Effect of Water on the Thermal Properties of Olivine With Implications for Lunar Internal Temperature

How water could affect thermal transport properties is a key question that needs to be quantified experimentally when it is incorporated as structurally bound hydroxyl groups in the lattice of mantle minerals. In this study, thermal diffusivity (D) and thermal conductivity (κ) of San Carlos olivine aggregates with various water contents (up to 0.2 wt.% H2O) were measured simultaneously using transient plane‐source method up to 873 K and 3 GPa. Experimental results demonstrate that water content can significantly reduce the thermal diffusivity (D) and thermal conductivity (κ) of olivine aggregate. With the increase of H2O content from 0.08 to 0.2 wt.%, the absolute values of D and κ for olivine samples decrease by 5–13% and 17–33% and by 3–8% and 14–21%, respectively. D and κ of olivine aggregate decrease with temperature but increase with pressure. Heat capacity is influenced by pressure negatively. Combining the present data with surface heat flow of the Moon as well as heat production, the calculated temperature profiles provide new constraints on the lunar geotherm and possible H2O content in the lunar interior. Plain Language Summary It is believed that incorporation of even trace amount of water can significantly affect thermophysical properties of olivine. Nevertheless, there have not been any robust experiments under high‐pressure and high‐temperature conditions simultaneously. In this study, thermal diffusivity and thermal conductivity of olivine were measured as a function of water content (from dry to 0.2 wt.% H2O) from 1 to 3 GPa and 300 to 873 K. Our results demonstrate a profound role of water in reducing thermal diffusivity and thermal conductivity of olivine. Using the present results, a temperature profile of the lunar mantle has been established based on surface heat flow and heat production of the Moon. Our model provides new constraints on temperature distribution and water content in the interior of the Moon. Key Points Effect of water on the D and κ of olivine were measured up to 873 K and 3 GPa D and κ decrease with temperature and water content but increase with pressure New constraints on temperature and H2O content of the lunar interior were provided