Experimental study of sulfur solubility in silicate-carbonate melts at 5-10.5 GPa

Sulfur solubility in Ca-Mg-Fe silicate-carbonate melt was experimentally determined at 5-10.5 GPa and 1400-1600 degrees C. Melt was produced by reaction between natural carbonates (calcite and magnesite) and San Carlos olivine (X-Fo similar to 0.9), which was used as a container, and equilibrated with either Fe-Ni sulfide liquid under reducing conditions (in the presence of graphite) or CaSO4 liquid under oxidizing conditions (Re-ReO2 buffer). To overcome the problem of the presence of sulfide droplets within the silicate-carbonate melt and to reverse the equilibrium, two sample configurations were employed: (1) a carbonate-sulfide mixture placed in the center of the olivine container and (2) sulfide placed in the olivine container and carbonate initially positioned outside the container near the wall of the external Pt capsule. In the former case, silicate-carbonate melt with suspended sulfide melt droplets infiltrated through the olivine capsule, and the two melts were separated owing to their different physical properties. In the latter case, silicate-carbonate melt migrated through thin fractures in the olivine container to come into contact with sulfide. The results of the two experimental series constrained the solubility of sulfide S in silicate-carbonate melt at 0.02-0.10 wt%. The S-solubility increases with increasing FeO content in the melt and is less sensitive to pressure, temperature and other compositional parameters. The solubility of S in the presence of the Re-ReO2 buffer is much higher (up to 2-3 wt%) and dominated by S6+. The obtained results indicate that S is relatively inert during carbonate mantle metasomatism under reduced conditions, but can be transported under oxidizing conditions.