Early release of H2O during subduction of carbonated ultramafic lithologies

Abstract To investigate the effect of carbon-bearing phases on release fluids in subducted serpentinites, we performed high-pressure multi-anvil experiments representative ophicarbonate assemblages over a pressure range from 2.5 GPa to 5 and 450 °C 900 °C, across antigorite-out reaction. Parallel were carbonate-free serpentinites. In all experiments, monitored and/or controlled oxygen fugacity. The addition 20 wt. % CaCO 3 serpentinite assemblage at is found decrease onset serpentine dehydration by 100 comparison assemblages. Similarly, final disappearance also affected presence . For bulk content %, this causes maximum stability antigorite 50 °C. exceeding 25 difference can be as high warm 150 cold subduction zones, causing completely dehydrated 500 This results reaction with form clinopyroxene Mg-rich carbonates. reaction, however, no discernible proportion carbonate, indicating that amount released carbon insignificant. Whilst , therefore, influences stability, there significant hydrous carbonate stability. On other hand, MgCO -bearing system shows effects field. Further fugacity calculations indicate graphite not stable typical magnetite-bearing reduction carbonates would require fugacities are 1–2 log units below those confirms earlier studies indicates only occur through infiltration external H 2 -rich fluids.