Experimental Constraints on Composition of Lunar Magma Ocean from Physical Properties of Magma

Introduction: It has been widely accepted that the lunar anorthosite crust formed by floatation of anorthite in the magma ocean at the time of a giant impact of the Earth-Moon system formation. The positive Eu-anomaly in lunar anothosites and the absence of mafic components in the lunar crust that contain complementary negative Eu-anomalies can also be the evidence of formation of the anorthosite crust by large-scale differentiation. It is thus important to understand the formation process of the anorthosite crust in order to reveal the nature of large-scale differentiation in the cooling lunar magma ocean (LMO). Here we report out attempts to understand differentiation in LMO processes based on experimental constraints from physical properties of magma ocean. Lunar magma ocean: Many attempts have been made to estimate geophysical and/or geochemical conditions of the lunar magma ocean, and several models for differentiation of the moon in the cooling LMO have been proposed [e.g., references in [1] and references therein]. However, there are large disparities in the scale, composition, and cooling history of LMO. Fractional crystallization in the large-scale magma ocean occurs as a result of combination of several physical and chemical processes such as convection of magma that transports heat and mass, floatation/settling of minerals, formation of viscous boundary layer, nucleation/growth/dissolution of minerals, and so on. Many of key processes in the magma ocean depend on physical and chemical properties of minerals and silicate melts, but some have not yet been precisely determined. Thus, even with a proper model of the magma ocean, it may not necessarily be realistic modeling of LMO. The most critical but poorly constrained parameter is the bulk composition of LMO (≈ the bulk silicate composition of the moon). For instance, there have been a wide range of estimates for concentrations of Al 2 O 3 and FeO that have been inferred from lunar rocks or seismic data [e.g., 2-5]. The Al 2 O 3 and FeO concentrations in the melt, however, change the liquidus temperature of anorthite and the density and viscosity of the melt, which should affect the floatation of anorthite in LMO. Concept of this study: We have started working to constrain the composition of LMO by combining the physical modeling of LMO and experimental