Liquidus Phase Relations and Solid‐Liquid Partitioning in the Fe‐Si‐C System Under Core Pressures

Abstract

Abstract Both silicon and carbon have been proposed to be important light elements in the Earth's core, in particular in the inner core. Here we performed melting experiments on the Fe‐Si‐C ternary system at ∼50, ∼136, and ∼200 GPa and determined the liquidus phase relations and the solid/liquid partition coefficients ( D ) of C and Si. The liquidus field of Fe shrinks at higher pressures, which narrows down the possible outer core liquid composition. Our data also demonstrate that the Fe‐Si binary eutectic liquid reduces its Si concentration to ∼8 wt% with increasing pressure to 330 GPa. We found that the inner core is not an Fe‐Si‐C‐S alloy but likely includes hydrogen when considering the low D C and the strong enhancement of D Si with increasing liquid C abundance. The present‐day core does not include as much as ∼6 wt% Si, suggesting that at least a part of “missing” Si could be sequestrated elsewhere.