Collaborative Research: Volatiles in Aleutian-Alaska Arc Magmas

这个为期一年的项目的目标是确定利用阿留申群岛和阿拉斯加的火山岩来估计弧岩浆的含水量以及结晶的压力和温度的可行性。水是与俯冲带相关的岩浆起源和演化的核心，但目前很少有直接测量弧岩浆含水量的方法，迄今为止还没有关于阿留申-阿拉斯加火山的报告。研究人员从少量的阿留申-阿拉斯加火山收集基性火山灰，然后通过离子探针、电子探针和激光烧蚀电感耦合等离子体质谱分析橄榄石、斜辉石和斜长石斑晶中的玻璃状熔体包裹体，以获得水浓度数据，并应用各种温压湿度计。这些数据对于解决诸如拉斑岩与钙碱性火成岩分异趋势的起源、弧火山下的融化过程以及俯冲带的挥发性循环等基本问题是必要的。阿留申-阿拉斯加弧，由于其岩浆类型的多样性和地球物理参数的系统性变化，长期以来一直是许多争论的中心，但缺乏解决这些问题所需的水数据。

The goal of this one-year project is to determine the feasibility of using volcanic rocks from the Aleutian islands and Alaska to estimate the water content, as well as the pressure and temperature of crystallization, of arc magmas. Water is central to the origin and evolution of magmas associated with subduction zones, yet there are currently few direct measurements of the water content of arc magmas, and none to date published for Aleutian-Alaska volcanoes. The investigators are collecting mafic tephra from a small number of Aleutian-Alaska volcanoes, then analyzing glassy melt inclusions hosted in olivine, clinopyroxene and plagioclase phenocrysts by ion microprobe, electron microprobe, and laser ablation inductively coupled plasma mass spectrometry, in order to obtain water concentration data, and to apply various thermobarohygrometers. Such data are needed to address fundamental questions regarding the origin of tholeiitic versus calc-alkaline igneous differentiation trends, the melting process beneath arc volcanoes, and volatile cycling at subduction zones. The Aleutian-Alaska arc, because of its great diversity of magma types and systematic variations in geophysical parameters, has long been central to many of these debates, but lacking the water data needed to resolve them.