念青唐古拉山西缘拉布普韧性剪切带的厘定及其地质意义

摘要

通过野外地质调查和室内显微构造分析, 在念青唐古拉山西缘拉布普乡一带厘定出一条走向NEE, 倾向 NNW, 倾角 30° ～ 55°的左行滑覆型韧性剪切带.该韧性剪切带由若干条强变形带和其间的弱变形域组成, 呈平行带状展布, 出露长约 30 km, 宽约 2 km.强变形带内糜棱岩系列、糜棱面理、拉伸线理、书斜构造、S - C 组构及旋转碎斑系等构造发育.卷入该剪切带的二长花岗岩的 LA - ICP - MS 锆石 U - Pb年龄为 13. 096 ± 0. 072 Ma, 该年龄代表了念青唐古拉山西缘二长花岗岩体的结晶年龄, 同时限定了韧性剪切作用时代的下限.基于韧性剪切带宏观、微观构造特征及锆石 U - Pb 年代学研究, 结合区域资料, 认为拉布普韧性剪切带是念青唐古拉山北剪切带西段的构造形迹, 形成于中新世之后, 是晚新生代青藏高原伸展构造的产物.拉布普韧性剪切带的厘定为念青唐古拉山地区晚新生代以来构造演化及高原隆升提供了基础资料.%Based on the field geological investigation and microstructural observation,a NEE-striking sinistral detached ductile shear zone was determined in the Labupu area of western margin of Nyainqentanglha range, which dips NNW wards with angles of 30° - 55°. The Labupu ductile shear zone,about 30 km in length and 2 km in width,consists of several strong deformational zones and weak deformational domains. There occur many typical macroscopic structures and microstructures occured,such as mylonite series,foliation,stretching lineation, S - C fabrics,rotated porphyroclast system and domino structure in the strong deformational zone. The LAICP- MS zircon U - Pb age of the monzonitic granite involved in the shear zone is 13. 096 ± 0. 072 Ma,which represents the crystallization age of the monzonitic granite in the western margin of the Nyainqentanglha range. It also indicates that the shear deformation occurred after that. The macroscopic and microcosmic structures of the ductile shear zone,zircon U - Pb chronology,as well as regional geological data,suggest that it is a structural feature of the western NNS. The shear zone was created by extensional tectonics of Tibet Plateau in the Late Cenozoic, which was formed after Miocene. Thus,the determination of the Labupu ductile shear zone provides constraints on the Late Cenozoic tectonic evolution and Plateau uplift of the Nyainqentanglha area.