Revisiting the deformation and migmatization of the Tongbai complex in the Tongbai orogenic belt, central China

The Tongbai complex plays an important role in the understanding of the tectonic evolution of the Tongbai-Dabie orogenic belt. By detailed structural analysis, new zircon U–Pb dating, zircon Lu–Hf analysis and whole-rock elements for the rocks in the Tongbai complex and the wrapped shear zones, we suggested that the Tongbai complex was derived from the partial melting of the basement of Yangtze Block and experienced a uniform orogen-parallel extension with a top-to-NW shearing at 142–133 Ma. The migmatites yield a migmatization age of 116 ± 2 Ma and are identical to the metamorphic age of 115–111 Ma from the L and LS tectonites in the Tongbai complex. The late Early Cretaceous migmatization may give rise to the severance of the uniform top-to-NW shear zone and lead to an antiform folding of the Tongbai complex. The similar deformation and migmatization of the complexes in both the Tongbai and Dabie orogenic belts suggest that the Tongbai-Dabie orogenic belt is likely to have a similar tectonic transformation from orogen-parallel to orogen-perpendicular extension in the Early Cretaceous, namely a uniform orogen-parallel extension of the ductile lithosphere during the early Early Cretaceous and a widespread migmatization during the late Early Cretaceous.