东秦岭鮸鱼咀韧性剪切带构造变形特征及其年代学约束  

Deformational Characteristics and Geochronological Constraints on the Mianyuzui Ductile Shear Zone,Eastern Qinling Area

作　　者：陈龙耀[1,2] 李勇 刘晓春 曲玮[1,2] 胡娟 CHEN Long-yao;LI Yong;LIU Xiao-chun;QU Wei;HU Juan(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081;Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Natural Resources,Beijing 100081;Department of Natural Resources of Qinghai Province,Xining,Qinghai 810001)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081 [3]青海省自然资源厅,青海西宁810001

出　　处：《地球学报》2021年第1期32-42,I0006-I0007,共13页Acta Geoscientica Sinica

基　　金：国家自然科学基金项目(编号:41872059,41472064);国家重点基础研究发展计划(973计划)专题(编号:2015CB856104)联合资助。

摘　　要：东秦岭鮸鱼咀韧性剪切带是秦岭造山带晚古生代构造带武关杂岩和刘岭群的分界线,其变形作用的研究对揭示秦岭造山带晚古生代的构造演化具有重要意义。本文对这条剪切带进行了详细的几何学、运动学、锆石U-Pb和白云母40Ar/39Ar年代学研究。几何学和运动学指示鮸鱼咀韧性剪切带经历了两期主要的构造变形:早期由北向南的逆冲推覆变形和晚期左行走滑剪切变形。锆石U-Pb年代学研究表明构成剪切带主体的长英质糜棱岩中碎屑锆石主要的峰值年龄为448 Ma,最年轻的峰值年龄为390 Ma,其碎屑物质来源为北秦岭构造带,因此其原岩应该为一套沉积岩。眼球状白云母40Ar/39Ar同位素测年获得的坪年龄为(263±2)Ma。结合前人的变质变形年代学数据,认为早期的逆冲推覆与石炭纪大洋俯冲有关,晚期左行走滑是秦岭造山带晚二叠世"软碰撞"的构造响应。The Mianyuzui ductile shear zone in eastern Qinling area forms the boundary between the Wuguan Complex and the Liuling Group and represents the Late Paleozoic tectonic belt of the Qinling orogenic belt.The study of deformation of the Mianyuzui ductile shear zone is significant for detecting the Late Paleozoic tectonic evolutionary process of the Qinling orogenic belt.This paper reports geometry,kinematic indicators,U-Pb zircon dating results,and 40Ar/39Ar muscovite dating results of the Mianyuzui ductile shear zone.Geometric and kinematic evidence indicates that the Mianyuzui ductile shear zone underwent two stages of deformation:the early thrust from north to south and the late sinistral strike-slip.U-Pb zircon analyses reveal that detrital zircons from the felsic mylonites in the ductile shear have an age spectrum with a major peak at 448 Ma and a youngest peak at 390 Ma,which suggests that sediments were probably derived from the North Qinling tectonic belt.The flaky-type muscovites from the Mianyuzui ductile shear belt yielded a 40Ar/39Ar plateau age of(263±2)Ma.Combined with previously published dating data of metamorphic and deformational events,the authors infer that the early thrust from north to south might have been related to the Carboniferous subduction of oceanic crust.The late sinistral strike-slip shearing can be interpreted as a tectonic response caused by the"soft collision"between the Sino-Korean and Yangtze cratons during the Late Permain.

关 键 词：LA-MC-ICPMS 锆石U-PB年龄 白云母40Ar/39Ar年龄 构造变形 韧性剪切带 鮸鱼咀 东秦岭 

分 类 号：P548[天文地球—构造地质学] P597.3[天文地球—地质学]