辽西兴城娘娘顶地区花岗质片麻岩形成时代与变形样式

Formation Age and Deformation Characteristics of Granitic Gneiss in the Niangniangding Area,Xingcheng,Western Liaoning

辽西兴城地区出露的大面积花岗质岩石遭受了强烈的韧性变形改造,其独特的变形样式为研究华北克拉通东北缘中生代以来的构造演化提供了独特的视角。兴城娘娘顶地区出露的花岗质片麻岩塑性变形特征显著,矿物拉伸线理均以低角度向NNE倾伏,整体表现出上盘向SSW的逆冲型韧性剪切变形。最新的花岗质片麻岩中锆石U-Pb年代学结果显示,其原岩形成时代为(169.5±1.6)Ma,为中侏罗世。典型变形岩石的石英EBSD(电子背散射衍射)分析、流变学参数估算,指示变形岩石古差异应力值为13.8~17.7 MPa,应变速率为1.16×10^(-16)~2.20×10^(-14)s^(-1),变形温度介于350~450℃之间。综合研究认为该期变形为发育于中浅部地壳层次绿片岩相的缓慢变形,与晚侏罗世末期—早白垩世早期蒙古—鄂霍茨克洋俯冲闭合的远程效应和古太平洋板块俯冲作用的叠加影响有关。

A large number of granitic rocks exposed in the Xingcheng area of western Liaoning have undergone strong ductile deformation,and their unique deformation patterns provide a unique perspective for unraveling the tectonic evolution of the northeastern margin of the North China craton during the Mesozoic.The granitic gneiss exposed in the Niangniangding area Xingcheng,displays significant ductile deformation characteristics,with the mineral stretching lineations consistently dipping towards NNE at low angles,indicative of top-to-SSW thrust ductile shear deformation.Zircon U-Pb dating results show that the protolith of granitic gneiss was formed at Middle Jurassic(169.5±1.6 Ma).In addition,the quartz EBSD fabric and rheological analyses indicate that the paleo-stress is 13.8-17.7 MPa,the strain rate is 1.16×10^(-16)-2.20×10^(-14)s^(-1),and the deformation temperature is 350-450℃for the deformed rocks.Comprehensive studies suggest that the observed deformation was characterized by a slow deformation process under the greenschist facies condition prevalent in the middle to shallow crust,which originated from the superposition of the closure of the Mongol-Okhotsk Ocean and the subduction of the Paleo-Pacific plate during the latest Late Jurassic to earliest Early Cretaceous.