Hydrothermal Systems in Peridotites of Slow-Spreading Mid-Oceanic Ridges. Modeling Phase Transitions and Material Balance: Downwelling Limb of a Hydrothermal Circulation Cell

摘要

A model is development for the kinetic and thermodynamic simulation of the interaction of seawa_ter and its metamorphosed derivatives with crustal rocks in slow-spreading ridges. The thermodynamic modu_lus of the model is based on the GEOCHEQ complex, which makes it possible to simulate equilibria in systems of aqueous solutions-minerals-gases. The calculating code was modified and adjusted for the thermodynamic_kinetic simulation of the passage of irreversible solution-rock reactions with time. The simulations were carried out for a simplified crustal vertical section of slow-spreading (Hess-type) ridges, which consist only of mantle peridotites (spine' harzburgites). The results of our simulations demonstrate that the degree of peridotite ser_pentinization under the effect of low-temperature seawater when the rocks are exposed at the seafloor surface remains very low even after 10000 years of interaction. Serpentinization becomes efficient only at temperatures of 130-150℃ at crustal depths of 3.5-4.5 km. The results of our simulations allowed us to develop a thermo_dynamic model for the origin of hydrothermal systems in peridotites in slow-spreading ridges, with regard for the major stages in the material and tectonic evolution of the Hess crust.