부산대학교 도서관

The behaviour of sulfur in magmas is complex because it dissolves as both sulfide (S2−) and sulfate (S6+) in silicate melt. Interesting aspects of the behaviour of sulfur are the solubility minimum (SSmin) and maxima (SSmax) observed with varying oxygen fugacity (fO2). We use a simple ternary model (silicate–S2–O2) to explore the varying fO2 paths where these phenomena occur. Both SSmin and SSmax occur when S2− and S6+ are present in the silicate melt in similar quantities owing to the differing solubility mechanisms of melt species containing these oxidation states of sulfur. At constant T, a minimum in dissolved total S content in vapour-saturated silicate melt (wSTm) occurs along paths of increasing fO2 and either constant fS2 or constant P. For paths on which wSTm is held constant with increasing fO2 , the SSmin is expressed as a maximum in P. The SSmin occurs when the fraction of S6+ in the melt ([S6+/ST]m) is 0.25 for constant fS2 and [S6+/ST]m ≈ 0.75 for constant wSTm and P. A minimum in wSTm is not encountered during closed- or open-system depressurization in the simple system we modelled. However, the SSmin marks a change from reduction to oxidation during degassing. Various SSmax occur when the silicate melt is multiply saturated with at least two phases: vapour, sulfide melt, and/or anhydrite. The SSmin and SSmax are potentially important features of magmatic process involving S, such as mantle melting, magma mixing, and degassing. These concepts influence calculations of the pressures of vapour-saturation, fO2 , and SO2 emissions using melt inclusions. Supplementary material: Additional information and data used to create the figures are available at https://doi.org/10.6084/m9.figshare.c.6274527 Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/topic/collections/sulfur-in-the-earth-system [ABSTRACT FROM AUTHOR]