Rheology of Mantle Rocks at High Pressure

地球是一个动态的天体，不断进化，改变着海洋的形状，建造着山脉。我们对这些现象的理解包括对矿物在高温下的塑性行为的认识。板块构造论认为，稳定的地表板块与地球深处是机械隔离的。热演化模式通过矿物的垂直流动输送热量。冰川的反弹证明了下面的粘性流动。本项目旨在研究压力对地球过渡带主要矿物塑性特性的影响。虽然在过去的几年里，我们对矿物流动特性的理解有了很大的提高，但压力诱导相变的影响仍然很有限。高压形式的橄榄石和辉石的流动特征，控制地球深处流动的阶段，实际上是未知的。已经开发出能够解决这个问题的新工具。使用同步加速器x射线源，可以测量样品在高压和高温下的多砧压机中的衍射光谱和直接图像。现在可以从x射线衍射信号确定应力场，从阴影图像确定应变。一个完整的数据收集周期产生应力和应变值大约需要五分钟。因此，300秒的时间分辨率是可能的，并且可以得到这些参数的时间导数。应力精度为几十MPa，应变速率为10-7 s-1。DDIA已被证明可以成功地产生10%应变的稳态流动条件。从而使织构和缺陷组织在实验过程中达到平衡，得到定量流动规律。该项目旨在研究瓦德利石、环伍德石和高压石榴石在高压下的定量流动特性。样品在石溪的高压实验室中合成。布鲁克海文国家实验室的同步加速器用于流变学研究。这些结果对深震源地震和地幔黏度结构的意义进行了解释。还研究了俯冲带条件下橄榄石的大应变流变性。这些结果被量化为对深震源地震的约束。这项研究为学生提供了一个学习经验，包括准备博士学位的研究生和暑期研究项目的本科生。这些结果将被用于整个地球科学，作为地球内部行为的基本信息。开发的工具将提供给其他研究人员用于研究材料的强度相关特性。这些工具（软件和硬件）将立即成为COMPRES操作的同步加速器设施的一部分，并可供社区中所有希望使用它们的人使用。

The Earth is a dynamic body, constantly evolving, changing the shapes of oceans, building mountains. Our understanding of these phenomena includes a recognition of the plastic behavior of minerals at high temperature. Plate tectonics asserts that stable surface plates are mechanically isolated from the deep Earth. Thermal evolutionary models transport heat by vertical flow of minerals. The rebound from glaciers is testimony to the viscous flow beneath. This project is to study the effects of pressure on the plastic character of the major minerals of the Earth's transition zone. While we have vastly improved our understanding of the flow properties of minerals over the past several years, the effects of pressure induced phase transitions are still poorly constrained. The flow characteristics of the high-pressure forms of olivine and pyroxene, the phases that control flow in the deep Earth, are virtually unknown.New tools have been developed that are capable of attacking this problem. Using synchrotron x-ray sources, it is possible to measure both diffraction spectra and direct images of samples in a multi-anvil press while the sample is at high pressure and temperature. It is now possible to determine the stress field from the x-ray diffraction signal and strain from shadow-graph images. One complete data collection cycle that yields values of stress and strain takes about five minutes. Thus, time resolution of 300 seconds is possible and time derivatives of these parameters can be obtained. Stress accuracy is a few tens of MPa, and strain rates of 10-7 s-1 can be resolved. The DDIA has proven successful in generating a steady state flow condition for 10's of per cent strain. Thus, texture and defect structures can equilibrate during the experiment and quantitative flow laws obtained.This program is investigating the quantitative flow properties of wadsleyite, ringwoodite, and high-pressure garnet at high pressure. Samples are synthesized in the high-pressure laboratory at Stony Brook. The synchrotron at Brookhaven National Labs is used for the rheology study. The results are interpreted in terms of their implications on deep focus earthquakes and mantle viscosity structure. The rheology of olivine at subduction zone conditions with large strains is also being studied. The results are being quantified as a constraint on deep focus earthquakes. This research is providing a learning experience for students including graduate students in the preparation of their PhD and undergraduates students in the focus of a summer research project. The results will be used throughout the Earth sciences as fundamental information on the behavior of the Earth's interior. The tools that are developed will be made available to other researchers for studying strength related properties of materials. These tools (software and hardware) will immediately become part of the COMPRES operated synchrotron facility and available to all in the community that wish to use them.