Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure

Whether Earth's core is a significant repository of noble gases is an open question because their partitioning between liquid metal and silicate melt during core formation is poorly known. Here we calculated the He and Ar partition coefficients (D) between liquid Fe and MgSiO3 melt from 20 to 135 GPa at 5,000 K using ab initio molecular dynamics combined with thermodynamic integration. Our simulations show that D-He does not change significantly with pressure, while D-Ar increases strongly with increasing pressure. Furthermore, we found that the metal/silicate partitioning behaviors of He and Ar are controlled by their atomic size and the charge density properties of the host compositions. These results indicate that Earth's core is a plausible reservoir for He-3 and could possibly account for the high He-3/He-4 ratios in the OIBs that associated with deep-rooted plumes, but the core is unlikely to be a significant source for Ar-36.