桂北地区三门韧性剪切带的厘定及其构造意义

通过野外地质调查、室内显微组构分析和磁组构测量，在桂北三门地区厘定出一条大型韧性剪切带；并利用热液锆石U-Pb定年约束其变形时代.三门韧性剪切带发育密集的透入性片理、旋转碎斑系、拉伸线理、眼球构造、书斜构造、A型褶皱、波状消光、机械双晶、核幔构造和S-C组构等宏观和微观韧性变形特征.磁各向异性度（P值）显示其走向呈NNE向，倾向呈NWW向.运动学指向显示早期具有左旋逆冲剪切，晚期具有右旋正滑剪切的运动学性质.磁化率椭球体扁率（E值）显示岩石变形以压扁型应变为主，暗示运动学方向以左旋逆冲剪切为主.镁铁质糜棱岩的热液锆石U-Pb定年结果为441±2 Ma，代表三门韧性剪切带的变形时代.在磁组构、运动学和年代学研究的基础上，结合区域地质资料，认为该韧性剪切带是华南加里东期华夏陆块由SE向NW逆冲到扬子陆块受阻后反冲作用的产物.这一认识揭示了扬子陆块和华夏陆块碰撞拼合的方式和时代，为深化华南加里东构造运动的认识提供了新的资料. 

Discovery of Sanmen Ductile Shear Zone in North Guangxi and Its Tectonic Significances

Based on the field geological investigation, microstructural observation and magnetic fabric of tectonites, it recognized a large ductile shear zone in Sanmen area of North Guangxi, also defined the deformation age of Sanmen ductile shear zone by hydrothermal zircon U-Pb dating. The ductile shear zone has typical macroscopic and microstructural characteristics of mylonite series, such as penetrating schistosity, rotational porphyroclast systems, stretching lineation, eyeball structures, domino structures, A-type fold, wavy extinction, deformation twins, core and mantle textures and S-C fabric. Anisotropy of magnetic susceptibility (P values) shows Sanmen ductile shear zone trending in NNE and inclination of NWW. Kinematics orientation research shows that the Sanmen ductile shear zone has left-lateral thrust shear in the early stage and right-lateral normal slip shear in the late stage, magnetic susceptibility ellipsoid (E values) indicates that the rock deformation in Sanmen ductile shear zone is mainly flattened strain, suggesting that its kinematic direction is mainly left-lateral thrust shear. The hydrothermal zircon U-Pb dating result of mafic mylonite is 441±2 Ma, which represents the deformation age of Sanmen ductile shear zone. Based on the study of magnetic fabric, kinematics and tectonic chronology of Sanmen ductile shear zone, combined with regional geological data, it is considered that Sanmen ductile shear zone is the product of the recoil of the Caledonian Cathaysian block in South China from SE to NW to the Yangtze block. The discovery of the Sanmen ductile shear zone reveals the way and age of collision of Yangtze and Cathaysian blocks, and deepens the understanding of Caledonian tectonic evolution of the South China.