Element partitioning constraints on core-mantle differentiation

High pressure high temperature experiments have been conducted to study the partitioning of Ni, Co, Cr, Mn, P, Cu, K, Se, Pb, I, S, O and Si between liquid Fe-alloy (LA) and various mantle phases, including liquid silicate (LS), olivine, garnet, magnesiowustite and Mg-perovskite. The results are applied to core-mantle differentiation in the Earth.; It is found that both Ni and Co become less siderophile with pressure and temperature. The effect of pressure and temperature are more pronounced for Ni than for Co, so that the partition coefficients of Ni and Co between liquid Fe-alloy and liquid silicate ({dollar}Dsbsp{lcub}rm Ni{rcub}{lcub}rm LA/LS{rcub}{dollar} and {dollar}Dsbsp{lcub}rm Co{rcub}{lcub}rm LA/LS{rcub}{dollar}) converge at high pressure and high temperature. Consequently, the observed high abundances and near-chondritic ratio of Ni and Co in the Earth's upper mantle are consistent with chemical equilibrium between molten Fe-alloy and molten silicate at {dollar}sim{dollar}24 GPa and {dollar}{lcub}sim{rcub}2400spcirc{dollar}C, indicating that core formation may have taken place in a magma ocean down to the upper and lower mantle boundary.; Volatile element composition of the Earth is calculated by correcting for the effect of core formation based on measured partition coefficients. It appears that when a large number of elements are considered, depletion of volatile elements in the Earth is poorly correlated to the calculated condensation temperatures for an assumed solar nebular condition. Therefore, the depletion trend formed by moderately volatile lithophile elements may not reflect the nature of volatile element depletion in the bulk Earth.; Sulfur has a strong affinity for Fe-Ni-alloy at all experimental conditions investigated. Partition coefficients of sulfur between liquid Fe-Ni-alloy and liquid silicate ({dollar}Dsbsp{lcub}rm S{rcub}{lcub}rm LA/LS{rcub}{dollar}) increases with pressure and decreases with temperature. By extrapolation, {dollar}Dsbsp{lcub}rm S{rcub}{lcub}rm LA/LS{rcub} sim{dollar}530 at the proposed pressure and temperature of core-mantle equilibrium during early differentiation. If sulfur content of present mantle was established by equilibrium core formation, Men the core should have approximately 13 wt.% of sulfur. Combined with limited solubility of oxygen and silicon in the liquid Fe-Ni-alloy (up to {dollar}sim{dollar}1 wt.% for oxygen and {dollar}sim{dollar}0.1 wt.% for silicon), this study shows that sulfur remains the most plausible candidate for the principle light element in the core.