The adsorption behavior of H2O in forsterite pore under high pressure and high temperature by Monte Carlo simulation

To elucidate the mechanisms of water storage and transport within the Earth's mantle, the adsorption characteristics of H₂O within the slit-like pores of forsterite were investigated using the Grand Canonical Monte Carlo method under varying conditions (P = 0–100 MPa, T = 700–1500 K, H = 5.0–20.0 Å). Isosteric heat for H₂O in forsterite varies between −105.8 to −235.7 kJ/mol, suggesting a chemical adsorption process. Analysis of the Poisson distributions of interaction energies indicates that H₂O adsorption within forsterite pores can be categorized into three distinct patterns. The formation of H bonds between H₂O and forsterite enhances H₂O adsorption within the pores. Isothermal adsorption studies indicate that the water uptake by forsterite increases sharply within the depth range of 0 to 5 km. Variations in temperature influence the water content differences observed between cold and hot subduction zones. The calculation results show that the influence of temperature on the adsorption capacity of water in forsterite is very significant. The differences in the adsorbed water content in minerals under the obvious temperature differences of cold and hot subduction plates can provide a new perspective for explaining the differences in water occurrence in subduction plates.