Implications of variable initial water content for mobilising magmatic metals in arc volcanoes

金属元素在岩浆系统内的迁移和封存调节了火山喷发和矿藏开发对环境的影响(Edmonds等人，2022年Tattich等人，2021年)。许多被公共卫生机构归类为“环境污染物”的元素在硅酸盐熔体中是挥发性的(Ilyinskaya等人，2021年)。不同构造环境中的火山释放出不同的微量金属“指纹”，这与蒸汽和硫化物饱和的相对时间不同有关(Edmonds等人，2018年)。弧形火山喷发的岩浆含有广泛的原生水含量，范围从不到1wt%到超过7wt%的H2O，继承自地幔来源和俯冲贡献的不均一性(Plank等人，2013 Ruscitto等人，2012年)。岩浆水含量影响硅酸盐熔体的物理和化学性质(例如粘度和结晶动力学)，因此是控制蒸气饱和的时间/压力的关键--因此，根据微量元素的熔体-流体分配系数，是否存在可供痕量元素分配的含水流体相--以及岩浆在地壳中储存的条件(Edmonds等人，2022)。该项目确定了两座弧形火山--危地马拉的Fuego和Pacaya，它们的岩浆水含量分别较低和较高(Lloyd等人，2014，Walker等人，2003)。总体目标是利用既定的岩石学战略重建和比较它们的痕量金属货物的演化。将Fuego和Pacaya作为岩浆含水率的终端成员比较的目标，避免了可能影响金属行为的额外不确定性，例如板坯流量或地壳厚度的沿弧或弧间变化。这项研究将包括对喷发的岩石和气体羽流中释放的金属气溶胶进行现场采样。实验室工作将重点放在熔融包裹体和玻璃的岩石学分析上，包括挥发性成分的离子探针分析，以及过滤器上收集的羽状气溶胶样本的地球化学分析。岩石学和热力学模拟将提供一个框架来解释我们的地球化学数据，特别是将金属行为与结晶过程和硅酸盐熔体中出溶的挥发性相的组成联系起来。该项目还将探讨开发非传统方法评估火山排放的环境影响的潜力：特别是利用植被、土壤和水文样本中的痕量金属评估火山成因痕量金属污染物向环境的输送机制和途径的可行性，从而对生态科学和危害评估产生影响。

The migration and sequestration of metallic elements within magmatic systems modulates the environmental impacts of volcanic emissions and the development of ore deposits (Edmonds et al., 2022 Tattitch et al., 2021). Many elements classified as "environmental pollutants" by public health agencies are volatile in silicate melts (Ilyinskaya et al., 2021). Volcanoes in different tectonic settings emit contrasting trace metal "fingerprints", which are linked to differences in the relative timings of vapour and sulfide saturation (Edmonds et al., 2018). Arc volcanoes erupt magmas containing a wide range of primary water contents, spanning less than 1 wt% to more than 7 wt% H2O, inherited from heterogeneities in mantle source and subduction contributions (Plank et al., 2013 Ruscitto et al., 2012). Magmatic water content influences the physical and chemical properties of silicate melts (e.g., viscosity and crystallisation dynamics) and is consequently a key control on the timing/pressure of vapour saturation - and therefore availability of a hydrous fluid phase for trace elements to partition into according to their melt-fluid partition coefficients - and the conditions under which magmas are stored in the crust (Edmonds et al., 2022). However, the role of primary water content on metal partitioning has yet to be investigated systematically.This project identifies two arc volcanoes-Fuego and Pacaya, Guatemala-with low andhigh magmatic water contents, respectively (Lloyd et al., 2014 Walker et al., 2003). Theoverarching aim is to reconstruct and compare the evolution of their trace metal cargoes using established petrological strategies. Targeting Fuego and Pacaya for end-member comparisons of magmatic water content avoids introducing additional uncertainties that may influence metal behaviour such as along-arc or inter-arc variations in slab flux or crustal thickness. This research will involve field sampling of erupted rocks and emitted metal aerosols in the gas plume. Laboratory work will focus on petrological analysis of melt inclusions and glasses, including ion probe analyses of volatile contents, together with geochemical analysis of plume aerosol samples collected on filters. Petrological and thermodynamic modelling will provide a framework to interpret our geochemical data and, in particular, to relate metal behaviour to crystallisation processes and the composition of the exsolved volatile phase in silicate melts. This project will also explore the potential for developing non-traditional approaches to assess the environmental impact of volcanic emissions: in particular, the feasibility of using trace metals in vegetation, soil, and hydrological samples to assess the delivery mechanisms and pathways of volcanogenic trace metal pollutants to the environment, with consequent implications for ecological science and hazard assessment.