Effect of chemical disequilibrium during metal-silicate partitioning on the thermal state of the early core and implications on the dynamics of metal/silicate segregation

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 some amount of chemical disequilibrium during the segregation of the core in the magma ocean phase. At the minimum equilibrium rate in metal and silicate phases, the final temperature of the core by $\sim$ 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. Furthermore, we combined our model outputs with a previously published parameterization linking the Reynolds number and the equilibrium rate of Ni and Co at the end of accretion. We then showed that if one consider large diapirs (100 - 1000 km radius) of metal equilibrating with the magma ocean, then the only way to obtain a bulk silicate Earth composition is to consider the magma ocean to have high viscosity (10\textsuperscript{8} to 10\textsuperscript{15} Pa.s). These results imply that at the end of accretion, the existence of a fully molten, only liquid, magma ocean is highly unlikely; with the reality being closer to a mushy magma ocean with some degree of crystallization equilibrating with large diapirs.