华南武功山早古生代花岗岩构造变形特征及其形成机制

Structural Characteristics and Deformation Mechanism of Early Paleozoic Granite in the Wugongshan Area,South China

华南武功山地区早古生代花岗岩发育强烈的韧性变形,其变形特征和形成机制是认识武功山地区构造样式和成因的关键。在详细的野外地质调查基础之上,对武功山早古生代片麻状状岩花岗岩进行了有限应变分析、运动学涡度测量以及温度估算。有限应变分析表明早古生代片麻状花岗岩主应变轴比X/Z介于1.33~5.07,Y/Z介于1.17~2.59;对数付林参数K值介于0.05~6.88之间;三个主方向应变强度ε1、ε2、ε3大小范围分别为0.13~1.35、-0.26~0.28、-0.54^-0.18;应变型式从边部到核部呈扁型—长型与扁型共存—长型的变化规律;应变大小从边部到核部呈增大又减小的趋势,即中间地带为应变较强的一个带。运动学涡度测量和温度估算表明武功山地区片麻状花岗岩经历了两期构造变形,早期以纯剪变形为主,形成温度为500~600℃;晚期变形表现为简单剪切,形成温度为300~400℃。结合年代学资料,探讨了武功山早古生代花岗岩韧性变形的形成机制。

Strong ductile deformation,which occurs in the Early Paleozoic granite in the Wugongshan area,South China,is the key to understand its structural styles and origin.On the basis of the detailed geological survey,this paper analyzes finite strain,measures kinematic vorticity and temperature of Early Paleozoic gneissic granite in the Wugongshan area.Study of finite strain for the Early Paleozoic gneissic granite shows the X/Z ratios of 1.33 ～ 5.07,Y/Z ratios of 1.17 ～ 2.59,and flinn parameters K of between 0.05 and 6.88.Strain strength （ε1,ε2 andε3） along three main principalaxes are 0.13～1.35,-0.26～-0.28,-0.54～-0.18,respectively.Strain presents change regularity,which changes from flat,coexist of flat and long to long from the edge to the core.The strength of the strain also increases and then decreases from the edge to the core,with strong deformation occurring between transition zone from edge to core.Calculation of kinematic vorticity and estimation of temperature show that early Paleozoic gneissic granite underwent at least two structural deformation events in Early Paleozoic.The early stage was pure shear deformation developed at 500 ～ 600℃ while late stage simple shear at 300 ～ 400℃.Combined with chronological data,this article also discusses the mechanism of ductile deformation of Early Paleozoic granite in the Wugongshan area.