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

Abstract

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.

Influence of water on the physical properties of olivine, wadsleyite, and ringwoodite

“…2b for hydrogen diffusion in (Mg,Fe) 2 SiO 4 ringwoodite, the experimental data reported by Kudo et al (2006) are comparable with that calculated by the cB model (Zhang, 2012). Sun et al (2015) reported a hydrogen self-diffusion coefficient in Fe-bearing ringwood- (Hae et al, 2006); Z12 (Zhang, 2012); S18 (Sun et al, 2018); K06 (Kudo et al, 2006); K04 (Kubo et al, 2004); H09 (Holzapfel et al, 2009); S04 (Shimojuku et al, 2004); S09 (Shimojuku et al, 2009); S10 (Shimojuku et al, 2010); Z11 (Zhang et al, 2011); Z15a (Zhang and Shan, 2015a); Z15b (Zhang and Shan, 2015b); Z19b (B. H. Zhang et al, 2019b); Z21 (Zhang et al, 2021).…”

“…However, the activation energy for O diffusion in ringwoodite reported by Shimojuku et al (2009) is inconsistent with that determined by Zhang et al (2011). (Fei et al, 2013); F14 (Fei et al, 2014); F18 (Fei et al, 2018); H05 (Hier-Majumder et al, 2005); S19 (Sun et al, 2019); Z19b (B. H. Zhang et al, 2019b); Z21 (Zhang et al, 2021).…”

“…A relatively small water exponent (r = 0.25) suggests the non-negligible role of water in enhancing Fe-Mg interdiffusion in ringwoodite. The activation energy (140 kJ/mol) determined by B. H. Zhang et al (2019b) was much lower than that (345 kJ/mol) reproduced in terms of bulk elastic and expansivity data through a thermodynamic model that interconnects point defect parameters with bulk properties (Zhang and Shan, 2015a).…”

“…Fe-Mg. To date, only B. H. Zhang et al (2019b) have determined the kinetics of Fe-Mg interdiffusion in ringwoodite aggregates as a function of water content (40-6000 ppm H 2 O) at 20 GPa and 1373-1673 K by using the diffusion couple method. A relatively small water exponent (r = 0.25) suggests the non-negligible role of water in enhancing Fe-Mg interdiffusion in ringwoodite.…”

“…Water incorporation in NAMs (even a trace amount of water) has long been proposed to have dramatic influences on many physical and chemical properties, such as thermal conductivity (κ) (Chang et al, 2017;B. H. Zhang et al, 2019a), diffusivity (D) (e.g., Kubo et al, 2004;Hier-Majumder et al, 2005;Costa and Chakraborty, 2008;Fei et al, 2013Fei et al, , 2018Sun et al, 2015Sun et al, , 2018Sun et al, , 2019B. H. Zhang et al, 2019b), electrical conductivity (σ ) (e.g., Karato, 1990;Huang et al, 2005;Yoshino et al, 2006Yoshino et al, , 2008Poe et al, 2010;Yang, 2012;B.…”