Thermal Conductivity and Thermal Diffusivity of Ferrosilite under High Temperature and High Pressure

Orthopyroxene is an important constitutive mineral in the crust and the upper mantle. Its thermal properties play a key role in constructing the thermal structure of the crust and the upper mantle. In this study, we developed a new method to synthesize polycrystalline ferrosilite, one end-member of orthopyroxene, via the reaction of FeO + SiO2 -> FeSiO3. We found that the P-T condition of 3 GPa and 1 273 K is suitable to synthesize dense ferrosilite samples with low porosity. We employed the transient plane-source method to investigate the thermal conductivity kappa and thermal diffusivity D of synthetic ferrosilite at 1 GPa and 293-873 K, of which, kappa = 1.786 + 1.048 x 10(3)T(-1)-9.269 x 10(4)T(-2) and D = 0.424 + 0.223 x 10(3)T(-1) + 1.64 x 10(4)T(-2). Our results suggest phonon conduction should be the dominant mechanism at P-T conditions of interest since the thermal conductivity and the thermal diffusivity of ferrosilite both decrease with increasing temperature. The calculated heat capacity of ferrosilite at 1 GPa increases with temperature, which increases with increasing temperature with about 10% per 100 K (<500 K) and 4% per 100 K (>500 K). Iron content of an asteroid significantly influences its thermal evolution history and temperature distribution inside. It is expected that the mantle temperature of the Fe-rich asteroid will be higher and the Fe-rich asteroid's cooling history will be longer.