Dabie Orogenic Belt South Margin Tectonic Belt Tectonic Geometric Characters Of The Formation And Evolution

Based on structural geology, petrology, geochemistry and geophysics, the structure, composition and evolution of the south marginal structural belt of the Dabie orogen has been comprehensively studied. Major progresses of this work are as follows:1. This study ascertained that the southern margin tectonic belt of the Dabieshan is experienced Iong,complicated evolvement,especially the intracontinental overthrust structure formed by collision and congruence of ocean-continent since Meso-Cenozoic.The main characteristics of tectonic geometry are as follows:(1)The tectonic belts extends in linear or arc shape. (2) In a profile, orogen thrusted outward onto the Yangtze block in the way of nappe structures in various types and different depth, which is composed of large—scale thrusted and superimposed geometry structures of the intercontinental crust. (3) Now the southern border tectonic belt of the Dabieshan is formed in the three-dimensional of geometric model, which mostly trending EW on the top , throughing the aclinic beds of passage intermediately to the gradient or erect flow structure at the bottom.2. The existence of dismembered ophiolitic melange and the preserve of the island arc volcanic rocks in the south structural belt of the Dabie orogen have been determined. This shows that the Mianlue belt should be extended eastward to the south part of the Dabie orogen.The same occurrence of the dismembered ophiolitic melange belt and the relics of island arc volcanic rocks show that the south of the Dabie orogen had undergone tectonic processes from the oceanic island arc to the continental margin island arc. Compared with the remained ophiolite and volcanic rocks in different section of the Mianlue suture of the Qinling tectonic belt, it shows that the Mianlue suture of the Qinling tectonic belt, which is eastwardly through Huashan to south area of the Dabie orogen.The ophiolite blockes and island-arc volcanic rock in southern border tectonic belt of the Dabieshan are presented survival state and distributed promisecuously, because of the deep subduction-collision between lands and frequently uplift of UHP in Indosinian epoch, and intense intracontinental tectonic effect in yanshannian. They are bared in the rock of orogenic belt root and in the old rock of Cambrian period, in the middle or under the middle including the rock of Mianlue suture zone are eroded, or be buried by the forcing of Dabieshan. So, in southern border tectonic belt of the Dabieshan,the old ophiolite and island-arc volcanic rock are existent and the new are not.3. The paper has discussed the formation and uplift significance, effect and its continental dynamical significance of the formation and evolution of the southern border tectonic zone of the Dabieshan to the Dabie orogenic belt and the Dabie high-pressure and ultrahigh-pressure metamorphic belt.The southern border tectonic belt of the Dabieshan went through five long and intricate evolvements, including that the formation of source rokes in metamorphic basement rock series , continetal margin of Yangtze platform in Sinian Period-Middle Triassic deposited passively, the collision-orogenic and deep subduction period in Indosinian epoch, trust tectonics and uplift of UHP in late Indosinian- Yanshanian, and intracontinental tectonic stage in Meso-Cenozoic.The existence of subduction zone of the southern margin of Dabieshan maked the cceleration of the subduction of Yantze Platform to the depth of the Mantle, forming the UHP rocks, we need to emphasize the regional convergence of the Yangtze plate and North China plate and double-plate subduction of southen and northen Dabieshan. The subduction of the sorthen margin improved the northen deep subduction and exhumation.This is the main reason and meaning by which we do the research in this paper,also,it is important new cognition in this paper.4. Deformation of the foreland fold and thrust belt of Dabie orogen are studiedThe foreland fold and thrust belt are product of the collision between the Dabie orogen and the lower Yangtze block in Indosinian age, which underwent at least three—stage deformation. The earlier deformation resulted from the northward subduction of the Yangtze block. The main deformation is from the ultra high—pressure returning processes, and the last one is southward thrusting and napping.