Rock types of South Pole-Aitken basin and extent of basaltic volcanism

The enormous pre-Nectarian South Pole-Aitken (SPA) basin represents a geoph ysically and compositionally unique region an the Moon. We present and anal yze the mineralogical diversity across this basin and discuss the implicati ons for basin evolution. Rock types are derived from Clementine multispectr al data based on diagnostic characteristics of ferrous absorptions in fresh materials. Individual areas are characterized as noritic (dominated by low -Ca pyroxene), gabbroic/basaltic (dominated by high-Ca pyroxene), feldspath ic (<3-6% FeO), and olivine-gabbro (dominated by high-Ca pyroxene and olivi ne). The anorthositic crust has effectively been removed from the interior of the basin. The style of volcanism within the basin extends over several 100 Myr and includes mare basalt and pyroclastic deposits. Several areas of ancient (pre-Orientate) volcanism, or cryptomaria, have also been identifi ed. The nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically. We inter pret this to represent impact meltlbreccia deposits derived from the lower crust. A few localized areas are identified within the basin that contain m ore diverse lithologies (gabbro, olivine-gabbro), some of which may represe nt material from the deepest part of the lower crust and perhaps uppermost mantle involved in the SPA event.