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

可变初始水含量对弧火山中岩浆金属流动的影响

• 批准号: 2698388
• 金额: --
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2698388
• 关键词: Implications; variable; initial; water; content

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.

岩浆系统内金属元素的迁移和隔离调节火山喷发和矿床开发的环境影响（Edmonds等人，2022 Tattitch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发出对比鲜明的微量金属“指纹”，这与蒸汽和硫化物饱和度的相对时间差异有关（Edmonds等人，2018年）。弧火山喷发的岩浆含有范围广泛的原生水含量，范围从小于1重量%到大于7重量%的H2O，继承自地幔来源和俯冲贡献的不均匀性（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）并且因此是对蒸汽饱和的时间/压力的关键控制-并且因此是对痕量元素根据其熔体-流体分配系数分配进入的含水流体相的可用性的关键控制-以及岩浆存储在地壳中的条件（Edmonds等人，2022年）。然而，原生水含量对金属分配的作用还有待系统研究。该项目确定了两个弧火山-危地马拉的Fuego和Pacaya-分别具有低和高岩浆水含量（Lloyd等人，2014年步行者等人，2003年）。首要目标是重建和比较的演变，他们的微量金属货物使用既定的岩石学策略。以Fuego和Pacaya为目标进行岩浆水含量的端元比较，避免了引入可能影响金属行为的额外不确定性，例如板片通量或地壳厚度的沿弧或弧间变化。这项研究将涉及对喷发岩石和气体羽流中排放的金属气溶胶进行实地采样。实验室工作将侧重于对熔融包裹体和玻璃进行岩石学分析，包括对挥发物含量进行离子探针分析，以及对过滤器上收集的羽流气溶胶样品进行地球化学分析。岩石学和热力学建模将提供一个框架来解释我们的地球化学数据，特别是，与金属行为的结晶过程和硅酸盐熔体中的出溶挥发相的组成。该项目还将探讨是否有可能制定非传统办法来评估火山排放物对环境的影响：特别是是否有可能利用植被、土壤和水文样本中的微量金属来评估火山微量金属污染物向环境的输送机制和途径，从而对生态科学和危害评估产生影响。