RUI: Over-Printing of Crystallographic Preferred Orientation Patterns in Quartz Aggregates: A Program of Experimental Deformation of Natural Mylonite

晶体学择优取向模式已被用来解释变形岩石的应变历史多年。最近，这种解释已经扩展到包括岩石非常复杂的变形历史，大概是造成叠印图案。此外，晶体学优选取向模式可以产生如此强的晶轴对齐，使得矿物颗粒在随后的变形事件中更难以变形。在这个项目中进行的研究旨在阐明一个以上的变形事件对所产生的晶体学择优取向的影响。该项目有三个目标：1）确定预先存在的组构对地壳岩石强度的影响; 2）量化重置组构所需的剪切应变; 3）研究重结晶过程中晶界迁移对晶体学择优取向模式的影响。在严格约束的条件和应变路径下，对具有晶体学择优取向和微观结构的天然变形岩石进行了实验变形。实验采用固体介质，活塞缸变形装置变形条件下促进位错蠕变石英糜棱岩。用相对于原始织物的各种取向的样品进行一系列实验。用岩相学和透射电子显微镜分析了由此产生的显微结构，用电子背散射衍射方法分析了晶体学择优取向。地壳在应力作用下的力学行为取决于岩石的物理性质，并对评估构造活动区的地震危险性有影响。晶体学优选取向可以改变岩石，使得其物理性质是各向异性的，即性质在不同方向上具有不同的值。地震波速度的各向异性会影响一个地区地震资料的解释，从而影响地震危险性的评价。晶体学优选取向模式的演化对于具有长运动历史的断层是重要的（即，圣安德烈亚斯断层）。此外，随着更深的岩石被带到地表，变形条件发生变化-即岩石更冷（即，新西兰阿尔卑斯山断层（Alpine Fault）在矿物石英中，这种冷却会导致不同滑动系统的运作，并可能加强地壳，再次影响地壳的地震特性。

Crystallographic preferred orientation patterns have been used to interpret strain history in deformed rocks for many years. Recently that interpretation has expanded to include rocks with very complex deformation histories presumably resulting in the overprinting of the patterns. In addition, crystallographic preferred orientation patterns may create such a strong alignment of the crystal axes that the mineral grains are more difficult to deform in subsequent deformation events. Research being carried out in this project seeks to shed light on the effects of more than one deformation event on the resulting crystallographic preferred orientation. The project has three objectives: 1) To determine the effect of pre-existing fabric on the strength of crustal rocks; 2) To quantify the shear strain needed to reset fabrics; and 3) To investigate the effect of grain boundary migration during recrystallization on crystallographic preferred orientation patterns. Naturally deformed rocks with documented crystallographic preferred orientation s and microstructures are experimentally deformed under well-constrained conditions and strain paths. The experiments employ a solid media, piston-cylinder deformation apparatus to deform quartz mylonite under conditions promoting dislocation creep. Suites of experiments are conducted with the samples in various orientations with respect to the original fabric. The resulting microstructures are analyzed with petrographic and transmission electron microscopy and the crystallographic preferred orientation s are analyzed by electron backscatter diffraction methods.How the crust behaves mechanically when stress is applied to it depends on the physical properties of the rock, and has implications for assessing seismic hazards in tectonically active regions. Crystallographic preferred orientations can modify the rock such that its physical properties are anisotropic, that is, the properties have different values in different directions. Anisotropy of seismic wave velocity can affect the interpretation of seismic data of a region, and thus affect the evaluation of seismic hazards. The evolution of crystallographic preferred orientation patterns is important for faults with long histories of movement (i.e., the San Andreas fault). Also, as deeper rocks are brought to the surface, the conditions of deformation change- namely the rocks are cooler (i.e., the Alpine fault in New Zealand). In the mineral quartz, this cooling should lead to the operation of different slip systems, and possible strengthening of the crust, again affecting the seismic properties of the crust.