The solution behaviour of siderophile elements during earth differentiation: An experimental study

Earth differentiation models were tested by experimental studies of metal-silicate and solid-liquid metal partitioning of select trace elements under controlled conditions. Experiments were designed to simulate trace element behaviour during metallic liquid separation from molten silicate during core formation, and the subsequent differentiation of the core into a solid inner and liquid outer region. The precise conditions of Earth differentiation are neither well constrained, nor routinely attainable by experiment. Although reducing oxygen fugacities of core formation can be replicated, element partitioning is typically established at lower pressures and temperatures, and trends are then used to infer partitioning behaviour at more extreme conditions.;It is possible that liquid metal from the outer core may have reacted with silicates and oxides in the lower mantle. The suggestion that outer core liquid caused Os isotopic anomalies in mantle-derived materials requires an outer core with super-chondritic Pt/Os and Re/Os. It is evident from experimental results of this study and those of the literature that the element fractionations necessary to produce this composition did not occur upon solidification of metal in the core, rendering the outer core nearly-chondritic in Pt/Os and Re/Os composition.;It is possible to determine the oxidation state of highly siderophile elements dissolved in silicate glass spectroscopically, as demonstrated by our study involving Pd. Due to compositional impurities in the silicate melt, experimental glasses produced at oxygen fugacity conditions lower than 10 -2 contained neutral Pd, therefore future studies should focus on in situ techniques.;Siderophile and chalcophile elements Te, Se, and S are equally depleted from the modeled primitive mantle, yet this behaviour is not reflected in metal-silicate partitioning experiments. Results suggest that initial metal segregation from silicate during core formation produced a mantle roughly 3-5 times more depleted in these elements, as well as a sub-chondritic Te/Se fractionation. An Earth accretion model involving the late addition of siderophile-bearing material after core formation is favoured by our results.