Abstract We use microstructural, electron backscatter diffraction (EBSD), and crystal vorticity axis (CVA) analyses to evaluate the effects of quartz Dauphine twinning on strain localization. We compare a granodiorite mylonite and a tonalite mylonite from the Grebe Shear Zone, a mid-crustal transpressional shear zone in Fiordland, New Zealand. EBSD analysis reveals identical quartz grain boundary migration dynamic recrystallization microstructures in both samples, with abundant Dauphine twinning only in the granodiorite mylonite. Bulk CVA patterns further distinguish the untwinned and Dauphine-twinned samples, indicating a transition from simple shear-to pure shear-dominated transpression, respectively. The quartz CVA pattern from the Dauphine-twinned sample indicates that twinned and untwinned grains record a transition from simple shear-to pure shear-dominated deformation, respectively. Pole figures of the Dauphine-twinned sample reveal high-temperature slip systems in the untwinned and Dauphine-twinned grains. We conclude that Dauphine twinning formed early in transpression, and rendered the twinned grains less deformable relative to the untwinned grains over time. The effectiveness of Dauphine twinning in localizing strain is therefore strongly influenced by its timing relative to the evolving shear zone kinematic deformation geometry.

中文翻译：

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石英 Dauphiné 孪晶对中地壳剪切带应变局部化的影响

摘要 我们使用微观结构、电子背散射衍射 (EBSD) 和晶体涡旋轴 (CVA) 分析来评估石英 Dauphine 孪晶对应变局部化的影响。我们比较了来自新西兰峡湾中地壳挤压剪切带 Grebe 剪切带的花岗闪长岩糜棱岩和灰闪长岩糜棱岩。EBSD 分析揭示了两个样品中相同的石英晶界迁移动态再结晶微观结构，仅在花岗闪长岩糜棱岩中具有丰富的 Dauphine 孪晶。Bulk CVA 模式进一步区分了非孪晶和 Dauphine 孪晶样品，分别表明从简单的剪切主导向纯剪切主导的压缩的转变。来自 Dauphine 孪晶样品的石英 CVA 图案表明孪晶和非孪晶晶粒分别记录了从简单剪切到纯剪切主导变形的转变。Dauphine 孪晶样品的极图揭示了非孪晶和 Dauphine 孪晶晶粒中的高温滑移系统。我们得出结论，多芬孪晶在受压早期形成，随着时间的推移，孪晶晶粒相对于非孪晶晶粒的变形较小。因此，Dauphine 孪晶在局部应变方面的有效性受到其相对于不断变化的剪切区运动变形几何形状的时间的强烈影响。我们得出结论，多芬孪晶在受压早期形成，随着时间的推移，相对于非孪晶晶粒，孪晶晶粒的变形较小。因此，Dauphine 孪晶在局部应变方面的有效性受到其相对于不断变化的剪切区运动变形几何形状的时间的强烈影响。我们得出结论，多芬孪晶在受压早期形成，随着时间的推移，相对于非孪晶晶粒，孪晶晶粒的变形较小。因此，Dauphine 孪晶在局部应变方面的有效性受到其相对于不断变化的剪切区运动变形几何形状的时间的强烈影响。