Segregation of core melts by permeable flow in the lower mantle

We measured the dihedral angle of molten iron in (Mg,Fe)SiO3-perovskite aggregate with increasing pressure and temperature using laser-heated diamond anvil cell. Results demonstrate that it decreases from 94° at ∼27 GPa and ∼2400 K to 51° at ∼47 GPa and ∼3000 K. This value is smaller than the critical angle of 60°, thus allowing iron melt to wet the grain boundaries of silicate perovskite and develop an interconnected melt network within the perovskite-dominant matrix, even at very small melt fractions. The quenched liquid iron contained substantial amounts of oxygen and silicon as pressure and temperature increase. Such a decrease in the dihedral angle is likely due to a reduction in the iron-perovskite interfacial energy by dissolving oxygen and silicon into the liquid iron from coexisting silicate perovskite. These suggest that a wetting behaviour of core melts in the solid silicate mantle changes above ∼40 GPa, corresponding to ∼1000 km depth in the present Earth, and efficient metal segregation may have proceeded by permeable flow in a late stage of accretion. Oxygen and silicon incorporated during core formation and later by core–mantle boundary process may be important light elements in the Earthʹs core.