Melting Experiments on Liquidus Phase Relations in the Fe‐S‐O Ternary System Under Core Pressures

Abstract

AbstractMelting experiments on the Fe‐S‐O ternary system were performed to 208 GPa in a laser‐heated diamond‐anvil cell. Compositions of liquids and coexisting solids in recovered samples were examined using a field‐emission‐type electron microprobe. The results demonstrate that the ternary eutectic point shifts toward the oxygen‐rich, sulfur‐poor side with increasing pressure, in accordance with changes in eutectic liquid compositions in the Fe‐O and Fe‐S binary systems. We also found that solid Fe crystallizing from liquid Fe‐S‐O does not include oxygen, while the partitioning of sulfur into solid Fe is enhanced with increasing pressure. These indicate that oxygen‐rich, sulfur‐poor liquid crystallizes Fe at the inner core boundary; however, it makes a large density difference between the liquid and solid core, which is inconsistent with observations. Alternatively, we found that a range of C‐bearing, S‐poor/O‐rich liquids account for the density and velocity in the outer core and the density in the inner core.