The global distribution of pure anorthosite on the Moon

Pure lunar anorthosite Based on analyses of lunar samples of anorthosite, the igneous rock made up mainly of plagioclase feldspar that predominates there, the light-coloured crust of the lunar highlands is thought to have been formed by the crystallization and flotation of plagioclase from a global magma ocean. The exact mechanism by which such a crust formed remains a matter for debate. Spectroscopic data from SELENE, the main orbiter component of the Japanese KAGUYA lunar mission, have now been used to produce a clear and high spatial resolution view of the composition of the lunar crust. The data, from 69 different locations, reveal the widespread existence of virtually pure —100% plagioclase — anorthosite. This contrasts to previous estimates of 82 to 92 vol% plagioclase, providing a valuable constraint on models of lunar magma ocean evolution. It has long been thought that the lunar highland crust was formed by the crystallization and floatation of plagioclase from a global magma ocean, but the exact mechanism by which such a crust formed remains debated. Data from the Japanese SELENE spacecraft are now used to produce a clear and high spatial resolution view of the composition of the lunar crust. The existence of widely distributed crustal rocks with compositions approaching 100 per cent (by volume) plagioclase is revealed. It has been thought that the lunar highland crust was formed by the crystallization and floatation of plagioclase from a global magma ocean 1 , 2 , although the actual generation mechanisms are still debated 2 , 3 . The composition of the lunar highland crust is therefore important for understanding the formation of such a magma ocean and the subsequent evolution of the Moon. The Multiband Imager 4 on the Selenological and Engineering Explorer (SELENE) 5 has a high spatial resolution of optimized spectral coverage, which should allow a clear view of the composition of the lunar crust. Here we report the global distribution of rocks of high plagioclase abundance (approaching 100 vol.%), using an unambiguous plagioclase absorption band recorded by the SELENE Multiband Imager. If the upper crust indeed consists of nearly 100 vol.% plagioclase, this is significantly higher than previous estimates of 82–92 vol.% (refs 2 , 6 , 7 ), providing a valuable constraint on models of lunar magma ocean evolution.