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Stable isotopes in Allan Hills 84001: An ion microprobe study

Eiler, J. M. and Valley, J. W. and Stolper, E. M. (1997) Stable isotopes in Allan Hills 84001: An ion microprobe study. Meteoritics and Planetary Science, 32 (S4). A38-A38. ISSN 1086-9379. doi:10.1111/j.1945-5100.1997.tb01599.x.

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The temperature of formation of carbonates in ALH 84001 provide a test of the hypothesis that they contain features produced by ancient martian life [1], and contributes to our understanding of the global budgets of martian volatiles. We have determined the micrometer-scale distribution of O and C isotope ratios in carbonate concretions, enstatite, and SiO_2 in ALH 84001 by ion microprobe as a means of constraining the range of possible temperatures of fluid-rock interaction [2]. The principal results are: (1) Carbonate δ^(18)O is 9.5-20.6‰, SMOW, significantly expanding the range from bulk analysis. The magnesite rim is higher in δ^(18)O than Ca-rich (0.07 ≤ X_(ca) ≤ 0.13) cores. (2) Variations in δ^(18)O occur over length scales as small as 50 µm. (3) Interiors of fractured orthopyroxene that hosts carbonate are homogeneous to within ±1‰. (4) Secondary SiO_2 has a δ^(18)O of 20.4‰. These data are inconsistent with mutual O isotope equilibrium among carbonate and silicate minerals and indicate either fine-scale mineral-mineral equilibrium at a range of temperatures ≤ 300°C or a failure to attain mineral-mineral equilibrium. Mineralogical evidence for disequilibrium supports the latter interpretation. Our δ^(18)O values for carbonates have been confirmed by two studies [3], and extended to compositions of carbonate not found in our sample.

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Stolper, E. M.0000-0001-8008-8804
Additional Information:© 1997 The Meteoritical Society.
Issue or Number:S4
Record Number:CaltechAUTHORS:20130709-094347673
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Official Citation:(1997), Abstracts. Meteoritics & Planetary Science, 32: A5–A147. doi: 10.1111/j.1945-5100.1997.tb01599.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39264
Deposited By: Tony Diaz
Deposited On:10 Jul 2013 18:19
Last Modified:09 Nov 2021 23:43

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