江西抚州盆地南西段白垩系构造变形特征及其动力学背景

    Deformation characteristics of Cretaceous strata and its dynamic background, southwestern Fuzhou Basin, Jiangxi

    • 摘要: 抚州盆地南西段潭丘—戴坊一带出露陆相红色碎屑沉积岩,锆石U-Pb测年限定该套地层的沉积下限为109 Ma,印证了前人将其划归为上白垩统的认识。野外构造观测和显微应变测量表明,上白垩统发育2期挤压构造变形:第一期NNW向挤压以NEE向共轭剪节理和压扁状钙质结核为主要识别特征,岩石应变类型主要为压扁型;第二期NE向挤压作用以发育NW向逆冲剪切破裂为识别标志,小规模切割错断第一期变形构造。结合中新生代中国东部构造演化历史,探讨并提出上述构造变形的动力学背景如下:第一期NNW向挤压可能与古近纪早期印度板块北向运移与欧亚大陆间的碰撞作用有关;第二期NE向挤压事件可能与赣江断裂带右行走滑派生的局部挤压应力场有关,其动力背景可能为古近纪中晚期印度板块对欧亚板块碰撞引发青藏高原物质东向挤出。

       

      Abstract: The continental red clastic sedimentary rocks are exposed in the Tanqiu-Daifang area in the southwestern part of Fuzhou Basin.Zircon U-Pb dating sets the sedimentary lower limit of this formation at 109 Ma, confirming the previous understanding that it was classified as the Upper Cretaceous.Field observations show that there are two stages of compressional tectonic deformation developed in the Upper Cretaceous strata.The first stage of NNW-trending compression was mainly characterized by NEE-trending conjugate joints and flattened calcareous concretions.Systematic measurements of finite strain of calcareous concretions in the calcareous siltstone indicate the strain type was mainly flattening strain.The second stage of NE-trending compression was marked by the development of NW-trending thrusting fractures, which cut the first stage of deformations on a small scale.Combined with the tectonic evolution history of eastern China in the Mesozoic and Cenozoic, the dynamic backgrounds of these deformations are determined: the first stage NNW-trending compression may be related to the northward migration of Indian Plate and subsequent collision with the Eurasia Plate in the Early Paleogene; the second stage of NE-trending compression may be associated with the local compressive stress field derived from the dextral strike sliping of the Ganjiang fault zone, and its dynamic background may be the eastward escape of Tibetan Plateau caused by the collision between Indian and Eurasian plates during the middle to Late Paleogene.

       

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