Collaborative Research: Experimental Determination of the Influence of Water on the Strength of Rocks

在地球内部普遍存在的高压和高温下，在地质时代，固体岩石可以像粘性流体一样流动。岩石的流动涉及到重要的地质过程，如构造板块的运动。它还控制着地球表面在大冰原融化后的反弹，以及地震断层上应力的积累。这些过程的模型，为过去和未来的事件提供信息，依赖于我们对岩石流动方式的理解。对岩石粘度的估计--也就是它们对流动的阻力--主要来自实验室实验。许多努力已经指向测量和预测在各种条件下的岩石粘度。矿物中存在的水的量已被证明对高温下岩石的粘度具有关键影响。然而，基本上没有关于低温下这种效应的数据。 这限制了我们理解构造板块内部过程和评估相应危害的能力。在这里，研究人员通过对潮湿岩石进行低温变形实验来填补这一数据空白。 他们研究两种重要的矿物，橄榄石和石英，这是地球地幔和大陆地壳的主要成分。他们使用最先进的高压设备，设置在国家同步加速器设施。 在那里，强大的X射线可以测量地球内部极端条件下冷岩石的粘度。结合室内压力下的变形试验和理论模拟，这些数据逐渐揭示了水对冷岩流动的影响。 该项目还为两名女性早期职业科学家提供支持，并为本科生提供培训，特别是来自科学领域代表性不足的群体。 在这里，该团队的目标是确定水在低到中等温度下弱化的微观物理机制。有几种理论模型可以描述水如何影响矿物质流动。然而，他们的预测差异很大，这使得他们可以通过实验进行测试。该团队进行了实验，以确定位错速度是否由扭结的浓度或扭结的速度控制。在明尼苏达大学的Paterson装置中，在高温下合成期间使样品水合。在宾夕法尼亚大学用仪器化纳米压痕进行变形实验，并在高级光子源（阿贡国家实验室）用变形-DIA进行变形实验。用电子背散射衍射（EBSD）表征了成品的微观结构。纳米压痕实验在室温下进行，并允许材料的行为进行评估的微观结构的不同组成部分。在室温至1000°C的温度范围内进行的变形-DIA实验允许评估散装材料的行为。该项目的最终目标是评估水的影响-即，矿物中溶解的羟基--论重要的地质现象这些包括板块在俯冲带的挠曲，断层带底部应力的松弛，以及摩擦断层表面粗糙度的演变。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

At the high pressures and temperatures prevailing within the Earth, and over geological times, solid rocks can flow like viscous fluids. The flow of rocks is involved in important geological processes such as the movement of tectonic plates. It also controls Earth’s surface rebounds after the melting of large ice sheets, and the way stresses buildup on earthquake-producing faults. Models of these processes, which inform past and future events, rely on our understanding of how rocks flow. Estimates of rock viscosity - that is, their resistance to flow - come primarily from laboratory experiments. Much effort has been directed towards measuring and predicting rock viscosity in various conditions. The amount of water present in minerals has been shown to have a critical effect on rocks viscosity at high temperature. Yet, there are essentially no data on this effect at low temperature. This limits our ability to understand processes within tectonics plates and assess the corresponding hazards. Here the researchers fill this data gap by carrying out low-temperature deformation experiments on wet rocks. They study two important minerals, olivine and quartz, which are major constituents of the Earth's mantle and continental crust. They use state-of-the-art high-pressure devices set at a national synchrotron facility. There, powerful x-rays allow measuring the viscosity of cold rocks at the extreme conditions of Earth’s interior. Coupled with deformation tests at room pressure and theoretical modeling, these data gradually unveil the effect of water on the flow of cold rocks. This project also provides support for two female early-career scientists, as well as training for undergraduate students, notably from groups underrepresented in Science. Here, the team aims to determine the microphysical mechanism(s) of water weakening at low to moderate temperatures. Several theoretical models exist to describe how water affects mineral flow. Yet, their predictions vary greatly which allows testing them experimentally. The team carry out experiments to determine whether dislocation velocity is controlled by the concentration of kinks or the velocity of kinks. Samples are hydrated during synthesis at high temperature in a Paterson rig at the University of Minnesota. Deformation experiments are conducted with instrumented nanoindentation at the University of Pennsylvania, and with the Deformation-DIA at the Advanced Photon Source (Argonne National Laboratory). Run-product microstructures are characterized by electron backscatter diffraction (EBSD). Nanoindentation experiments are conducted at room temperature and allow material behavior to be evaluated for different components of the microstructure. Deformation-DIA experiments, conducted at temperatures ranging from room temperature to 1000°C, allow the bulk material behavior to be evaluated. The project’s ultimate goal is to evaluate the effect of water - i.e., hydroxyls dissolved in minerals - on important geological phenomena. These include the flexing of plates at subduction zones, the relaxation of stresses at the base of fault zones, and the evolution of roughness on frictional fault surfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.