Computer Science
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33..721g&link_type=abstract
Meteoritics & Planetary Science, vol. 33, no. 4, pp. 721-736.
Computer Science
32
Scientific paper
Isotopic abundances of the noble gases were measured in the following Martian meteorites: two shock glass inclusions from EET79001, shock vein glass from Shergotty and Y793605, and whole rock samples of ALH84001 and QUE94201. These glass samples, when combined with literature data on a separate single glass inclusion from EET79001 and a glass vein from Zagami, permit examination in greater detail the isotopic composition of Ne, Ar, Kr, and Xe trapped from the Martian atmosphere. The isotopic composition of Martian Ne, if actually present in these glasses, remains poorly defined. The 40Ar/36Ar ratio of trapped Martian atmospheric Ar is probably considerably lower than the nominal ratio of 3000 measured by Viking, and data on impact glasses suggest a value of ~1900. The atmospheric 36Ar/38Ar ratio is (4.0. Martian atmospheric Kr may be enriched in lighter isotopes by ~0.5%/amu compared to both solar wind Kr and to the Martian composition previously reported. The isotopic composition of Xe in these glasses agrees with that previously reported in the literature. The Martian atmospheric 36Ar/132Xe and 84Kr/132Xe elemental ratios are higher than those reported by Viking by factors of ~2.5-1.6 (depending on the 40Ar/36Ar adopted) and ~1.8, respectively and are discussed in a separate paper. Cosmogenic gases indicate space exposure ages of 2.7 (0.6 Myr for QUE94201 and Shergotty and 14(1 Myr for ALH84001. Small amounts of 21Ne produced by energetic solar protons may be present in QUE94201, but are not present in ALH84001 or Y793605. The space exposure age for Y793605 is 4.9 (0.6 Myr and appears to be distinctly older than the ages for basaltic shergottites. However, uncertainties in cosmogenic production rates still makes somewhat uncertain the number of Martian impact events required to produce the exposure ages of Martian meteorites.
Bogard Donald D.
Garrison Daniel H.
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