Structural pattern of the Wutai Complex and its constraints on the tectonic framework of the Trans-North China Orogen

Wutai Complex is a key to test controversial models for the tectonic evolution of the Trans-North China Orogen (TNCO), along which the Eastern and Western Blocks amalgamated to form the North China Craton. Three stages of deformation (D1 to D3) were identified in the Wutai Complex. D1 is characterized by NE–SW-trending foliations S1 and NW–SE-orientated lineations L1, indicating an initial NW–SE-directed compression. Associated with D1 was prograde metamorphism (M1). D2 progressively overprinted D1 and generated ‘Z’-shaped folds and NEE–SWW-trending ductile shear zones. D2 resulted in a fan-shaped structural pattern of the complex with top-to-the-NW thrusting in the northwestern part and opposite top-to-the-SE thrusting in the southeastern part. During D2, the crust was doubled through thickening, leading to peak metamorphism (M2). D3 developed during post-collision exhumation and deformed the early fabrics to be open folds, resulting in near-isothermal decompression (M3) and late cooling metamorphism (M4). The overall structure of the Wutai Complex is characterized by a fan-shaped pattern with structural divergence. Structural features of the Wutai Complex, combined with those of the adjacent Hengshan and Fuping Complexes, indicate that the TNCO is characterized by a fan-shaped orogenic wedge with opposite senses of thrust. This orogenic wedge could have resulted from an eastward subduction and collision between the Western and Eastern Blocks to finally form the TNCO at ∼1.85 Ga.

► Wutai Complex experienced superimposition of polyphase deformation and metamorphism.
► Wutai Complex is characterized by a fan-shaped pattern with structural divergence.
► Trans-North China Orogen is a fan-shaped orogenic wedge with opposite geometries.
► This orogenic wedge was resulted from an eastward subduction and collision.