The Effects of Melt Depletion and Temperature on the Densities and Seismic Velocities of Garnet Lherzolite

We examine the effects of melt depletion, temperature, and partial melt on V_P, V_S, V_P/V_S, and density of the mantle, based on the melting relations of fertile garnet peridotites (MM3 and FER-E) at high pressures. We incorporate the effects of variable mineral mode and composition into a parameterization of mantle density and velocity, based on literature values for thermal expansivity, bulk moduli, shear moduli, and their derivatives for olivine, orthopyroxene, clinopyroxene, and garnet. Forward modeling shows that as mantle is depleted by melting at high pressure, changes in residual mineralogy and composition both result in a decrease in density of the residuum. For example, at 3.6 GPa, 10% partial melting reduces the density of the residuum by 0.6%. In contrast, we find under the same conditions melt depletion has a nearly negligible influence on V_P and V_S. This behavior is compared to that found for melting of spinel lherzolite at 1 GPa. Finally, we calculate the effects of temperature on velocity, and present new anharmonic velocity-temperature derivatives for realistic mantle compositions. The effects of depletion, temperature and melt on density are explored, and applied to the Yellowstone Swell mantle to constrain temperature variations.