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爆炸性的变量。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。这项研究采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区的岩浆储存深度和上升速率。被捕获在不断生长的橄榄石晶体中的小块岩浆被称为熔融包裹体。这些熔融包裹体中水和二氧化碳的浓度保存了岩浆库深度的信息。 包裹体中水的浓度和同位素组成的变化提供了关于宿主岩浆上升到表面需要多长时间的信息。这些来自埃里伯斯火山区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度。该项目的成果将为了解与全世界碱性火山活动有关的火山灾害提供一个框架。 此外，该项目还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。技术项目简介岩浆的储存深度、喷发前的挥发性成分以及上升到地球表面的速度是火山爆发动力学的重要控制因素。玄武岩浆在开始从地幔上升通过地壳时，可能是蒸汽不饱和的，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，岩浆开始脱气，其喷发前的挥发物含量在很大程度上取决于它在地壳内的深度。储存在较深储层中的岩浆往往经历较少的喷发前脱气作用，并且比岩浆较浅储层更富含挥发物。岩浆从储层上升到地表的速率通过其对蒸汽泡成核、生长和聚结效率的影响而影响喷发样式。拟议的工作将通过结合实地和分析研究计划，促进我们对喷发前储存条件和同步喷发上升速率的理解。从橄榄石托管熔融包裹体的挥发性测量将被用来系统地调查岩浆储存深度和上升速率与碱性火山在埃里伯斯火山省。 该项目的一个中心目标是提供一个空间和时间框架，用于解释埃里伯斯山火山现今火山过程研究的结果。 南极洲的埃里伯斯火山区特别适合于这类调查，因为：（1）那里有许多暴露的镁铁质火山渣锥、裂隙喷口和玻璃碎屑岩（暴露在海崖），产生迅速淬火，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，以及比较含捕虏体喷发的上升速率与根据沉降速度估算的时间;（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火山灰保存得非常好。该项目提供了评估火山灾害的新工具，促进了来自三个不同机构（WHOI，U怀俄明州和U俄勒冈州）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地球仪上碱性火山活动相关的火山灾害至关重要。

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.