安徽张八岭隆起东缘基底走滑韧性剪切带的发现及其构造意义  

Discovery of a basement strike-slip ductile shear zone on the eastern margin of the Zhangbaling uplift, Anhui, China, and its tectonic significance

作　　者：胡博[1] 张岳桥[1] 

机构地区：[1]南京大学地球科学系,江苏南京210093

出　　处：《地质通报》2007年第3期256-265,共10页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号40572120)资助。

摘　　要：张八岭隆起位于华南地块与华北地块碰撞拼接的构造转换部位,其西界为著名的郯庐断裂带,东缘属于扬子地块盖层前陆逆冲褶皱构造带。在张八岭隆起东缘来安地区基底变质岩中发现了一条宽达2.5km的走滑韧性剪切带,对其进行了详细的野外测量和岩石学、显微组构、变形运动学分析。结果显示,韧性剪切带由初糜棱岩带、糜棱岩带和超糜棱岩带组成;糜棱岩叶理近直立,叶理面上的拉伸线理向SW缓倾(倾伏角为10～30°);S-C组构和不对称旋转碎斑指示以左旋剪切为主。根据石英位错密度估算的差应力为65～75MPa。糜棱岩矿物成分和显微组构特征分析显示基底韧性剪切带的形成温度在250～400℃之间,形成深度为10～20km。该基底走滑剪切带的发现为张八岭地块的斜向走滑折返机制提供了重要的构造地质学制约。The Zhangbaling uplift is located in a tectonic transition zone（collision-amalgamation zone）between the North and South China blocks. It is bounded on the west by the famous Tanlu fault zone, and on its eastern side there occurs a foreland fold-and-thrust belt of the pre-Jurassic sedimentary cover of the Yangtze block. The authors found a 2.5 km wide strike-slip ductile shear zone in the metamorphic basement rocks in the Lai＇an area along the eastern side of the Zhangbaling uplift. Detailed field surveys and analyses of the lithology, microfabrics and deformation kinemics of this strike-slip shear zone have been conducted. The results show that the shear zone is composed of protomylonite, mylonite and ultramylonite; the foliations are nearly upright and the lineations on the foliations dip gently dipping to SW at plunge angles of 10-30°. S-C fabrics and asymmetric rotational augens in mylonite indicate sinistral shear and locally dextral shear. Based on the dislocation density measurements in matrix quartz, the differential stresses have been estimated at 65-75 MPa for this shear zone. Analysis of the mineral composition and microstructures of mylonite suggests that the basement ductile shear zone formed at temperatures of 250-400℃ and at depths equivalent to the transition zone（10-20 km deep）between the upper and lower crust.

关 键 词：安徽 张八岭隆起 基底韧性剪切带 糜棱岩 显微组构 构造挤出折返 

分 类 号：P542.3[天文地球—构造地质学]