西藏南羌塘晚三叠世陆缘俯冲增生造山带的褶皱-冲断与增生杂岩双层结构厘定  

Fold-thrust belt of South Qiangtang,Tibet and the double-layer structure of the South Qiangtang accretionary complex

作　　者：李典 王根厚[2] 刘正勇 李鹏胜 冯翼鹏 唐宇 李超[3] 李阳[1] LI Dian;WANG Genhou;LIU Zhengyong;LI Pengsheng;FENG Yipeng;TANG Yu;LI Chao;LI Yang(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]中国地质科学院地质研究所,北京100037

出　　处：《地学前缘》2022年第4期231-248,共18页Earth Science Frontiers

基　　金：国家自然科学基金项目(42172259)。

摘　　要：增生型造山带形成于活动大陆边缘,以宽阔且延伸稳定的增生杂岩为代表,在大洋板块向大陆板块发生缓慢而复杂的俯冲、碰撞过程中,大洋板块、火山岛弧、海山、大陆碎块等沿逐渐后退的海沟拼贴,仰冲板块前端发生刮削作用、底垫作用和构造剥蚀等作用,使得洋壳物质在海沟内壁增生,具体表现为增生杂岩的形成、垂向和侧向的生长,最终实现陆壳的横向生长。陆陆碰撞期间,加入俯冲通道的被动陆缘也将遭受类似的构造作用,从而形成规模较大的陆缘增生杂岩。因此,造山带增生杂岩的物质组成与结构、形成机制和演化过程对解剖洋陆转换过程中的复杂地球动力学过程具有极为关键的作用。西藏南羌塘增生杂岩是近年来通过走廊性地质填图以及多学科交叉工作得到的研究认识。然而,该增生杂岩的物质组成和结构等关键内容还未得到系统的研究,严重阻碍了对其形成机制和演化过程的理解。因此,本文以时空演化为主线,解剖杂岩物质组成和结构,结合俯冲期和同碰撞期大地构造单元,洞察南羌塘增生杂岩的形成演化过程。本次研究显示:(1)南羌塘增生杂岩具有俯冲杂岩在下、褶皱-冲断带在上的双层结构,二者间为大规模的拆离断层系统;(2)俯冲杂岩内不只含有洋板块地层单元,还含有大量的南羌塘被动陆缘物质;(3)褶皱-冲断带虽主要由被动陆缘物质变形改造而来,也含有属于洋板块地层系统的海山和洋内岛弧等物质。结合同俯冲期弧前盆地和楔顶盆地、同碰撞期晚三叠世岩浆的时空分布,高压变质岩的形成与折返时限,南羌塘增生杂岩内的双层结构应主要是陆陆碰撞过程中被动陆缘俯冲的结果,少量形成于大洋俯冲期间的俯冲反向过程中。本文提出的陆缘俯冲导致南羌塘增生杂岩双层结构的研究认识,对理解南羌塘地壳结构、中生代盆地基底形成演�The accretionary orogens formed in the active continental margin are represented by extensive and stable accretionary complexes.During the slow and complex oceanic subduction and collision,oceanic plate,intra-oceanic arc,seamount,and continental fragments are accreted onto the retreating oceanic trench through off-scrapping,underplating,and tectonic erosion at the leading edge of the overriding plate.Continental crust thus grows laterally as significant accretion of oceanic crusts at the inner wall of the trench.Via a similar tectonic process during the continental collision passive margin are incorporated into the subduction channel,where a crustal accretionary wedge similar to but much larger than oceanic accretionary prisms are expected to form.Therefore the composition,structure,and evolution of accretionary complex in orogenic belt play a key role in understanding the complex geodynamic process during the ocean to continent transformation.The accretionary complex of South Qiangtang,Tibet was recently recognized through corridor geological mapping and multidisciplinary research.However,the composition and structure of the complex are not well studied,which greatly hinders the understanding of its formation mechanism and evolution.Therefore in this paper,focusing on its spatiotemporal evolution,we researched in detail the composition and structure of the South Qiangtang accretionary complex to understand its formation and evolutionary processes.We show that(1)the South Qiangtang accretionary complex has a double-layer structure,with the subduction complex at the bottom,the fold-thrust belt at the top,and a regional detachment fault system separating the upper and lower layers.(2)The subduction complex contains not only the ocean plate stratigraphy but also a large part of the South Qiangtang passive margin.(3)Although the fold-thrust belt is mainly deformed passive continental margin,it also contains ocean plate stratigraphic units like seamounts and intra-oceanic arcs.Based on the spatiotemporal distribution

关 键 词：南羌塘增生杂岩 陆缘俯冲 双层结构 

分 类 号：P542.2[天文地球—构造地质学] P548[天文地球—地质学]