松潘-甘孜地体早中生代褶皱变形与岩体侵位的构造关系研究

Songpan-Ganzi terrane locates in the convergence area between the North China block, Yangtze block and Qiangtang block within the eastern Paleo-Tethys domain. Following with the continental collision between the North and South China in early Mesozoic, the Songpan-Ganzi terrane experienced a tectonic transformation from deep-water flysch deposition to compressional deformation and granitic emplacement with planar distribution during Late Triassic-Early Jurassic in a short time（~30Ma）. And the tectonic setting and mechanism of this tectonic event is not clear at present. This process is associating with the understanding of the Mesozoic tectonic evolution of middle China because of the special tectonic location of the Songpan-Ganzi terrane. We have noticed that the tectonic relationship between the fold deformation and granitic intrusion is key point to understand these events, which are rapid deposition, linear tight folds and areal distribution of granites within the Songpan-Ganzi terrane in Late Triassic-early Jurassic. Therefore, we intend to study the connection between the folds and granitic emplacement structures through the tectonic deformation, tectonic stress field and tectonic chronology in some representative areas of the granite exposed, restore the deformation process in Late Triassic-Early Jurassic, discuss the tectonic mechanism for this characteristic tectonics, and reconstruct the collisional history and tectonic development process of the eastern Paleo-Tethys domain during the early Mesozoic.

松潘-甘孜地体位于东古特提斯域内华北地块、扬子地块和羌塘地块的交汇部位。在早中生代中国南、北大陆碰撞拼贴阶段，松潘-甘孜地体在晚三叠世-早侏罗世较短（约30 Ma）的时间内，经历了由深水复理石沉积作用向挤压缩短变形和面状分布花岗岩体侵位的构造转换。目前对于这种快速转换的构造背景和构造机制还不清楚。鉴于松潘-甘孜地体所处的特殊构造位置，这个构造过程很可能成为认识中国中部中生代构造过程的关键所在。申请人注意到，松潘-甘孜地体在晚三叠世-早侏罗世所经历的快速沉积、线状紧闭褶皱和花岗岩侵入等事件中，褶皱变形与花岗岩体侵位的构造关系是认识它们的关键环节之一。因此，申请人拟选择具有代表性的岩体出露地区，通过构造变形解析、构造应力场分析和构造年代学测定等方面的研究，确认褶皱变形与岩体侵位的构造关系，恢复晚三叠世-早侏罗世变形过程，讨论其构造机制，探讨并重建东古特提斯构造域早中生代构造发展过程。

松潘-甘孜地体位于东古特提斯域内华北地块、扬子地块和羌塘地块的交汇部位。在早中生代中国南、北大陆碰撞拼贴阶段，松潘-甘孜地体在晚三叠世-早侏罗世较短（约30 Ma）的时间内，经历了由深水复理石沉积作用向挤压缩短变形和面状分布花岗岩体侵位的构造转换。目前对于这种快速转换的构造背景和构造机制还不清楚。针对这一关键的构造转换过程，本项目选择地体北部的黑水-毛尔盖岩体与周缘三叠系地层的紧闭褶皱变形的构造关系开展相关研究。通过岩体周缘褶皱变形的构造解析，确认了早期变形为北东-南西向主压应力条件下形成的北西走向直立褶皱，晚期可能受岩体侵位的影响，岩体南侧的北西向褶皱遭受叠加变形而形成直立褶皱，而西北侧褶皱则主要遭受了由南往北的逆冲而使早期褶皱转变为同斜褶皱。通过岩体不同位置的磁组构分析结果表明，岩体内部发育近东西走向的磁面理，与岩体构造面理近一致，显示了侵入过程中遭受近南北向挤压的特征。通过锆石U-Pb和Ar-Ar年代学分析结果表明，岩体侵位的时代要略早于地层变形，但是时间间隔仅为10 Ma左右。从而表明松潘-甘孜地体内岩体侵位与围岩地层褶皱变形的时代基本同期，岩体侵位造成周缘地层早期褶皱发生叠加变形，从而形成与岩体边界近平行的弧形褶皱。