Noble gases in two shergottites and one nakhlite from Antarctica: Y000027, Y000097, and Y000593
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概要
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We have investigated secondary influences on the noble gas budget in rim and interior pairs of three Martian meteorites from Antarctica: the lherzolitic shergottites Y000027 and Y000097, and the nakhlite Y000593. Three factors have been found to influence the original Martian noble gas budget: shock metamorphic overprint, cosmic irradiation, and terrestrial weathering. The ^3He/^4He ratio of the shergottites is between 0.189 and 0.217, which indicates almost complete loss of radiogenic ^4He. This is expected from the high shock pressure observed in the shergottite samples. The concentration of ^4He in these shergottite samples ranges from 33.8 to 39.4 × 10^<−8> ccSTP/g. ^<22>Ne in the shergottites is on the order of 14 × 10^<−9> ccSTP/g. The nakhlite has 800 × 10^<−8> ccSTP/g 4He and 26 × 10^<−9> ccSTP/g ^<22>Ne. An indication for solar cosmic ray contribution to the neon budget can be found in the shergottites. As Y000027 and Y000097 are reported to be paired we conclude the cosmic ray exposure (CRE) age T_(3+21) of this shergottite to be 4.41 ± 0.54 Ma. For the nakhlite Y000593 T_(3+21) is 11.8 ± 0.3 Ma. Heavy noble gas concentrations show large differences between rim and interior samples with the rim samples having 1.3–2.9, 1.7–38, and 1.4–20 times as much ^<36>Ar, ^<84>Kr, and ^<132>Xe, respectively. The enrichment of heavy noble gases in the rim samples indicates severe terrestrial contamination. The relation between ^<129>Xe/^<132>Xe and ^<84>Kr/^<132>Xe in the rim samples shows that the incorporation mechanism caused elemental fractionation of Kr and Xe to the extent that in the Y000027 shergottite samples any Martian signature is completely masked by terrestrial contamination, if the total is taken. Only the 1400 °C steps show clear evidence for Martian atmosphere. The Y000593 nakhlite interior sample, on the other hand, shows low ^<84>Kr/^<132>Xe in relation to ^<129>Xe/^<132>Xe, which is characteristic for fractionated Martian atmosphere observed in nakhlites.
著者
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Schwenzer S.P.
Max-Planck-Institut fur Chemie, J.-J. Becherweg 27, 55128 Mainz, Germany
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Herrmanna S.
Max-Planck-Institut fur Chemie, J.-J. Becherweg 27, 55128 Mainz, Germany
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Ott U.
Max-Planck-Institut fur Chemie, J.-J. Becherweg 27, 55128 Mainz, Germany
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Ott U.
Max-planck-institut Fur Chemie J.-j. Becherweg 27 55128 Mainz Germany
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Herrmanna S.
Max-planck-institut Fur Chemie J.-j. Becherweg 27 55128 Mainz Germany
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Schwenzer S.p.
Max-planck-institut Fur Chemie J.-j. Becherweg 27 55128 Mainz Germany
関連論文
- Noble gases in two shergottites and one nakhlite from Antarctica: Y000027, Y000097, and Y000593
- Yamato-82042: An unusual carbonaceous chondrite with CM affinities