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

拟议的实验研究将阐明(S)岩浆混合对硫及其仿硫元素活动性的影响。特别是，这项研究调查了来自地幔的富硫岩浆与更演化的岩浆的相互作用，这些岩浆通常长期储存在火山大楼下方的岩浆室中，并且硫浓度相对较低。了解硫在这种混合过程中的行为应该会显著提高我们预测火山行为的能力。在大气中，火山释放的硫(通常是在岩浆混合期间)调节气候，并在潮湿的火山地区导致酸雨。此外，岩浆混合过程中硫的迁移被认为促进了金属从硅酸盐熔体向岩浆水流体的迁移，这对社会上重要的岩浆-热液矿床的演化起到了作用。在安山岩和英安岩岩浆混合过程中，硫是如何被活化的，以及它是如何促进质量传输的，这一定量理解仍有待于实验探索。当岩浆在扩散再平衡过程中混合时，含硫相的稳定性随时间和氧化状态的变化而变化。在扩散偶实验中，由于不同组分的扩散系数不同，扩散梯度导致了局部环境的瞬变，在这种环境中，硫化物和/或硫酸盐可能在一个点析出，而在另一个区域则可能被溶解。这推动了镁铁质岩浆和长英质岩浆之间的复杂质量转移。还原和氧化条件将使研究小组能够评估硫氧化状态在这些过程中的作用。

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.