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 endmember 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 κ and thermal diffusivity D of synthetic ferrosilite at 1 GPa and 293–873 K,of which,κ = 1.786 + 1.048 × 10～3 T-1– 9.269 × 10～4 T-2 and D = 0.424 + 0.223 × 10～3 T-1+ 1.64 × 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.