Reaction of iron and silica at core–mantle boundary conditions

Chemical interaction between iron and silica have been studied at pressures up to 140 GPa and temperatures over 3800 K in electrically- and laser-heated diamond anvil cells and in multianvil apparatus. At pressures below 55–60 GPa and high temperatures, iron and silica react to form iron oxide and iron–silicon alloy with up to 5 wt.% Si. However, at pressures from 85 to 140 GPa reaction between iron and SiO2 was not detected. Our results suggest that the silicon-rich alloy produced by re-equilibration of proto-core metal that equilibrated with silicates in a magma ocean, or produced at the CMB by reaction between iron and silicate will accumulate at the boundary between the lower mantle and core.