Collaborative Research: The Behavior of Sulfur During Magma Mixing and Implications for Magma Degassing and Ore Formation

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The proposed experimental study will elucidate the effect(s) of magma mixing on the mobility of sulfur and sulfur-affine elements. In particular, this study investigates the interaction of sulfur-rich magmas coming from the mantle that mix with more evolved magmas that are typically stored for extended times in magma chambers below the volcanic edifice and have relatively low sulfur concentrations. Understanding the behavior of sulfur during such mixing should significantly improve our ability to forecast volcanic behavior. In the atmosphere, volcanic-released sulfur (often during magma mixing) modulates climate and leads to acid rain in humid volcanic regions. Furthermore, sulfur mobility during magma mixing is thought to facilitate metal transport from silicate melt to magmatic aqueous fluids that are responsible for the evolution of societally important magmatic-hydrothermal ore deposits. A quantitative understanding of how sulfur is mobilized and how it facilitates mass transport during magma mixing of andesite and dacite magma remains unexplored experimentally. As magmas hybridize during diffusive re-equilibration, sulfur-bearing phase stability is investigated as a function of time and oxidation state. Given differential diffusivities of different components in diffusion-couple experiments, diffusive gradients lead to transient local environments, in which sulfides and/or sulfates may in one spot be precipitated while in another area they may be dissolved. This drives complex mass transfer between the mafic and felsic magma. Reduced and oxidized conditions will allow the team to assess the role of sulfur oxidation state on these processes.