Young magmatism and Si‐rich melts on Mars as documented in the enriched gabbroic shergottite NWA 6963. (17th October 2022) - Lindner, Miles
Abstract: 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.