A partially molten magma ocean model

Under the assumption that the outer 300-400 km of the moon was at first only partially, rather than fully molten, an explanation of the properties of the lunar crust and upper mantle is obtained according to which nuclei of anorthositic crust formed over localized bodies of magma segregated from the partial melt, and then grew peripherally until fully covering the moon. Over most of its growth period, the anorthosite crust floated on a layer of magma whose thickness was regulated by the opposing forces of (1) loss of material by fractional crystallization, and (2) addition of magma from the partial melt below. The clustering of Eu, Sr and Mg values found among pristine ferroan anorthosites are predicted by this model.