Development of Microstructure and Creep Strength of Marble

碳酸盐岩(石灰岩、白云岩、大理石)是地壳的重要组成部分。值得注意的是，石灰岩和白云岩属于主要山脉褶皱冲断带内的褶皱和断层单元，例如爱达荷州-怀俄明州逆冲推覆带和阿尔卑斯山推覆带。这些带包含主要的油气储集层。组成矿物的变形过程对于了解这些带是如何形成以及地壳深部是如何变形至关重要的。这个项目通过一系列实验探索碳酸盐岩变形的详细机制，在这些实验中，组成矿物在一系列应变率、围压和温度范围内变形。一种新的微尺度应变作图方法与各种高分辨率显微镜方法相结合，将使人们能够前所未有地理解碳酸盐矿物变形的原子尺度机制。结果将与从阿尔卑斯山收集的自然变形的碳酸盐岩进行比较。该项目将通过以下方式促进预期的社会成果：(1)通过博士后培训发展具有全球竞争力的STEM劳动力；(2)通过国际合作增加伙伴关系；(3)通过开发开放式课程材料来加强教育基础设施。该项目的主要目标是研究碳酸盐岩石在蠕变过程中微观结构和强度演变的物理和动力学，并确定解释自然变形岩石力学历史所需的微结构特征元素。该项目与GFZ德国地球科学研究中心和蒙彼利埃大学的科学家合作，在该研究小组先前工作的基础上，将包括测试和观察天然和合成大理石在剪切应变率为每秒10^-3到10^-6之间、围压低于300兆帕、温度在500-1000K之间的常规三轴和扭转载荷下变形的样品的微观结构。将使用光学显微镜、扫描电子显微镜、电子显微镜和EBSD对微观结构进行观察，以将位错结构、LPO的产生、动态再结晶和强度的演变联系起来。两种新的技术，微尺度应变映射和顺序微观分析，将被用来理解应变在变形机制中的动力学和分配。尽管实验室研究很重要，但只有结合和协调实验室实验、野外和微结构观测、地球物理调查以及理论和计算处理，才能彻底和基本地理解构造。因此，继续观察自然变形的大理石中的微结构是这一项目的重要组成部分。该团队将与伯尔尼大学的研究人员合作，观察来自海尔维特推覆体的糜棱岩的微观结构，从而有机会研究温度对应变局部化的影响，研究不同的石英和白云石含量对碳酸盐中应变局部化的影响，并在变形条件受到很好限制的位置将位错微结构、颗粒结构和相化学关联起来。

Carbonate rocks (limestone, dolomite, marble) are important constituents of the Earth's crust. Notably, layers of limestone and dolomite are among the folded and faulted units within the fold-and-thrust belts of the major mountain ranges - the Idaho-Wyoming overthrust belt and the Alpine nappes, for example. These belts contain major hydrocarbon reservoirs. The processes by which the constituent minerals deform is essential in the understanding of how these belts form and how the deep crust deforms. This project explores the detailed mechanisms by which carbonate rocks deform through a series of experiments in which the constituent minerals are deformed over a range of strain rates, confining pressures, and temperatures. A new novel micro-scale strain mapping method when coupled with various high-resolution microscopy methods, will allow for unprecedented understanding of the atomic scale mechanisms of carbonate mineral deformation. Results will be compared to naturally deformed carbonate rocks collected from the Alps. The project would advance desired societal outcomes through: (1) development of a globally competitive STEM workforce through postdoctoral fellow training; (2) increased partnerships through international collaboration; and (3) enhanced infrastructure for education through development of Open Courseware materials.The main goals of this project are to investigate the physics and kinetics of the evolution of microstructure and strength of carbonate rocks during creep, and to identify characteristic elements of microstructure necessary to interpret the mechanical history of naturally deformed rocks. The project, in collaboration with scientists at GFZ German Research Centre for Geosciences and Université Montpellier builds on previous work by this research group and will include testing and observations of the microstructure in samples deformed under conventional triaxial and torsion loading of natural and synthetic marbles at shear strain rates between 10^-3 and 10^-6 per second, confining pressures less than 300 MPa, and temperatures between 500-1000 K. Observations of microstructure will be made using optical microscopes, SEM, TEM, and EBSD to correlate dislocation structure, generation of LPO, dynamic recrystallization, and the evolution of strength. Two novel techniques, micro-scale strain mapping and sequential microanalyses, will be used to understand the kinetics and partitioning of strain amongst the deformation mechanisms. Although lab investigations are important, thorough and fundamental understanding of tectonics will come only by combining and reconciling lab experiments, observations of field- and micro- structure, geophysical investigations, and theoretical and computational treatments. Thus, continued observations of microstructures in naturally deformed marbles are an important part of this project. In collaboration with researchers at Universität of Bern, the team will observe microstructure in mylonites from the Helvetic Nappes, which provides opportunities to investigate the influence of temperature on strain localization, to study the influence of varying quartz and dolomite content on strain localization within the carbonates, and to correlate dislocation microstructure, grain structure, and phase chemistry at locations where deformation conditions are well constrained.