Experimental and Textural Constraints on the Eruptive Behavior of Basic Magmas in Subduction Zones

俯冲带中玄武岩和玄武岩安山岩（基性）岩浆的喷发在斯特隆堡期和强烈的次普林尼期（很少有普林尼期）之间的喷发风格不同。为什么俯冲带基性岩浆的喷发方式与夏威夷火山的喷发方式截然不同？是因为与俯冲有关的岩浆含有更多的气体，还是它们的上升路径或上升速度更有利于爆炸性喷发？本研究试图通过研究气体含量、储存、上升和脱气对俯冲带基性岩浆喷发方式的影响来回答这些问题。研究人员的研究重点是阿留申火山弧基性岩浆的三次关键喷发：1999年的Shishaldin火山、1997年的Okmok火山和1991-92年的Westdahl火山。这些火山喷发是本研究的理想选择，因为它们的喷发风格（斯特龙堡式、火喷泉式和次普林尼式）变化很大，包括每次喷发期间。此外，所有三次喷发都是用地震和大地测量来监测的，这对岩浆运动和喷发特征有重要的限制。研究者建议在三个相关的任务中检查对爆发风格的影响。任务1将定义三次喷发之间以及喷发的不同阶段之间的纹理差异（晶体和囊泡）。任务2将结合玻璃包裹体测量和实验岩石学工作，确定三种岩浆的喷发前气体含量和喷发前储存条件。任务3将通过一系列实验岩石学工作，确定减压（上升）速率与最终产物的结构差异之间的关系。这三项任务的结果，结合对火山喷发的现有地球物理限制，将允许对阿留申群岛基性岩浆的气体含量、储存、上升、脱气和喷发进行调查。实验将在阿拉斯加费尔班克斯大学的实验岩石学实验室进行，所有产品将在阿拉斯加费尔班克斯大学的先进仪器实验室进行分析。

GardnerEAR-0229290Eruptions of basaltic and basaltic andesitic (basic) magma in subduction zones can vary in style between strombolian to intense sub-Plinian (and rarely Plinian). Why can subduction-zone basic magmas erupt in such dramatically different styles, as compared to Hawaiian eruptions? Is it because subduction-related magmas contain greater amounts of gas, or are their ascent paths or ascent rates more conducive to explosive eruptions? This study seeks to answer those questions by investigating the influences that gas content, storage, ascent, and degassing have on the eruptive style of basic magma in subduction zones. The investigators' study focuses on three key eruptions of basic magma from the Aleutian volcanic arc: Shishaldin volcano in 1999, Okmok volcano in 1997, and Westdahl volcano in 1991-92. Those eruptions are ideal for this study because they varied greatly in eruptive style (strombolian, fire fountain, and sub-Plinian), including during each eruption. In addition, all three eruptions were monitored with seismic and geodetic measurements, which place important constraints on magma motion and eruptive character. The investigators propose to examine influences on eruptive style in three related tasks. Task 1 will define textural differences (both crystals and vesicles) between the three eruptions and between different phases of the eruptions. Task 2 will define pre-eruptive gas contents and pre-eruptive storage conditions of the three magmas, with a combination of glass inclusion measurements and experimental petrologic work. Task 3 will define the relationship between decompression (ascent) rate and textural differences in the resulting products, through a series of experimental petrologic work. Results from the three tasks, combined with the existing geophysical constraints on the eruptions, will allow the investigation of the gas contents, storage, ascent, degassing, and eruption of basic magma in the Aleutians. Experiments will be performed in the Experimental Petrology Laboratory at the University of Alaska Fairbanks, and all products will be analyzed in the Advanced Instrumentation Laboratory at the University of Alaska Fairbanks.