Computer Science
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33..677t&link_type=abstract
Meteoritics & Planetary Science, vol. 33, no. 4, pp. 677-684.
Computer Science
14
Scientific paper
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 40K-40Ar isochron for the Shergotty minerals yields a gas retention age of 196 Ma, within errors in agreement with previously determined Rb-Sr internal isochron ages. Argon that was trapped at this time has a 40Ar/36Ar ratio of 1100. For Chassigny and Yamato-793605 we obtain trapped 40Ar/36Ar ratios of 1380 and 950, respectively. Using these results and literature data we show that the three shergottites Shergotty, Zagami, and QUE94001, the lherzolites ALH77005, LEW88516, and Yamato-793605, as well as Chassigny and ALH84001 contain a mixture of martian mantle and atmospheric Ar, whereas the trapped (40Ar/36Ar) 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 3He-, 21Ne-, and 38Ar- based cosmic-ray exposure ages of 3.0 Ma and for the lherzolite Yamato-793605 4.0 Ma, confirming our earlier conclusion that the lherzolites were ejected from Mars about 1 Ma before the shergottites. Chassigny yields the previously known ejection age of 11.6 Ma
Burger Mario
Eugster Otto
Jakob Alfred
Krohenbohl Urs
Terribilini Dario
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