Phase Equilibria in the System CaCO3-MgCO3-FeCO3
- 1 April 1987
- journal article
- Published by Oxford University Press (OUP) in Journal of Petrology
- Vol. 28 (2) , 389-415
- https://doi.org/10.1093/petrology/28.2.389
Abstract
Hydrothermal experiments on natural samples of trachyandesite and dacite bulk composition show that anhydrite (CaSO4) may occur as a stable phenocryst phase at oxygen fugacities greater than or equal to 1.0 to 1.5 log fO2 units above the Ni–NiO equilibrium. The dissolved sulfur concentration in anhydrite saturated melts from MnO–Mn3O4 buffered experiments decreases with decreasing temperature, from approximately 2300 p.p.m.S at 1025°C to 250 p.p.m.S at 850°C (all at 2 kb Pfluid = Ptotal). In FeS-saturated melts equilibrated at the Ni–NiO buffer and 2 kb pressure, the concentration of dissolved sulfur also decreases with decreasing temperature, varying from approximately 400 p.p.m. S at 1025°C to less than 100 p.p.m. S at 850°C. At NNO or lowerfO2s, decreasing melt FeO content due to crystal fractionation may explain the observed decrease in sulfur solubility with decreasing temperature.Keywords
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