碧口地块东南缘韧性剪切带构造特征浅析  

ANALYSIS OF TECTONIC CHARACTERISTICS OF THE DUCTILE SHEAR ZONE IN THE SOUTHEASTERN PART OF THE BIKOU TERRANE

作　　者：张咪咪 赵德军[1] Zhang Mimi;Zhao Dejun(College of Earth Sciences,Chengdu University of Technology,Chengdu Sichuan 610059,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059

出　　处：《矿物岩石》2021年第4期80-93,共14页Mineralogy and Petrology

基　　金：马角坝实习基地建设专项(项目编号:20Z06)。

摘　　要：碧口地块东南缘发育多条倾向不同、呈NEE走向逆冲平行展布的韧性剪切带,地质信息丰富,对碧口地块构造特征解析意义重大。为探讨地块东南缘韧性剪切带的地质构造特征,对剪切带中发育的糜棱岩化绿泥石英片岩、糜棱岩进行了野外观测、显微组构和石英c轴组构分析,估算了剪切带变形温度、差应力、应变速率及运动学涡度。结果显示,韧性剪切带变形温度介于300~500℃之间,形成环境大致为高绿片岩相到低绿片岩相;差应力值大多集中于100~350 MPa,较一般韧性剪切带的差应力值(20~200 MPa)略高;应变速率介于4.12×10^(-21)〜4.33×10^(-14)s^(-1),符合一般韧性剪切带的应变速率。越接近青川断裂,不同韧性剪切带的变形温度、差应力值及应变速率值越大,显示碧口地块东南缘韧性剪切带的剪切中心为青川断裂带。利用石英c轴组构结合斜交面理法及石英c轴组构结合有限应变法所计算的韧性剪切带运动学涡度值绝大多数大于0.75,显示剪切带变形类型主要以简单剪切为主。地块东南缘韧性剪切带呈左行剪切的运动特征,反映了印支期造山作用下华南和华北板块碰撞后华南板块继续顺时针旋转、碧口地块呈楔形与扬子陆块区及秦-祁-昆造山系汇聚碰撞的地质过程。There are several NEE trending ductile shear zones with different dipping directions in southeastern edge of the Bikou terrane.Mylonized chalcoquartz schist and mylonite are well developed in the shear zones.Microfabrics of these deformed rocks are studied and the deformation temperature,differential stress,strain rates and kinematic vorticity of the ductile shear zones are estimated so as to unravel the structural characteristics of the Bikou terrane.The results show that the deformation temperature of the ductile shear zones ranges from 300 to 500℃,and the formation environment is generally from high green schist facies to low green schist facies.Most of the differential stress values are concentrated in the range of 100-350 MPa,which is slightly higher than that of the general ductile shear zone(20-200 MPa).The strain rates range from 4.12×10^(-21) to 4.33×10^(-14)s^(-1),consistent with the strain rates of general ductile shear zones.The closer to the Qingchuan fault,the greater the deformation temperature,differential stress and strain rates of different ductile shear zones,indicating that the shear center of the ductile shear zone in the southeastern margin of the Bikou terrane is the Qingchuan fault zone.Most of the kinematic vorticity values of the ductile vshear zone calculated by using quartz c-axis fabric combined with oblique plane texture method and quartz c-axis fabric combined with finite strain method are greater than 0.75,indicating that the deformation of the ductile shear zone is mainly simple shear.The ductile shear zones in the southeastern margin of the Bikou terrane show left-lateral shear movement,which reflects the geological process of the south China plate rotating clockwise after the collision of the North China plate and the Wedge-shaped Bikou terrane convergent collision with the Yangtze block and the Qin-Qi-Kun orogenic system during the Indosinian orogeny.

关 键 词：碧口地块 韧性剪切带 石英C轴组构 费氏台 运动学涡度 

分 类 号：P545[天文地球—构造地质学]