Deuterium-Hydrogen Interdiffusion in Mantle Materials

氢或水存在于地球内部岩石中的含量非常小（百万分之几十到几百）。 即使在这样低的浓度下，内陆的水总量也可能等于或超过海洋。 这些少量的水对地球物质的物理性质有非常显著的影响，如粘度，强度，熔化温度，电导率和扩散速率。 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，板块构造被认为发生在地球上，而不是其他类地行星，因为地球地幔中有少量的水。 因此，重要的是量化水对物理性质的影响。 这项对橄榄石和其他地幔矿物中氘和氢（即氢的同位素）相互扩散的研究将提供有助于理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匀化速率的数据。 从最广泛的意义上说，这些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中化学元素的总体丰度和分布。该项目是一项实验性努力，以确定氢氘相互扩散地幔物质（如橄榄石）在地球上地幔的温度和压力下的（自扩散）系数。氘和氢的分析将使用二次离子质谱（西姆斯）的新技术进行。结果将被解释的缺陷机制，可以与模型的离子过程。 以前在橄榄石和地幔材料中的氢扩散测量通常是使用氢掺入法进行的，即测量氢扩散到“干”材料中。 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。我们新的相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，这些测量将能够比较含水地幔矿物的电导率测量。 这项研究的结果将揭示在各种地质环境中的物理传输过程的新的光，并将是重要的大地电磁数据的解释和建模。 最终的好处将是更详细地了解地球内部深处的温度分布和物质的物理状态，这项工作将扩展我们对地幔材料中氢扩散和点缺陷的理解，并将有助于材料科学和地球科学的知识基础。 该项目支持的研究生将培养实验开发，解决问题，微观分析技术，计算数值分析和跨学科环境中的协作技能。他/她将出席美国地球物理学联盟等国家会议，这些会议将多样性作为优先事项，使他/她能够与来自地球仪各地的科学家进行互动。她或他将帮助指导本科生的研究，参加课堂练习，并参与推广工作。这项工作将在共享的多用户设施中进行，与来自地球科学，化学，材料科学，物理学和其他领域的学生和研究人员合作，来自亚利桑那州立大学以及来自世界各地的其他机构。 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.