Physical and chemical constraints on core-mantle differentiation in terrestrial planets

Abstract

In this study a physical mechanism and geochemical parameters have been examined in high pressure and high temperature experiments in order to place constraints on the conditions and the manner by which core-mantle differentiation occurred on Earth and terrestrial planets. The wetting characteristics of liquid Fe-Si alloys in a matrix of the respective predominating stable silicate mantle mineral (forsterite or silicate perovskite) at pressures of 2 - 5 and 25 GPa and temperatures of 1600 - 2000 ʿC were studied by determining the liquid metal-solid silicate contact angles. The median angle values from texturally-equilibrated samples were found to be independent of pressure, temperature, silicate mineralogy and the Si content in the metal fraction and range between 130ʿ and 140ʿ which is far above the critical wetting boundary of 60ʿ. This shows that within the studied range of conditions dissolved Si does not lower the surface energies between Fe-rich liquids and silicate mantle grains. As a consequence, under reducing conditions the presence of Si in the metal phase of planetary bodies would not have induced or aided percolative flow as the metal-silicate separation process...