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Water Diffusion in Olivine: Experiments and Application to Phenocrysts

橄榄石中的水扩散：斑晶的实验及其应用

基本信息

批准号：
1449699
负责人：
Elizabeth Ferriss
金额：
$ 22.2万
依托单位：
Columbia University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2015
资助国家：
美国
起止时间：
2015-03-01 至 2017-02-28
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1449699&HistoricalAwards=false
关键词：
Water Diffusion Olivine Experiments Application

项目摘要

Measurements of water in the mineral olivine and its melt inclusions provide constraints on fundamental Earth processes such as the occurrence of plate tectonics, planetary melting, and volcanic explosivity. However, interpretations of these measurements are highly debated because of the possibility that water may exchange rapidly with the surrounding environment during transport from the earth's interior to the site of collection. The extent of this exchange depends on how fast water diffuses in olivine. Water diffusion in olivine can occur by several different mechanisms, some of which are orders of magnitude faster than others at the same temperature, resulting in considerable uncertainty about which diffusion rate to apply. This project aims to resolve that ambiguity while supporting an early-career female scientist; undergraduate students will also contribute to the investigation. The research results will be shared with the general public and the research community.This project will include targeted dehydration experiments as well as measurements of natural samples to elucidate the role of different diffusion mechanisms as a function of oxygen fugacity, temperature, and time. Oriented single crystals of olivine will be first completely dehydrated and equilibrated at the temperature of interest, then fully hydrated at high pressure, and finally placed in a 1-atm gas-mixing furnace and heated in steps until fully dehydrated. After each step, infrared spectroscopy (FTIR) measurements will be taken along profiles in each dimension of the sample to quantify the internal water concentration and extent of diffusion. This approach takes advantage of a new numerical technique for interpreting infrared spectroscopic measurements through uncut crystal blocks, allowing for the first time a time-series of hydrogen diffusion data on the same sample in multiple orientations. These laboratory experiments will be complemented by FTIR measurements of various sized olivine phenocrysts from Fuego Volcano. This study will be the first attempt to identify and apply site-specific diffusivities in samples that are well-characterized for their degassing and ascent history.

矿物橄榄石及其熔融包裹体中的水的测量提供了对地球基本过程的限制，例如板块构造的发生，行星熔化和火山爆发。然而，对这些测量结果的解释存在很大争议，因为在从地球内部运输到收集地点的过程中，水可能会与周围环境迅速交换。这种交换的程度取决于水在橄榄石中扩散的速度。水在橄榄石中的扩散可以通过几种不同的机制发生，其中一些机制在相同温度下比其他机制快几个数量级，导致应用哪种扩散速率存在相当大的不确定性。该项目旨在解决这一模糊性，同时支持职业生涯早期的女科学家;本科生也将有助于调查。研究结果将与公众和研究界分享。该项目将包括有针对性的脱水实验以及对天然样品的测量，以阐明不同扩散机制作为氧逸度，温度和时间的函数的作用。橄榄石的定向单晶将首先在感兴趣的温度下完全脱水和平衡，然后在高压下完全水合，最后置于1个大气压的气体混合炉中并逐步加热直到完全脱水。在每个步骤之后，将沿着样品每个维度的剖面沿着进行红外光谱（FTIR）测量，以量化内部水浓度和扩散程度。这种方法利用了一种新的数值技术，通过未切割的晶体块解释红外光谱测量，允许第一次在同一样品上的多个方向的氢扩散数据的时间序列。这些实验室的实验将由富埃戈火山的各种大小的橄榄石斑晶的FTIR测量补充。这项研究将是第一次尝试，以确定和应用特定地点的扩散率的样品，以及其脱气和上升的历史。