Elasticity of Mantle Minerals at High Pressures by Brillouin Scattering

通过布里渊散射研究高压下地幔矿物的弹性

• 批准号: 0738510
• 负责人: Thomas Duffy
• 金额: $ 37.47万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-02-01 至 2012-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738510&HistoricalAwards=false
• 关键词: Elasticity; Mantle; Minerals; Pressures; Brillouin

Understanding the structure, composition, and evolution of Earth's mantle is a central goal of geophysical research. The most direct information about the interior structure of the Earth comes for analysis of seismic waves. Interpretation of seismic data requires a detailed understanding of how the sound velocities and hence elastic and anelastic properties of minerals vary with pressure, temperature, crystal structure, and composition. The elastic stiffness tensor characterizes the anisotropic elastic response of crystals. Elastic moduli are also fundamental to a range of solid-state phenomena including mechanical stability, inter-atomic interactions, material strength, compressibility, and phase transition mechanisms.In this project, Thomas Duffy of Princeton University is using Brillouin scattering to determine the high-pressure elastic properties of selected minerals of the Earth's crust and mantle. Measurements by Brillouin scattering at high pressures are especially useful because of their ability to constrain not only the bulk and shear modulus but also the variation of elastic anisotropy with compression. Olivine polymorphs and pyroxenes are among the most abundant minerals in the upper mantle. There are a number of fundamental unsolved problems connected to the elasticity of these phases. In recent years, there has been growing recognition that olivine polymorphs have the capacity to accommodate appreciable amounts of hydrogen as structural defects. The presence of hydrogen even in small amounts might strongly influence a number of important properties of the mantle. However, there are no measurements yet to enable us to constrain the effects of hydrogen on the elastic stiffnesses of olivine or its high-pressure polymorph, wadsleyite, at high pressure. Similarly, the effects of H2O incorporation on the elasticity of other upper mantle minerals such as orthopyroxene are poorly known but have potentially important geophysical implications. In this proposal, Duffy is measuring how hydrogen incorporation affects the elasticity of olivine polymorphs up to pressures corresponding to 400-km depth in the Earth. He and his students are also measuring the elastic properties of mantle-relevant pyroxene minerals to similar conditions. The elastic properties of quartz and stishovite are being measured at high pressures. For stishovite, Duffy and his students are extending single-crystal elasticity measurements to as high as 50 GPa, corresponding to pressures of Earth's lower mantle. They are also using polycrystalline Brillouin scattering to study the aggregate elasticity of minerals at 20-100 GPa. Using such data, Duffy and his students are interpreting seismic data for the deep Earth in terms of the composition and crystal structure of the constituent minerals. The results of this research are yielding a better understanding of the structure, composition, and evolution of deep planetary interiors.

了解地球地幔的结构，组成和进化是地球物理研究的核心目标。 关于地球室内结构的最直接信息是用于分析地震波。对地震数据的解释需要详细了解矿物质的声速以及矿物质的弹性和弹性特性如何随压力，温度，晶体结构和组成而变化。 弹性刚度张量表征了晶体的各向异性弹性反应。弹性模量也是一系列固态现象的基础地壳和地幔的选定矿物质的压力弹性特性。 布里鲁因在高压处进行测量特别有用，因为它们不仅可以约束散装和剪切模量，而且还可以通过压缩来限制弹性各向异性的变化。 橄榄石多晶型和辉石是上地幔中最丰富的矿物之一。 与这些阶段的弹性有关，有许多基本的未解决问题。 近年来，人们越来越认识到橄榄石多晶型物具有可容纳大量氢作为结构缺陷的能力。 即使在少量的情况下，氢的存在也可能强烈影响地幔的许多重要特性。 但是，尚无测量方法可以使我们能够在高压下限制氢对橄榄石或其高压多晶岩的弹性刚度的影响。 同样，H2O掺入对其他地幔矿物（如邻苯二苯甲；）的弹性的影响鲜为人知，但具有潜在的重要地球物理意义。 在此提案中，达菲正在测量氢融合如何影响橄榄石多晶型物的弹性，直到对应于地球400公里深度的压力。 他和他的学生还测量了与地幔相关的辉石矿物质的弹性特性。 石英和Stishovite的弹性特性正在高压下测量。 对于Stishovite，Duffy和他的学生正在将单晶弹性测量扩展到高达50 GPA，对应于地球下层的压力。 他们还使用多晶光纤蛋白散射来研究20-100 GPA矿物质的聚集弹性。 使用此类数据，Duffy和他的学生正在用组成矿物的组成和晶体结构来解释深层地球的地震数据。 这项研究的结果对深度行星内部的结构，组成和演变有了更好的了解。