First Principles Molecular Dynamics Simulations of Fe-Bearing Melts at High Pressure

Abstract:

The stability and mobility of deep mantle melts depend on relative densities of the constituent melts and surrounding solid materials. Iron perhaps is the most important component that influences the density of the relevant melts. However, the inclusion of Fe into melt simulations is challenging. We have recently performed first-principles molecular dynamics simulations of (Mg,Fe)O and MORB melts within density functional theory with the use of spin LDA/GGA. These simulations allow us to assess the effects of Fe on melt structure and properties. In particular, the calculated densities of the Fe-bearing melts increase rapidly with increasing pressure with their values even exceeding the seismic mantle density at some depths. We find that the MORB density is higher than the mantle density around 14 and 23 GPa corresponding to the 410 and 670 km seismic discontinuities, and also at all pressures above 70 GPa. For (Mg,Fe)O system, the calculated iso-chemical density differences become so small at high pressure that an excess of as low as 5 wt.% Fe dissolved in the liquid phase would be sufficient to cause the liquid-solid density crossover. Our first-principles results thus support the possibility that Fe-bearing melts may be buoyantly stable in the deep mantle.