西秦岭弧形逆冲推覆构造变形特征及其形成的动力学机制

Mesozoic-Cenozoic intracontinental tectonic deformation mechanisms, processes and dynamics are one of the core issues of Continental Dynamics. The west Qinling is located in the northeastern margin of the Tibetan Plateau, north to the Qilian orogenic belt, south to the Songpan Ganzi terrane, east to the Kunlun orogenic belt, which is a key area of combination and structural transformation of a number of orogenic belts. A series of arcuate thrust nappe structure toward to the south in the west Qinling, are a commendable carrier and laboratory about study of the process of intracontinental tectonic deformation details, the dynamic mechanism of the west qinling arcuate structure and the structure transformation relationship between the west qinling and adjacent tectonic units. This study choice in the west qinling arcuate thrust nappe structure as the breakthrough point, based on the research of the field geological in the west qinling mountain and adjacent regions, through the detailed structure analysis, distinguishing different structural deformation Style and characteristics and stack with each other transformation relationship, to determine the structural deformation sequence in west qinling area. Use of the mutual intercept relations between the geological body and structural deformation and method of structural thermochronology, this project will establishes geochronology framework of structural deformation in the west qinling area. Meanwhile, Combined with adjacent geologic body uplift and tectonic evolution relationship, this project will explain the dynamic mechanism of arcuate structure, and then explore the west Qinling Mesozoic tectonic evolution and geodynamic setting.

中、新生代陆内构造变形机制、过程及其动力学是大陆动力学的核心问题之一，西秦岭位于青藏高原东北缘，北接祁连造山带、南连松潘甘孜地体，西邻昆仑造山带，是多个造山带和地体结合和构造转化的关键部位。西秦岭内部一系列近东西走向的向南弧形突出的弧形逆冲推覆构造，是研究陆内构造变形细节、西秦岭弧形构造形成机制以及西秦岭与相邻构造单元相互构造转化关系等大陆动力学问题的良好载体和实验室。本研究选择西秦岭弧形逆冲推覆构造为切入点，在西秦岭及邻区野外地质调研的基础上，通过详细的构造解析，筛分不同期次构造变形样式、特征及其相互叠加改造关系，厘定西秦岭地区构造变形序列；利用地质体与构造变形的相互截切关系以及构造热年代学方法，建立西秦岭构造变形的年代学格架；结合西秦岭弧形逆冲推覆构造相邻地质体的隆升及构造演化关系，解释西秦岭弧形逆冲推覆构造形成的动力学机制；进而探讨西秦岭中生代构造演化过程及其动力学背景。

西秦岭位于青藏高原东北缘，北接祁连造山带、南连松潘-甘孜地体和碧口地块，西邻昆仑造山带，是多个造山带和构造转化的关键部位。西秦岭近东西走向的向南弧形突出的构造带，是研究陆内构造变形、西秦岭弧形构造形成机制的良好载体和实验室。本研究选择西秦岭弧形构造为切入点，在野外构造解析的基础上，筛分不同期次构造变形样式、特征及其相互叠加改造关系，厘定西秦岭地区构造变形序列；利用地质体与构造变形的相互截切关系以及构造热年代学方法，建立西秦岭构造变形的年代学格架；结合西秦岭及相邻地质体的隆升及构造演化关系，解释西秦岭弧形构造形成的动力学机制；进而探讨西秦岭中生代构造演化过程及其动力学背景。本次研究，获得了西秦岭构造变形的几何学和运动学特征，西秦岭由北向南依次发育岷县-成县、武都-舟曲和康县-文县三条弧形构造带，平面上向南弧形突出。弧形构造东翼以左行走滑为主，弧顶及西翼以斜向西南逆冲为主。西秦岭经历了四期构造变形，第一期为南北向的逆冲断裂和前侏罗纪褶皱变形，形成于晚三叠纪-早侏罗纪；第二期为南北向伸展形成了西秦岭内部侏罗纪断陷盆地；第三期为北东东-南西西向挤压形成的弧形构造带，形成于早白垩纪-古近纪；第四期为青藏高原隆升向东北挤出对西秦岭的远程效应引起的在西秦岭西缘北东向的多和茂右行走滑断裂，形成于新近纪晚期。西秦岭地区经历了晚三叠纪-早侏罗纪的快速隆升过程，中侏罗-早白垩纪缓慢隆升过程和在晚白垩纪-古近纪快速隆升降温过程。岷县-成县-太白弧形构造带向东延伸，切过秦岭造山带，表现为倾向北的斜向西北伸展的韧性剪切变形，形成于早白垩纪晚期（114 ±1.2 Ma）。在白垩纪-古近纪北东-南西向挤压应力下，由于受到南侧不同能干性的松潘-甘孜地体、碧口地块的阻隔，西秦岭东西差异性变形最终形成一系列向南突出的弧形构造带。