Phases of the Fe–C–N system as hosts of mantle carbon and nitrogen: Experimental studies at 7.8 GPa and 1350°C

Abstract

Parts of the Fe–C–N system were studied in experiments at 7.8 GPa and 1350°C. It was shown that the admixture of nitrogen extends considerably the domain of melt stability in the system at temperatures close to the Fe–Fe₃C eutectic temperatures. Nitrogen solubility in cementite in equilibrium with the nitrogen- rich melt is below the detection limit of the EMPA technique applied. The metal melt is the only nitrogen concentrator (up to 4 wt % of N) in the range of compositions considered. The data obtained permit the conclusion that, in the case of complete dissolution of carbon and nitrogen, which might occur in the enriched mantle, native iron at ~250 km depth should either be completely molten or consist of a melt and carbide of iron.