Phase equilibria experiments to constrain magma storage at Mt Churchill, Alaska; refining the magmatic source of the White River Ash eruptions

产生爆炸性喷发的火山是非常危险的，因为它们会产生广泛的火山灰云，这对航空来说是危险的，并导致破坏性的火山灰落在顺风处。在阿拉斯加东部和加拿大西部发现的白河火山灰（WRA）英安岩火山灰层是由北美丘吉尔火山在过去2000年里最猛烈的三次喷发（VEI 6）造成的。这些火山喷发伤害了居住在今天加拿大顺风地区的土著迪尼人，导致他们向南迁移出受影响的地区。目前全球空中交通的覆盖范围和顺风地区人口的增加意味着，丘吉尔山类似规模的喷发可能会对经济和人类造成灾难性的影响。尽管存在潜在的危险，但人们对其爆炸性的硅质岩浆的来源知之甚少。这项研究将帮助我们更好地了解丘吉尔火山喷发的岩浆储存在地壳中的位置。虽然这座火山没有专门的地震监测网络，但了解火山下面岩浆的位置可以帮助我们更好地估计，如果火山将来再次变得不稳定，可能会发生什么。学生们将在UAF的PI教授的两个暑期课程中参与这项研究。这些课程将包括实地考察，了解阿拉斯加东部的WRA矿床，收集样本，然后学生将学习如何在实验室进行实验。这项资助将用于支付学生的学费和实地考察的费用，以鼓励历史上被排斥的群体的学生广泛参与，帮助增加地球科学的多样性。作为阿拉斯加火山观测站的成员，PI将与AVO的同事密切合作，将这项工作的结果纳入AVO的运营和推广工作。本研究将利用高压和高温实验为WRA火山喷发建立岩浆管道系统模型。该团队将以先前研究的岩石学数据为基础，包括实验所需的矿物学、温度和氧逸度估计。他们将使用斜长石为主的熔体包裹体，通过对H2O和CO2（如果存在）的微傅里叶红外分析和对S和Cl的电子探针分析来估计夹带压力和挥发性成分。如果发现反应的角闪岩，结构分析将使研究小组能够利用先前的实验校准来估计岩浆上升速率。WRA tephra的岩石学非常适合相平衡实验，并且受先前工作限制的相对较低的温度范围允许适合学生工作的实验方法，并且故障率相对较低。这些实验将有助于建立WRA邱吉尔火山喷发的岩浆管道系统模型。这些结果也将提供给维护热力学模型的研究人员，以帮助增加他们的经验数据集，以提高应用于斜长石和含角闪岩英安岩到流纹岩岩浆的准确性。该项目由岩石地球化学和促进竞争性研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Volcanoes that produce explosive eruptions are very hazardous because they can create widespread ash clouds that are risky for aviation and cause damaging ash fall downwind. The White River ash (WRA) dacite tephra beds found in eastern Alaska and western Canada resulted from three of the most explosive eruptions (VEI 6) from a North American volcano, Mt Churchill, in the past ~2000 years. Those eruptions harmed the indigenous Dene people living in the areas downwind in present day Canada, resulting in a southward migration out of the impacted area. The current global reach of air traffic and the increased human population in downwind regions today mean that a similar-sized eruption from Mt Churchill could potentially cause catastrophic economic and human impacts. Despite its potential hazards, little is known about the source of its explosive, silicic magmas. This study will help us better understand where the magmas that feed Mt Churchill’s eruptions are stored in the crust. Although this volcano does not have a dedicated seismic monitoring network, knowledge of where the magmas live beneath the volcano can help us better estimate what might happen if the volcano becomes restless again in the future. Students will take part in this research during two summer courses taught by the PI at UAF. These courses will involve field trips to learn about the WRA deposits in eastern Alaska, collect samples, and then students will learn how to conduct experiments in the lab. The support from this grant will help cover student fees and field trip costs to encourage broad participation of students from historically excluded groups to help increase diversity in the geosciences. As a member of the Alaska Volcano Observatory, the PI will work closely with AVO colleagues to incorporate the results from this work into AVO operations and outreach efforts.This study will use high pressure and temperature experiments to create a magma plumbing system model for the WRA eruptions. The team will build on petrological data from prior studies, which include mineralogy, temperature, and oxygen fugacity estimates needed for the experiments. They will use plagioclase-hosted melt inclusions to estimate entrapment pressures and volatile compositions by micro-FTIR analyses of H2O and CO2 (if present) and electron microprobe analyses of S and Cl. If reacted amphiboles are found, textural analysis will enable the team to estimate magma ascent rates using prior experimental calibrations. The petrology of the WRA tephra is well-suited for phase equilibria experiments, and the relatively low temperature range constrained by prior work allows for experimental methods that are suitable for student work and have a relatively low failure rate. The experiments will contribute to a magma plumbing system model for the WRA eruptions from Mt Churchill. These results will also be provided to researchers maintaining thermodynamical models to help augment their empirical datasets for increased accuracy applied to plagioclase and amphibole-bearing dacite to rhyolite magmas.This project is jointly funded by Petrology & Geochemistry and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.