Hf and W partitioning between liquid metal and silicate melt calculated by ab initio thermodynamic i

Abstract

Isotopic variations in ¹⁸²W result from the fractionation of Hf and W that occurred during the existence of ¹⁸²Hf, which has a short half-life. Since Hf and W are lithophile and siderophile, respectively, Hf is thought to remain in the silicate melt phase and W in the molten metal phase during earth core formation. As a result, the initial mantle is thought to have high W isotopic ratios, and the metallic core is thought to have low isotopic ratios. After that, late veneer with low W isotopic ratios are thought to have lowered the W isotopic ratios in the mantle to the present values in the upper mantle.In this study, we investigate the Hf-W partitioning between silicate melts and molten iron using ab initio free energy calculations under high temperature and pressure conditions, which are difficult to achieve in laboratory experiments. We also calculated whether the partition coefficient changes when iron is mixed with silicate and vice versa. It was confirmed that W remained siderophile and Hf remained lithophile in both cases. Based on these results, clarifying the W isotope evolution is necessary.