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在柴北缘锡铁山地区元古宇达肯大坂群与奥陶系滩涧山群之间发育一条呈NW向展布的基底韧性剪切带。本文对该韧性剪切带中的宏观构造(鞘褶皱、不对称褶皱、塑性流变组构、S-C组构、旋转碎斑系、构造透镜体、粘滞型石香肠构造)和糜棱岩微观构造(云母鱼构造、压力影构造、动态重结晶、雪球状旋转构造、波状消光和云母扭折)特征作了详细的研究。对锡铁山基底韧性剪切带中花岗质糜棱岩进行白云母Ar-Ar同位素测年,获得坪年龄为398±4 Ma,等时线年龄为399±4 Ma,二者基本一致,代表了锡铁山基底韧性剪切带的形成时间。综合上述特征判断,锡铁山韧性剪切带是一条由元古宇达肯大坂群向SW斜向逆冲所形成的右行逆冲韧性剪切带,该韧性剪切带与早古生代柴达木地块向NE斜向俯冲碰撞造山作用有关,并可能导致了超高压变质体折返到浅部地壳层次。同样,该韧性剪切带的存在,也对锡铁山铅锌矿起到了十分重要的后期构造控制作用。
A NW ductile shear zone developed in the NW direction was developed between the Proterozoic Dakar-Daban Group and the Ordovician Tanjian Shan Group in the Xizanshan area of northern Qaidam Basin. In this paper, the macrostructure (sheath fold, asymmetric fold, plastic rheological structure, SC structure, rotational crush, tectonic lens, viscous sausage structure) and mylonite microscopic Structure (mica structure, pressure shadow structure, dynamic recrystallization, snowball rotation structure, wavy extinction and mica kinks) were studied in detail. The Ar-Ar isotope dating of muscovite from the granitic mylonites in the Xishishan basement ductile shear zone shows a plateau age of 398 ± 4 Ma and an isochron age of 399 ± 4 Ma, It represents the formation time of the Xisha Tieshan basement ductile shear zone. Judging from the above characteristics, the Xishishan ductile shear zone is a right-hand thrust ductile shear zone formed by the diagonal thrusting of the Proterozoic Dakken-Osaka group SW. This ductile shear zone is similar to that of the Early Paleozoic Qaidam The block is related to the oblique subduction collision orogeny of the NE and may lead to the reversion of the UHP metamorphic body to the shallow crustal level. Similarly, the existence of this ductile shear zone also plays a very important role in post-tectonic control of the Xieshan lead-zinc mine.