摘要:
通过野外观察、室内显微构造分析和磁组构测量方法,在桂北四堡地区浅变质地层中厘定出一条NE30°走向,南东倾,倾角约40°的大型左旋斜冲韧性剪切带——四堡韧性剪切带;该韧性剪切带内发育糜棱岩系列、糜棱面理、拉伸线理、A 型褶皱、S-C 组构、亚颗粒、显微分层及石英条带等宏观和微观构造特征;磁各向异性度测量结果显示四堡韧性剪切带由一宽约4 km 的强应变带及边缘弱带组成,全带宽达10 km,长度超30 km;在对韧性剪切带运动学、构造年代学研究的基础上,结合区域地质资料,认为四堡韧性剪切带是华南加里东晚期华夏地块由南东向北西作低角度斜冲到扬子地块的产物。这一发现揭示了扬子地块与华夏地块碰撞拼合的方式,为深化华南构造演化提供了新资料。
Abstract:
Based on field geological investigation, microstructural observation and magnetic fabric of tectonites, the authors recognized a sinistral thrust ductile shear zone trending in NE30° direction in the Sibao area of northern Guangxi. The ductile shear zone has typical macroscopic and microstructural characteristics of mylonite series, mylonite foliation, stretching lineation, A type folds, S-C foliation, subparticles and ribbons of quartz. Anisotropy of magnetic susceptibility (AMS) indicates that the Sibao ductile shear belt which is 10km wide and more than 30 km long consists of a strong strain zone about 4 km in width and some weak strain zones. The kinematics characteristics of the shear zone as well as the tectonic chronological and regional geological data suggest that the Sibao ductile shear zone was formed by Caledonian Movement in the Late Ordovician. The discovery of the Sibao ductile shear zone plays a critical role in understanding the tectonic evolution of the South China Block.
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