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    Melting relations in the Fe–S–Si system at high pressure and temperature: Implications for the planetary core

    Sakairi T, Ohtani E, Kamada S, Sakai T, Sakamaki T, Hirao N

    Planetary core, melting relations, Fe–S–Si system, diamond anvil cell

    The melting curves of Fe and Fe-light element systems. Temperature profiles of the cores of Mars and Mercury are also shown.

    The phase and melting relations in the Fe–S–Si system were determined up to 60 GPa by using a double-sided laser-heated diamond anvil cell combined with X-ray diffraction. On the basis of the X-ray diffraction patterns, we confirmed that hcp/fcc Fe–Si alloys and Fe3S are stable phases under subsolidus conditions in the Fe–S–Si system. Both solidus and liquidus temperatures are significantly lower than the melting temperature of pure Fe and both increase with pressure. The slopes of the Fe–S–Si liquidus and solidus curves determined here are smaller than the adiabatic temperature gradients of the liquid cores of Mercury and Mars. Thus, crystallization of their cores started at the core–mantle boundary region.