Shock temperature and melting in iron sulfides at core pressures

The temperatures of shock-compressed FeS and FeS 2in the pressure ranges 125-170 GPa nd 100-244 GPa, respectively, are reported and used to constrain the melting curves and thermodynamic properties to core pressures. A fit of the Lindemann lawparameters corresponding to the usual functional form for the lattice Grtineisen parameter gives YL = 1.17:L'0.13 andnœ = 0.5_+0.5 for the high-pressure phase ofFeS at p = 5340 kg/m 3 and YL TM 2.18:L-0.32 and nL = 1.6_+0.7 for FeS 2at p = 5011 kg/rn 3.The entropies of fusion are -203 J kg '1 K -• for FeS at 120 GPa nd -180 J kg '1 K '1 for FeS 2at 220 GPa. We find that the melting temperature ofFeS is 3240-•00 K, 4210-!-_700 K, and 4310-2:750 K at 136 GPa, 330 GPa, and 360 GPa, respectively. For FeS 2, the melting temperatures are 3990'•_300 K, 5310-!-_700 K, and 5440-!-_750 K, respectively, for the same pressures. The electronic specific heat for FeS is given by Ce= [•0 (P0/P) • with •0 = 0.25:L-0.10 J kg '1K -2 and 7e = 1.34 for P0 TM 5340 kg/m 3 for the highpressure solid phase and •o = 0.05 J kg -1 K -2 and 3⁄4e =1.34 for P0 = 5150 kg/m 3 for the liquid phase. For FeS 2, there is no detectable 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 indicates these approximately agree, but they do not resolve the disagreement between the extrapolated static diamond anvil cell data sets. Fe should melt at -6600 K at 243 GPa and 69003:750 K at 330 GPa (the pressure of the inner coreouter core boundary). Because the FeS melting curve falls well below that of FeS 2, FeS may eventually undergo petitecftc melting at high pressures, while FeS 2 melts congmently.