Phase and melting relationships in the Fe-S system under high pressures: Application to the temperature profile in the core

The Earth's core has been considered to contain light elements, and sulfur, in particular, is one of the most plausible light elements. Knowledge of the melting relationships of the iron-sulfide system is thus essential in understanding of the physical and chemical properties of the core. In situ X-ray diffraction experiments in the Fe-Fe3S system were performed up to 220 GPa and 3300 K using a laser-heated diamond anvil cell. Hcp Fe and Fe3S coexisted stably up to 220 GPa and 3300 K. Both phases are therefore candidates of the constitution of the inner core. The solid iron (hcp Fe) contained 7.5 at% of sulfur at 126 GPa and 2370 K. This suggests that the inner core might be able to contain significant amount of sulfur. Our results revealed that the eutectic composition becomes nonsensitive to pressure. This is likely that the eutectic composition becomes to be constant around 20 at% of sulfur at pressures above 40 GPa.