古北口逆冲推覆构造及土城子组脆韧性变形带特征

Gubeikou thrust nappe structure and brittle-ductile deformation belt of the Tuchengze Formation

古北口逆冲推覆构造在区域上位于“尚义-平泉”大断裂带的中段,属燕山期板内造山运动产物。发育在中生代断陷盆地的北侧,由两条主断裂控制上、下两个推覆体由北向南依次逆冲,原地系统由中生代土城子组及以下地层构成。根据对断裂带中同构造期的石英正长岩脉的样品K-Ar法测年,获得同位素年龄为(16.1±2.3)Ma,故认为本区逆冲推覆构造形成时代应在中侏罗世—晚侏罗世之间。中生代地层中局部形成脆韧性变形带。

Regionally located in the central segment of the Shangyi-Pingqu an fault belt,the Gubeikou thrust nappe structure is the product of the Yansha nian intraplate orogenic movement.It is developed on the northern side of the Mesozoic down-faulted basin.Controlled by two major faults,the upper and lo wer nappes were successively thrust from north to south.The autochthonous syst em consists of the Mesozoic Tuchengzi Formation and the strata below it.K-Ar dating of samples from a syntectonic quartz syericte dike in the fault zone yi elded an isotope age of 16.1±2.3Ma;so it is considered that the thrust nappe structure in the area formed between the Middle Jurassic and Late Jurassic .A brittle-ductile defor-mation belt is formed locally in the Mesozoic strata .