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We report lattice thermal conductivities of MgO and MgSiO3 in the perovskiteand post-perovskite structures at conditions of the Earth's lower mantle,obtained from equilibrium molecular dynamics simulations. Using an advancedionic interaction potential, the full conductivity tensor was calculated bymeans of the Green-Kubo method, and the conductivity of MgSiO3 post-perovskitewas found to be significantly anisotropic. The thermal conductivities of allthree phases were parameterized as a function of density and temperature.Assuming a Fe-free lower-mantle composition with mole fractions xMgSiO3 = 0.66and xMgO = 0.34, the conductivity of the two-phase aggregate was calculatedalong a model geotherm. It was found to vary considerably with depth, risingfrom 9.5 W/(mK) at the top of the lower mantle to 20.5 W/(mK) at the top of thethermal boundary layer above the core-mantle boundary. Extrapolation ofexperimental data suggests that at deep-mantle conditions, the presence of arealistic amount of iron impurities lowers the thermal conductivity of theaggregate by about 50% (Manthilake et al., 2011). From this result and ourthermal conductivity model, we estimate the heat flux across the core-mantleboundary to be 10.8 TW for a Fe-bearing MgO/MgSiO3 perovskite aggregate and10.6 TW for a Fe-bearing MgO/MgSiO3 post-perovskite aggregate.

Thermal conductivity of MgO, MgSiO3 perovskite and post-perovskite in the Earth's deep mantle