In worldwide orogenic belts, crustal-scale ductile shear zones are important tectonic channels along which the orogenic root (i.e., high-grade metamorphic lower-crustal rocks) commonly experienced a relatively quick exhumation or uplift process. However, their tectonic nature and geodynamic processes are poorly constrained. In the Trans–North China orogen, the crustal-scale Zhujiafang ductile shear zone represents a major tectonic boundary separating the upper and lower crusts of the orogen. Its tectonic nature, structural features, and timing provide vital information into understanding this issue. Detailed field observations showed that the Zhujiafang ductile shear zone experienced polyphase deformation. Variable macro- and microscopic kinematic indicators are extensively preserved in the highly sheared tonalite-trondhjemite-granodiorite (TTG) and supracrustal rock assemblages and indicate an obvious dextral strike-slip and dip-slip sense of shear. Electron backscattered diffraction (EBSD) was utilized to further determine the crystallographic preferred orientation (CPO) of typical rock-forming minerals, including hornblende, quartz, and feldspar. EBSD results indicate that the hornblendes are characterized by (100) <001> and (110) <001> slip systems, whereas quartz grains are dominated by prism and prism slip systems, suggesting an approximate shear condition of 650–700 °C. This result is consistent with traditional thermobarometry pressure-temperature calculations implemented on the same mineral assemblages. Combined with previously reported metamorphic data in the Trans–North China orogen, we suggest that the Zhujiafang supracrustal rocks were initially buried down to ∼30 km depth, where high differential stress triggered the large-scale ductile shear between the upper and lower crusts. The high-grade lower-crustal rocks were consequently exhumed upwards along the shear zone, synchronous with extensive isothermal decompression metamorphism. The timing of peak collision-related crustal thickening was further constrained by the ca. 1930 Ma metamorphic zircon ages, whereas a subsequent exhumation event was manifested by ca. 1860 Ma syntectonic granitic veins and the available Ar-Ar ages of the region. The Zhujiafang ductile shear zone thus essentially record an integrated geodynamic process of initial collision, crustal thickening, and exhumation involved in formation of the Trans–North China orogen at 1.9–1.8 Ga.

中文翻译：

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衡山综合体朱家坊韧性剪切带的宏观和微观结构分析：华北-北半球造山带演化的构造性质和地球动力学意义

在世界范围的造山带中，地壳尺度的韧性剪切带是重要的构造通道，造山带根（即高级变质下地壳岩石）通常沿其相对较快的发掘或隆升过程。但是，它们的构造性质和地球动力学过程受到的约束较弱。在华北地区的造山带中，地壳尺度的朱家坊韧性剪切带代表了一个主要的构造边界，将造山带的上，下地壳分开。它的构造性质，结构特征和时间安排为了解这一问题提供了重要的信息。详细的现场观察表明，朱家坊韧性剪切带经历了多相变形。可变的宏观和微观运动学指标被广泛保存在高度剪切的斜长石-长白云母-闪长闪长岩（TTG）和壳上岩石组合中，并显示出明显的右旋走滑和倾滑剪切感。利用电子背散射衍射（EBSD）进一步确定典型的成岩矿物（包括角闪石，石英和长石）的晶体学优选取向（CPO）。EBSD结果表明，角质掺混料的特征是（100）<001>和（110）<001>滑移系统，而石英颗粒主要由棱镜和棱镜组成 利用电子背散射衍射（EBSD）进一步确定典型的成岩矿物（包括角闪石，石英和长石）的晶体学优选取向（CPO）。EBSD结果表明，角质掺混料的特征是（100）<001>和（110）<001>滑移系统，而石英颗粒主要由棱镜和棱镜组成 利用电子背散射衍射（EBSD）进一步确定典型的成岩矿物（包括角闪石，石英和长石）的晶体学优选取向（CPO）。EBSD结果表明，角质掺混料的特征是（100）<001>和（110）<001>滑移系统，而石英颗粒主要由棱镜和棱镜组成滑移系统，表明剪切条件约为650–700°C。该结果与对相同矿物组合进行的传统热压法压力-温度计算相一致。结合先前报道的华北—北半球造山带的变质资料，我们认为朱家房上地壳岩最初被埋藏到约30 km的深度，那里高的差应力触发了上地壳和下地壳之间的大规模延性剪切。因此，高品位的低地壳岩石沿着剪切带被向上挖掘，并伴随着广泛的等温减压变质作用。与峰值碰撞相关的地壳增厚的时间进一步受到了ca的限制。1930年Ma变质锆石年龄，而随后的掘尸事件由ca. 1860 Ma构造的花岗脉和该地区可用的Ar-Ar年龄。因此，朱家坊韧性剪切带记录了一个初始碰撞，地壳增厚和发掘活动的综合地球动力学过程，涉及到华北造山带在1.9-1.8 Ga的形成。