Density and seismic velocity of hydrous melts under crustal and upper mantle conditions

Abstract

We present a new model for calculating the density of hydrous silicate melts as a function of P, T, H2O concentration, and melt composition. We optimize VPr,Tr ∂V/∂T; ∂V/∂P; ∂V2/∂T∂P, and K’ of H2O end-member components in hydrous silicate melts, as well as K’ of anhydrous silicate melts, using previously reported experimental results. The parameter set for H2O end-member component in silicate melt optimized in this study is internally consistent with the parameter values for the properties of anhydrous silicate melt reported by Lange and Carmichael (1987, 1990). The model calculation developed in this study reproduces the experimentally determined densities of various hydrous melts, and can be used to calculate the relationships between pressures, temperatures, and H2O concentrations of various hydrous melts from ultramafic to felsic compositions at pressures of 0–4.29 GPa. Using the new parameter set, we investigate the effects of H2O content on the seismic velocity of hydrous melts, as well as seismic velocities in partially molten regions of subduction zones. The results show that water content in silicate melt plays a key role in determining seismic velocity structure, and therefore must be taken into account when interpreting seismic tomography.