Possible mantle origin of olivine around lunar impact basins detected by SELENE

The composition, structure and evolution of the Moon's mantle is poorly constrained. The mineral olivine, one of the main constituents of Earth's mantle, has been identified by Earth-based telescopic observations at two craters on the near side of the Moon, Aristarchus and Copernicus(1-3). Global reflectance spectra in five discrete spectral bands produced by the spacecraft Clementine(4-6) suggested several possible olivine-bearing sites, but one of the candidate occurrences of olivine was later re-classified, on the basis of continuous reflectance spectra over the entire 1 mu m band, as a mixture of plagioclase and pyroxene(7). Here we present a global survey of the lunar surface using the Spectral Profiler onboard the lunar explorer SELENE/Kaguya(7,8). We found many exposures of olivine on the Moon, located in concentric regions around the South Pole-Aitken, Imbrium and Moscoviense impact basins where the crust is relatively thin. We propose that these exposures of olivine can be attributed either to an excavation of the lunar mantle at the time of the impacts that formed the basins(3), or to magnesium-rich pluton in the Moon's lower crust. On the basis of radiative transfer modelling(4,8-10), we suggest that at least some of the olivine detected near impact basins originates from upper mantle of the Moon.