SHOCK TEMPERATURE AND MELTING IN IRON SULFIDES AT CORE PRESSURES

The temperatures of shock-compressed FeS and FeS2 in the pressure rang es 125-170 GPa and 100-244 GPa, respectively, are reported and used to constrain the melting curves and thermodynamic properties to core pre ssures. A fit of the Lindemann law parameters corresponding to the usu al functional form for the lattice Gruneisen parameter gives gamma(L) = 1.17+/-0.13 and n(L) = 0.5+/-0.5 for the high-pressure phase of FeS at rho = 5340 kg/m(3) and gamma(L) = 2.18+/-0.32 and n(L) = 1.6+/-0.7 for FeS2 at rho = 5011 kg/m(3). The entropies of fusion are similar to 203 J kg(-1) K-1 for FeS at 120 GPa and similar to 180 J kg(-1) K-1 f or FeS2 at 220 GPa. We find that the melting temperature of FeS is 324 0+/-200 K, 4210+/-700 K, and 4310+/-750 K at 136 GPa, 330 GPa, and 360 GPa, respectively. For FeS2, the melting temperatures are 3990+/-300 K, 5310+/-700 K, and 5440+/-750 K, respectively, for the same pressure s. The electronic specific heat for FeS is given by C-e = beta(0) (rho (0)/rho)(gamma e) with beta(0) = 0.25+/-0.10 J kg(-1) K-2 and gamma(e) = 1.34 for rho(0) = 5340 kg/m(3) for the high-pressure solid phase an d beta(0) approximate to 0.05 J kg(-1) K-2 and gamma(e) = 1.34 for rho (0) = 5150 kg/m(3) for the liquid phase. For FeS2, there is no detecta ble electronic contribution, and the lattice specific heat is only 67% of the Dulong-Petit limit, possibly implying tight S-S binding in S-2 units. A reexamination of all shock wave melting data for Fe indicate s these approximately agree, but they do not resolve the disagreement between the extrapolated static diamond anvil cell data sets. Fe shoul d melt at similar to 6600 K at 243 GPa and 6900+/-750 K at 330 GPa (th e pressure of the inner core-outer core boundary). Because the FeS mel ting curve falls well below that of FeS2, FeS may eventually undergo p eritectic melting at high pressures, while FeS2 melts congruently.