Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.469g&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 469
Other
26
Carbon, Chemical Composition, Meteoritic Composition, Nitrogen, Pyroxenes, Abundance, Chemical Analysis, Isotopic Enrichment
Scientific paper
Reclassification of ALH 84001 as an orthopyroxenite related to SNCs brings the total number of martian meteorites to 10. Preliminary descriptions of ALH 84001 and the more detailed analysis that followed highlighted the presence of abundant Fe, Mg-carbonates distributed heterogeneously throughout the specimen. Previous studies of SNCs identified four discrete carbon-bearing components: materials that combusted at temperatures usually associated with organics, carbonates, magmatic carbon, and trapped martian atmospheric carbon dioxide. The isotopic compositions of these species are distinctive, and have been used to constrain the operation of martian surficial processes. Given the relatively high carbonate abundance in ALH 84001, detailed isotopic analyses of the specimen will undoubtedly provide further information on the formation mechanisms of these minerals. Nitrogen analysis could identify the presence of any N-bearing salts and trapped atmospheric species. This abstract reports the first results from analysis of carbon in ALH 84001. A high-resolution stepped combustion of 5.099 mg of powdered ALH 84001 was performed. The most outstanding feature of the analysis was the release of almost 50% of the total C across a narrow temperature range from 450-525 C, with (delta)C-13 is approximately +40%. The enrichment C-13 in carbonates from ALH 84001 indicates beyond any doubt that these salts are truly indigenous to the meteorite, rather than an Antarctic weathering product. Wright et al. defined a linear relationship between yield and C isotopic composition of carbonate in SNCs; the datum from ALH 84001 extends this association. For the carbonate to be formed by interaction of martian atmospheric CO2 with regolith material, reaction would need to have occurred at temperatures around 100 C. Such a high temperature is unlikely on the martian surface, and therefore the carbonates more probably formed in a hydrothermal environment.
Douglas Craig C.
Grady Michael
Pillinger Colin T.
Wright Ian P.
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