Martian xenon components in Shergotty mineral separates: Locations, sources, and trapping mechanisms

Abstract

Isotopic signatures and concentrations of xenon have been measured in Shergotty mineral separates by laser step heating. Martian atmosphere and martian interior xenon are present, as is a spallation component. Martian atmospheric xenon is 5-10 times more concentrated in opaque minerals (magnetite, ilmenite, and pyrrhotite) and maskelynite than in pyroxenes, perhaps reflecting grain size variation. This is shown to be consistent with shock incorporation. A component consisting of solar xenon with a fission contribution, similar to components previously identified in martian meteorites and associated with the martian interior, is best defined in the pyroxene-dominated separates. This component exhibits a consistent 129Xe (129Xe/132Xe ~1.2) excess over solar/planetary (129Xe/132Xe ~1.04). We suggest that gas present in the melt, perhaps a mixture of interior xenon and martian atmosphere, was incorporated into the pyroxenes in Shergotty as the minerals crystallized.