Stability of Carbonates during Subduction: Influence of the Dehydration Regime of Chlorine-Bearing Metapelite

Abstract

Abstract It was shown that, at a pressure of 3.0, 5.5, and 7.8 GPa and a temperature of 750–1030°C, a set of reactions occurred in carbonate and Cl-bearing pelite that is finally converted into an eclogite-like assemblage and formed a H2O–CO2 Cl-bearing fluid. The eclogite-like assemblage remains stable when the P–T conditions change concordantly with hot subduction geotherms, whereas carbonate is completely dissolved in the fluid already at ≥5.5 GPa. The CO2 content in the quenched fluid reaches 20–30 wt %. However, preliminary defluidization of pelite at 3.0 GPa and 750°С leads to chlorine removal and carbonate stabilization at 5.5 GPa and at 7.8 GPa in equilibrium with the next chlorine-free portions of the fluid. Comparison of the data available for simplified model systems and new data on carbonate and Cl-bearing pelite indicate that chlorine fluid essentially contributes to carbonate dissolution in the fluid. Thus, the stability of carbonates under P–T conditions typical of subduction zones is dependent on the behavior of chlorine during defluidization of marine sediments.