辽西兴城—台里韧性剪切带北段变形特征

Deformation characteristics of northern part of Xingcheng-Taili ductile shear zone,western Liaoning

辽西兴城—台里地区发育系列花岗质岩石,强烈构造变形特征均显示其具有韧性剪切带的特点。对剪切带北段进行详细宏微观构造解析,结合岩石变形强度差异性分析、有限应变测量、石英C轴EBSD测试以及古差异应力值估算等研究,结果表明剪切带内花岗质片麻岩和眼球状花岗质片麻岩具有NEE向左行剪切变形特征,变形岩石为S-L构造岩,应变类型属于平面应变,古差异应力值介于30~40 MPa之间。长石-石英矿物温度计以及石英C轴EBSD组构指示剪切带以中低温变形为主,温度在400℃~500℃,属绿片岩相变质,具中-低温韧性剪切带特征。韧性剪切带内普遍存在变形分解现象,弱变形带内岩石残斑含量较高,眼球状构造和S-C组构较为发育;强变形带岩石残斑含量较低,剪切面理较为发育,糜棱面理发育较弱或者不发育。

A series of granitic rocks occur in the Xingcheng-Taili area of western Liaoning Province,which have the characteristics of ductile shear zone as indicated by intense tectonic deformation.The macro and micro structures in the northern part of the shear zone were analyzed,combined with the analysis of rock deformation strength differences,the measurement of finite strain,the EBSD test of quartz C-axis and the estimation of paleo differential stress values.The result shows that the granitic gneiss and augen granitic gneiss are characterized by NEE sinistral shear deformation.The deformed rocks are S-L tectonic rocks,with strain types of plane strain andpaleo differential stress values of 30 ～ 40 MPa.The mineralogical thermometer of feldspar-quartz and the EBSD fabrics of quartz C-axis indicate that medium and low temperature deformation take dominance in the shear zone,with temperatures ranging from 400℃ to 500℃.This demonstrates that the shear zone developed under greenschist facies metamorphic conditions and has the characteristics of medium and low temperature ductile shear zone.Deformation partitioning is common in the ductile shear zone.In weak deformation zone,it shows high content of porphyroclast and the augen structure and S-C structure are well-developed.In strong deformation zone,it shows a low porphyroclast content,with shear foliation well-developed,but mylonitic foliation poorly developed or undeveloped.