Thermal Conductivity of Hydrous Wadsleyite Determined by Non‐Equilibrium Molecular Dynamics Based on Machine Learning

Abstract

Subduction of slabs couples the Earth's interior with its exterior, and powers the unique plate tectonics on our planet. The temperature of the slabs controls a series of subduction processes. Slab temperature influences the composition and the density of subducting slabs, which determines the fate of the slabs (Ganguly et al., 2009;Litasov et al., 2004). Low temperature can kinetically inhibit the gradual dissolution of pyroxene into garnet (Nishi et al., 2013;van Mierlo et al., 2013), which plays a critical role for the stagnation of the relative cold slabs above the depth of 660 km (King et al., 2015) because pyroxene is less dense than majoritic garnet. The phase transformations of the surviving pyroxene and pyrope could account for multiple discontinuities at the depths of ∼600-750 km in some cold subduction zones such as Northeast China and Tonga (Ai et al., 2003;Deuss et al., 2006;Zang et al., 2006). Temperature also controls slab devolatilization and affects the component of arc magma and the amount of volatiles recycling to the surface (Hsieh et al., 2022;Rüpke et al., 2004;van Keken et al., 2011). The partition coefficients of key elements that define arc geochemical signatures also exhibit strong temperature dependence (Kessel et al., 2005). The thermal structure of the slabs is believed to have a large effect on seismicity (

Thermal Conductivity of MgSiO3‐H2O System Determined by Machine Learning Potentials

“…As the temperature and pressure increase, the impact of water on κ of Brg and pPv gradually decreases, which leads to a weakening in the temperature dependence of κ of Brg from T −0.61 to T −0.50 with the presence of 0.14 wt% water. This finding is consistent with the previous MLP prediction of κ of wadsleyite, which shows that the temperature dependence changes from T −0.45 to T −0.33 with 0.81 wt% water, and then further weakens to T −0.25 for an increased water content of 1.63 wt% (D. Wang et al., 2022). This pattern also mirrors the influence of iron on κ (Manthilake et al., 2011; Y. Zhang et al., 2019; Ohta et al., 2017).…”

“…Our temperature dependence of pPv agrees very well with that reported by Z. Zhang and Wentzcovitch (2021), and other experimental and theoretical studies that capture full phonon anharmonicity also show wilder temperature dependence than T −1 in various minerals (see Supplemental Material of D. Wang et al. (2022)). In contrast, Z. Zhang and Wentzcovitch (2021) show a substantially lower κ of Brg at high temperatures and low pressures (Figure 1b), resulting in a much stronger temperature dependence of Brg ( T −1.01 ) than our results.…”

“…This is likely due to the a‐direction, which has the longest phonon MFP, being the most sensitive to the occurrence of phonon‐defect scattering. This finding indicates a reduced anisotropy of pPv with the incorporation of water, mirroring the negative effect of water on the anisotropy of wadsleyite (D. Wang et al., 2022).…”

“…D. Wang et al. (2022) predicted κ of dry and hydrous wadsleyite using NEMD simulations, and found that κ of wadsleyite is reduced by ∼10% under the mantle transition zone conditions by the presence of 0.81 wt% water. Chang et al.…”

“…The water solubility in Brg remains controversial, with experimental estimates ranging from less than 10 ppm (Bolfan-Casanova et al, 2003), ∼1,000 ppm (Fu et al, 2019) to as much as ∼0.4 wt% (Murakami et al, 2002), while H 2 O and MgSiO 3 melt exhibit near-complete miscibility across the entire mantle (Mookherjee et al, 2008). Previous studies find that the presence of water diminishes κ of olivine and its high-pressure polymorphs (Chang et al, 2017;Marzotto et al, 2020;D. Wang et al, 2022).…”