Qinling Yan Shan Tectonic Characteristics And Evolution

The Qinling erogenic belt is a composite continental orogen which has evolved in different tectonic regimes during different geologic period and is characterized by complex structure and a prolonged complex history. It had been formed during Indo-China orogeny while the Qinling ocean finally closed and the North china and the Yangtse plates eventually collided with each other. According to luonan fault and shandan fault extending roughly from East to West, the Qinling erogenic belt is divided into three parts: the South margin of north china block, the Northern Qinling and the Southern Qinling. The Xiaoqinling area locates in the South margin of north china block which is bounded on the north by the taiyao fault and on the south by the luonan fault. By yanshanian the Qinling orogenic belt had the characteristics of intra-continent orogeny, which falls into two successive stages: Yanshanian intra-plate orogeny and late Mesozoic- Cenozoic intra-plate extension.Based on the theory of plate tectonics and the new knowledge of continental dynamics, this paper starts mostly with tectonic analysis and then makes a comprehensive view on the characteristic of stratum composition, gold mine mineralized, magmatic activity as well as ruptures activity to discuss the Yanshanian tectonic evolution of the Xiaoqinling area under the regional tectonic framework of Qinling orogenic belt.Stratum composition in Xiaoqinling represents early Precambrian crystal basement and Mesoproterozoic Era cover rocks of the typical North china craton. There aren't late Paleozoic-Mesozoic structural layer in Xiaoqinling, so Taihua Group upheaval area and its bilateral ruptures are critical sectors of investigation.Tectonic analysis controlling gold mine mineralization in Taihua group suggest that ductile fractures chang into brittle-ductile ones going with upliftling of Xiaoqinling area after In-china orogeny. Brittle fractures form on the basis of brittle-ductile ones that develop and inherit the characteristic of the latter stress field.Folds and faults analysis in Taihua group and its bilateral reveal that Yanshanian tectonic evolution of Xiaoqinling area undergo at least three phases of deformation. The first phase involves the formation of thrusting and napping towards NWW accompanied by extensive igneous activity and mineralization. The second phase corresponds to the development of asymmetrical small fold downwards north and south. The final phase the Cenozoic is marked by strong brittle fractures activity resulting in the sharp heave of the landform of Xiaoqinling aera. According to granite ages cutting ruptures, mineralized quartz veins ages corresponding to fold deformation and formation ages of bilateral faulted basin, deformation age are limited, that are 100~65Ma for one and form 65Ma to the present for two and three.In summary, this paper indicates that Yanshanian tectonic process of Xiaoqinling aera give priority to deformation of thrusting and napping and coexist with deformation of extending and pullapart. Taihua group was rapid uplifted in Yanshanian that resulted in both compressive thrusting and napping and extending process.