Carbon isotope fractionation between CO2 and carbon in silicate melts at high temperature

The isotopic fractionation of carbon between CO2 gas and silicate melts is a crucial parameter to understand the carbon cycle at the planetary scale that requires accurate quantification. In this study, we conducted experiments to determine the carbon isotope fractionation between CO2 gas and carbon dissolved in silicate melt at 350-420 MPa and 1160-1225°C, across a range of melt compositions. A linear relationship emerges between the fractionation coefficient and the degree of polymerization of the melt (NBO/T; non-bridging oxygens per tetrahedral cation) with the fractionation coefficient increasing for depolymerized melts (e.g., basalt) and decreasing for polymerized melts (e.g., rhyolite): 1000lnαgas-melt=2.847×NBO/T+0.068 (R2=0.74) or 1000ln