The Tectonic Evolution of the Tongbai‐Dabie Orogen Since Mesozoic in Eastern China and Its Geological Significance

ABSTRACT The geometry form of the Tongbai‐Dabie Orogen is a large antiform structure. It has been formed under the background of the collision and compression between the North China Block and the Yangtze Block after the Indosinian period. The material of the Tongbai‐Dabie Orogen was derived from the rock basement of the South China Block. The Yindian‐Malong Shear Zone and Xiaotian‐Mozitan Shear Zone belong to the same tectonic layer of the antiform structure, because of the later weathering and denudation, the top part of the antiform structure has been eroded, which has made the Tongbai Complex and Dabie Complex exposed, so only the two shear zones in two sides of the antiform structure have been preserved. The eastward extrusion of the Tongbai‐Dabie Orogen under the background of compression from the late Indosinian to the early Yanshanian is not a whole extrusion. The Tongbai‐Dabie Orogen is comparable with a large tunnel, and the tunnel is composed of many layers which are linked by a special detachment surface. At the same time of extrusion, layer and layer will slide and the detachment surface is the sliding lubricant, and we call this phenomenon tubular flow structure. The tubular rheology of the Tongbai‐Dabie Orogen began from 220 to 210 Ma, and the deep part is plastic rheological. At around 180 Ma, with the end of plate compression and collision, the Tongbai‐Dabie Orogen was generally in a ‘silent’ state. Due to the existence of differential rheological boundaries, an antiform zone with strong deformation (compared to outside the pipeline) was formed, and plastic deformation occurred within the boundary, while solid motion occurred relatively outside the boundary. With the formation of the north–south shear zone and the accumulation of the deep Tongbai‐Dabie Complex from west to east in the eastern part of the Dabie Mountains, the tubular rheological strength became weakened. At around 150 Ma, Yanshanian magmatic activity occurred extensively in eastern China, which lasted until around 130 Ma when shear activity and tubular rheology gradually declined and stopped. At the end of shear activity and tubular rheology, the magmatic activity became strongest. After 110 Ma, the magmatic activity gradually became weakened, and then strong extensional activity occurred in the area. Under the weathering and erosion of the late Cenozoic and small‐scale tectonic activities, the Tongbai‐Dabie Orogen has formed its current tectonic pattern.