MOONS MIDDLE MANTLE COMPOSITION

Chemical and mineral composition of the Moon's middle mantle (270-500 km) has been determined by means of mathematic simulation of phase rel ations and physical properties in the system CaO-FeO-MgO-Al2O3-SiO2. C onstraints have been set on the contents of petro-genic oxides. Physic al properties of pyroxenite models with 50-52% SiO2 and 15-16% FeO hav e been shown to well correlate with the experimental seismic data and geophysical constraints on the density and momentum. Middle mantle has bimineral pyroxenite composition (pyroxene + olivine) and enriched in silica and iron as compared to the lower mantle. No one of the consid ered geochemical models of total composition of the Moon obey the seis mic constraints both in the upper, middle, and lower mantle simultaneo usly. Phase transition spinel peridotite --> garnet peridotite can not explain the nature of seismic boundaries at the depth of 270 and 500 km. A conclusion has been made about chemical stratification of lunar mantle.