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

研究人员正在执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)和温度(T)下的弹性性质。他们的目标是测量最重要的物质的速度，这些物质包括地球过渡带(从410-660公里深)、下地幔、俯冲构造板块和邻近的上地幔。这项工作的动机来自于对地球深部S的地震学研究，该研究提供了纵波(Vp)和横波(Vs)的速度随深度的函数，以及速度相对于全球平均模型的横向变化。这些地震结果是关于地球-S地幔原位性质的最直接信息，从而为地球深部的化学、矿物学、热学和地球动力学模型以及地球随时间的演化提供了强有力的约束。声速测量是充分利用地震数据的关键，他们在高压和高温条件下进行这些测量，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的高压区域(在T室)测量速度和弹性性质，以及在常压下进行高温测量。当务之急是测量被认为是地球上最丰富的固体相？S地幔(深度2900公里)。他们试图测量这些矿物中铁的电子状态的变化对声速的影响，并对俯冲构造板块中携带氢(或水)进入地球深处并将其储存在那里的水合相进行初步测量。2)该团队正在继续开发一种仪器，以测量在地幔实际压力-温度条件下矿物的声速。这是通过对在钻石顶压室(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。他们预计将在至少T=2500 K和P50 Gpa的条件下测量矿物的速度，跨越地球上大约1300公里深处可能存在的P-T条件范围。低温测量是用电加热的DAC进行的。这些实验的结果将提供比目前对地球内部化学成分和温度的限制要强得多的条件？S。该社区将定位于更充分地开发详细的地震信息的潜力，以了解地球的结构及其深度的不均一性。这些实验也推动了P-T升高条件下的实验速度测量技术，进入了以前仅限于理论领域的领域。预期的发现对整个光谱学社区(化学、物理、材料科学等)都是有益的。对极端条件下的实验感兴趣。本研究涉及研究生和本科生的培养。这些学生有独特的机会参与前沿的实验研究，并接受该领域一些最先进的实验技术的培训。

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.