Abstract Crustal-scale continental strike-slip fault systems are typically thought to be thermally segregated into an upper seismogenic expression and a lower zone of ductile deformation likely extending into the lower crust. The ability of the lower crust to sustain stress is fundamental to understanding the mechanical behavior of the lithosphere, yet significant debate exists regarding the strength of the ductile crust. The Cora Lake shear zone in the western Churchill Province of the Canadian Shield is a 4–7 km wide zone of granulite-to upper amphibolite-facies mylonite which hosts synkinematic pseudotachylyte, suggesting a locally strong lower crust. Kilometer-scale mapping suggests that the shear zone localized at a major lithological and terrane boundary, with the pseudotachylyte network centered within the ca. 1 km-wide more intensely deformed, finer-grained ultramylonitic core. In this contribution, we use optical petrography and electron-backscatter diffraction to describe microstructure across a transect of the Cora Lake shear zone. By combining these observations with grain size piezometry, experimental flow laws, and regional pressure-temperature paths, we conclude that stress amplification from a relatively common type of km-scale lithological heterogeneity and cooling history is the most reasonable explanation for the deep crustal pseudotachylyte.

中文翻译：

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加拿大西部地盾含假速凝液深地壳剪切带的流变演化

摘要 地壳尺度的大陆走滑断层系统通常被认为是热分离成上地震带和可能延伸到下地壳的韧性变形下带。下地壳承受应力的能力是理解岩石圈力学行为的基础，但关于韧性地壳的强度仍存在重大争论。加拿大地盾丘吉尔省西部的 Cora Lake 剪切带是一个 4-7 公里宽的麻粒岩到上部角闪岩相糜棱岩带，其中含有同运动假速凝岩，表明局部强的下地壳。公里尺度映射表明剪切带位于主要的岩性和地体边界处，pseudotachylyte 网络集中在约。1 公里宽的变形更强烈、粒度更细的超糜棱岩核。在这篇文章中，我们使用光学岩相学和电子背散射衍射来描述 Cora Lake 剪切带横断面的微观结构。通过将这些观察结果与晶粒尺寸测压法、实验流动规律和区域压力-温度路径相结合，我们得出结论，相对常见的千米级岩性非均质性和冷却历史类型的应力放大是对深部地壳假速凝岩最合理的解释。