Effect of pressure, temperature, and oxygen fugacity on the metal-silicate partitioning of Te, Se, and S: Implications for earth differentiation

We have measured liquid Fe metal-liquid silicate partitioning (D_i) of tellurium, selenium, and sulfur over a range of pressure, temperature, and oxygen fugacity (1-19 GPa, 2023-2693 K, fO₂ −0.4 to −5.5 log units relative to the iron-wüstite buffer) to better assess the role of metallic melts in fractionating these elements during mantle melting and early Earth evolution. We find that metal-silicate partitioning of all three elements decreases with falling FeO activity in the silicate melt, and that the addition of 5-10 wt% S in the metal phase results in a 3-fold enhancement of both D_Te and D_Se. In general, Te, Se, and S all become more siderophile with increasing pressure, and less siderophile with increasing temperature, in agreement with previous work. In all sulfur-bearing experiments, D_Te is greater than D_Se or D_S, with the latter two being similar over a range of P and T. Parameterized results are used to estimate metal-silicate partitioning at the base of a magma ocean which deepens as accretion progresses, with the equilibration temperature fixed at the peridotite liquidus. We show that during accretion, Te behaves like a highly siderophile element, with expected core/mantle partitioning of >10⁵, in contrast to the observed core/mantle ratio of ∼100. Less extreme differences are observed for Se and S, which yielded core/mantle partitioning 100- to 10 times higher, respectively, than the observed value. Addition of ∼0.5 wt% of a meteorite component (H, EH or EL ordinary chondrite) is sufficient to raise mantle abundances to their current level and erase the original interelement fractionation of metal-silicate equilibrium.