印度-欧亚正向与侧向碰撞构造的连接与转换

The diversity of the orogenic processes between the central region and the Eastern Syntaxis region of the Tibetan Plateau is due to the forward collision and the lateral collision between India and Eurasia respectively in these two regions. As the most representative collision structure that reflected the transition of the India-Eurasia collision processes, the India-Eurasia collision boundary fault had experienced distinguished structural transformation from the thrusting dominated activity in the forward collision region to the strike-slipping dominated activity in the lateral collision region. And the transformation process had been superposed by the activity of South Tibet Detachment System (STDS). This project will be focused on the connection style and transformation process of the India-Eurasia boundary fault in western area of the Eastern Syntaxis. The components and the framework of the India-Eurasia boundary fault and STDS will be detected through detailed field investigation, microscope observation of thin sections and the analysis of mineral composition. The deformation stages and the corresponding kinematics of the India-Eurasia boundary fault and STDS will be resolved by recognizing the deformation structures and textures both in the field scale and thin-section scale, and by analyzing the mineral lattice fabrics with the electron backscattered diffraction (EBSD). The active times of the India-Eurasia boundary fault and STDS will be determined from the micas/amphibole 40Ar-39Ar thermochronology and the zircon U-Pb geochronolgy of the syn-kinematic rocks from the fault zones. Based on the integration of the above analysis, the connection and the transformation of the India-Eurasia boundary fault between the forward and lateral collision regions will be figured out. And the internal correlation between the orogenic processes of the Tibetan Plateau in different regions will be further discussed.

青藏高原中部和东构造结地区造山过程的差异性与印度-欧亚在两地区分别发生正向与侧向碰撞有关。印度-欧亚碰撞边界断裂是最直接反映印度-欧亚碰撞转换过程的碰撞构造，显示了从正向碰撞地区以逆冲运动为主到侧向碰撞地区以走滑运动为主的构造转换，并在转换过程中叠加了藏南拆离系的活动。本项目聚焦于东构造结西侧印度-欧亚碰撞边界断裂的连接方式和转换过程，通过详细的野外调查、薄片观察和矿物成分分析，查明印度-欧亚碰撞边界断裂和藏南拆离系的物质组成和结构；借助露头和薄片尺度上构造要素和变形组构观测、EBSD矿物晶格组构分析，识别断裂带的变形期次和其对应的构造变形特征及运动学方向；选择同变形样品进行云母/角闪石40Ar-39Ar热年代学和锆石U-Pb年代学研究，限定断裂活动时代。综合上述研究，查明印度-欧亚碰撞构造在正向与侧向碰撞地区之间的连接与转换，探讨青藏高原造山过程在不同区域之间的内在联系。

印度-欧亚大陆碰撞在青藏高原中部和东构造结地区分别以正向碰撞和侧向碰撞为主，对正向与侧向碰撞构造之间连接方式和转换过程的研究，有助于对青藏高原不同造山过程之间内在联系机制的深入理解。雅鲁藏布缝合带（以下简称雅江缝合带）作为印度-欧亚碰撞边界，直接记录了碰撞变形过程。本项目以南迦巴瓦构造结西侧的碰撞构造转换地区为主要研究区，针对印度-欧亚碰撞边界断裂以及藏南拆离系物质结构、断裂构造变形特征和运动学方向、以及断裂活动时代进行综合研究。通过详细的野外调查和薄片观察、岩石成分分析、锆石年代学、40Ar-39Ar年代学等实验分析，取得了如下重要研究成果和进展：.（1）建立了印度-欧亚正向碰撞区新特提斯洋俯冲-增生过程：新特提斯洋初始俯冲时间不晚于早侏罗世，经历了白垩纪早期、晚白垩世两期主要的增生过程，形成雅江缝合带增生楔，构成印度-欧亚碰撞边界上盘。.（2）重建了侏罗纪晚期大印度古地理位置和空间大小。大印度北缘接近澳洲西北部的Argo深海平原，大印度的南北范围为~2400 km，且呈向北凸出的菱形，支持印度-欧亚大陆单阶段碰撞模式和初始碰撞从中部向两侧穿时性扩展的认识。.（3）初步识别出了印度-欧亚初始碰撞边界从正向碰撞区向侧向碰撞区的转换方式：南迦巴瓦构造结西侧保存了早始新世（~51 Ma）雅江前陆盆地，限定了构造结地区印度-欧亚初始碰撞时间。印度陆缘地层在延伸入构造结之后急剧收敛。构造结西侧初始碰撞边界构造变形主要受大反向逆冲断裂控制，而在构造结西边界为派乡左行走滑断裂，二者之间通过藏南拆离系相连；东边界为阿尼桥右行走滑断裂。.（4）约束了南迦巴瓦构造结边界断裂活动时限：东边界断裂活动时间分布在20.7-9.6 Ma，而西边界断裂活动时间分布在20 -5.4 Ma和2.8-2.3 Ma，指示了构造结的形成时间不晚于早中新世，且具有西侧比东侧更快的差异性隆升过程，并可能导致了构造结西侧的欧亚陆缘发生伸展拆离作用。