Rubin, Alan E. and Griset, Christian D. and Choi, Byeon-Gak and Wasson, John T. (2009) Clastic matrix in EH3 chondrites. Meteoritics and Planetary Science, 44 (4). pp. 589-601. ISSN 1086-9379 http://resolver.caltech.edu/CaltechAUTHORS:20090914-105926490
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Patches of clastic matrix (15 to 730 μm in size) constitute 4.9 vol% of EH3 Yamato (Y-) 691 and 11.7 vol% of EH3 Allan Hills (ALH) 81189. Individual patches in Y-691 consist of 1) ~25 vol% relatively coarse opaque grain fragments and polycrystalline assemblages of kamacite, schreibersite, perryite, troilite (some grains with daubréelite exsolution lamellae), niningerite, oldhamite, and caswellsilverite; 2) ~30 vol% relatively coarse silicate grains including enstatite, albitic plagioclase, silica and diopside; and 3) an inferred fine nebular component (~45 vol%) comprised of submicrometer-size grains. Clastic matrix patches in ALH 81189 contain relatively coarse grains of opaques (~20 vol%; kamacite, schreibersite, perryite and troilite) and silicates (~30 vol%; enstatite, silica and forsterite) as well as an inferred fine nebular component (~50 vol%). The O-isotopic composition of clastic matrix in Y-691 is indistinguishable from that of olivine and pyroxene grains in adjacent chondrules; both sets of objects lie on the terrestrial mass-fractionation line on the standard three-isotope graph. Some patches of fine-grained matrix in Y-691 have distinguishable bulk concentrations of Na and K, inferred to be inherited from the solar nebula. Some patches in ALH 81189 differ in their bulk concentrations of Ca, Cr, Mn, and Ni. The average compositions of matrix material in Y-691 and ALH 81189 are similar but not identical—matrix in ALH 81189 is much richer in Mn (0.23 ± 0.05 versus 0.07 ± 0.02 wt%) and appreciably richer in Ni (0.36 ± 0.10 versus 0.18 ± 0.05 wt%) than matrix in Y-691. Each of the two whole-rocks exhibits a petrofabric, probably produced by shock processes on their parent asteroid.
|Additional Information:||© 2009 The Meteoritical Society. Received 18 June 2008; revision accepted 22 January 2009. We are grateful to the curators at the National Institute of Polar Research, Japan, for the loan of the thin section of Y-691 and permission to analyze it with the ion microprobe. We also thank the curators at NASA Johnson Space Center and the Antarctic Meteorite Working Group for the loan of a section of ALH 81189. We thank Y. Guan of Caltech for technical assistance with the ion probe, C. Lau of UCLA for his help in determining the petrofabrics, and G. R. Huss of the University of Hawai’i for discussions about (and generation of new data on) the abundance of matrix material in EH3 chondrites. We are grateful to M. Kimura and S. Ebata for their reviews of the manuscript. This work was supported in part by NASA grants NNG06GF95G (A. E. Rubin) and NNG06GG35G (J. T. Wasson), and Korea Science and Engineering Foundation (KOSEF) grant R01-2006-000-10522-0 (B.-G. Choi).|
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|Deposited By:||Tony Diaz|
|Deposited On:||16 Sep 2009 22:27|
|Last Modified:||26 Dec 2012 11:22|
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