Solidification of the lunar magma ocean

Abstract We investigated the crystallization of a model lunar magma ocean composition using experimental petrology. Our results differ from classic numerical studies that are widely used in magma ocean modeling, likely due to the fact that these ignored the pressure effect on crystallization. 1. Introduction The Moon underwent a global magma ocean stage very early in its history [1]. The crystallization of this lunar magma ocean (LMO) is thought to have created a series of concentric cumulate layers with different mineralogical assemblages. The crystallization sequence and composition of these cumulate layers are of primary importance for subsequent key events in lunar evolution including the formation of a plagioclase-rich crust and an overturn in the mantle, with the latter triggering basaltic mare volcanism [1]. To date, numerical and petrological models studying cumulate overturn and other interior processes base their initial cumulate pile on the computations from Snyder et al. [2]. These authors used a simplified calculation path that does not incorporate the possible effect of pressure on crystallisation. In the present study, we determined in detail the crystallization behaviour of a magma ocean using experimental tools, simulating lunar interior conditions at depth and under shallow conditions. The aim of this approach is to solve three main questions: (1) can a thick anorthositic crust form, and if so, what is its mineralogical and chemical composition, (2) what is the extent of gravitational instability of the resulting cumulate pile, which forms a driving force for mantle overturn, and (3) how are the observed compositions of mare basalts and other volcanic products at the lunar surface linked to remelting processes of overturned cumulate piles.