Quantifying noble gas contamination during terrestrial alteration in Martian meteorites from Antarctica

摘要: We investigated exterior and interior subsamples from the Martian shergottite meteorites Allan Hills (ALH) A77005 Roberts Massif (RBT) 04261 for secondary minerals, oxygen isotopes, Ar-Ar, noble gas signatures. Electron microprobe investigations revealed that RBT does not contain any visible alteration even in its most fractures, whereas fracture fillings ALHA77005 penetrate into meteorite up to 300 μm, beyond which fractures are devoid of minerals. Light gases seem be almost unaffected by terrestrially induced both meteorites. Thus, a shock metamorphic overprint 30–35 GPa can deduced helium measurements 04261. Oxygen isotopes also weathering variations easily reconciled with differences modal mineralogy subsamples. The on irradiated samples (Ar-Ar) showed clear atmospheric contribution ALHA77005, but this is less apparent our sample Exterior show slight ages, overall results very similar between two. In contrast, krypton xenon severely affected terrestrial contamination, demonstrating ubiquitous presence elementally fractionated air Although seemingly contradictory, indicate was more contamination than ALHA77005. conclude irrespective planet occurred, exposure rocks atmosphere (or brine) introduces signatures relative respective composition rock, relationships process or mineralogical observations straightforward.