Collaborative Research: Linking Fluid-rock Interaction and Strain Accumulation in a Naturally Deformed Diamictite, Implications for Hydrolytic Weakening and Reaction Softening

了解大陆岩石圈的强度和力学行为是构造学的首要问题。岩石圈的力学行为在很大程度上取决于弱层和强层的发育。在实验室中，可以通过研究矿物中的反应和变形机制、流体流动和组构演化来洞察这一过程。在岩石圈变形中发挥作用的时间和空间尺度范围很广，这给将实验室研究结果外推到天然山带带来了挑战。通过对变形的透辉岩的研究，这些研究人员将评估降低岩石强度并导致集中变形的过程。变形将通过测量鹅卵石所经历的形状变化来解决。这些研究将提高我们对造山过程中地壳的强弱部分如何演化的理解，以及将变形定位于断裂带并部分控制大地震成核的过程。研究人员将对可变变形和蚀变的花岗片麻岩和石英岩进行野外、显微结构和微量化学分析，以量化递进应变、变形机制和流体化学过程之间的关系。辉绿岩的整体变形强度呈千米级的梯度，记录了水解性软化和反应软化过程。将使用Rf/？技术估算不同碎屑类型和大小的应变。体积变化将从地球化学变化和微结构关系来估计。变形机制将从显微结构的岩石学研究，结合晶格择优取向和亚晶界的电子背散射衍射分析来评估。控制水解性弱化的水和相关物质的数量和位置将使用傅里叶变换红外光谱和同步辐射红外辐射进行评估。阴极发光将提供有关石英新结晶和愈合微裂纹的位置的数据。碎屑和基质的整体化学成分的变化将使用X射线荧光、X射线光谱图和扫描电子显微镜进行量化。这一技术组合将提供有关渐进应变过程中变形、流体和化学过程之间相互作用的新信息。

Understanding the strength and mechanical behavior of the continental lithosphere is a first-order issue in tectonics. Mechanical behavior of the lithosphere depends mostly on the development of weak and strong layers. In the laboratory, insight into this process can be gained through the study of reactions and deformation mechanisms in minerals, fluid flow, and fabric evolution. The wide range of temporal and spatial scales at work in deforming lithosphere presents challenges in extrapolating results from laboratory studies to natural mountain belts. Through a study of deformed diamictites, rocks composed of mainly mud and cobbles, these researchers will evaluate processes that reduced the rock strength and resulted in concentrated deformation. The deformation will be addressed through measurements of the shape changes that the cobbles have undergone. These studies will improve our understanding of how strong and weak parts of the crust evolve during mountain building, and processes that localize deformation into fault zones and partly control nucleation of large earthquakes. The investigators will integrate field, microtextural, and microchemical analyses of variably deformed and altered granitic gneiss and quartzite to quantify relationships between progressive strain, deformation mechanisms, and fluid-chemical processes. The diamictite displays a km-scale gradient in bulk deformation intensity, providing a record of hydrolytic weakening and reaction softening processes. Strain will be estimated for different clast types and sizes using the Rf/?Ö technique. Volume change will be estimated from geochemical changes and microstructural relations. Deformation mechanisms will be evaluated from petrographic studies of microstructures, combined with electron backscatter diffraction analysis of lattice preferred orientation and subgrain boundaries. Amounts and locations of water and related species, which control hydrolytic weakening, will be evaluated using Fourier transform infrared spectroscopy and synchrotron infrared radiation. Cathodoluminescence will provide data on locations of quartz neocrystallization and healed microcracks. Changes in bulk chemical composition of clasts and matrix will be quantified using X-ray fluorescence, X-ray spectral mapping and scanning electron microscopy. This combination of techniques will provide new information on the interactions between deformation, fluids, and chemical processes during progressive strain.