On the source regions for mare picrite glasses

Models for the crystallization of the magma ocean, phase equilibria constraints, and geochemical criteria constrain the mare basalt source region to lie deep within the Moon and within olivine-orthopyroxene cumulate layers of the magma ocean. The Mg* compositions of the mare basalt source region, the ferroan anorthosite crust and the mg-suite troctolites, require that most if not all the cumulates were produced by a magma ocean undergoing fractional rather than equilibrium crystallization. Estimates of the depth of the elastic lithosphere, the existence of mascons, and the need to sequester some heat-producing elements in the lunar interior are consistent with the lunar overturn model which transports the refractory cumulates, the more fertile ilmenite-diopside cumulates and some of the KREEP components into the lunar interior.