中扬子区东缘中古生界对冲构造体系形成与演化

中扬子区东缘侏罗纪末期—白垩纪早期,受大洪山推覆区南西方向和江南雪峰逆冲推覆区北西方向的强烈挤压,形成了压扭性狭长的对冲构造体系; 两大推覆区的形成主要受深、浅变质岩结晶基底内幕两套拆离滑脱层系的作用,导致沉积盖层压缩沿基底面、志留系底面、泥盆系底面多层次滑脱推覆,产生了多样的挤压和压扭构造类型及其样式; 由造山带向盆内构造变形具有渐变的特点,为不对称式的仰冲(根带)—楔状掩冲(中带)—滑脱推覆(锋带)—对冲带; 持续压扭作用导致产生系列北东向左行走滑断裂将对冲构造体系分割; 白垩纪晚期—下第三纪,挤压转换为伸展环境,断裂负反转回滑成为中新生代断陷主控断裂,认为大洪山推覆区锋带已处于通海口—杨林尾—汉南一线,主体由于受洪湖走滑断裂和通海口断裂回滑的影响,接受了上白垩统—第四系沉积,仅保留了东、西两端弧形构造带古生界出露的构造面貌。

Formation and evolution of ramp structural system of Mesozoic and Paleozoic in the eastern edge of middle Yangtze region

During the time of Late Triassic to Early Cretaceous,owning to the strong compression of SW-trending Dahongshan nappe region and NW-trending Jiangnan-Xuefeng overthrust region,the eastern edge of the middle Yangtze region became the transpressional slim ramp tectonic system.For the influence of the internal two detachment fault system in hypo and epi metamorphic rock crystallizine basement,the two nappe regions were formed.It contributed to sedimentary cover compression and multiple detachments nappe along the base of the Silurian,the base of the Devonian,and formed a variety of compression and transpressional tectonic structural type and tectonic style.From orogeny belt to Intra-basin,Tectonic deformation was Gradual-Change,that is asymmetry obduction(root zone)-wedges overthrust(middle zone)-decollement nappe(front zone)-ramp belt.Continued compressive-torsional action resulted in a series of NE-trending right-lateral Strike-slip faults segmented ramp structure system.Compression turned into extension environment in Late Cretaceous-Paleaogene,negative fault inversion slipped back and became major fault of fault depression in Mesozoic and Cenozoic.It is generally believed that the front zone of Dahongshan nappe region is already in line with Tonghaikou-Yanglinwei-Hannan.Influenced by Honghu strike-slip fault and Tonghaikou fault slipped back,the main body accepts the Early Cretaceous-Neogene sedimentary and only remains the curvilinear structural belt tectonic features.