Hydrous silicate melt at high pressure

The structure and physical properties of hydrous silicate melts and the solubility of water in melts over most of the pressure regime of the Earth's mantle remain largely unknown. At low pressure, the solubility of water increases rapidly with increasing pressure and water has a large influence on the solidus temperature, density, viscosity and electrical conductivity. Mookherjee et al. report the results of first-principles molecular dynamics simulations of hydrous silicate melt, showing that pressure has a profound influence on speciation of the water component. They infer that the speciation changes from being dominated by hydroxyls and water molecules at low pressure to extended structures at high pressure. The authors link this change in structure to the finding that the water-silicate system becomes increasingly ideal at high pressure, indicating complete miscibility of water and silicate melt throughout almost the entire mantle pressure regime.