地球核形成過程における平衡と非平衡

Abstract

Metal droplets separating in the magma ocean have the radius less than 1cm, and it takes about 106 seconds to separate in the magma ocean. Metallic liquid accumulated in the bottom of the magma ocean starts to fall into the lower mantle when the metal drops grow into the radius of about 1km. The present theoretical analysis implies that the small metal droplets falling into the molten magma ocean are thermally and chemically in equilibrium with the silicate magma ocean, whereas the large metal pools falling in the lower mantle are disequilibrium with the surrounding silicates. Therefore it may be possible to estimate the depth of the magma ocean from the conditions of the metal-silicate equilibrium. Abundances of Ni and Co in the mantle may be accounted for by the chemical equilibrium between metal and silicate at 40 GPa and 2500°C, suggesting existence of the primordial terrestrial magma ocean with the depth of 1200 km.