Dynamical Influences of Pressure-Dependent Thermal Expansivity on Mantle Convection

Abstract

Recent experimental and theoretical studies have found a strong dependence of thermal expansion coefficient as a function of density and, conversely, of pressure. These experimental data have also important implications on the variations of the proportionality constant between seismic velocities and density as a function of pressure. We have studied the effects of pressure-dependent thermal expansion on mantle convection in an internally-heated, constant viscosity, compressible medium including constant and pressure-dependent thermal expansivity and pressure-dependent thermal conductivity. Results show that compressible convection in the lower mantle behaves more like incompressible convection in the presence of strong depth-dependence of thermal expansivity. With depth-dependent thermal conductivity the lower mantle is heated up and the thermal boundary layer at the core-mantle boundary is broadened. Large aspect-ratio cells are favored in time-dependent convection with depth-dependent thermal expansivity. The ascending flows in this type of time-dependent convection are found to remain relatively fixed with respect to one another.