Collaborative Research: Volatiles in Aleutian Arc Magmas

该项目旨在确定阿拉斯加阿留申群岛活火山喷发前岩浆中溶解的水和二氧化碳的含量。特别是水对这些岩浆的各个方面都至关重要，从火山下面的管道系统，到俯冲带的起源，再到火山喷发的气体成分。尽管水是最重要的，但只有有限数量的火山样本中确定了水。阿拉斯加的阿留申火山提供了一个主要的机会，将水含量与俯冲带的现有地球化学示踪剂，板块俯冲的地球物理参数，以及岩浆储存深度和火山变形的大地测量联系起来。 后一种联系将通过作为地球观测设施一部分的奥古斯丁和阿库坦火山上的板块边界观测站装置而成为可能。研究人员从10座阿留申火山收集了约100个火山灰样本，并计划从塞瓜姆火山收集更多样本。 初步数据是有希望的，显示在世界上最高的水含量测量在镁铁质弧熔体包裹体（7重量%）从奥古斯丁火山，这是目前正在爆发。本项目的主要工作是利用华盛顿卡内基研究所的离子探针分析橄榄石晶体中包裹体的挥发分（H_2O、CO_2、S、Cl），以及利用波士顿大学的激光烧蚀电感耦合等离子体质谱分析橄榄石晶体中微量元素（La、Ba、Sr、U、Th、Pb、Nb）。另一个主要重点将是开发新技术，用于估计单斜辉石晶体岩浆的含水量，一种是根据其稀土元素模式，另一种是根据其H2O含量。 该项目将使一名女研究生能够完成她的博士工作，并将支持波士顿大学的本科生研究。

This project aims to determine the amount of water and carbon dioxide dissolved in magma before it erupts from active volcanoes in the Aleutian islands, Alaska. Water in particular is critical to every aspect of these magmas, from their plumbing system beneath the volcanoes, to their very origin in the subduction zone, to their gas content which fuels eruptions. Despite its primary importance, water has been determined in only a limited number of volcanic samples. The Aleutian volcanoes of Alaska offer a prime opportunity to relate water contents to existing geochemical tracers from the subduction zone, geophysical parameters of plate subduction, and geodetic measurement of magma storage depths and volcano deformation. The latter linkage will be possible through Plate Boundary Observatory installations on Augustine and Akutan volcanoes as part of the EarthScope facility.This project follows from a one-year pilot study funded to collect appropriate samples. The researchers have ~ 100 tephra samples from 10 Aleutian volcanoes, and plan to collect more from Seguam volcano. Preliminary data are promising, showing among the highest water contents measured in the world in mafic arc melt inclusions ( 7 wt%) from Augustine volcano, which is currently erupting. The primary activity of the current project is to analyze melt inclusions trapped in olivine crystals for their volatile content (H2O, CO2, S, Cl,) by ion microprobe at the Carnegie Institution of Washington, and trace elements (including La, Ba, Sr, U, Th, Pb, Nb) by laser-ablation inductively coupled plasma mass spectrometry at Boston University. Another major focus will be the development of new techniques for estimating the water content of magmas from clinopyroxene crystals, one based on their rare earth element pattern, and the other on their H2O content. This project will enable a female graduate student to complete her PhD work, and will support undergraduate research at Boston University.