郯庐断裂带肥东北部文集地区构造岩类型与构造变形分析

Analysis of the tectonite types and tectonic deformations of Wenji area in the northern Feidong part of the Tan-Lu Fault Zone

位于郯庐断裂带中南部的肥东地区是郯庐断裂带内韧性剪切带出露的主体区域之一。本文从肥东北部文集地区的构造岩组成及其变形入手,通过详细的野外观测、室内显微构造变形分析来确定该地区构造变形的几何学形态及其涡度、有限应变、分维度、差异应力、应变速率等参数。研究区主要出露角闪岩相肥东变质杂岩,构造岩以糜棱岩和糜棱岩化片麻岩为主,岩石变形强烈。根据极摩尔圆法得到的运动学涡度值为0.729~0.870,指示区域内的韧性剪切活动以简单剪切为主。几何学形态上,肥东北部文集地区构造整体呈一背形展出,其枢纽走向NE-SW,轴面倾向SE,物质及变形强度等方面均表现出一定的规律和对称性。研究区内动态重结晶石英颗粒边界具有统计学上的自相似性,其分维值D在1.143~1.208之间,且自背形核部向两翼,颗粒粒径增大,分维值减小。差异应力Δσ介于17.86~55.18MPa之间,应变速率ε值在1.960×10^-13~7.330×10^-12s^-1之间,且背形核部差异应力和应变速率较两翼大,呈近似对称性分布。通过对比以上构造参数可以发现,区内差异应力和应变速率表现出一定的正相关性,自核部向两翼二者均呈减小趋势;动态重结晶石英颗粒则与应变速率呈负相关性,即核部颗粒细小、两翼增大。本文从几何学、运动学以及显微构造变形分析等方面对该区构造变形展开精细化研究,借此来分析肥东北部地区郯庐断裂带的构造形态和运动学特征,这对进一步认识郯庐断裂带的演化过程及构造模型的建立有着重要的意义。

The Feidong area,located in the south-central part of the Tan-Lu Fault Zone(TLFZ),is one of the main areas with outcrops of the ductile shear zone in the TLFZ.In this paper,starting from the Wenji area in the north of Feidong,we surveyed it’s geometric morphology and vorticity,finite strain,dimensions,differential stress,strain rate and the other parameters through detailed field investigations and indoor analyses of its microstructures.The study area mainly consists of amphibolite facies Feidong metamorphic complex.The main tectonites are mylonite and mylonitic gneiss which are strongly deformed.The results of analysis by the polar Mohr diagram method show that the kinematic vorticity is 0.729~0.870,indicating that the ductile shearing activity in the region is dominated by simple shear.In terms of geometry,the whole structure of the Wenji area in the north of Feidong appears to be an antiform,and its hinge strikes NE-SW with an axial plane trending to SE.And following the shape of the antiform,the substance and deformation strength show certain regularity and symmetry.The boundary of dynamically recrystallized quartz particles in the study area has a statistical self-similarity,and its fractal dimension D is between 1.143 and 1.208.From the antiform’s core to the both the wings,the particle size increases,and the fractal dimension decreases.The differential stressΔσis between 17.86 and 55.18 MPa,the strain rateεvalue is 1.960×10^-13~7.330×10^-12 s^-1,and both of which decreases from the antiform’s core to the wings,showing approximately symmetry.It can be found that the differential stress and strain rate in the study area show a certain positive correlation and both of them decrease from the core to the wings.While the dynamically recrystallized quartz particles’size is negatively correlated with the strain rate,the particles are smaller in the core than those in the two wings.Detailed studies upon the geometrical,kinematic and microstructural deformations of the ductile shear zone are carried out to analyze the structural morphology and kinematics characteristics in the north of Feidong part of the TLFZ,which are of great significance for further understanding of the evolution process and to establish the tectonic model of the TLFZ.