Young magmatism and Si-rich melts on Mars as documented in the enriched gabbroic shergottite NWA 6963

Enriched shergottites contain interstitial Si-rich mesostasis; however, it is unclear whether such mesostasis is formed by impact or magmatic processes. We use laser ablation multicollector inductively coupled plasma mass spectrometry U-Pb measurements of minerals within the interstitial Si-rich mesostasis and of merrillite within the coarse-grained groundmass of Martian-enriched gabbroic shergottite Northwest Africa (NWA) 6963. The date derived of tranquillityite, Cl-apatite, baddeleyite, and feldspar from the Si-rich mesostasis is 172.4 +/- 6.1 Ma, and the derived merrillite date is 178.3 +/- 10.6 Ma. We conclude, based on textural observation, that merrillite is a late magmatic phase in NWA 6963, that it was not produced by shock, and that its U-Pb-system was not reset by shock. The indistinguishable dates of the gabbroic merrillite and the minerals within the Si-rich mesostasis in NWA 6963 indicate that the Si-rich mesostasis represents a late-stage differentiated melt produced in the final phase of the magmatic history of the gabbroic rock and not a shock melt. This can likely be transferred to similar Si-rich mesostases in other enriched shergottites and opens the possibility for investigations of Si-rich mesostasis in enriched shergottites to access their magmatic evolution. Our results also provide a crystallization age of 174 +/- 6 Ma (weighted average) for NWA 6963.

Automated summary

This study focuses on the analysis of the Si-rich mesostasis in Martian shergottite NWA 6963 using laser ablation multicollector inductively coupled plasma mass spectrometry U-Pb measurements. The results indicate that the Si-rich mesostasis represents a late-stage differentiated melt produced in the final phase of the magmatic history, rather than a shock melt.