北阿尔金南缘韧性剪切带构造变形与年代学研究

The ductile shear zone in the south margin of the North Altun is located at the boundary between Azhong terrane and north Altun tectonic mélange belt. Structural features and formation age of the ductile shear zone have a significant implication for understanding the Early Paleozoic tectonic evolution of the North Altun. In this study, we will conduct large scale field mapping, geological profile survey and macro-to micro-structural analysis, in order to define the geometry and kinematic features of ductile shear zone. Quartz EBSD fabric analysis and dynamic recrystallization types of quartz and/or feldspar in the mylonites will be employed to estimate deformation temperature of the ductile shear zone. Ar-Ar thermochronological dating for syn-kinematic mica and other K-bearing minerals from the mylonite, and the SIMS zircon U-Pb geochronology from granitic dykes which intruded ductile shear zone with the different periods will be carried out to constrain the timing of ductile deformation. The main purpose of this study is to reveal the formation mechanism and tectonic implications of ductile shear zone, which provide direct and reliable structure evidence to understand structure deformation and tectonic evolution of the North Altun during the Early Paleozoic.

北阿尔金南缘韧性剪切带位于阿中地块和北阿尔金构造杂岩带的边界，其构造特征和形成时代对于理解北阿尔金早古生代增生造山过程具有重要启示。本申请拟通过对该韧性剪切带进行大比例尺地质构造填图、野外地质剖面测量和室内显微构造解析，确定韧性剪切带的几何学、运动学特征；采用石英EBSD组构分析与石英、长石等矿物变形方式相结合方法，估算剪切带的变形温度；挑选典型糜棱岩中同构造新生云母以及其它含钾矿物进行Ar-Ar年代学分析，辅以剪切带内不同时期侵位的岩体(脉)开展SIMS锆石U-Pb测年，精确限定剪切带变形时限，进而探讨该韧性剪切带的形成机制和构造意义，为深入刻画和解剖北阿尔金早古生代构造变形及其演化提供直接可靠的构造证据。

北阿尔金南缘韧性剪切带是分割北阿尔金增生杂岩地体与阿中地块的一条重要地质分界线，保留了北阿尔金早古生代增生造山过程中的宝贵信息。该剪切带长约200km，宽约0.5~1.5公里，其中发育有长英质糜棱岩、千糜岩、大理岩糜棱岩和“L”型构造岩，详细的构造要素测量表明糜棱面理呈NWW-SEE走向，总体向南西倾或向北东陡倾，矿物拉伸线理向南东倾伏，构造指向和拉伸线理揭示出该剪切带具有右旋走滑和转换挤压的运行学性质；利用变形岩石的石英EBSD组构分析和矿物变形组合特征揭示该剪切带发生了中-高温(500℃~600℃)-中温(420℃~500℃)-中-低温(380℃~420℃)的变形过程，但主要以中-低温变形为主；综合Ar-Ar测年和锆石U-Pb测年，精确限定该剪切带形成时限为447~453Ma，为晚奥陶世变形产物。结合区域构造演化，认为北阿尔金南缘韧性剪切带是北阿尔金洋消亡过程中增生地体与阿中地块斜向碰撞过程中的构造响应，这对正确认识北阿尔金早古生代增生造山作用过程中板块间运动学和动力学提供了关键信息。