Moho carbonation at an ocean-continent transition

Abstract Carbonation of mantle rocks during exhumation is reported in present-day oceanic settings, both at mid-ocean ridges and ocean-continent transitions (OCTs). However, the hydrothermal conditions carbonation (i.e., fluid sources, thermal regimes) remain poorly constrained. We focus on an exceptionally well-preserved fossil OCT where have been exhumed carbonated along a detachment fault from underneath continent to seafloor tectonic Moho. Stable isotope (oxygen carbon) analyses calcite indicate that resulted mixing between serpentinization-derived fluids ~175°C seawater. Strontium compositions suggest interactions seawater continental crust prior carbonation. This shows Moho occurs below breakup.