Orthopyroxenite ALH84001 and shergottite ALH77005: Additional evidence for a martian origin from noble gases

Concentrations and isotopic ratios of noble gases have been determined for two martian meteorites, ALH84001 and ALH77005. ALH84001, a newly recognized martian orthopyroxenite, has a high 129Xe132Xe ratio (≈2.1), which is similar to that observed for the glass portion (lithology C) of shergottite EETA79001. The elemental ratios of trapped Ar, Kr, and Xe, the cosmic-ray exposure age (14.5 ± 1.8 m.y.) and the KAr age (3–4 b.y.) of ALH84001 are not identical with those of EETA79001 or any other martian meteorite. Therefore, ALH84001 may not originate from the same area as the other martian meteorites. The noble gas data of ALH77005 shergottite are compatible with previously reported data. Argon, Kr, and Xe are heavily contaminated by elementally fractionated terrestrial atmospheric gases. A cosmic-ray exposure age of 2.9 ± 0.7 m.y. and a KAr age of 1.33 ± 0.13 b.y. were obtained for this meteorite.