First-principles calculations of the Hf-W partitioning between molten iron and silicate melt and its implications for ¹⁸²W isotopes in Ethiopian and Aden Bay basalts and ancient Indian komatiites

Abstract

¹⁸²W is produced by beta-decay of the currently extinct nuclide ¹⁸²Hf with a relatively short half-life of 8.9 million years. One of the proposed model of the Hf-W partitioning in the magma ocean is the affinity of Hf and W to mantle and core because of their litho- and sidero-phile behavior. Consequently, high and low Hf/W ratios lead to, respectively, high and low 182W/184W for the primitive mantle and core. Positive anomalies of u¹⁸²W (parts per million deviations relative to the average current upper mantle value of 0) have been found for several Archean komatiites (e.g., Rizo et al., 2019). On the other hand, negative anomalies have been reported for several ocean island basalts such as Hawaii and the Samoan islands u182W (e.g., Rizo et al., 2019). It suggests that core-derived W contributed to the mantle source of certain oceanic island basalts. We conducted the first-principles free energy calculations to constrain W and Hf partitioning in the magma ocean. We further analyzed the W isotopes of the deep-mantle originated basalts and ancient komatiites to discuss the ¹⁸²W evolution through the history of the Earth.