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

阿拉斯加丘吉尔山限制岩浆储存的相平衡实验；

• 批准号: 2308646
• 负责人: Jessica Larsen
• 金额: $ 30.87万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2308646&HistoricalAwards=false
• 关键词: Phase; equilibria; experiments; constrain; magma

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.

产生爆炸性喷发的火山非常危险，因为它们会产生大范围的火山灰云，对航空造成危险，并导致破坏性的火山灰顺风落下。在阿拉斯加东部和加拿大西部发现的怀特河火山灰 (WRA) 英安岩火山灰床是由过去约 2000 年来北美丘吉尔火山的三次最猛烈的喷发 (VEI 6) 造成的。这些火山喷发伤害了居住在当今加拿大顺风地区的土著迪内人，导致他们向南迁徙出受影响地区。目前全球范围内的空中交通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造成灾难性的经济和人类影响。尽管存在潜在危险，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丘吉尔山喷发的岩浆储存在地壳中的位置。尽管这座火山没有专门的地震监测网络，但了解火山下方岩浆的位置可以帮助我们更好地估计如果火山未来再次变得躁动不安，可能会发生什么。学生将在 UAF PI 教授的两门暑期课程期间参与这项研究。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。这笔赠款的支持将有助于支付学生费用和实地考察费用，以鼓励来自历史上被排除的群体的学生广泛参与，以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 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高温实验来创建 WRA 喷发的岩浆管道系统模型。该团队将建立在先前研究的岩石学数据的基础上，其中包括实验所需的矿物学、温度和氧逸度估计。他们将使用斜长石熔体包裹体，通过 H2O 和 CO2（如果存在）的微 FTIR 分析以及 S 和 Cl 的电子微探针分析来估计截留压力和挥发性成分。如果发现反应的角闪石，结构分析将使团队能够使用先前的实验校准来估计岩浆上升速率。 WRA 火山灰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且故障率相对较低的实验方法。这些实验将为丘吉尔山 WRA 喷发建立岩浆管道系统模型。这些结果还将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，以提高应用于斜长石和角闪石英安岩到流纹岩岩浆的准确性。该项目由岩石学与地球化学和刺激竞争性研究既定计划 (EPSCoR) 共同资助。该奖项反映了 NSF 的法定使命，并通过评估被认为值得支持 利用基金会的智力优势和更广泛的影响审查标准。