Deuterium-Hydrogen Interdiffusion in Mantle Materials

氢或水以极少量(百万分之几十到几百)的形式存在于地球内部的岩石中。即使在如此低的浓度下，内陆的总水量也可能等于或超过海洋的总量。这些少量的水对地球材料的物理性质有非常重要的影响，如粘度、强度、熔化温度、电导率和扩散速度。水引起的这些物理性质的变化可能与板块构造和火山作用有关。事实上，板块构造被认为是在地球上发生的，而不是在其他类地行星上发生的，因为地球地幔中有少量的水。因此，量化水对物理性质的影响是很重要的。这项关于氦和氢(即氢的同位素)在橄榄石和其他地幔矿物中相互扩散的研究将提供有助于了解地幔流动和流变学、地球内部水的分布以及地球内部不同区域均一化速率的数据。在最广泛的意义上，这一结果将有助于了解板块构造及其运作机制，地震和火山的起源，以及地球和其他行星上化学元素的总体丰度和分布。该项目是一项实验工作，旨在确定在地球上地幔的温度和压力下，地幔材料(如橄榄石)中的氢-氚互扩散(自扩散)系数。将使用二次离子质谱仪(SIMS)的新技术进行氢和氢的分析。这一结果将从与离子过程模型相关的缺陷机制的角度进行解释。以前的氢在橄榄石和地幔物质中的扩散测量通常是使用氢掺入方法，即测量氢在“干”材料中的扩散。这些实验被解释为H扩散和金属空位扩散的自扩散系数的值。我们新的互扩散测量将补充这些以前的测量，并能够描绘材料中氢离子迁移率的详细机制。此外，这些测量将能够与含水地幔矿物的电导率测量进行比较。这项研究的结果将为各种地质环境中的物理传输过程提供新的线索，并将对大地电磁数据的解释和建模具有重要意义。最终的好处将是更详细地了解地球内部深处物质的温度分布和物理状态。这项工作将扩大我们对地幔材料中氢扩散和点缺陷的理解，并将为材料科学和地球科学的知识库做出贡献。该项目资助的研究生将在实验开发、问题解决、微观分析技术、计算数值分析和跨学科环境中的协作方面培养技能。她或他将参加国家会议，如美国地球物理联盟会议，在这些会议上，多样性是优先事项，使她/他能够与来自全球各地的科学家互动。她或他将帮助指导本科生的研究，参与课堂练习，并参与外展工作。这项工作将与来自地球科学、化学、材料科学、物理和其他领域的学生和研究人员、亚利桑那州立大学以及来自世界各地的其他机构的学生和研究人员合作，在共享的多用户设施中进行。作为该项目的一部分，将开发分析和实验方法以及基础设施方面的新进展。

Hydrogen or water exists in very small amounts (tens to hundreds of parts per million) in the rocks of the Earth's interior. Even at these low concentrations, the total amount of water in the interior could equal or exceed that of the oceans. These small amounts of water have very significant effects on the physical properties of Earth materials, such as viscosity, strength, melting temperature, electrical conductivity, and diffusion rates. The variations of these physical properties induced by water may be related to the processes of plate tectonics and volcanism. Indeed, plate tectonics is thought to occur on the Earth and not on other terrestrial planets because of the small amounts of water in the Earth's mantle. Accordingly, it is important to quantify the effects of water on physical properties. This study of the interdiffusion of deuterium and hydrogen (that is, isotopes of hydrogen) in olivine and other mantle minerals will provide data that will contribute to the understanding of mantle flow and rheology, the distribution of water in the Earth's interior, and rates of homogenization of different regions of the Earth's interior. In the broadest sense, the results will contribute to understanding of plate tectonics and the mechanisms by which it operates, origins of earthquakes and volcanoes, and the overall abundance and distribution of the chemical elements in Earth and other planets.This project is an experimental effort to determine hydrogen-deuterium interdiffusion (self diffusion) coefficients in mantle materials such as olivine at temperatures and pressures of the Earth's upper mantle. Analysis of deuterium and hydrogen will be performed using novel techniques of Secondary Ion Mass Spectrometry (SIMS). The results will be interpreted in terms of defect mechanisms that can be related to models of ionic processes. Previous hydrogen diffusion measurements in olivine and mantle materials have generally been made using a hydrogen incorporation method, that is, measurement of diffusion of hydrogen into 'dry' material. Such experiments are interpreted to yield values of self diffusion coefficients for H diffusion and metal vacancy diffusion. Our new interdiffusion measurements will complement these previous measurements and enable delineation of detailed mechanisms of hydrogen ionic mobility in materials. Furthermore, these measurements will enable comparison to electrical conductivity measurements on hydrous mantle minerals. The results of this study will shed new light on physical transport processes in a variety of geological environments and will be important for the interpretation and modeling of magnetotelluric data. The ultimate benefits will be more detailed understanding of the temperature profile and physical state of matter at depth in the Earth's interior.This work will extend our understanding of hydrogen diffusion and point defects in mantle materials and will contribute to the knowledge base of Materials Science and Earth Science. The graduate student supported on this project will develop skills in experimental development, problem solving, microanalytical techniques, computational numerical analysis and collaboration in an interdisciplinary environment. She or he will attend national meetings, such as American Geophysical Union meetings, where diversity is a priority, enabling her/him to interact with scientists from around the globe. She or he will help mentor undergraduate students in research, participate in classroom exercises, and participate in outreach efforts. The work will be performed in shared multi-user facilities in collaboration with students and researchers from earth sciences, chemistry, materials science, physics and other fields, from Arizona State University as well as from other institutions from around the world. New advances in analytical and experimental methods and infrastructure will be developed as part of this project.