Collaborative Research: Determining Magma Storage Depths and Ascent Rates for the Erebus Volcanic Province, Antarctica Using Diffusive Water Loss from Olivine-hosted Melt Inclusion

合作研究：利用橄榄石熔体包裹体的扩散水损失确定南极洲埃里伯斯火山省的岩浆储存深度和上升速率

• 批准号: 1644027
• 负责人: Paul Wallace
• 金额: $ 2.8万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1644027&HistoricalAwards=false
• 关键词: Collaborative; Research; Determining; Magma; Storage

Nontechnical project descriptionGlobally, 500 million people live near and are threatened by active volcanoes. An important step in mitigating volcanic hazards is understanding the variables that influence the explosivity of eruptions. The rate at which a magma ascends from the reservoir within the Earth to the surface is one such variable. However, magma ascent rates are particularly difficult to determine because of the lack of reliable methods for investigating the process. This research applies a new approach to study magma storage depths and ascent rates at the Erebus volcanic province of Antarctica, one of Earth's largest alkaline volcanic centers. Small pockets of magma that become trapped within growing olivine crystals are called melt inclusions. The concentrations of water and carbon dioxide in these melt inclusions preserve information on the depth of magma reservoirs. Changes to the concentration and isotopic composition of water in the inclusions provide information on how long it took for the host magma to rise to the surface. In combination, these data from samples of olivine-rich volcanic deposits in the Erebus volcanic province will be used to determine the depths at which magmas are stored and their ascent rates. The project results will provide a framework for understanding volcanic hazards associated with alkaline volcanism worldwide. In addition, this project facilitates collaboration among three institutions, and provides an important educational opportunity for a postdoctoral researcher.Technical project descriptionThe depths at which magmas are stored, their pre-eruptive volatile contents, and the rates at which they ascend to the Earth's surface are important controls on the dynamics of volcanic eruptions. Basaltic magmas are likely to be vapor undersaturated as they begin their ascent from the mantle through the crust, but volatile solubility drops with decreasing pressure. Once vapor saturation is achieved and the magma begins to degas, its pre-eruptive volatile content is determined largely by the depth at which it resides within the crust. Magma stored in deeper reservoirs tend to experience less pre-eruptive degassing and to be richer in volatiles than magma shallower reservoirs. Eruptive style is influenced by the rate at which a magma ascends from the reservoir to the surface through its effect on the efficiency of vapor bubble nucleation, growth, and coalescence. The proposed work will advance our understanding of pre-eruptive storage conditions and syn-eruptive ascent rates through a combined field and analytical research program. Volatile measurements from olivine-hosted melt inclusions will be used to systematically investigate magma storage depths and ascent rates associated with alkaline volcanism in the Erebus volcanic province. A central goal of the project is to provide a spatial and temporal framework for interpreting results from studies of present-day volcanic processes at Mt Erebus volcano. The Erebus volcanic province of Antarctica is especially well suited to this type of investigation because: (1) there are many exposed mafic scoria cones, fissure vents, and hyaloclastites (exposed in sea cliffs) that produced rapidly quenched, olivine-rich tephra; (2) existing volatile data for Ross Island MIs show that magma storage was relatively deep compared to many mafic volcanic systems; (3) some of the eruptive centers ejected mantle xenoliths, allowing for comparison of ascent rates for xenolith-bearing and xenolith-free eruptions, and comparison of ascent rates for those bearing xenoliths with times estimated from settling velocities; and (4) the cold, dry conditions in Antarctica result in excellent tephra preservation compared to tropical and even many temperate localities. The project provides new tools for assessing volcanic hazards, facilitates collaboration involving researchers from three different institutions (WHOI, U Wyoming, and U Oregon), supports the researchers' involvement in teaching, advising, and outreach, and provides an educational opportunity for a promising young postdoctoral researcher. Understanding the interrelationships among magma volatile contents, reservoir depths, and ascent rates is vital for assessing volcanic hazards associated with alkaline volcanism across the globe.

非技术项目描述，globally，有5亿人居住在附近，受到活火山的威胁。 减轻火山危害的重要一步是了解影响喷发爆炸性的变量。岩浆从地球内的储层上升到表面的速率就是这样的变量。但是，由于缺乏可靠的研究过程方法，因此岩浆上升率尤其难以确定。这项研究采用了一种新的方法来研究岩浆储存深度和在地球最大的碱性火山中心之一的埃里布斯火山省南极洲的Erebus火山省。被困在生长的橄榄石晶体中的小口袋称为熔体夹杂物。这些熔体夹杂物中的水和二氧化碳的浓度保留了有关岩浆储层深度的信息。 夹杂物中水的浓度和同位素组成的变化提供了有关宿主岩浆上升到表面花费多长时间的信息。结合起来，这些数据来自Erebus火山省富含橄榄石的火山沉积物样品，将用于确定岩浆存储的深度及其上升速度。该项目的结果将为了解与全球碱性火山作用相关的火山危害提供一个框架。 此外，该项目促进了三个机构之间的合作，并为博士后研究人员提供了重要的教育机会。技术项目描述岩浆存储的深度，它们的爆发前的挥发物内容，以及它们升到地球表面的速度是火山喷发动态的重要控制。玄武岩岩浆通过地壳从地幔开始上升时可能是蒸气不饱和的，但是随着压力降低，挥发性溶解度下降。一旦实现了蒸气饱和并开始岩浆开始，其爆发前的挥发性含量很大程度上取决于地壳内的深度。储存在更深层的水库中的岩浆往往会比岩浆较浅的储层经历爆发前的脱水效率较低，并且在挥发物中富裕。喷发样式受到岩浆对蒸气气泡成核，生长和聚结的影响，岩浆从储层到表面上升到表面的速度的影响。拟议的工作将通过合并的领域和分析研究计划来提高我们对爆发前存储条件和综合式上升率的理解。来自橄榄石托管融合物的挥发性测量将用于系统地研究岩浆储存深度和与碱性火山省碱性火山症相关的岩浆储存深度和上升速率。 该项目的一个核心目标是提供一个空间和时间框架，以解释Erebus火山山的当今火山过程研究的结果。 南极火山省的Erebus火山省特别适合这种研究，因为：（1）有许多裸露的镁铁质Scoria锥，裂缝通风口和透视岩（在海悬崖中暴露）迅速淬火，橄榄石，橄榄石富含富丽的Tephra； （2）Ross Island Mis的现有挥发性数据表明，与许多镁铁质火山系统相比，岩浆存储相对深； （3）一些喷发中心弹出了地幔异种石，可以比较含异形和异种石的爆发的上升速率，并比较那些轴承异源石的轴向速率与从沉降速度估计的时间进行比较； （4）与热带甚至许多温带地区相比，南极洲的寒冷干燥条件可为Tephra提供出色的保存。该项目提供了用于评估火山危害的新工具，促进了涉及三个不同机构（Whoi，U Wyoming和U俄勒冈州）的研究人员的合作，支持研究人员参与教学，建议和推广活动，并为有希望的年轻博士后研究员提供教育机会。了解岩浆挥发物含量，储层深度和上升速率之间的相互关系对于评估与全球碱性火山症相关的火山危害至关重要。