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

全球有5亿人生活在活火山附近并受到其威胁。减轻火山灾害的一个重要步骤是了解影响火山爆发的各种变量。岩浆从地球内部的储藏库上升到地表的速度就是这样一个变量。然而，由于缺乏可靠的方法来研究这一过程，岩浆上升速率特别难以确定。这项研究应用了一种新的方法来研究地球上最大的碱性火山中心之一——南极洲埃里伯斯火山省的岩浆储存深度和上升速度。被困在生长中的橄榄石晶体中的岩浆小袋被称为熔体包裹体。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宿主岩浆上升到地表所需时间的信息。结合这些来自埃里伯斯火山省富含橄榄石的火山沉积物样本的数据，将用于确定岩浆储存的深度及其上升速率。该项目的结果将为了解世界范围内与碱性火山活动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。技术项目说明岩浆储存的深度、喷发前的挥发性成分以及岩浆上升到地球表面的速度是火山喷发动力学的重要控制因素。玄武岩岩浆在从地幔上升到地壳的过程中可能是蒸汽不饱和的，但挥发溶解度随着压力的降低而下降。一旦蒸汽达到饱和，岩浆开始脱气，其喷发前的挥发性含量在很大程度上取决于它在地壳中的深度。储存在较深储层中的岩浆在喷发前往往较少脱气，而且挥发物比较浅储层中的岩浆更丰富。喷发方式受岩浆从储层上升到地表的速度的影响，这是通过其对蒸汽泡成核、生长和合并效率的影响来决定的。这项工作将通过实地和分析相结合的研究计划，促进我们对喷发前储存条件和喷发同步上升速率的理解。对含橄榄石的熔融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作用相关的岩浆储存深度和上升速率。该项目的一个中心目标是提供一个空间和时间框架，用于解释埃里伯斯火山今天火山过程的研究结果。南极洲的埃里伯斯火山省特别适合这种类型的调查，因为：(1)那里有许多暴露的基性火山锥、裂缝喷口和透明质碎屑岩（暴露在海崖中），它们产生了迅速熄灭的富含橄榄石的火山；(2) Ross Island MIs的现有挥发性数据表明，与许多基性火山系统相比，岩浆储存相对较深；(3)一些喷发中心喷出地幔捕虏体，可以比较含捕虏体和不含捕虏体喷发的上升速率，以及含捕虏体喷发的上升速率与沉降速度估算的时间的比较；(4)与热带地区甚至许多温带地区相比，南极洲寒冷、干燥的条件导致了极好的麻风保存。该项目为评估火山灾害提供了新的工具，促进了来自三个不同机构（WHOI、U Wyoming和U Oregon）的研究人员的合作，支持研究人员参与教学、咨询和推广，并为有前途的年轻博士后研究人员提供了一个受教育的机会。了解岩浆挥发性含量、储层深度和上升速率之间的相互关系，对于评估全球范围内与碱性火山活动相关的火山危害至关重要。

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.