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.

非技术项目描述在全球范围内，有 5 亿人生活在活火山附近并受到活火山的威胁。 减轻火山灾害的一个重要步骤是了解影响火山爆发的变量。岩浆从地球内部的储层上升到地表的速率就是这样的变量之一。然而，由于缺乏可靠的方法来研究岩浆上升过程，因此确定岩浆上升速率特别困难。这项研究采用了一种新方法来研究南极洲埃里伯斯火山省（地球上最大的碱性火山中心之一）的岩浆储存深度和上升速率。被困在不断生长的橄榄石晶体中的小块岩浆称为熔体包裹体。这些熔体包裹体中水和二氧化碳的浓度保存了有关岩浆储层深度的信息。 包裹体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地表所需时间的信息。综合起来，这些来自埃里伯斯火山省富含橄榄石的火山矿床样本的数据将用于确定岩浆储存的深度及其上升速度。该项目的结果将为了解全球碱性火山活动相关的火山灾害提供一个框架。 此外，该项目促进了三个机构之间的合作，并为博士后研究员提供了重要的教育机会。技术项目描述岩浆储存的深度、喷发前的挥发物含量以及它们上升到地球表面的速率是对火山喷发动态的重要控制。当玄武岩岩浆开始从地幔上升穿过地壳时，其蒸气可能处于不饱和状态，但挥发性溶解度随着压力的降低而下降。一旦达到蒸汽饱和并且岩浆开始脱气，其喷发前的挥发物含量很大程度上取决于其在地壳内的停留深度。与岩浆较浅的储层相比，储存在较深储层中的岩浆往往经历较少的喷发前脱气，并且挥发物更丰富。喷发方式受到岩浆从储层上升到地表的速率的影响，其影响是通过影响蒸气泡成核、生长和聚结的效率。拟议的工作将通过结合实地和分析研究计划，增进我们对喷发前储存条件和同步喷发上升率的理解。橄榄石熔体包裹体的挥发性测量将用于系统地研究与埃里伯斯火山省碱性火山活动相关的岩浆储存深度和上升速率。 该项目的中心目标是提供一个时空框架来解释埃里伯斯火山当今火山过程研究的结果。 南极洲的埃里伯斯火山省特别适合此类调查，因为：（1）有许多暴露的镁铁质火山渣锥、裂隙喷口和透明碎屑岩（暴露在海崖中），产生快速淬火的富含橄榄石的火山灰； (2) 罗斯岛 MI 的现有挥发性数据表明，与许多镁铁质火山系统相比，岩浆储存相对较深； (3) 一些喷发中心喷射出地幔捕虏体，从而可以比较含捕虏体和无捕虏体喷发的上升速率，以及将含捕虏体喷发的上升速率与根据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，南极洲寒冷、干燥的条件使得火山灰保存得很好。该项目提供了评估火山危害的新工具，促进了来自三个不同机构（WHOI、怀俄明大学和俄勒冈大学）的研究人员的合作，支持研究人员参与教学、咨询和推广，并为有前途的研究人员提供了教育机会。年轻的博士后研究员。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全球碱性火山活动相关的火山灾害至关重要。