Sound Velocities and Elasticity of Deep-Earth Materials at High Pressures and Temperatures

研究人员正在进行一项为期三年的计划，通过布里渊散射测量声速来确定各种地球材料在高压（P）和高温（T）下的弹性特性。他们的目标是测量组成地球过渡带（深度为410-660公里）、下地幔、俯冲构造板块和邻近上地幔的最重要物质的速度。这项工作的动机源于地球的地震学研究？的深内部，提供纵向（VP）和剪切（Vs）声波的速度作为深度的函数，以及相对于全球平均模型的速度的横向变化。这些地震结果是最直接的信息，在原地性质的地球？的地幔，从而提供了强大的约束化学，矿物学，热，地球动力学模型的深部内部，并通过时间的地球演化。声速测量对于充分利用地震数据至关重要，他们是在高压和高温条件下进行这些测量的，这些条件非常接近地球深处的实际条件。 研究人员正在进行两大类活动：1）在高达100 GPa区域（在T室）的高压下测量速度和弹性特性，以及在常压下测量高温。 第一个优先事项是对地球上被认为最丰富的固体相进行测量？的地幔（至2900公里深度）。他们正试图测量这些矿物中铁的电子状态的变化如何影响声速，并正在对将氢（或水）带入俯冲构造板块中的地球深部并将其储存在那里的含水相进行一些初步测量。 2)该小组正在继续研制一种仪器，以测量地幔实际压力-温度条件下矿物的声速。这是通过对在金刚石砧室（DAC）中压缩并用红外激光加热的样品进行布里渊测量来完成的。他们希望在至少T=2500 K和P50 GPa的条件下测量矿物的速度，跨越地球深度约1300 km的可能P-T条件范围。低温测量是用一个电加热的DAC进行的，这些实验的结果将提供比目前对地球化学成分和温度的限制更强的限制。的内部。该社区将能够更充分地利用详细的地震信息的潜力，以了解地球的结构及其在深度上的异质性。这些实验也推动了在升高的P-T条件下的实验速度测量技术，进入了以前仅属于理论领域的领域。预期的发现对整个光谱学社区（化学，物理，材料科学等）都有好处。对极端条件下的实验感兴趣。这项研究涉及研究生和本科生的培训。这些学生有一个独特的机会参与尖端的实验研究，并在该领域的一些最先进的实验技术进行培训。

The investigators are carrying out a three-year program to determine the elastic properties of a wide range of Earth materials at high pressures (P) and temperatures (T) by Brillouin scattering measurements of sound velocities. Their goal is to measure the velocities of the most important materials comprising the transition zone of the Earth (from 410-660 km depth), the lower mantle, subducting tectonic plates and the adjacent upper mantle. The motivation for this work stems from seismological studies of Earth?s deep interior, which provide the velocities of longitudinal (VP) and shear (Vs) sound waves as a function of depth, and the lateral variations of velocity relative to global average models. These seismic results are the most direct information on the in-situ properties of Earth?s mantle, thus providing strong constraints on chemical, mineralogical, thermal, and geodynamic models of the deep interior, and evolution of the Earth through time. The sound velocity measurements are critical for fully utilizing the seismic data, and they are making these measurements under high pressure and high temperature conditions that closely mimic the actual conditions in the Earth at great depth. The investigators are pursuing two broad classes of activities: 1) Measurements of velocities and elastic properties at high pressures up to the 100 GPa region (at room T), and high temperature measurements at normal pressure. The first priority is measurements on what are believed to be the most abundant solid phases in the Earth?s mantle (to 2900 km depth). They are attempting to measure how changes in the electronic state of iron in these minerals affect on the sound velocities, and are performing some preliminary measurements on hydrous phases that carry hydrogen (or water) into the deep earth in subducting tectonic plates and store it there. 2) The team is continuing to develop an apparatus to measure the sound velocities of minerals at the actual pressure-temperature conditions of the mantle. This is being done by Brillouin measurements on samples compressed in a diamond anvil cell (DAC) and heated with an infrared laser. They expect to measure velocities on minerals at conditions of at least T=2500 K and P50 GPa, spanning the likely range of P-T conditions that exist in the Earth at depths of about 1300 km. Lower-temperature measurements are being made with an electrically-heated DAC.The results of these experiments will provide far stronger constraints than are currently available on the chemical composition and temperature of the Earth?s interior. The community will be positioned to more fully exploit the potential of detailed seismic information for understanding the structure of the Earth and its heterogeneity at depth. These experiments are also pushing forward the technology of experimental velocity measurements at elevated P-T conditions, into a regime that has previously been the realm of theory alone. The expected findings are of benefit to the entire spectroscopy community (chemistry, physics, materials sciences, etc.) interested in experiments under extreme conditions. This research involves the training of graduate and undergraduate students. These students have a unique opportunity to be involved in cutting-edge experimental research and be trained in some of the most advanced experimental techniques in this field.