Thermal conductivity near the bottom of the Earth's lower mantle: Measurements of pyrolite up to 120 GPa and 2500 K.

(a) Schematic cross-section of experimental setup, including electron backscatter image of sample recovered from high pressure and sliced in half. The pyrolite sample is coated, insulated and compressed to 80 GPa in a diamond anvil cell. Lasers 1 and 2 are continuous and pulsed lasers, respectively, which heat the pyrolite sample to the temperature of interest. (b) Measured temperature evolution from left side (red) and right side (blue) at 80 GPa during the heating experiment represented in (a), along with modeled temperature evolutions (black). • Lattice thermal conductivity of pyrolite is between 2.8 and 5.3 W/m/K at 80 GPa, 2000 to 2500 K. • Lattice thermal conductivity of pyrolite is between 3.6 and 9.9 W/m/K at 124 GPa, 2000 to 3000 K. • Measurements combined diamond anvil cells, continuous and pulsed laser heating, and spectroradiometry. • Data analysis used finite element modeling. Knowledge of thermal conductivity of mantle minerals is crucial for understanding heat transport from the Earth's core to mantle. At the pressure-temperature conditions of the Earth's core-mantle boundary, calculations of lattice thermal conductivity based on atomistic models have determined values ranging from 1 to 14 W/m/K for bridgmanite and bridgmanite-rich mineral assemblages. Previous studies have been performed at room temperature up to the pressures of the core-mantle boundary, but correcting these to geotherm temperatures may introduce large errors. Here we present the first measurements of lattice thermal conductivity of mantle minerals up to pressures and temperatures near the base of the mantle, 120 GPa and 2500 K. We use a combination of continuous and pulsed laser heating in a diamond anvil cell to measure the lattice thermal conductivity of pyrolite, the assemblage of minerals expected to make up the lower mantle. We find a value of 3.9 + 1.4 − 1.1 W/m/K at 80 GPa and 2000 to 2500 K and 5.9 + 4.0 − 2.3 W/m/K at 124 GPa and 2000 to 3000 K. These values rule out the highest calculations of thermal conductivity of the Earth's mid-lower mantle (i.e. k < 6 W/m/K at 80 GPa), and are consistent with both the high and low calculations of thermal conductivity near the base of the lower mantle. [ABSTRACT FROM AUTHOR]