Experimental Constraints on an MgO Exsolution-Driven Geodynamo

Abstract

MgO exsolution has been proposed to drive an early geodynamo. Experimental studies, however, have drawn different conclusions regarding the applicability of MgO exsolution. While many studies suggest that significant Mg can dissolve into the Earth's core, the amount of MgO exsolved out of the core, which hinges on the temperature dependence of MgO solubility, remains unclear. Here we present new high-temperature experiments to better constrain the temperature and compositional dependence of Mg partitioning between Fe alloys and silicate liquids. Our experiments show that Mg partitioning is weakly dependent on temperature, while confirming its strong dependence on oxygen content in Fe alloys. This implies that MgO exolution is limited as the core cools but can help drive an early geodyanamo if the core heat loss is slightly subadiabatic. If an exosolution-driven geodynamo did occur, it was likely over a limited time span that depends on the core thermal history and conductivity.