1567

The abundances of refractory and common nonvolatileelements in chondritic meteorites are similar to those in

the Sun's photosphere. These meteorites represent unfrac-tionated samples of the solid materials that existed in theearly solar nebula. Different groups of chondrites have dis-tinct bulk compositions and mineralogical and textural char-acteristics; researchers infer that each group was derivedfrom a separate asteroid. The large number of meteorite

samples discovered in Antarctica in the last 25 years (morethan 15,000) has led to the discovery of new chondritegroups. During the last year, we analyzed members of twonew groups by instrumental neutron activation analysis todetermine the concentrations of 27 elements with differentgeochemical affinities. We combined these data with miner-alogical and petrographic studies to characterize the chon-drite groups.

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The CR carbonaceous chondrite group comprises sixindependent meteorites, four of which are from Antarctica(Weisberg et al. 1993; Kallemeyn, Rubin, and Wasson 1994).These chondrites have refractory lithophile element abun-dances of approximately 1.OxCI, that is, they are approxi-mately equal to those in CI carbonaceous chondrites (thegroup most similar in composition to the Sun). The abun-dance of metallic iron-nickel (Fe-Ni) is 100-160 milligramsper gram, unusually high for carbonaceous chondrites. Chon-drules are large (approximately 900 micrometers) and some-what irregular in shape; magnetite framboids are common.Previous studies of metallic Fe-Ni grains in CR chondrites(Lee, Rubin, and Wasson 1992) have shown that these mete-orites experienced some reduction during weak thermalmetamorphism. The magnetite framboids formed fromhydrothermal alteration of metal-rich precursors on the par-ent asteroid.

Several years ago, we described a new grouplet of chon-drites that were not members of the ordinary, carbonaceous orenstatite chondrite classes; we called these meteorites CarlisleLakes chondrites after the largest member (Rubin and Kale-meyn 1989). Since that time, several new specimens have beendescribed, most from Antarctica (e.g., Rubin and Kallemeyn1994), but one observed 1934 fall from Rumuruti, Kenya,recently turned up in the Berlin collection, and the group hasbeen renamed R chondrites after this specimen (Schulze et al.1994). The R chondrites constitute the 12th major chondritegroup: they are characterized by a high degree of iron oxida-tion, a low chondrule/groundmass modal abundance ratio,and a high abundance of the oxygen isotope 170 (e.g., Weis-berg et al. 1991; Bischoff et al. 1994). Refractory lithophileabundances are about 0.9xCI, indicating a moderate depletionin these elements relative to CI chondrites. All of the R chon-drites exhibit moderate metamorphic re crystallization and

most exhibit significant brecciation and/or moderate impactmelting. Several of the samples are regolith breccias that onceresided at the surface of their parent asteroid: they consist oflight-colored, highly metamorphosed clasts surrounded byless-metamorphosed, dark-colored material containing solar-wind-implanted noble gases.

This work was supported in part by National ScienceFoundation grant EAR 91-19065.

References

Bischoff, A., T. Geiger, H. Palme, B. Spettel, L. Schultz, P. Scherer, T.Loeken, P. Bland, R.N. Clayton, T.K. Mayeda, U. Herpers, B. Melt-zow, R. Michel, and B. Dittrich-Hannen. 1994. Acfer 217—A newmember of the Rumuruti chondrite group (R). Meteoritics, 29(2),264-274.

Kallemeyn, G.W., A.E. Rubin, and J.T. Wasson. 1994. The composi-tional classification of chondrites: VI. The CR carbonaceous chon-drite group. Geochimica et CosmochimicaActa, 58(13), 2873-2888.

Lee, M.S., A.E. Rubin, and J.T. Wasson. 1992. Origin of metallic Fe-Niin Renazzo and related chondrites. Geochimica et CosmochimicaActa, 56(6), 2521-2533.

Rubin, A.E, and G.W. Kallemeyn. 1989. Carlisle Lakes and Allan Hills85151: Members of a new chondrite grouplet. Geochimica et Cos-mochimicaActa, 53(11),3035-3044.

Rubin, A.E., and G.W. Kallemeyn. 1994. Pecora Escarpment 91002: Amember of the new Rumuruti (R) chondrite group. Meteoritics,29(2), 255-264.

Schulze, H., A. Bischoff, H. Palme, B. Spettel, G. Dreibus, and J. Otto.1994. Mineralogy and chemistry of Rumuruti: The first meteoritefall of the new R chondrite group. Meteoritics, 29(2), 275-286.

Weisberg, M.K., M. Prinz, H. Kojima, K. Yanai, R.N. Clayton, and T.K.Mayeda. 1991. The Carlisle Lakes-type chondrites: A new groupletwith high A 170 and evidence for nebular oxidation. Geochimica etCosmochimica Acta, 55(9), 2657-2669.

Weisberg, M.K., M. Prinz, R.N. Clayton, and T.K. Mayeda. 1993. TheCR (Renazzo-type) carbonaceous chondrite group and its implica-tions. Geochimica et CosmochimicaActa, 57(7), 1567-1586.

Stability of antarctic blue icefields over the last 300,000 years:Meteorites as surface exposure markers

PAUL H. BENOIT, JOYCE ROTH, HAZEL SEARS, and DEREK W.G. SEARS, Department of Chemistry and Biochemistry, University ofArkansas, Fayetteville, Arkansas 72701

Bare "blue" icefields are found in the inland portions of theantarctic ice sheet and are especially common in places

where ice flow is disturbed by interaction of the ice withmountain chains, nunataks, and sub-ice topography (Delisleand Sievers 1991; Takahashi et al. 1992, pp. 128-139). Theablation of deep ice on these icefields sometimes results in theaccumulation of entrained rocks on the ice surface, and thecomposition of these "moraines" can be indicative of regionaliceflow dynamics (Faure et al. 1987). Among the rocks in themoraines are sometimes found meteorites; at some icefields,meteorites are the most common type of morainal specimen,with hundreds of meteorite fragments collected on the ice sur-

face (Whillans and Cassidy 1983; Cassidy et al. 1992). Using theactivity of cosmogenic radionuclides, one can determine howlong each individual meteorite has been on Earth, that is, itsterrestrial age. In this article, we discuss the use of thermolu-minescence of antarctic meteorites to determine how longindividual meteorites have been exposed on the ice surface asopposed to being buried within the ice, that is, a surface expo-sure age. These data, coupled with terrestrial age data, permitstudy of the stability of the iceflelds on which the meteoriteswere found over the last 500,000 years or so.

The interaction of cosmic rays with meteorites in spaceresults in the production of radionuclides, including carbon-

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