NI Huai-wei

CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Abstract：Water is a primary volatile component in terrestrial magma. As water is highly soluble in silicate melts, it depresses the melting temperature of rocks. This study reviews the speciation and solubility of water in silicate melts at lithospheric p-t conditions and the influence of water on the physical properties of silicate melts. Water dissolved in silicate melts is present in two forms, molecular H2O and hydroxyl(OH).Water solubility in silicate melts increases with pressure. When the p-t condition lies above the critical cuve of a hydrous silicate system, a supercritical fluid may form with composition intermediate between silicate melt and aqueous fluid. Water lowers the density and viscosity of silicate melt, which facilitates melt segregation from the source region and upward movement of the melt. Water promotes element diffusion and the growth of crystals and gas bubbles. Water also enhances electrical conductivity of silicate melts and therefore electrical anomaly of partially molten zones. The effects of water on the transport properties of silicate melts and its solution behavior are all strongly associated with water speciation reaction. The role of water must be taken into account in studying melting-related geological processes.

Key words：silicate melts water solubility diffusivity electrical conductivity

E-Mail: hwni@ustc.edu.cn

Bulletin of Mineralogy, Petrology and Geochemistry Vol.36, No.1, 2017, page 1-5