Collaborative Research: Experimental determination of the influence of water on the viscosity 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。岩石的流动参与了重要的地质过程，如构造板块的运动。它还控制着大冰盖融化后地球表面的反弹，以及产生地震的断层上的应力积聚方式。这些过程的模型依赖于我们对岩石流动方式的理解，这些模型可以告诉我们过去和未来的事件。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。在测量和预测各种条件下的岩石粘度方面已经做了大量的工作。矿物中水分的含量对岩石在高温下的粘度有至关重要的影响。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部过程和评估相应危害的能力。在这里，研究人员通过在湿岩石上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，它们是地幔和大陆地壳的主要成分。他们使用国家同步加速器设施中最先进的高压设备。在那里，强大的x射线可以测量地球内部极端条件下寒冷岩石的粘度。结合室内压力下的变形试验和理论建模，这些数据逐渐揭示了水对冷岩石流动的影响。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的本科生。在这里，研究小组的目标是确定水在低温到中等温度下变弱的微观物理机制。有几个理论模型可以描述水如何影响矿物流动。然而，他们的预测差异很大，这使得他们可以通过实验来验证。研究小组进行了实验，以确定错位速度是由扭结的浓度还是扭结的速度控制的。样品在明尼苏达大学帕特森钻机的高温合成过程中水化。变形实验由宾夕法尼亚大学的纳米压痕仪器和阿贡国家实验室先进光子源的形变dia进行。利用电子背散射衍射（EBSD）技术对产品微结构进行了表征。纳米压痕实验是在室温下进行的，并允许在微观结构的不同组成部分评估材料的行为。变形dia实验在室温到1000℃的温度范围内进行，可以评估大块材料的行为。该项目的最终目标是评价水（即溶解在矿物中的羟基）对重要地质现象的影响。这些变化包括俯冲带板块的挠曲、断裂带底部应力的松弛以及摩擦断层表面粗糙度的演化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.