Sound Velocities and Elastiicity of Deep-earth Mat

地球内部的性质是高度不确定的，尽管它与地球表面的过程密切相关，如地震活动、火山活动、构造造山过程以及水和二氧化碳进入地球内部的再循环。地球的内部结构也与它的热状态、物质的对流流动及其随时间的演变有关。很少有直接从地幔中提取的岩石样本，即使是这些岩石样本也只提供了一个非常不完整的地幔图像，深度只有几百公里。到目前为止，我们所掌握的关于地球内部地幔和地核的最完整的信息来自地震学，即速度结构的三维层析成像。对这些地震信息的解释，例如化学成分和热状态，需要实验室测量可能存在于深处的材料的声速。然而，在地球内部的极端压力-温度条件下进行这种测量是相当具有挑战性的，直到最近，在大多数情况下在技术上是不可行的。该项目将使用最近开发的实验设备和技术，在30-2900公里深度的地幔实际压力和温度下测量候选地幔矿物的速度。该项目建立在美国国家科学基金会资助的PI实验室十多年的技术开发基础上，使这种测量成为可能。这个项目的结果将使我们对地幔的状态有更好、更准确的了解，对地幔的三维化学成分、横向和径向非均质性以及热结构的性质有更严格的限制。在这个项目的过程中取得的技术进步应该是在同源凝聚态科学和材料工程的极大兴趣。该项目将为研究生和博士后研究人员提供先进的科学训练，并应更好地使他们追求自己的职业目标。该项目将包括在与地幔中存在的极端压力-温度条件相匹配或接近的条件下测量地幔候选材料的声速。实验将采用布里渊光散射技术在金刚石砧池（DAC）中压缩的样品上进行。硅酸盐和氧化物样品将使用CO2红外激光器加热，以产生与实际地幔条件非常接近的极端同时压力-温度条件。在可能的情况下，将对单晶样品进行测量，从而提供有关速度各向异性的信息，这些信息可用于约束深度处材料的动态流动。测量也将在各向同性多晶样品上进行。重点将放在上地幔、过渡带和下地幔最可能的候选阶段。这个项目的结果应该对地幔的化学成分、矿物学和热结构，包括任何可能的径向化学分层和横向化学非均质性，施加更严格的限制。

The nature of Earth's interior is highly uncertain, despite its intimate relationship to processes on Earth's surface such as seismicity, volcanism, tectonic mountain-building processes, and re-cycling of water and carbon dioxide into Earth's interior. Earth's internal structure is also related to its thermal state, the convective flow of material, and its evolution through time. There are few direct samples of rocks from the Earth's mantle, and even these give a highly incomplete view of Earth's mantle, down to only several hundred kilometers depth. By far, the most complete information we have on Earth's interior mantle and core come from seismology in the form of 3-D tomographic images of velocity structure. Interpretations of this seismological information in terms of, for example, chemical composition and thermal state, require laboratory measurements of sound velocities on the materials that are likely present at depth. However, such measurements at the extreme pressure-temperature conditions of Earth's interior are quite challenging and until recently were in most cases not technically feasible. This project will use recently-developed experimental facilities and techniques to measure the velocities of candidate mantle minerals at the actual pressures and temperatures of the Earth's mantle, from 30-2900 km depth. This project builds upon over a decade of NSF-funded technology development in the PI's laboratory which makes such measurements possible. The results of this project should give far better and more accurate understanding of the state of the Earth's mantle, placing far tighter constraints on its 3-D chemical composition, the nature of lateral and radial heterogeneity, and thermal structure. Technical advances made in the course of this project should be of great interest in cognate condensed matter sciences, and in materials engineering. This project will provide advanced scientific training for graduate students and a post-doctoral researcher, and should better enable them to pursue their career goals.This project will involve the measurement of sound velocities of candidate materials of Earth's mantle at extreme pressure-temperature conditions matching or close to those present in the mantle. Experiments will be performed by the technique of Brillouin light scattering on samples that are compressed in a diamond anvil cell (DAC). Silicate and oxide samples will be heated using a CO2 infrared laser to produce extreme simultaneous pressure-temperature conditions closely approximating actual mantle conditions. Measurements will be carried out on single-crystal samples where possible, thus giving information on velocity anisotropy which can be used to constrain dynamic flow of material at depth. Measurements will be performed on isotropic polycrystalline samples as well. Emphasis will be put on the most likely candidate phases of the upper mantle, transition zone, and lower mantle. The results of this project should place much tighter constraints on the chemical composition, mineralogy, and thermal structure of the mantle, including any possible radial chemical stratification and lateral chemical heterogeneity.