帕米尔构造结东部阿尔塔什叠加褶皱研究

The superimposition of fold structures found in orogenic zones usually shows considerable geometric complexity, and the study on refolded, focusing on geometry, kinematic characteristic, geodynamic and deformation phases, can provide significant information of multi-phases structure evolution for a complex orogen. Pamir salient is located at northwest Tibet, has underwent complicate and multi-phases intraplate orogenesis after the India-asia collision. So far, however, it is still controversial on stress-strain and kinematic characteristic between difference terrains in the process of orogenesis. This project majorly focused on the Aertashi superposed folds developing in the Kashgar-Yecheng transfer system, Pamir salient, northwestern Tibet. By systematic field mapping of those superposed folds, this project aims at collecting various kinds of geometry data, describing all structure elements including fold axis and axial plane of superposed folds. Compared to the Ramsay’s and Ghosh’s classical Mode of superposed folds, this study will summarize the interference pattern of those refolded folds which developed in the Kashgar-Yecheng Tansfer system, eastern Pamir. Moreover, this study will analyse the tectonic setting in which the superposed folds formed, defining whether they were related to shear, extension or contraction environment. Finally, combined with low-temperature thermal geochronology and regional geologic data, this study will discuss the Cenozoic structural evolution of the eastern Pamir.

叠加褶皱常见于复杂造山带中，对其几何学、运动学特征、动力学来源及其变形期次的研究，能够提供造山带多期次构造演化的重要信息。帕米尔构造结位于青藏高原西北部，受印度-欧亚大陆碰撞的影响，经历了复杂的、多期次的陆内造山运动，然而对其形成过程中块体之间的应力应变方式及其运动学特征，仍存在较大的争议。本项目主要以帕米尔地区阿尔塔什叠加褶皱为研究对象，通过系统的大比例尺填图，构造几何学数据采集，求解出叠加褶皱的各种几何学要素，对比叠加褶皱的基本分类方式，确定叠加褶皱的干涉类型。进而探讨叠加褶皱的形成过程、构造背景与动力学机制，并结合年代学数据，以及区域地质资料，探讨帕米尔地区阿尔塔什一带的新生代构造演化历史。

通过详实的野外填图工作，确定了帕米尔地区叶尔羌河流域阿尔塔什叠加褶皱的几何学形态（干涉类型）为Ramsay Type 2型叠加褶皱。早期垂直线理指示了近东西向的挤压应力作用，晚期水平线理指示了受走滑断层控制的晚期褶皱叠加作用。通过对叠加褶皱及其相关断层临近出露的花岗岩进行深入的低温热年代学研究，得出早期的褶皱变形时间应该在35Ma之前，晚期受走滑断层影响的褶皱应该发生在14.5-20Ma之间。早期褶皱的动力学来源可能与新特提斯洋的关闭相关，晚期褶皱的动力学来源为印度板块俯冲的远程效应影响。碰撞后的陆内变形特征，通过对比喀什-叶城走滑系统的走滑速率与南天山前陆盆地的缩短速率，得到整个塔里木克拉通周缘呈现西部受强应力、中东部受较弱应力影响的特征。通过对研究区酸性岩、基性岩及其相关沉积岩地球化学年代学的研究得出：晚寒武纪之前，499Ma的辉长岩形成于原特提斯洋中的大同海山。随着洋洋俯冲的进行，奥陶纪（447Ma-486Ma）形成大同岛弧，大同海山向大同岛弧移动，并最终就位到增生楔中。原特提斯洋在晚志留纪（424Ma）之前基本闭合，塔里木克拉通和大同岛弧拼贴到一起，沉积地层开始接受两边的物质来源。