江南造山带东段璜茅-五城-屯溪韧性剪切带塑性变形及流变学研究  

Study on Plastic Deformation and Rheology of Ductile Shear Belt of Huangmao-Wucheng-Tunxi in Southern Jiangnan Orogen

作　　者：胡军 余心起[1] 刘孟言 刘俊来[1] 刘秀[1] 曾严 HU Jun;YU Xinqi;LIU Mengyan;LIU Junlai;LIU Xiu;ZENG Yan(School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《大地构造与成矿学》2018年第4期612-627,共16页Geotectonica et Metallogenia

基　　金：国家自然科学基金重大项目"大陆中部地壳天然固态流变与应变局部化"(41430211);安徽省公益性地质(科技)工作项目"休宁-歙县整装勘查区内推覆构造;韧性剪切带及其与金矿成矿关系的研究"(2014-k-1)联合资助

摘　　要：江南造山带东段皖赣相邻区璜茅-五城-屯溪韧性剪切带野外现象、室内显微构造特征表明其经历了较为强烈的韧性剪切变形。岩石经历了NNE向右行剪切改造,变质变形程度为初糜棱岩-糜棱岩阶段,少量达超糜棱岩阶段。结合石英普遍发育边界迁移重结晶、长石多以塑性拉长和少量膨凸重结晶的变形行为特征、石英C轴组构显示出中-高温柱面和菱面滑移为主、重结晶石英颗粒大小-频数及分形维数(1.1646～1.2007),Kruhl温度计测算,揭示了璜茅-五城-屯溪韧性剪切带以中高温位错蠕变变形为主,变形和糜棱岩化环境在450～600℃的中深地壳范围,相当于中高绿片岩相-低角闪岩相。同时,岩石变形的古差异应力为20.76～30.04 MPa,估算所得应变速率主要介于10^(-14)～10^(-11) s^(-1),指示了中高温、低应变速率的韧性变形条件。已有的变形年龄显示,该韧性剪切带为加里东构造事件产物,主要的动力来源与江山-绍兴断裂带发育的陆内俯冲作用主应力在远离造山带的转变相关。The Huangmao-Wucheng-Tunxi ductile shear zone,which is located in the eastern segment of the Jiangnan orogenic belt,is characterized by intensive ductile shear deformation as shown by its field appearance and the microstructures.The rocks were metamorphosed and deformed as protomylonite to mylonite,and locally as ultramylonite due to the NNE trending right-lateral ductile shearing.The quartz grains mostly occur as dynamic recrystallization including subgrain rotation and grain boundary migration recrystallization.Meanwhile,most of feldspar porphyroclasts are enlongated and some are fully bulging recrystallized.Quartz C-axis fabric demonstrates that quartz fabrics are mainly middle-high temperature prismatic slip system and low-middle temperature rhomb slip system.The size of quartz recrystallized particles is mainly 20 to 140μm.Fractal analysis suggests that the fractal dimension of boundaries of the recrystallized quartz grains is 1.1646 to 1.2007.All above characteristics reveal that the deformation type of this ductile shear zone belongs to dislocation creep at middle-high temperature.The calculation of the Kruhl thermometer with fractal method indicates that the ductile deformation and mylonitization temperatures range from 400 to 600℃,which is equivalent to the metamorphic conditions of middle-high greenschist facies to lower amphibolite facies.In addition,the differential stress and strain rate of the ductile shear zone are estimated at 20.76 to 30.04 MPa,10^-14 to 10^-11 s^-1,which indicates that the ductile deformation condition is medium-high temperature and low strain rate.Because the deformation is believed to take place in the Caledonian,we therefore suggest that the geodynamics of this ductile shear zone is related to transition of the principal stress that is remotely affected by the Caledonian intracontinental subduction along the Jiangshan-Shaoxing fault zone.

关 键 词：韧性剪切带 EBSD 分形维数 古差异应力 应变速率 

分 类 号：P542[天文地球—构造地质学]