Thermodynamic and elastic properties of grossular (Ca3Al2(SiO4)3, the calcium‐aluminium end‐member of garnet) at high pressures and temperatures are obtained using the first‐principles calculations based on the density functional theory. Our calculated results agree well with available experimental data. The elastic moduli and wave velocities of grossular exhibit the nonlinear pressure and temperature dependences. Although the bulk moduli of grossular are similar to those of pyrope (Mg3Al2(SiO4)3) and almandine (Fe3Al2(SiO4)3), its shear moduli are significantly larger than those of pyrope and almandine. Combining our calculated results with previously calculated elasticity of other upper‐mantle minerals, we estimated density and wave velocity profiles for the pyrolitic and eclogitic compositions along different mantle geotherms. We find that a pyrolitic composition along the normal geotherm can well reproduce the reference velocities and densities for the upper mantle, supporting a pyrolitic upper mantle. Although an eclogitic composition also has similar velocities to reference seismic models above 300 km, it is significantly denser than the pyrolitic composition and the ambient mantle. However, the velocities of eclogite along the cold geotherm are relatively larger than those of the pyrolitic composition, indicating that the presence of eclogite in subduction zones could produce high‐velocity anomalies. In addition, the decomposition of grossular to calcium perovskite and corundum at the conditions of the mantle transition zone can produce considerable velocities and density jumps, which probably provides an interpretation for the seismically observed multiple reflections at ~660 km.
Subduction is one of the unique geological features of the Earth that carry water to the deep mantle. The slab-derived fluids could melt the surrounding mantle and generate the hydrous melt and the aqueous fluid with a miscibility gap. In the deeper subduction zones with higher temperature, the miscibility gap diminishes to form the supercritical fluid. The supercritical fluids with fluid-like viscosity and melt-like element carrying ability play a fundamental role in the chemical transport in the subduction zone. Yet, the atomic structures and their effect on transport properties of supercritical fluids remain poorly understood.Here, we perform the first-principle molecular dynamic calculations on supercritical fluid of the composition of diopside with 0 ~ 78 wt.% water (CaMgSi 2 O 6 -xH 2 O) at 3000 K. We find that all the cation-anion coordination numbers decrease with water content, while bonding O (BO) and non-bonding O (NBO) change to free O as the water content increases. H occurs mostly as hydroxyl at water-poor condition and switches to H 2 O molecule at water-rich condition. The diffusion coefficients appear as
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.