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

TL;DR

This study calculates the lattice thermal conductivities of MgO and MgSiO3 in different structures at Earth's lower mantle conditions, revealing significant anisotropy and depth-dependent variations, and estimates heat flux across the core-mantle boundary.

Contribution

It provides the first detailed lattice thermal conductivity calculations for MgO and MgSiO3 in perovskite and post-perovskite phases at deep mantle conditions using molecular dynamics simulations.

Findings

Thermal conductivity varies from 9.5 to 20.5 W/(mK) with depth.

MgSiO3 post-perovskite exhibits significant anisotropy.

Estimated heat flux across the core-mantle boundary is around 10.7 TW.

Abstract

We report lattice thermal conductivities of MgO and MgSiO3 in the perovskite and post-perovskite structures at conditions of the Earth's lower mantle, obtained from equilibrium molecular dynamics simulations. Using an advanced ionic interaction potential, the full conductivity tensor was calculated by means of the Green-Kubo method, and the conductivity of MgSiO3 post-perovskite was found to be significantly anisotropic. The thermal conductivities of all three phases were parameterized as a function of density and temperature. Assuming a Fe-free lower-mantle composition with mole fractions xMgSiO3 = 0.66 and xMgO = 0.34, the conductivity of the two-phase aggregate was calculated along a model geotherm. It was found to vary considerably with depth, rising from 9.5 W/(mK) at the top of the lower mantle to 20.5 W/(mK) at the top of the thermal boundary layer above the core-mantle boundary. Extrapolation of experimental data suggests that at deep-mantle conditions, the presence of a realistic amount of iron impurities lowers the thermal conductivity of the aggregate by about 50% (Manthilake et al., 2011). From this result and our thermal conductivity model, we estimate the heat flux across the core-mantle boundary to be 10.8 TW for a Fe-bearing MgO/MgSiO3 perovskite aggregate and 10.6 TW for a Fe-bearing MgO/MgSiO3 post-perovskite aggregate.