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.

岩浆系统中金属元素的迁移和封存调节了火山排放物对环境的影响和矿床的开发（Edmonds etal ., 2022 . tadoch etal ., 2021）。许多被公共卫生机构列为“环境污染物”的元素在硅酸盐熔体中挥发（Ilyinskaya et al., 2021）。不同构造环境下的火山会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差异有关（Edmonds etal ., 2018）。弧火山喷发出的岩浆含有广泛的原生水含量，从小于1wt %到大于7wt %的水，继承自地幔源的非均质性和俯冲作用（Plank et al., 2013 Ruscitto et al., 2012）。岩浆含水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），因此是蒸汽饱和时间/压力的关键控制因素——因此是微量元素根据其熔体-流体分配系数划分的含水流体相的可用性——以及岩浆在地壳中储存的条件（Edmonds et al., 2022）。然而，原生含水量对金属分配的影响尚未得到系统的研究。该项目确定了两个弧火山——危地马拉的富埃戈火山和帕卡亚火山——分别具有低和高的岩浆含水量（Lloyd et al., 2014 Walker et al., 2003）。总体目标是利用已建立的岩石学策略重建和比较其痕量金属货物的演化。以Fuego和Pacaya为目标进行岩浆含水量的端元比较，避免了引入额外的不确定性，这些不确定性可能影响金属的行为，例如沿弧或弧间的板通量或地壳厚度变化。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实地取样。实验室的工作将集中在熔融包裹体和玻璃的岩石学分析，包括离子探针分析挥发性成分，以及对过滤器收集的羽流气溶胶样本进行地球化学分析。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，特别是将金属行为与结晶过程和硅酸盐熔体中溶解挥发相的组成联系起来。该项目还将探讨发展非传统方法来评估火山排放物对环境的影响的可能性：特别是利用植被、土壤和水文样本中的微量金属来评估火山源微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。