Program > Browse abstracts by speaker > Wang Bo

The recycling efficiency of carbon in subduction zones controls the distribution of carbon between Earth's deep and surface reservoirs, which further impacts on the productivity of diamond as well as paleoclimate. In warm and hot subduction zones, sediments and altered oceanic crust (AOC) in the subducted slab can undergo partial melting, but the capacity of slab melt in transporting carbon is not well constrained. In this study, we conducted equilibrium experiments between calcite and slab melts with varying 1-7 wt% H2O at 3 GPa and 1100–1300°C in a piston-cylinder apparatus. Despite the crystallization of limited amount of silicate minerals, coexisting calcite and silicate melt were found in all the experimental products. FTIR measurement indicates that carbon in the melt is present mainly as CO32-, including not only those linked to the silicate network but also free CO32-. Carbon solubility (CO2 content in the melt) was determined by FTIR to be 2-4 wt%, showing a positive correlation with melt H2O content and temperature. The finding of more CaO dissolved into the melt than CO2 suggests that a fraction of CO2 escaped into a fluid phase, which is consistent with the observation of vesicles in the quenched melt. In CaCO3-rich hot subduction zones, therefore, melt and fluid may collectively mobilize carbon from subducted slab. Experimental determination of CO2 in the melt and in the fluid allows us to evaluate global carbon flux by slab melt and fluid and the recycling efficiency of carbon in warm and hot subduction zones.