Abstract This study investigates the grain-scale mechanisms that facilitated strain localization in the lower crust within the East Athabasca Mylonite Triangle of northern Saskatchewan, Canada. There, two distinct lithotectonic units, the Upper Deck and Northwestern Domain, are juxtaposed across a km-scale shear zone that has been previously interpreted to record thrust and/or normal-sense displacement. Our study reports new quartz c-axis opening angle, Ti-in-biotite and Ti-in-quartz geothermometry and amphibole-plagioclase geothermobarometry within syn-kinematic phases indicating that both units were deformed and metamorphosed at upper amphibolite to granulite facies (~725 °C and ~0.8 GPa). While sharing similar conditions, the dominant mechanisms of deformation across the two units are strongly linked to modal proportion of syn-kinematic hydrated mineral phases. Detailed microstructural and crystallographic preferred orientation (CPO) analyses reveals that specimens poor in hydrated minerals ( 10%) pressure solution and (re)precipitation processes enhanced phase mixing and promoted grain boundary sliding resulting in weakly developed or absent quartz CPO. These results indicate a strong mineralogical and fluid control on deformation and, therefore, which strain softening process (es) may dominate in lower crustal shear zones.

中文翻译：

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含水矿物含量对长英质麻粒岩竞争应变定位机制的影响

摘要 本研究调查了在加拿大萨斯喀彻温省北部东阿萨巴斯卡糜棱岩三角区下地壳中促进应变定位的晶粒尺度机制。在那里，两个不同的岩石构造单元，Upper Deck 和 Northwestern Domain，并列在一个公里尺度的剪切带上，该剪切带以前被解释为记录推力和/或正常位移。我们的研究报告了新的石英 c 轴张角、黑云母中的钛和石英中的钛地热测量以及同运动相内的角闪石-斜长石地热测量，表明这两个单元在上部角闪岩到麻粒岩相（~725 °C 和 ~0.8 GPa）。在共享相似条件的同时，两个单元的主要变形机制与同运动水合矿物相的模态比例密切相关。详细的微观结构和晶体择优取向 (CPO) 分析表明，缺乏水合矿物 (10%) 压力溶液和（再）沉淀过程的样品会增强相混合并促进晶界滑动，从而导致石英 CPO 发育较弱或不存在。这些结果表明对变形有很强的矿物学和流体控制，因此，应变软化过程可能在下地壳剪切带中占主导地位。详细的微观结构和晶体择优取向 (CPO) 分析表明，缺乏水合矿物 (10%) 压力溶液和 (再) 沉淀过程的样品会增强相混合并促进晶界滑动，从而导致石英 CPO 发育较弱或不存在。这些结果表明对变形有很强的矿物学和流体控制，因此，应变软化过程可能在下地壳剪切带中占主导地位。详细的微观结构和晶体择优取向 (CPO) 分析表明，缺乏水合矿物 (10%) 压力溶液和（再）沉淀过程的样品会增强相混合并促进晶界滑动，从而导致石英 CPO 发育较弱或不存在。这些结果表明对变形有很强的矿物学和流体控制，因此，应变软化过程可能在下地壳剪切带中占主导地位。