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

非技术项目描述全球有5亿人居住在活火山附近，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喷发爆炸性的变量。岩浆从地球内部的储集层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调查这一过程，岩浆上升速度尤其难以确定。这项研究应用了一种新的方法来研究南极埃里伯斯火山省的岩浆储存深度和上升速度，埃里巴斯火山省是地球上最大的碱性火山中心之一。困在成长中的橄榄石晶体中的小块岩浆被称为熔融包裹体。这些熔融包裹体中的水和二氧化碳浓度保存了有关岩浆储集层深度的信息。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。综合起来，这些来自埃里巴斯火山省富含橄榄石的火山沉积物样本的数据将被用来确定岩浆的储存深度及其上升速度。该项目的成果将为了解全世界与碱性火山作用有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一个重要的教育机会。技术项目说明岩浆的储存深度、喷发前的挥发性成分以及它们上升到地球表面的速度是控制火山喷发动态的重要因素。玄武岩岩浆开始从地幔上升穿过地壳时，很可能是蒸汽不饱和的，但挥发分的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，其喷发前的挥发性含量在很大程度上取决于它在地壳中的深度。与较浅的岩浆储集层相比，储存在较深储集层中的岩浆往往经历较少的喷发前脱气作用，并具有更丰富的挥发分。喷发方式受岩浆从储集层上升到地表的速度的影响，它通过影响气泡的成核、生长和融合的效率来影响喷发方式。这项拟议的工作将通过现场和分析研究相结合的方案，促进我们对喷发前储存条件和同期喷发上升速率的理解。来自橄榄石寄生的熔体包裹体的挥发性测量将用于系统地调查与埃里巴斯火山省碱性火山作用有关的岩浆储存深度和上升速率。该项目的一个中心目标是为解释埃里伯斯山火山现今火山过程的研究结果提供一个空间和时间框架。南极洲埃里伯斯火山省特别适合于这种类型的调查，因为：(1)有许多裸露的镁铁质火山锥、裂隙喷口和透明碎屑岩(暴露在海崖上)，产生了快速淬灭的富含橄榄石的盖夫拉；(2)罗斯岛现有的挥发性数据表明，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包体，从而可以比较有包裹体和无包裹体的喷发的上升率，以及那些含有包裹体的包体的上升率与根据速度估计的时间的比较；(4)与热带地区甚至许多温带地区相比，南极洲寒冷、干燥的条件使其具有很好的保护性。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、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、建议和推广，并为有前途的年轻博士后研究人员提供了教育机会。了解岩浆挥发分含量、储集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作用有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.