Quartz grain-boundary topology as a stress and strain-rate meter and a new flow law

地球表面不断受到由构造板块运动引起的应力，这些应力通常会导致威胁生命和基础设施的地震等事件。为了量化由板块构造引起的应力，地质学家研究了矿物（如石英）的形状、大小和其他微观结构特征。根据这些特征，结合实验室实验，地质学家们已经建立了将施加的应力与岩石流动速率联系起来的数学方程。这些被称为流动定律的方程是有价值的，但不确定性仍然很大。在这里，研究人员将联合收割机基于现场的数据和建模与实验室实验相结合，开发出一种从岩石中提取应力和流速信息的新方法，这些信息可以直接与应用流动定律获得的结果进行比较。他们量化了矿物颗粒边界的粗糙度如何直接记录应力和流速。他们开发了使用电子束方法测量粗糙度的新协议。该跨学科项目支持博士后助理，以及在缅因州大学的本科生和研究生的培训。通过公共门户网站公开提供所制定的守则和分析协议。这些成果可以应用于地球科学之外的材料科学和工程，特别是金属，陶瓷和先进复合材料的强度工程。本项目的目标是：1）使用石英产生新的实验校准，以细化温度，应力，流量和晶界粗糙度之间的多项式关系; 2）从美国缅因州诺伦贝加断层系统的沙丘角剪切带获得一套完整的石英晶界粗糙度数据，以测试和应用新的实验校准; 3）开发和完善利用光学和电子反向散射衍射技术确定晶界周长的方法，并为该方法提供光学和反向散射衍射校准。解决上述目标提供了一个机会，以量化变形条件和所产生的岩石微观结构之间的关系，并开发一种新的方法来估计应力和应变率，可以单独使用或与流动定律。所选择的方法应用的模型和概念，主要来源于材料和工程界，主要是构成地球科学的新研究。在地球科学和材料工程中，人们越来越认识到微观结构对宏观行为的重要性，并越来越有能力对其进行定量处理。该项目的成果将为这两个领域的未来努力以及它们之间的合作提供一个框架。该奖项反映了NSF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。

The surface of Earth is constantly subjected to stresses caused by the movement of tectonic plates, and these stresses commonly cause events such as earthquakes that threaten life and infrastructure. To quantify the stresses caused by plate tectonics, geologists examine the shape, size, and other microstructural characteristic of minerals such as quartz. From these characteristics combined with laboratory experiments geologists have developed mathematical equations that relate the applied stress to the rate of rock flow. These equations, known as flow laws, are valuable but the uncertainties remain significant. Here the researchers combine field-based data and modeling with laboratory experiments to develop a new method for extracting stress and flow-rate information from rocks that can be directly compared to results obtained from applying flow laws. They quantify how the roughness of mineral grain boundaries directly records stress and flow rate. They develop new protocols for measuring roughness using electron beam methods. The interdisciplinary project supports a postdoctoral associate, as well as the training of undergraduate and graduate students at the University of Maine. The developed codes and analytical protocols are made openly available through public portals. These outcomes can be applied beyond Earth Sciences in Material Sciences and Engineering, notably to engineer the strength of metals, ceramics, and advanced composite materials.The objectives of this project are to: 1) Generate a new experimental calibration using quartz to refine the polynomial relations among temperature, stress, flow rate and grain-boundary roughness; 2) Obtain a complete set of quartz grain-boundary roughness data from the Sandhill Corner shear zone in the Norumbega fault system, Maine USA, to test and apply the new experimental calibrations; 3) Develop and refine methods for determining grain-boundary perimeters using optical and electron backscatter diffraction techniques, and provide optical and backscatter diffraction calibrations for the method. Addressing the above objectives provides an opportunity to quantify the relations between deformation conditions and resulting rock microstructures, and to develop a new method for estimating stresses and strain rates that can be used independently or in concert with flow laws. The chosen approach applies models and concepts that originate largely in the materials and engineering communities, and mostly constitutes novel research in the geosciences. Recognition of the importance of microstructure for macroscopic behavior and the ability to treat it quantitatively is growing in both Earth Sciences and Materials Engineering. Outcomes of this project will provide a framework for future efforts in both fields, and for collaborations between them.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.