A model of the chemical differentiation of the Moon

On the basis of geophysical constraints on elastic wave velocities, the mom ent of inertia, mass of the Moon and the method of mathematical modeling of phase relations and physical properties in the system CaO-FeO-MgO-Al2O3-Si O2, we examined the hypothesis of chemical differentiation of the Moon as a result of partial melting of initially homogeneous material (hypothetical magma ocean). The solution of the inverse problem and estimation of the che mical composition of the Moon and the size of its core are based on the min imization of the deviation of calculated geophysical parameters relative to observed values. The chemical differentiation of a 500-km thick magma ocea n (producing crust, upper and middle mantle) relative to the lower (primary ) mantle is consistent with the combined geophysical constraints on the ela stic wave velocity profile, moment of inertia, and mass of the Moon. The ch emical compositions were calculated for the differentiated and undifferenti ated components of the silicate Moon. Pyroxene appeared to be the dominatin g mineral in all shells. It was shown that the chemical composition of the Moon bears no genetic relationship to the peridotite material of the Earth, as well as to that of any known chondrite class. The radius of the Moon's core is estimated as 320-390 km for a Fe core and 490-600 km for a FeS core . The ratio of total iron to silicon for the Moon, which is one of the most important cosmochemical parameters, is Fe/Si (wt) = 0.44-1.5, which is bel ow values determined for other bodies of the Solar system.