Martian atmospheric xenon contents of Nakhla mineral separates: implications for the origin of elemental mass fractionation

Analyses of mineral separates from Nakhla reveal that Martian atmosphere-derived xenon is present in olivine and pyroxene in concentrations close to that of the bulk meteorite, and at elevated concentrations in mesostasis. We argue that neither aqueous alteration nor adsorption followed by shock incorporation are plausible mechanisms for incorporating this gas component into the meteorite, and suggest trapping occurred on formation. Direct dissolution of Martian atmosphere in the parent melt is unlikely since it would require a partial pressure of xenon in the Martian atmosphere greater than consideration of the I–Xe system realistically allows. The melt appears to have been insufficiently hydrated for water transport to have been solely responsible. Addition of as little as 500 ppm of Martian soil to the melt could account for the observed composition and elemental mass fractionation.