Abstract:

The tectonic zonation of Longmen Mountain thrust zone is the key problem in the study of Longmen Mountain structure. According to the field measured geologic section and the geological survey as well as the different structural types of the different part within the thrust zone, the northern front range of Longmen Mountain thrust zone is divided into three tectonic sub-belts, Tangwangzhai-Yangtianwo klippe and gliding nappe tectonic subbelt, Louziba-Yanmenba-Majiaoba imbricate thrust subbelt and Kuangshanliang-Tianjingshan-Erlangmiao thrust and anticline subbelt, namely. Each has the different tectonically deformation. The klippe and gliding nappe tectonic subbelt is characterized by structural superimposition and tectonic evolution of nappe and addition gliding nappe. The thrust structure of the imbricate thrust subbelt is well developed, different systems, different formation in the same system as well as the different member in the same formation in the imbricate thrust subbelt thrusts from northwest to southeast, from older to younger in turn and forms the typical imbricate structural type. The thrust faults take on listric inclination westward and converge above the basal thrust plane of the thrust zone. There well developed fault-propagation folds in the structural rock fragments. These folds have almost the same axial strike and axial-plane occurrence as those faults in the imbricate thrust zone, and all fall toward foreland. The thrust anticline subbelt has the dual feature, on the one hand, it shows as brachyanticline on the surface or the near surface, on the other hand, thrust sheets are distributed in the deep crust of earth. In Xiasi-Jinzishan-Houba foreland, the thrusts are of scarcity, small scale and weak deformation in the shallow which mainly shows that monoclinal structure dipps toward southeast. Whereas, buried thrust faults has been well developed in the depth. Thrust zone has the tendency of regular decreasing gradually in its deformation strength, the involved strata gradually becoming new and the deformation levels gradually becoming shallow from front range to foreland, which demonstrates that thrust structures have the fore-expanding feature. Thrust structures are the product of both Later Triassic and Cenozoic era tectonic deformation. The tectonical deformation during Later Triassic is intensive and belongs to the major formation stage of  Longmen Mountain foreland thrust zone, the tectonical deformation in Cenozoic era, however, is weak and superposed and changed the tectonical deformation formed in Later Triassic era.

Key words: Longmen Mountain, thrust zone, front range, foreland, tectonic zonation, structural feature, geology tectonics