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Noble gases and chemical composition of Shergotty mineral fractions, Chassigny, and Yamato 793605: The trapped argon‐40/argon‐36 ratio and ejection times of Martian meteorites
Author(s) -
TERRIBILINI DARIO,
EUGSTER OTTO,
BURGER MARIO,
JAKOB ALFRED,
KräHENBÜHL URS
Publication year - 1998
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.1998.tb01673.x
Subject(s) - meteorite , achondrite , martian , isochron , geology , mars exploration program , isotopes of argon , chemical composition , pyroxene , argon , noble gas , astrobiology , martian surface , mineralogy , geochemistry , chondrite , chemistry , olivine , physics , organic chemistry
Abstract— We report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene, maskelynite/mesostasis glass, and bulk material of Shergotty and of bulk samples from Chassigny and Yamato 793605. The 40 K‐ 40 Ar isochron for the Shergotty minerals yields a gas retention age of 196 Ma, which is, within errors, in agreement with previously determined Rb‐Sr internal isochron ages. Argon that was trapped at this time has a 40 Ar/ 36 Ar ratio of 1100. For Chassigny and Y‐793605, we obtain trapped 40 Ar/ 36 Ar ratios of 1380 and 950, respectively. Using these results and literature data, we show that the three shergottites, Shergotty, Zagami, and QUE 94001; the lherzolites ALH 77005, LEW 88516, and Y‐793605; as well as Chassigny and ALH 84001 contain a mixture of Martian mantle and atmospheric Ar; whereas, the trapped 40 Ar/ 36 Ar ratio of the nakhlites, Nakhla, Lafayette, and Governador Valadares cannot be determined with the present data. We show that Martian atmospheric trapped Ar in Martian meteorites is correlated with the shock pressure that they experienced. Hence, we conclude that the Martian atmospheric gases were introduced by shock into the meteoritic material. For the Shergotty minerals, we obtain 3 He‐, 21 Ne‐, and 38 Ar‐based cosmic‐ray exposure ages of 3.0 Ma, and for the lherzolite Y‐793605, 4.0 Ma, which confirms our earlier conclusion that the lherzolites were ejected from Mars ∼1 Ma before the shergottites. Chassigny yields the previously known ejection age of 11.6 Ma.