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

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 H 2 O–CO 2 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 CO 2 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.