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 theP-Tcondition 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 conductivityκand thermal diffusivityDof synthetic ferrosilite at 1 GPa and 293–873 K, of which,κ= 1.786 + 1.048 × 10³T^-1 – 9.269 × 10⁴T^-2 andD= 0.424 + 0.223 × 10³T^-1 + 1.64 × 10⁴T^-2. Our results suggest phonon conduction should be the dominant mechanism atP-Tconditions 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.