Deformation history of the Hengshan Complex: Implications for the tectonic evolution of the Trans-North China Orogen

Structural analysis indicates that the Hengshan Complex underwent five distinct episodes of deformation (D1–D5). The D1 episode formed small isoclinal folds (F1), penetrative axial planar foliations (S1) and mineral stretching lineations (L1). D1 fabrics were reworked by following D2 deformation. Associated with D2 was the development of NW-verging asymmetric folds and accompanying thrust faults. Both D1 and D2 resulted from crustal thickening and coherent with prograde and peak metamorphism. D2 deformation was followed by transpressional dextral shearing (D3), including top-to-NW oblique-slip shearing and NNE–SSW dextral strike-slip shearing. Ongoing collision led to development of the Zhujiafang ductile shear zone (D4), a near E–W trending high strain belt across the Hengshan Complex. D5 deformation is characterized by F5 open folds and associated normal faults, probably related to exhumation of the complex. Structural patterns of the Hengshan Complex can place important insights into a recently proposed tectonic model suggesting that an ocean between the Eastern and Western Blocks underwent eastward-directed subduction beneath the western margin of the Eastern Block, and closure of this ocean finally led to collision between the two blocks to form the coherent North China Craton.