U solubility in the core of Earth

Abstract

Uranium is the most important heat producing element in the Earth. The presence of an appreciable amount of U in the core of Earth would have an important influence on geodynamics. In this study, the solubility of U in Fe-10wt% S and in Fe-35wt% S was measured by partitioning experiments with a mixture of peridotite, uraninite, Fe and FeS powder at pressure (P) of 0-9 GPa and temperature (T) of 1500-2200 oC. Comparisons with the run products containing pure Fe as the metal phase in our previous study and re-analysis of run products were made in this study. We found that in all run products, including Fe-10wt% S, Fe-35wt% S and pure Fe groups, the solubility and partitioning of U in the pure metal or metal-sulfide phase relative to the silicate phase (DU) increases with increasing P and T. With a molten silicate phase, DU is generally 3-6 times larger than with a solid silicate phase. While DU has a positive dependence on S concentration of the metal-sulfide phase, there is a negative correlation between Ca and U. According to our calculations based on these experimental results, if the core has formed from a magma ocean at a P of 26 GPa at its base and the core contained 10wt% S, then it could have incorporated at least 10 ppb U. Alternatively, if the core formed by percolation and contained 10wt% S, then it could have incorporated 5-22 ppb U. The geophysical implications of U in the core of Earth are discussed.