Geochemical Constraints for the Bulk Composition of the Moon
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The bulk composition of the silicate Moon (crust + mantle, BSM) is determined on the basis of inversion of gravitational and seismic data. It is shown that the mantle refractory oxides form two different groups depending on the thermal state. By the bulk Al2O3 content of ~3.0–4.6 wt %, the cold BSM models span the range of Al2O3 content of the silicate Earth (Bulk Silicate Earth, BSE), whereas the hot BSM models are significantly enriched in the Al2O3 content of ~5.1–7.3 wt % (Al2O3 content of ~1.2–1.7 × BSE) relative to BSE. In contrast, apart from the distribution of temperature, both BSM models are characterized by almost constant values of bulk FeO contents (~12.2–13.2 wt %) and MG# values (80.0–81.5), which are strongly distinct from those for BSE (~8 wt % FeO and 89 MG#). The results show that, for the geophysically possible distribution of temperatures, the silicate fraction of the Moon is enriched in FeO and depleted in MgO relative to BSE.
This work was supported by the Russian Foundation for Basic Research (project nos. 18-05-00225 and 17-35-50099 mol_nr) and the Presidium of the Russian Academy of Sciences, program no. 17.
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