大巴山弧形构造带中段渔渡地区侏罗纪叠加变形研究

大巴山构造带是秦岭造山带南部发育的一个以逆冲推覆构造为特征的构造带。通过在大巴山弧形构造带中段渔渡地区进行的详细构造解析发现,大巴山构造带在侏罗纪以来经历了至少两期变形叠加,变形地层三叠系嘉陵江组—侏罗系沙溪庙组。早期变形以与滑脱构造相关的轴向北西—北北西向箱状或隔挡状褶皱为主,并在深部发育顺层滑脱构造,变形时代为晚侏罗世到早白垩世。晚期变形与北侧逆冲相关,导致右行走滑变形,主要形成右行走滑断层和北西—北北西向紧闭褶皱,变形时代比第一期稍晚,为晚侏罗世之后到早白垩世。两期变形形成的褶皱延伸方向一致,与区域构造线的方向协调,而且在远离北侧镇巴断裂的地区变形强度有减弱的趋势,两期变形叠加形成共轴或斜交叠加构造。研究表明,变形与大巴山冲断—推覆构造带向南逆冲有关。

Study on Jurassic Superposed Deformation in Yudu Area Located in the Middle of Dabashan Tectonic Belt

Dabashan tectonic belt characterized by thrust nappe structure is developed in the southern of Qinling orogenic belt.Through detailed structural analysis in Yudu area located in the middle of Dabashan tectonic belt,the results show that Dabashan tectonic belt has undergone at least two superposed deformation since Jurassic.The deformed strata are Triassic Jialingjiang Formation to Jurassic Shaximiao Formation.Early deformation is predominantly NW-NNW axes trending box fold or partition wall style fold and decollement structure developed at deep.The time of early deformation is late Jurassic to early Cretaceous.The late deformation relates to thrust movement of its north side and results in dextral strike slipping deformation which composed of dextral strike slipping fault and NW-NNW trending tight folds.The time of late deformation is between late Jurassic and early Cretaceous.Folds formed by two stages deformation have similar extend direction and are consistent with the direction of regional tectonic line.Away from the northern Zhenba fault,the deformation intensity has a weaken tendency.The two stage deformations form coaxial or oblique superimposed structure.Study shows that the deformation relates to the southward thrusting of Dabashan thrust nappe belt.