Abstract:

Abstract:  The Dabashan structural belt is a part of south Qinling Mountains, which has been regarded as a foreland thrusting belt of the collisional belt of the north and south China plates. The results of the researches show that the curvilinear structural belt, to the south of ChengkouFangxian thrust fault in the Dabashan mountains, has undergone strong superimposed deformation during the Mesozoic. The Dabashan curvilinear structural belt is composed of linear folds with curvilinear fold hinges and some curvilinear thrust faults (D2), which was formed during the major phase of deformation of south Dabashan. In the western curvilinear structural belt, the folds of D2 with fold axes of nearly south to north trending superimposed on the early wide folds with axis of nearly west to east (D1), and formed a typical cross superimposed structure. In the central and eastern parts, fold axes of D2 were gradually turned to nearly eastwest. The geological mapping shows that there existed a phase of deformation that the fold axes were of north to nearly south to north direction before the formation of the curvilinear structural belt. Based on the deformational sequence, deformed strata, and regional geology, the authors believe that the time of D1, both in western and in central and eastern Dabashan curvilinear structural belt, is the late Triassic to the early Jurassic. It is possible that the deformation D1 was related to the collision between north China block and Yangtze block. On the other hand, the geological relationship, geochronology and AFT data show that the main deformation time of D2, is about the late Jurassic to the early Cretaceous(160110 Ma). So the Dabashan curvilinear structural belt recorded two phases of deformation which were formed during different tectonic settings. It is of great significance for the understanding of the evolution of Qinling orogen.

Key words: Key words: Qinling orogen; Dabashan curvilinear structural belt; Mesozoic deformation; detachment deformation