Pressure dependence of metal–silicate partitioning explains the mantle phosphorus abundance

Abstract

Previous experiments performed below 20 GPa suggested that the metal/silicate partition coefficient of phosphorus (P), DP, extrapolated to typical high-pressure and -temperature conditions of the Earth’s core formation gives too high P concentration in the core unless a large amount of silicon was included in metals. Here we examined DP between liquid metal and coexisting molten silicate at 27–61 GPa and 3820–4760 K, corresponding to conditions of core-forming metal segregation from silicate, by measuring recovered samples using a high-resolution imaging technique coupled with secondary ion mass spectrometry. The results demonstrate that the pressure dependence of DP changes from positive to negative above 15 GPa, likely because of an increase in the coordination number of P5+ in silicate melt. With the present new partitioning data, the observed mantle P abundance may indicate ~ 0.2 wt% P in the core, consistent with the cosmo-/geochemical estimates, based on both single-stage and multi-stage core formation models without involving high amounts of silicon in metals.