Effect of Iron Content on the Thermal Conductivity and Thermal Diffusivity of Orthopyroxene

The thermal properties of major minerals play a key role in understanding the internal dynamic mechanism and thermal evolution of the Earth and rocky planets. In this study, we first investigated the effect of Fe on the thermal conductivity (kappa) and the thermal diffusivity (D) of orthopyroxene at 1-3 GPa and 293-873 K by the transient plane source method. The kappa and D both decrease with increasing temperature and decreasing pressure. With increasing Fe content, the two parameters both quickly decrease from the beginning and then slack off. We further modeled the thermal evolution of S-type asteroids, which strongly depends on the composition model and the dimension of the planet. Combining the present data with surface heat flow and heat production, the lunar's geotherm until 1,400 km is constructed. The core-mantle boundary temperature of the Moon is refined from 1,883 to 1,754 K. The thermal state and the thermal evolution of rocky planets are strongly influenced by the thermal properties of the major constituent minerals. Orthopyroxene is one of such minerals for rocky planets (e.g., S-type asteroids and moon). The Fe content can potentially affect the thermal properties of orthopyroxene. However, there are no relevant studies up to now. In this study, we systematically measured the thermal conductivity and the thermal diffusivity of pyroxene with variable Fe content at high temperature and high pressure. Our research shows that the thermal conductivity and the thermal diffusivity of orthopyroxene decrease with increasing Fe content. Adopting the results of this study, we simulate the thermal evolution of S-type asteroids with different compositions and dimensions and construct the lunar's geotherm until the core-mantle boundary. Both the thermal conductivity and the thermal diffusivity of orthopyroxene decrease with temperature and increase with pressure The thermal conductivity and the thermal diffusivity of orthopyroxene quickly decrease with iron content The thermal evolutions of S-type asteroids are first simulated and the thermal structure of the lunar interior until the CMB is constrained