What Controls Mafic Eruption Style? The Causes and Consequences of Coupled Vesiculation and Crystallization Kinetics in Ascending Basaltic Andesite Magmas

什么控制镁铁质喷发方式？上升玄武安山岩岩浆中囊泡化和结晶动力学耦合的原因和结果。 涉及镁铁质岩浆的爆炸性喷发对活火山附近的危害具有重要意义。特别是斯特龙博利安火山喷发产生大量的细灰，高灰羽和大面积的分散区域，可能会严重影响周围的人口。大量研究表明，爆炸性与气体从上升、减压岩浆中排出有关，而上升、减压岩浆又取决于岩浆的孔隙度-渗透率特性和碎裂方式。在试图阐明的脱气过程及其对喷发风格的影响，建议实验研究实验减压的镁铁质硅酸盐熔体的渗透性的发展，特别侧重于镁铁质岩浆中的结晶作用作为喷发风格的控制。具体来说，如何同升微晶结晶影响连接囊泡网络和渗流阈值的发展，以及这些因素如何影响气体分离的导管和喷发风格的转变？ 待检验的假设包括：[1]晶体数密度是否与减压速率直接相关（即，由于在泡状化过程中含水镁铁质熔体的快速结晶）？2)熔体渗透率与岩浆粘度成反比吗？3)减压结晶驱动的结晶是否改变了渗滤阈值（即，通过限制气泡膨胀或通过对气泡放置的空间控制）？4)减压速率是否通过控制脱气效率和同生喷发结晶的深度和效率而影响镁铁质喷发的类型？ 这些问题将通过减压实验的合成玄武安山岩熔体的组成类似的喷发在Okmok火山（阿拉斯加），并与纯水和混合H2O-CO2流体相研究CO2的结晶和vesiculation动力学的影响。这些实验将与中全新世中Scoria Okmok火山的天然样品进行比较，该火山产生了猛烈的Strombolian到subplinian和火山喷发沉积物。 A？渗透性？将建造一个用于测量实验样品和天然样品的渗透率，以估计渗透阈值，其结果将用于模拟爆炸性基性岩喷发期间的气体分离和破碎。 更广泛的影响：该项目将支持博士生，并在UAF本科生助理。将与UAF阿拉斯加土著科学与工程项目（ANSEP）建立新的联系，目的是雇用阿拉斯加土著本科生为该项目进行研究。该项目还将涉及与火山学家Kathy Cashman（布里斯托大学）的国际合作。私家侦探？与阿拉斯加火山观测站的联系也促进了这项研究的应用，以评估与阿拉斯加和卡斯卡迪亚活火山猛烈的镁铁质喷发有关的火山灾害。在UAF实验岩石学实验室开发新的研究设备也将加强UAF的基础设施，并提供新的设备，可以满足地质学和火山学研究以外的研究需求，包括其他物理科学和工程学科的应用。

What controls mafic eruption style? The causes and consequences of coupled vesiculation and crystallization kinetics in ascending basaltic andesite magmas. Explosive eruptions involving mafic magmas pose important implications for hazards near active volcanoes. In particular, Strombolian eruptions produce large volumes of fine ash, high ash plumes, and large dispersal areas that may severely impact surrounding populations. Numerous studies suggest that explosivity is related to expulsion of gases from ascending, decompressing magmas that in turn depends on porosity-permeability properties of the magma and fragmentation style. In an attempt to elucidate the degassing process and its effect on eruptive style, it is proposed to investigate experimentally the development of permeability in experimentally decompressed mafic silicate melts with particular focus on the role of crystallization in mafic magmas as a control on eruptive style. Specifically, how does syn-ascent microlite crystallization influence development of connected vesicle networks and the percolation threshold, and how do these factors influence gas separation in the conduit and transitions in eruptive style? Hypotheses to be tested include: [1] Are crystal number densities related directly to decompression rate (i.e., due to rapid crystallization of hydrous mafic melts during vesiculation)? 2) Is melt permeability inversely related to magma viscosity? 3) Does decompression­driven crystallization change the percolation threshold (i.e., by limiting bubble expansion or by spatial control on bubble placement)? 4) Does decompression rate affect the style of mafic eruptions by controlling degassing efficiency and the depth and efficiency of syn­eruptive crystallization? These questions will be investigated via decompression experiments on synthetic basaltic andesite melts similar in composition to those erupted at Okmok volcano (Alaska), and with both pure water and mixed H2O­CO2 fluid phase to examine the influence of CO2 on crystallization and vesiculation kinetics. The experiments will be compared with natural samples from the mid­Holocene Middle Scoria Okmok volcano, which produced violent strombolian to subplinian and vulcanian eruption deposits. A ?permeameter? will be constructed to measure permeabilities of both experimental and natural samples to estimate percolation thresholds, and the results will be used to model gas segregation and fragmentation during explosive mafic eruptions. Broader Impacts: This project will support a PhD student, and undergraduate student assistant at UAF. A new link will be forged with the UAF Alaska Native Science and Engineering Program (ANSEP) with the aim to hire Alaska Native undergraduate student(s) to perform research for the project. The project will also involve international collaboration with volcanologist Kathy Cashman (University of Bristol). The PI?s association with the Alaska Volcano Observatory also facilitates application of this research to assessment of volcanic hazards related to violent mafic eruptions at active volcanoes in Alaska and Cascadia. Development of new research equipment in the UAF Experimental Petrology lab will also enhance the infrastructure at UAF and provide new equipment that could fill research needs beyond geology and volcanology studies, including applications in other physical sciences and engineering disciplines.