The Tectonic Evolution Of Bikou Terrane

Bikou terrane is wedging shaped between Western Qinling orogeny. Longmenshan belt and Songpan-ganzi Orogeny, and it is bordered by Mianxian-lueyang belt, Qingchuan-Yangpingguan fult and Minshan-Huya falt. Because of its special location, sating on the structural translating part of the central orogenic belt, Helan-Longmen tectonic belt and Tibetan Plateau, Bikou Terrane has been one of the best important regions in the study of continental tectonics in China. The stratum outcropped in this area is mainly volcanic rocks of Bikou group, Neoproterozoic, which is significant different from the adjacent areas of phanerozoic. The structural features in Bikou terrane are mainly N-NE distribution, crosscutting that in adjacent units, which shows the unique geologic features.Based on the analysis of the geometric and kinetic features of the deformations and recovery the paleo-stress in the three main boundary faults of Bikou terrane, this paper systematically analyzed the main structural evolution stages of the faults and the deformation features in each stage, and identified the influences on Bikou terrane. caused by the boundary faults. We discussed the control action on Bikou terrane in its evolution history by the boundary faults in detail. Combined structural analysis and magnetic fabric study, we conclude that the magnetic fabric of the rocks is well consistent with the structural features, which may reflect the strain characteristics. The magnetic fabric study is an effective method to study the deformation in this area that strongly weathered and lack of geological mark.According to the study results on the three main boundary faults and the regional geology, we divide the evolution of Bikou terrane into 5 main stages:1) Jinningian, the conformation of the transition cap (Bikou Group) in Bikou terrane.2) Caledonian. Bikou terrane break-off from the edge of Yangzi Plate.3) Indosinian, the main structural framework of Bikou terrane formed during the strong orogeny,4) Yanshanian, the superimposed deformation and westward escape of the Bikou terrane under the action of the intra-continental orogeny,5) Himalayan, the final conformation of Bikou terrane. In addition, we analyzed the deformation features in each main stage and discussed their geodynamics. on which the tectonic evolution model is established.