Temperature dependence of sulfide and sulfate solubility in olivine-saturated basaltic magmas

The sulfur concentration at pyrrhotite- and anhydrite-saturation in primitive hydrous basaltic melt of the 2001-2002 eruption of Mt. Etna was determined at 200 MPa, T = 1050-1250 degrees C and at log fO(2) from FMQ to FMQ+2.2 (FMQ is Fayalite-Magnetite-Quartz oxygen buffer). At 1050 degrees C Au sample containers were used. A double-capsule technique, using a single crystal olivine sample container closed with an olivine piston, embedded in a sealed Au80Pd20 capsule, was developed to perform experiments in S-bearing hydrous basaltic systems at T > 1050 degrees C. Pyrrhotite is found to be a stable phase coexisting with melt at FMQ-FMQ+0.3, whereas anhydrite is stable at FMQ+1.4-FMQ+2.2. The S concentration in the melt increases almost linearly from 0.12 +/- 0.01 to 0.39 +/- 0.02 wt.% S at FeS-saturation and from 0.74 +/- 0.01 to 1.08 +/- 0.04 wt.% S at anhydrite-saturation with T ranging from 1050-1250 degrees C. The relationships between S concentration at pyrrhotite and/or anhydrite saturation, MgO content of the olivine-saturated melt, T, and logfO(2) observed in this study and from previous data are used to develop an empirical model for estimating the magmatic T and fO(2) from the S and MgO concentrations of H2O-bearing olivine-saturated basaltic melts. The model can also be used to determine maximum S concentrations, if fO(2) and MgO content of the melt are known. The application of the model to compositions of melt inclusions in olivines from Mt. Etna indicates that the most primitive magmas trapped in inclusions might have been stored at logfO(2) slightly higher than FMQ+1 and at T = 1100-1150 degrees C, whereas more evolved melts could have been trapped at T <= 1100 degrees C. These values are in a good agreement with the estimates obtained by other independent methods reported in the literature. (C) 2011 Elsevier Ltd. All rights reserved.