HIGH-PRESSURE AND HIGH-TEMPERATURE REACTIONS BETWEEN SILICATES AND LIQUID-IRON ALLOYS, IN THE DIAMOND ANVIL CELL, STUDIED BY ANALYTICAL ELECTRON-MICROSCOPY

We report new experimental results on mixtures of iron alloys and silicates (Fe + forsterite, Fe + (Mg0.89,Fe0.11)SiO3 enstatite, Fe + (Mg0.89,Fe0.11)2SiO4 olivine, Fe + FeS + (Mg0.83,Fe0.17)2SiO4 olivine, and FeS + (Mg0.83,Fe0.17)2SiO4 olivine) reacted at about 70 GPa and 130 GPa, at high temperature in a laser-heated diamond anvil cell. The recovered samples were studied by analytical transmission electron microscopy. We found that chemical reactions occurred between molten iron alloys and solid oxides, leading to a dissolution of oxygen in the molten metallic phase, and a drastic depletion of iron in the oxides in contact with the metallic phase. Chromium and manganese partition into the liquid iron. Oxygen is therefore a serious candidate for being a light element in the Earth's core, and oxides which have experienced a high-pressure contact with molten iron should have a rather low Fe/Fe + Mg ratio