Origin of gabbroic shergottite Northwest Africa 6963 from an ~180-million-year-old flood basalt province on Mars

To understand chemical variability within individual martian meteorites, we report major, minor, trace, and highly siderophile element abundances, as well as ¹⁸⁷Re-¹⁸⁷Os, for four separate rock fragments of gabbroic shergottite Northwest Africa (NWA) 6963. The compositions of these aliquots are consistent with data for NWA 6963 from Filiberto et al. (2018). Data reported for NWA 6963 in Day et al. (2018) and Tait and Day (2018) should no longer be used due to doubt in provenance of the sample fragment used in those studies. Genuine fragments of NWA 6963 show significant variability in elements due to different modal proportions of minerals. Terrestrial weathering effects appear to be most pronounced for Ba and Pb. The age and composition of NWA 6963 indicate that it may be related to enriched basaltic shergottites and some olivine–phyric and poikilitic shergottites that are referred to here as the “enriched shergottite group.” The ¹⁸⁷Re-¹⁸⁷Os systematics of the enriched shergottite group all conform to generation at ~180 million years from the same or similar mantle sources with long-term Re/Os enrichment on Mars. They show coherent fractional crystallization trends in plots of compatible elements with the possibility for impact-contaminated regolith assimilation in NWA 6963. The enriched shergottite group may represent magmatism akin to terrestrial continental flood basalt provinces. Entrainment of incompatible trace element enriched upper mantle in an otherwise deeply-derived incompatible trace element depleted mantle plume head in Mars at 180 million years ago may explain the similar crystallization ages of both enriched shergottites and some intermediate shergottites.