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

提出的实验研究将阐明岩浆混合对硫和硫仿射元素流动性的影响。特别地，这项研究调查了来自地幔的富硫岩浆与更进化的岩浆的相互作用，这些岩浆通常在火山大厦下面的岩浆房中储存了很长时间，硫浓度相对较低。了解这种混合过程中硫的行为将大大提高我们预测火山行为的能力。在大气中，火山释放的硫（通常在岩浆混合期间）调节气候，导致潮湿的火山地区出现酸雨。此外，岩浆混合过程中的硫流动性被认为促进了金属从硅酸盐熔体向岩浆含水流体的运输，这是对社会上重要的岩浆热液矿床的演化负责。在安山岩和英安岩岩浆混合的过程中，硫是如何被动员的，以及它是如何促进物质运输的，这一定量的理解仍未得到实验的探索。当岩浆在扩散再平衡过程中发生杂化时，研究了含硫相稳定性随时间和氧化态的变化规律。在扩散偶实验中，由于不同组分的扩散系数不同，扩散梯度会导致短暂的局部环境，其中硫化物和/或硫酸盐可能在一个地方沉淀，而在另一个地方则可能溶解。这推动了镁质岩浆和长英质岩浆之间复杂的质量传递。还原和氧化条件将允许团队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.