勉略构造带构造变形过程及其地质意义  

Tectonic deformation processes of the Mianlue tectonic zone and its geological significance

作　　者：赵金祥 李玮[1] 康文彬 ZHAO Jinxiang;LI Wei;KANG Wenbin(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an,Shannxi 710069,China)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,陕西西安710069

出　　处：《地质学报》2021年第11期3220-3233,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41872218、41572179和41372204);地质学系科研团队项目和大陆动力学国家重点实验室联合资助的成果。

摘　　要：勉略构造带是印支期华北板块与扬子板块碰撞,并叠加后期陆内变形作用形成的复杂蛇绿构造混杂岩带,勉略构造带的形成演化对全面理解秦岭造山带构造演化具有非常重要的研究意义。本文以勉略构造带广泛发育的褶皱、断裂等构造现象为研究对象,通过详细的构造解析和古应力反演,揭示出勉略构造带经历三期构造变形:D_(2)期变形为NW—SE向挤压,以发育轴面直立的紧闭同斜褶皱和高角度逆断层为特征,形成于早—中三叠世华北与扬子两大块体碰撞阶段;D_(2)期变形为NE—SW向挤压,主要发育左行走滑剪切变形,叠加于早期构造形迹之上,构造带内普遍发育东西向近水平拉伸线理,局部发育倾竖褶皱,形成于晚三叠世—中侏罗世,该阶段秦岭造山带由早期的碰撞转为陆内变形,沿东西向断裂带发生大规模左行走滑;D_(2)期变形为N—S向挤压,在晚侏罗世—白垩纪多向汇聚构造体制下,勉略构造带受南北向挤压,形成一系列共轭剪切断裂,该期断裂切割前两期构造变形,区域上表现为北侧的大巴山、西秦岭向南逆冲推覆,扬子北缘沿米仓山一带向北楔入秦岭造山带,形成向南突出的大巴山弧形逆冲推覆构造带、西秦岭武都-舟曲弧形构造带和一系列北东、南西走向的共轭剪切断裂系。The Mianlue tectonic zone is located in the southern Qinling orogenic belt.It is a complex ophiolite mélange belt formed by an Indosinian collision between North China and Yangtze Plate,superimposed with late intracontinental deformation.It is of great value to understand the tectonic processes of the Qinling orogenic belt.In this paper,through detailed structural analysis and paleostress inversion,it is revealed that Mianlue tectonic zone experienced three stages of structural deformation:the D_(2)stage was NW—SE compression,characterized by tight syncline fold with vertical axial plane and high angle reverse fault,which were formed in the collision between North China and the Yangtze in Early—Middle Triassic.The D_(2)stage is NE—SW compression,mainly developed left strike-slip shear deformation,superimposed on the early deformation structure track.The nearly horizontal stretching lineation of E—W direction is generally developed in the structural belt,and locally developed vertical folds formed in the Late Triassic to Middle Jurassic.In this stage,the Qinling orogenic belt transformed from early collision to intracontinental deformation,and large-scale left strike-slip occurred along the E—S trending fault belt.The D_(2)stage is N—S compression.Under the multi-directional convergence structure system from Late Jurassic to Cretaceous,the Mianlue tectonic zone was compressed in the N—S direction,forming a series of conjugate shear faults,cutting the early deformation.The Dabashan Mountain and Western Qinling on the north side were thrust to the south,the northern margin of Yangtze Plate wedge into Qinling orogenic belt along the Micangshan area,forming a southward protruding Dabashan arc thrust nappe structural belt,Wudu-Zhouqu arc structural belt in the western Qinling,and a series of NE and SW trending conjugateshear faults.

关 键 词：古应力反演 陆内变形 构造演化 勉略构造带 秦岭造山带 

分 类 号：P542[天文地球—构造地质学]