Abstract Cambrian quartzite along the western margin of the Blue Ridge near Front Royal, Virginia records significant penetrative strain under subgreenschist-facies conditions. Strain analyses of the quartzite indicate general flattening and octahedral shear strain values up to 1.25 (X:Z up to 5.7:1). Samples with X:Z as low as 1.5:1 have crystallographic preferred orientations that record a dominance of basal slip and patterns consistent with coaxial flattening. In most samples quartz has undergone minor amounts of dynamic recrystallization with mean grain sizes ~4–5 μm. Locally, the quartzite is brittlely deformed, and subgrains and recrystallized bulges are present along fractures and extinction bands. Fluid-inclusion planes and fluid inclusions along deformation lamellae are abundant, and quartz FTIR analyses yield average H:106Si values of 1100–3300, indicating fluid flow and high intragranular water content during deformation. Higher strain samples generally record lower water contents, which may indicate that fluids migrated to grain boundaries during deformation. Dissolution microstructures are rare in high strain samples, and we interpret most strain to have been accommodated by dislocation creep. Thermal modeling of zircon low-temperature thermochronology data coupled with quartz c-axis opening angle thermometry suggest deformation temperatures were likely ~250–280 °C. These deformation temperatures are lower than what is typically considered the brittle-plastic transition in quartz. We attribute localization of this high strain zone and dislocation creep at these temperatures to hydrolytic weakening and a relatively low strain rate estimated to be ~10−15 s−1.

中文翻译：

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弗吉尼亚蓝岭同轴剪切带的流变学：~250-280 C 湿石英岩位错蠕变

摘要 弗吉尼亚州 Front Royal 附近蓝岭西缘的寒武纪石英岩在亚绿片岩相条件下记录了显着的穿透应变。石英岩的应变分析表明一般扁平化和八面体剪切应变值高达 1.25（X:Z 高达 5.7:1）。X:Z 低至 1.5:1 的样品具有结晶优选取向，记录了基底滑移和与同轴扁平一致的图案的优势。在大多数样品中，石英经历了少量的动态再结晶，平均晶粒尺寸约为 4-5 微米。局部石英岩发生脆性变形，沿裂隙和消光带存在亚晶粒和再结晶凸起。流体包裹体平面和沿变形片层的流体包裹体丰富，石英 FTIR 分析产生平均 H：106Si 值为 1100-3300，表明变形过程中流体流动和高粒内含水量。较高应变的样品通常记录较低的含水量，这可能表明流体在变形过程中迁移到晶界。在高应变样品中，溶解微观结构很少见，我们认为大多数应变已被位错蠕变所适应。锆石低温热年代学数据的热建模结合石英 c 轴张角温度测量表明变形温度可能约为 250–280 °C。这些变形温度低于通常认为的石英脆塑性转变温度。我们将这种高应变区的局部化和在这些温度下的位错蠕变归因于水解弱化和相对较低的应变率，估计约为 10-15 s-1。