Elasticity of Mantle Minerals at High Pressures and Temperatures

在地球表面如此戏剧性地表现出来的地质活动，最终源于内部深处的过程。为了加深我们对地球内部动力学和结构的了解，有必要将地震学等地球物理观测与有关地质物质物理性质的直接实验测量结合起来。这项研究的目的是测量高压下矿物的声速，并将结果与地震数据结合起来，建立改进的地球上地幔组成和结构模型。利用布里渊光谱学，我们将对包括橄榄石及其高压晶型在内的上地幔主要相的高压弹性性质进行新的测量。矿物的弹性性质对于解释地球的地震数据是必不可少的。体积和剪切模数以及密度决定了纵波和横波的速度，可以直接与地震数据进行比较。结合我们之前对含水橄榄石晶型的研究，这些研究将对铁和氢如何影响上地幔主要相的弹性性质产生新的理解。特别是，我们的研究将为我们以前的工作中观察到的含水和无水镁橄榄岩之间的速度交叉提供新的线索。该项目的另一个目标是开发和应用在同时高压和高温(高达600摄氏度)的情况下使用外部加热的钻石顶压室的布里渊光谱技术。这项工作将首次为一些关键的地幔矿物提供高P-T弹性张量的实验约束。最后，我们将对我们目前对矿物弹性性质的化学和结构控制及其对解释地震数据的重要性的理解进行全面的综合。

The geological activity that manifests itself so dramatically at the Earth's surface ultimately originates from processes in the deep interior. To improve our understanding of the interior dynamics and structure of the Earth, it is necessary to combine geophysical observations such as those from seismology with direct experimental measurements of the physical properties of the relevant geological materials. The aim of this study is to measure the sound velocities of minerals at high pressure and to use the results in combination with seismic data to construct improved models of the composition and structure of the Earth's upper mantle. Using Brillouin spectroscopy we will carry out new measurements of the high-pressure elastic properties of major phases of the upper mantle including olivine and its high-pressure polymorphs. The elastic properties of minerals are essential for the interpretation of seismic data for the Earth. The bulk and shear moduli along with density determine compressional and shear wave speeds which can be directly compared to seismic data. In combination with our previous work on hydrous olivine polymorphs, these studies will yield new understanding of how iron and hydrogen affect the elastic properties of the major phases of the upper mantle. In particular, our studies will shed new light on the velocity crossover between hydrous and anhydrous forsterite observed in our previous work. Another goal for this project is to develop and apply techniques for Brillouin spectroscopy at simultaneous high pressures and temperatures (to as high as 600oC) using an externally heated diamond anvil cell. This work will provide the first experimental constraints on the high P-T elastic tensor for some key mantle minerals. Lastly, we will undertake a comprehensive synthesis of our current understanding of chemical and structural controls on mineral elastic properties and their importance for interpreting seismic data.