Isotopic evidence for a martian regolith component in martian meteorites.

Noble gas measurements in gas-rich impact-melt (GRIM) glasses in EET79001 shergottite showed that their elemental and isotopic composition is similar to that of the Martian atmosphere [1-3]. The GRIM glasses contain large amounts of Martian at-mospheric gases. Those measurements further sug-gested that the Kr isotopic composition of Martian atmosphere is approximately similar to that of solar Kr. This suggestion was validated by [4] after detailed comparison of the lunar and Martian meteorite noble gas data. Subsequently, Garrison and Bogard [5] car-ried out improved noble gas measurements on GRIM glasses (,8 and ,104) which showed that the lighter isotopes of Kr in GRIM glasses are slightly enriched relative to the lighter Kr isotopes in solar wind im-planted into lunar soils, suggesting a mass-fractionation trend of 0.5-1.0% per amu (Fig. 1). The data-average from [2] and [3] for GRIM glass ,27 shows a slightly lower mass fractionation trend com-pared to the data-average from [5] for ,8A and ,8B glasses. Considering the uncertainities in the meas-urements of ,27 and ,8 glasses, we adopt a value of 1.03 for (