Solubility of sulfur in basaltic melts
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Abstract
VUELCO Conference, 2013, Barcelona (Spain)
Sulfur is the third most abundant volatile element in magmatic melts, after H2O and CO2. Involved as a chief actor in many igneous processes, from the volcanic degassing to the formation of ore deposits, and due to the strong dependence between speciation and oxygen fugacity, sulfur always attracted the geochemical community in the effort to understand and model its behavior in magmatic systems. In the framework of Vuelco, we are interested to the volcanic degassing aspect, with an affect on volcanic hazard, not forgetting the impact on global climate change.
We want to produce solubility data for sulfur under well controlled conditions to calibrate an accurate fluid-melt sulfur saturation model. We will perform experiments using a sample of basaltic pumice from Stromboli Island, PST9. To rigorously attain to this aim, we plan three series of experiments: 1) Fe pre-saturation of Pt capsules using a 1-atm furnace withCO-CO2 gas mixture; 2) calibration of fS2 using a 1 atm-furnace with CO-CO2-SO2 gas mixture; and finally 3) sulfur solubility experiments, doping the PST9 sample with about 1 wt% pyrrhotite (FeS), slightly under-saturated in H2O, at T = 1200 °C, logfO2 NNO and in a range of pressure between 200 and 20 MPa.
Series 1 allows us to minimize iron loss from the silicate melt during the high P experiments (series 3), and series 2 to calculate the fugacities of S-bearing species in the fluid in the high P experiments.
At present the first series of experiments is complete. We checked the efficiency of the method comparing the simple PST9 with the PST9 pre-loaded with Fe, either 5 % or 13 %. The addition of 5% Fe accelerates the kinetics of Fe transport without dramatically changing the original melt composition, encouraging us to test a direct enrichment of the sample at high pressure, shortening the whole process.
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