Measurement of Lattice Thermal Conductivity of Lower Mantle Minerals under High Pressures using a Pulsed Light Heating Thermoreflectance Technique

Abstract

Thermal conductivity of lower mantle minerals is essential for controlling the rate of core heat loss and long-term thermal evolution of the Earth, but it has been poorly constrained at the high pressures of the Earth's lowermost mantle. We have newly developed an apparatus for measuring the thermal diffusivity using a pulsed light heating thermoreflectance technique under high pressure in a diamond anvil cell. The new method enabled us to determine the lattice thermal diffusivity of both MgSiO₃ perovskite and post-perovskite, the main constituent of the Earth's lower mantle, at room temperature and at high pressures up to 144 GPa greater than the core-mantle boundary pressure. Lattice thermal conductivity of perovskite-dominant lowermost mantle assemblage obtained in this study is about 11 W·m⁻¹·K⁻¹, while post-perovskite bearing rocks exhibit ～60% higher conductivity. Such perovskite value is comparable to the conventionally assumed lowermost mantle conductivity of 10 W·m⁻¹·K⁻¹.