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，以及在整个地质时代，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盖融化后的反弹，以及在孕育地震的断层上应力积累的方式。这些过程的模型，告诉我们过去和未来的事件，依赖于我们对岩石如何流动的理解。对岩石粘度的估计--即它们的流动阻力--主要来自实验室实验。为了测量和预测各种条件下的岩石粘度，已经做了大量的工作。矿物中的水含量已被证明对高温下岩石的粘度有重要影响。然而，基本上没有关于低温下这种影响的数据。这限制了我们理解构造板块内的过程并评估相应危险的能力。在这里，研究人员通过对潮湿的岩石进行低温变形实验来填补这一数据空白。他们研究了两种重要的矿物，橄榄石和石英，这两种矿物是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中。在那里，强大的X射线可以测量地球内部极端条件下冰冷岩石的粘度。结合常压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。该项目还为两名职业生涯早期的女性科学家提供支持，并为本科生提供培训，特别是对在科学领域代表性不足的群体的培训。在这里，该团队的目标是确定水在中低温下变弱的微物理机制(S)。有几个理论模型可以描述水是如何影响矿物质流动的。然而，他们的预测差异很大，这使得他们可以在实验中进行测试。该团队进行了实验，以确定位错速度是由扭结的浓度控制还是由扭结的速度控制。在明尼苏达大学帕特森实验室的高温合成过程中，样品被水合。形变实验是在宾夕法尼亚大学使用仪器纳米压痕进行的，而形变-DIA是在高级光子源(阿贡国家实验室)进行的。用电子背散射衍射(EBSD)对连续产物的微观结构进行了表征。纳米压痕实验是在室温下进行的，可以评估微观结构中不同成分的材料行为。在从室温到1000°C的温度范围内进行的形变-DIA实验允许评估散体材料的行为。该项目的最终目标是评估水--即溶解在矿物中的羟基--对重要地质现象的影响。其中包括俯冲带板块的弯曲、断裂带底部应力的松弛和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优势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.