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.

了解地幔的结构、组成和演化是地球物理研究的中心目标。有关地球内部结构的最直接信息来自对地震波的分析。对地震数据的解释需要详细了解矿物的声速以及弹性和滞弹性如何随压力、温度、晶体结构和成分的变化而变化。弹性刚度张量表征了晶体的各向异性弹性响应。弹性模数也是一系列固态现象的基础，包括机械稳定性、原子间相互作用、材料强度、可压缩性和相变机制。在这个项目中，普林斯顿大学的托马斯·达菲正在使用布里渊散射来确定地壳和地幔中选定矿物的高压弹性性质。高压下的布里渊散射测量特别有用，因为它们不仅能约束体积和剪切模数，而且能约束弹性各向异性随压缩的变化。橄榄石多晶型和辉石是上地幔中最丰富的矿物。与这些阶段的弹性有关的许多根本问题尚未解决。近年来，人们越来越认识到，橄榄石的多晶型具有容纳相当数量的氢作为结构缺陷的能力。氢的存在，即使是少量的，也可能强烈地影响地幔的一些重要性质。然而，目前还没有测量方法能够限制氢对高压下橄榄石或其高压晶型瓦兹利石的弹性硬度的影响。同样，水掺入对斜方辉石等其他上地幔矿物弹性的影响知之甚少，但具有潜在的重要地球物理意义。在这项研究中，达菲正在测量氢的加入如何影响橄榄石多晶型在地球400公里深处对应的压力下的弹性。他和他的学生还在类似的条件下测量与地幔相关的辉石矿物的弹性性质。在高压下测量了石英和辉石的弹性性质。对于辉石，达菲和他的学生们正在将单晶弹性测量扩展到高达50 GPA，与地球下地幔的压力相对应。他们还使用多晶布里渊散射来研究20-100 Gpa范围内矿物的聚集弹性。利用这些数据，达菲和他的学生正在根据组成矿物的组成和晶体结构来解释地球深处的地震数据。这项研究的结果有助于更好地了解行星深部内部的结构、组成和演化。