Multiple lithic clasts in lunar breccia Northwest Africa 7948 and implication for the lithologic components of lunar crust. (25th January 2018) - Zeng, Xiaojia
Abstract: This study presents the petrography, mineralogy, and bulk composition of lunar regolith breccia meteorite Northwest Africa (NWA) 7948. We identify a range of lunar lithologies including basaltic clasts (very low‐titanium and low‐titanium basalts), feldspathic lithologies (ferroan anorthosite, magnesian‐suite rock, and alkali suite), granulites, impact melt breccias (including crystalline impact melt breccias, clast‐bearing impact melt breccias, and glassy melt breccias), as well as regolith components (volcanic glass and impact glass). A compositionally unusual metal‐rich clast was also identified, which may represent an impact melt lithology sourced from a unique Mg‐suite parent rock. NWA 7948 has a mingled bulk rock composition (Al2 O3 = 21.6 wt% and FeO = 9.4 wt%) and relatively low concentrations of incompatible trace elements (e.g., Th = 1.07 ppm and Sm = 2.99 ppm) compared with Apollo regolith breccias. Comparing the bulk composition of the meteorite with remotely sensed geochemical data sets suggests that the sample was derived from a region of the lunar surface distal from the nearside Th‐rich Procellarum KREEP Terrane. Our investigations suggest that it may have been ejected from a nearside highlands‐mare boundary (e.g., around Mare Crisium or Orientale) or a cryptomare region (e.g., Schickard‐Schiller or Mare smythii) or a farside highlands‐mare boundary (e.g., Mare Australe, Apollo basin in the South Pole–Aitken basin). The distinctive mineralogical and geochemical features of NWA 7948 suggest that the meteorite may represent lunar material that has not been reported before, and indicate that the lunar highlands exhibit wide geological diversity.