The system Fe-FeO revisited

Abstract

The results of a reconnaissance investigation of melting relationships in the system Fe-FeO at 16 GPa were recently described by Kato and Ringwood (1989). The principal sources of uncertainties in those experiments were caused by loss of FeO to sample capsules during runs and the estimation of sample temperatures by an indirect method, based upon a prior calibration of the relationship between power input and temperature. A further set of 24 runs at 16 GPa has been carried out using improved experimental techniques. The melting temperatures of iron and wüstite at 16 GPa are found to be 1945±20° C and 1875±25° C respectively. (Quoted errors do not include possible effects of pressure on thermocouple emf). The Fe-FeO eutectic is now located at 10±2 wt% FeO and 1670±20° C (previously 15.5±3 wt% FeO and 1700±25° C). The new determination of the depression of the melting point of iron by solution of FeO is 27.5° C/wt% FeO as compared to the previous value of 23° C/wt% FeO. The present results show that the contraction of the liquid immiscibility field in the system at high pressure is somewhat larger than was estimated previously. This study confirms the general topology of high pressure phase relationships in the Fe-FeO system obtained by Kato and Ringwood (1989) and has similar implications for the process of core formation within the Earth.