The Fe-rich liquidus in the Fe–FeS system from 1 bar to 10 GPa

The composition and evolution of a metallic planetary core is determined by the behavior with pressure of the eutectic and the liquidus on the Fe-rich side of the Fe–FeS eutectic. New experiments at 6 GPa presented here, along with existing experimental data, inform a thermodynamic model for this liquidus from 1 bar to at least 10 GPa. Fe–FeS has a eutectic that becomes more Fe-rich but remains constant in T up to 6 GPa. The 1 bar, 3 GPa, and 6 GPa liquidi all cross at a pivot point at 1640 ± 5 K and FeS37 ± 0.5. This liquid/crystalline metal equilibrium is T–x-fixed and pressure independent through 6 GPa. Models of the 1 bar through 10 GPa experimental liquidi show that with increasing P there is an increase in the T separation between the liquidus and the crest of the metastable two-liquid solvus. The solvus crest decreases in T with increasing P. The model accurately reproduces all the experimental liquidi from 1 bar to 10 GPa, as well as reproducing the 0–6 GPa pivot point. The 14 GPa experimental liquidus ( Chen et al., 2008a and Chen et al., 2008b) deviates sharply from the lower pressure trends indicating that the 0–10 GPa model no longer applies to this 14 GPa data.