Effect of chemical disequilibrium during metal-silicate partitioning on the thermal state of the early core

Vincent Clesi , Renaud Deguen

In this study, we improved a previously published numerical model linking the core composition to the core temperature during accretion by introducing the possibility of chemical disequilibrium during the segregation of the core in the magma ocean phase. Our study shows that at least 60% of the accreting metal needs to be equilibrated in order to obtain a chemically coherent Earth, thus favoring a rapid core formation according to the Hf-W chronometer. The dilution factor of this equilibrated metallic mass needs to be 4 (for 100% of metallic mass equilibrated) to 40 (for 60% of the metallic mass equilibrated)  in order to obtain concentrations of major and trace element close to the Bulk Silicate Earth composition. At the minimum degree of equilibrium in metal and silicate phases, the final temperature of the core is increased by ~ 250 K compared to the fully equilibrated case. The chemical disequilibrium could be then one factor favoring the hot core hypothesis, but has to be coupled with other phenomena (gravitational energy dissipation, radiogenic heat production) to produce a hot core.