Carbon isotope fractionation during high pressure and high temperature crystallization of Fe–C melt

Abstract

There is a growing body of experimental evidence that iron carbides can play an important role in the mantle both as a host of carbon and as a redox couple (Fe–C) determining the nature of reduced phases. If carbides are significant in the mantle, it could be of interest to know if any carbon isotope fractionation accompanies carbide crystallization. A series of high-pressure and high-temperature experiments were performed on carbide crystallization from a Fe–C melt. An offset of 2‰ was observed between the δ13C values of Fe3C and Fe–C melt at 6.3GPa and 1400°C. The carbon isotopic compositions of Fe3C and diamond crystallizing from a single carbon source near the peritectic region at 6.3GPa differ by 2.5‰. Fe7C3 was detected as a quench phase during Fe–C melt quenching. Our results have important implications for understanding carbon isotope distributions in iron meteorites and indicate that iron carbide crystallization may be a significant mechanism for carbon isotope heterogeneity in the Earth's mantle.