Stability of Carbonates during Subduction: The Role of Dissolution in Dehydration Fluids

The dissolution of carbonates in dehydration fluids during subduction can significantly affect the efficiency of carbonate transport to the mantle and, in general, determine the deep carbon cycle. This study provides experimental data on the solubility of aragonite in aqueous fluids with varying NaCl content, measured at pressures and temperatures typical of an average subduction geotherm. At 3.0 GPa and 750°C, the solubility of aragonite in aqueous fluids is found to be 2.4 ± 0.2 wt %, which is consistent with the previous estimates. It is demonstrated for the first time that, at 5.5 GPa and 850°C, the solubility of aragonite increases significantly, reaching 12.1 ± 0.6 wt %. Moreover, increasing the NaCl concentration in aqueous fluid up to 9 wt % does not affect the solubility of aragonite within the measurement error. Therefore, aqueous fluids formed at pressures above 5.5 GPa during the dehydration of the serpentinized oceanic lithosphere can facilitate the dissolution and removal of a substantial amount of carbonates from a subducted slab into the surrounding mantle.