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Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru

机译：秘鲁Cortillera Blanca Shear区的Syn-Grentgent延伸期间的变形条件

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Strain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ～200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment. Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we evaluate the deformation conditions and mechanisms in quartz and feldspar across the CBSZ. Deformation temperatures derived from asymmetric strain-induced myrmekite in a subset of tectonite samples are 410 ± 30 to 470 ± 36 °C, consistent with TitaniQ temperatures of 450 ± 60 to 490 ± 33 °C and temperatures 400 °C estimated from microstructural criteria. Brittle fabrics overprint ductile fabrics within ～150 m of the detachment that indicate that deformation continued to lower-temperature (～280–400 °C) and/or higher-strain-rate conditions prior to the onset of pervasive brittle deformation. Initial deformation occurred via high-temperature fracturing and dissolution-precipitation in feldspar. Continued subsolidus deformation resulted in either layering of mylonites into monophase quartz and fine-grained polyphase domains oriented subparallel to macroscopic foliation or the interconnection of recrystallized quartz networks oriented obliquely to macroscopic foliation. The transition to quartz-controlled rheology occurred at temperatures near ～500 °C and at a differential stress of ～16.5 MPa. Deformation within the CBSZ occurred predominantly above ～400 °C and at stresses up to ～71.4 MPa prior to the onset of brittle deformation.
机译：脆性延性过渡的应变定位是适应中地壳中的构造运动的基本过程。 Teactonical上活跃的Cordillera Blanca剪切区（CBSZ）是一个〜200公里长的正常感剪切区，位于秘鲁和秘鲁andes中离散的Syn-Convergent Intentialional Fauly的脚壁内，是一个优秀的现场实验室，用于探索这种过渡。场和微观观测表明一致的自上而下至西南剪切感和一系列的构造序列通过米隆矿石通过米隆矿石，最终沿着脱离的断层斑块。使用微观结构分析，双链孔和Ti-in-in-Quartz（TITANIQ）温度，重结晶的石英古倾象测量和石英晶体优选取向的分析，我们评估了跨越CBSZ的石英和长石中的变形条件和机制。源自不对称菌株诱导的细胞石矿样品的菌诱导的Myrmekite的变形温度为410±30至470±36°C，与450±60至490±33°C和温度＆gt的泰坦尼Q温度一致。400°C从微观结构估计标准。脆性织物套印型延性织物在〜150米内，表明在普遍性脆性变形之前，变形持续低温（〜280-400℃）和/或更高的应变率条件。通过高温压裂和长石溶解沉淀发生初始变形。持续的子葡萄酒变形导致髓鞘分层为单相石英和细粒化多相结构域，以便以宏观叶或倾斜地定向的重结晶的石英网络倾斜，呈宏观叶片。在〜500℃附近的温度和差压〜16.5MPa的差分应力下发生到石英控制流变学的过渡。 CBSZ内的变形主要在〜400°C以上发生，在脆性变形开始之前在〜400°C的胁迫下高达约71.4MPa。

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