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

地球表面不断受到构造板块运动造成的压力，这些压力通常会导致地震等事件，威胁到生命和基础设施。为了量化板块构造引起的应力，地质学家检查矿物（如石英）的形状、大小和其他微观结构特征。从这些特征和实验室实验结合起来，地质学家们发展出了将施加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，研究人员将基于现场的数据和建模与实验室实验相结合，开发了一种从岩石中提取应力和流速信息的新方法，可以直接与应用流动定律获得的结果进行比较。他们量化了矿物晶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。该跨学科项目支持一名博士后，以及缅因大学本科生和研究生的培训。开发的代码和分析协议通过公共门户网站公开提供。这些成果可以应用于地球科学以外的材料科学和工程领域，特别是金属、陶瓷和先进复合材料的强度设计。本课题的目标是：1)利用石英生成一种新的实验定标，以细化温度、应力、流速和晶界粗糙度之间的多项式关系；2)在美国缅因州Norumbega断裂系统的Sandhill Corner剪切带获取了一套完整的石英晶界粗糙度数据，对新的实验标定进行了测试和应用；3)发展和完善利用光学和电子后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后向散射衍射校准。解决上述目标提供了一个机会来量化变形条件和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，可以独立使用或与流动规律相一致。所选择的方法应用的模型和概念主要源于材料和工程社区，并且主要构成了地球科学的新研究。在地球科学和材料工程中，微观结构对宏观行为的重要性的认识以及定量处理微观结构的能力正在增长。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。

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.