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非常危险，因为它们会产生广泛的火山灰云，对航空造成风险，并导致破坏性的火山灰顺风而下。在阿拉斯加东部和加拿大西部发现的白河火山灰(WRA)英安岩盖夫拉层是过去2000年来北美丘吉尔火山(Mt Churchill)三次最具爆炸性的喷发(VEI 6)的结果。这些喷发伤害了生活在今天加拿大顺风向地区的土著德内人，导致他们向南迁出受影响的地区。目前全球空中交通的覆盖范围，以及今天顺风地区人口的增加，意味着丘吉尔火山类似规模的喷发可能会造成灾难性的经济和人类影响。尽管它存在潜在的危险，但人们对其爆炸性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为丘吉尔火山喷发提供资金的岩浆在地壳中的储存位置。虽然这座火山没有专门的地震监测网，但了解火山下面岩浆生活的地方可以帮助我们更好地估计如果火山未来再次变得不安可能会发生什么。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，以了解阿拉斯加东部的WRA矿藏，收集样本，然后学生将学习如何在实验室进行实验。这笔赠款的资助将用于支付学生学费和实地考察费用，以鼓励历史上被排斥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一员，PI将与AVO的同事密切合作，将这项工作的结果纳入AVO的操作和推广工作中。这项研究将使用高压和温度实验来创建WRA喷发的岩浆管道系统模型。该团队将以先前研究中的岩石学数据为基础，其中包括实验所需的矿物学、温度和氧逸度估计。他们将利用斜长石赋存的熔体包裹体，通过水和二氧化碳的显微FTIR分析(如果存在)以及电子探针分析S和氯来估计成藏压力和挥发性成分。如果发现有反应的角闪石，质地分析将使该团队能够使用先前的实验校准来估计岩浆上升速度。WRA tephra的岩石学非常适合于相平衡实验，而受先前工作限制的相对较低的温度范围允许使用适合学生工作且故障率相对较低的实验方法。这些实验将有助于建立丘吉尔火山WRA喷发的岩浆管道系统模型。这些结果也将被提供给维护热力学模型的研究人员，以帮助增强他们的经验数据集，以提高应用于斜长岩和含角闪英安岩到流纹岩岩浆的准确性。该项目由岩石学和地球化学以及已建立的刺激竞争研究计划(EPSCoR)联合资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.