秦岭商丹缝合带俯冲期构造变形的精细解析

The Qinling orogenic belt is the collision zone of the Yangtze Plate and the North China Plate. The Shangdan suture zone, as the boundary between of the South and North Qinling, is one of the best places to study the formation, evolution, dynamics of the continental orogenic belt and the deformation of the continental margin. Under the guide of the plate tectonics and the continental dynamics, the detailed structural analysis of the Shangdan suture zone during the subduction will be carried out. The Liuling group and fore-arc sedimentary unit with typical characteristics of deformation in the south margin of the Shangdan suture zone are taken as the starting point. Various structural elements such as foliations, lineations and fold hinges are measured and analyzed statistically, use method of structural analysis to identify deformations during the subduction. Then the three dimensional geometry features and kinematics characteristics of deformations will be fully studied. Kinematic vorticity, finite strain analysis and deformation partitioning are used to calculate the convergence factors such as the direction of plate motion and subduction angle. According to the correlation of geological events, the ages of subduction and collision between the South and North Qinling are constrained. The relationship between the plate convergence and the deformation of continental margin is discussed. This project is significant to deepen the tectono-physical process of orogeny, explore the dynamics mechanism of continental accretion and preservation, enrich the research content and method of deformation of continental margins and push for new progress of continental dynamics.

秦岭造山带是扬子板块和华北板块的碰撞拼合带。商丹缝合带作为南、北秦岭的分界线，是研究大陆造山带的形成、演化、动力学以及大陆边缘变形的绝佳场所。本项目以板块构造学和大陆动力学探讨为指导，开展商丹缝合带俯冲期构造变形的精细研究。以商丹缝合带南侧具有特征构造变形的刘岭群及弧前沉积体作为切入点，大量统计变形地质体的面理、线理等各种构造要素、利用构造解析方法正确识别出俯冲期的构造变形，查明构造变形的三维几何学、运动学特征；利用运动学涡度分析、有限应变测量、变形分解等方法，量化南秦岭构造带俯冲方向、角度等汇聚因子；根据地质事件的相关性，利用多种年代学测试手段，约束南、北秦岭俯冲、碰撞所发生的时代；探讨板块汇聚因子与大陆边缘变形作用细节之间的关系。该项目对于深化造山作用的构造物理过程，探索大陆增生和保存的动力学机制，丰富大陆边缘变形研究的内容和方法、以及推动大陆动力学的进展具有重要意义。

秦岭造山带是扬子板块和华北板块的碰撞拼合带。商丹缝合带作为南、北秦岭的分界线， 是研究大陆造山带的形成、演化、动力学以及大陆边缘变形的绝佳场所。本项目以板块构造学 和大陆动力学理论为指导，选取商丹断裂带及其南侧的弧前沉积体为研究对象，开展商丹缝合带俯冲期构造变形的精细研究。我们识别出了商丹洋俯冲期及南北秦岭碰撞期的构造变形记录，并对两期构造变形的几何学、运动学、动力学和年代学进行了较为详细的研究。结果商丹洋的俯冲方向、角度分别为34°和49°，俯冲至少持续到早石炭世。俯冲期构造变形表现为轴面北倾南倒的同斜紧闭褶皱和由北向南的逆冲剪切，碰撞期变形表现为商丹左行挤压走滑韧性剪切带的发育。作为俯冲带上盘的武关杂岩和龟山杂岩，均有弧前沉积和不同时代的岛弧相关的火山岩混杂构成，沉积时代下限约350Ma，变质时代为320Ma，变质温压条件为T=560-632℃，P=0.59-0.76GPa，属角闪岩相变质。上述结果深化造山作用的构造物理过程，探索大陆增生和保存的动力学机制，丰富大陆边缘变形研究的内容和方法、以及推动大陆动力学的进展具有重要意义。