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是非常危险的，因为它们会产生广泛的火山灰云，对航空造成危险，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怀特河火山灰（WRA）英安岩火山灰层是北美丘吉尔火山在过去~2000年中三次最大爆发（VEI 6）的结果。这些火山爆发伤害了居住在今天加拿大下风地区的土著Dene人，导致他们向南迁移出受影响的地区。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。尽管它有潜在的危险，但人们对它的爆炸源--岩浆--知之甚少。这项研究将帮助我们更好地了解滋养丘吉尔火山喷发的岩浆在地壳中储存的位置。虽然这座火山没有专门的地震监测网络，但了解火山下岩浆的位置可以帮助我们更好地估计如果火山在未来再次变得不平静会发生什么。学生将在UAF PI教授的两个夏季课程中参加这项研究。这些课程将涉及实地考察，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斥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一员，PI将与AVO同事密切合作，将这项工作的结果纳入AVO业务和推广工作。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。他们将使用斜长石托管的熔融包裹体，通过对H2O和CO2（如果存在）的显微FTIR分析以及对S和Cl的电子探针分析来估计包封压力和挥发性成分。如果发现反应的角闪石，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火山灰岩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，并且具有相对较低的失败率。这些实验将有助于建立丘吉尔山WRA喷发的岩浆管道系统模型。这些结果也将提供给维护岩石学模型的研究人员，以帮助增强他们的经验数据集，从而提高斜长石和含角闪石的英安岩到流纹岩岩浆的准确性。&该奖项反映了NSF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。