郯庐断裂带桐城段构造变形解析

Analysis of structural deformation in Tongcheng section of Tanlu fault zone

郯庐断裂带桐城段韧性剪切带位于大别造山带东北缘.首先对剪切带两端的两套片麻岩进行宏观构造特征、矿物组成以及锆石U-Pb年代学研究,确定片麻岩为印支造山期高压变质产物.之后由于郯庐断裂带左行韧性走滑叠加,在原来近东西向造山带片麻岩基础上形成了NE-SW向的糜棱岩—超糜棱岩带.根据糜棱岩中主要矿物的变形行为,估算剪切带的变形温度约为450℃~530℃,局部可达550℃,为高绿片岩相—低角闪岩相变质;有限应变测量和应变强度计算的结果表明,矿物在韧性剪切过程中经历了强烈的拉长变形,剪切带中间位置变形程度最强,向两边慢慢减弱;运用多种方法对糜棱岩进行运动学涡度的测量计算,结果表明郯庐断裂带桐城段为一以简单剪切为主导的减薄型一般剪切带.

The Tongcheng segment of Tanlu fault zone is located in the northeastern margin of the Dabie orogenic belt. Firstly, the macrostructural characteristics, mineral composition and zircon U-Pb chronology of two sets of gneiss at both ends of the shear zone are studied, and it is determined that the gneiss was the product of high-pressure metamorphism during Indosinian orogeny. Later, due to the sinistral ductile strike-slip activity superposition of Tanlu fault zone, NE-SW-trending mylonite-supermylonite zone was formed on the basis of gneiss in the original EW-trending orogenic belt. According to the deformation behavior of the main minerals in mylonite, it is estimated that the deformation temperature of the shear zone was about 450 ℃~530 ℃, which can reach 550 ℃ locally, which indicates that it has undergone high greenschist facies to low amphibolite facies. The results of finite strain measurement and strain strength calculation show that the minerals have undergone intense elongation deformation during ductile shear activity, and the deformation degree is the strongest in the middle of the shear zone and weakens slowly toward both sides. Kinematic vorticity measurements of mylonite by various methods show that the Tongcheng section of Tanlu fault zone is a thin tape of general shear zone dominated by simple shear.