大别造山带东缘桐城—潜山段构造解析和年代学研究

发布时间：2018-03-10 12:33

  本文选题：大别山东缘　切入点：糜棱岩　出处：《合肥工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：大别造山带是研究高压-超高压岩石折返的经典地区。前人对其进行了多年的研究工作,但目前对造山带折返过程仍存在很大的争议。由于早白垩世的穹窿活动改造了造山带折返的构造信息,加大了研究的难度,而现有的折返模式大都没有考虑早白垩世隆升对其构造信息的影响。大别山东缘桐城-潜山段出露高压变质岩,其位于北大别单元岳西穹窿东侧,受穹窿抬升的影响相对比较单一,更容易恢复至其原始的构造特征。因此在该区开展构造和年代学研究,可以为研究大别造山带的折返过程提供证据。详细的野外观察发现,大别山东缘桐城-潜山段出露一系列近东西走向的韧性剪切带,与出露的郯庐北东-北东东向韧性剪切带产状明显不同,且向西进入北大别单元后即消失不见,其形成应当与造山活动有关。因此本次以该区出露的韧性剪切带为研究对象,对该区进行薄片分析、石英c轴组构分析和U-Pb锆石定年,并对其进行构造恢复。详细的显微镜下观察显示,近东西向韧性剪切带内的糜棱岩样品中长石主要发生脆性破裂,石英主要发生SR动态重结晶,指示变形温度为400℃左右;残斑拖尾、书斜构造、云母鱼等指示为左行剪切;糜棱岩石英c轴组构的主控滑移系同样记录了400℃左右的变形温度。锆石CL图像显示该区锆石大部分具有核-边结构,核部岩浆锆石具明显的震荡环带,Th/U比值为1左右,获得了730-770 Ma的年龄;边部锆石具明显的变质锆石特征,Th/U比值小于0.1,获得220 Ma左右的年龄。通过对其构造恢复,发现近东西向韧性剪切带的原始产状具有一致的面理陡立,走向近东西,左行剪切,线理向西倾20°左右的特征。通过这些研究,并结合前人的研究,可以得出,本次测得的220Ma左右的锆石变质年龄可能代表了该区高压岩石早期折返的时间;而近东西向韧性剪切带的活动发生在220Ma之后,190Ma之前,与高压岩石的折返同时发生,发生在折返的晚期阶段,近东西向韧性剪切带可能是该区高压岩石向东折返时南部比北部折返的速度更快而造成的“错位”形成的。
[Abstract]:The Dabie orogenic belt is a classic area for studying the exhumation of high-pressure and ultra-high pressure rocks. However, the exhumation process of orogenic belt is still controversial at present. Because of the early Cretaceous dome movement, the tectonic information of orogenic belt exhumation has been modified, which makes it more difficult to study. However, most of the existing exhumation models do not consider the influence of early Cretaceous uplift on the tectonic information. High pressure metamorphic rocks from Tongcheng to buried hill member in the eastern margin of Dabie Mountain are located on the east side of Yuexi fornix of the Beidabie unit. The influence of dome uplift is relatively simple, and it is easier to recover to its original structural characteristics. Therefore, the study of structure and chronology in this area can provide evidence for studying the exhumation process of Dabie orogenic belt. A series of east-west trending ductile shear zones appeared in the Tongcheng buried hill section on the eastern margin of the Dabie Mountains, which were obviously different from the Tan-Lu east-north east-north ductile shear zone, and disappeared when they entered the Beidabie unit in the west. Its formation should be related to orogenic activity. Therefore, the ductile shear zone exposed in this area is taken as the research object, and thin slice analysis, quartz c-axis fabric analysis and U-Pb zircon dating are carried out in this area. The detailed microscopic observation shows that the feldspar is mainly brittle rupture in mylonite samples in the near east-west ductile shear zone, and SR dynamic recrystallization occurs in quartz, indicating that the deformation temperature is about 400 鈩，

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