The relationship between the shear zones flanking Tongbai orogenic belt and implications for the tectonic evolution

The Yindian-Malong shear zone and the Hongyihe-Tongbai shear zone flanking south side and north side of Tongbai orogenic belt respectively are two most important boundary zones which segmented the core complex and high-pressure metamorphic rocks. Through the detailed field observation, microstructural analysis and quartz C axis analysis, our studies indicate that the Yindian-Malong and Hongyihe-Tongbai shear zones have the same deformed characteristics with symmetric kinematics, suggesting that the two shear zones may derive from a uniform detachment shear zone characterized with nearly EW extension. The L tectonites and sheath fold occurred by constrictional deformation beneath the detachment shear zone. The S-L rocks (mylonitic rocks) formed by flattening strain in the detachment shear zone. The uniform detachment shear zone exhibited a top-to-NWW movement at the top of the Tongbai complex, which suggests an orogen-parallel extension of the Tongbai complex in a nearly W-E direction. This orogen-parallel extension gave rise to the widely development of the linear structure in the Tongbai orogenic belt. The similar features of the top-to-NWW shearing were also widely observed in the Dabie orogenic belt, which suggests that a uniform detachment shearing of the ductile lithosphere may occur in the Qinling-Tongbai-Dabie-Sulu orogenic belt at the Early Cretaceous.