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

Abstract

Structural analysis indicates that the Hengshan Complex underwent five distinct episodes of deformation (D 1-D 5). The D 1 episode formed small isoclinal folds (F 1), penetrative axial planar foliations (S 1) and mineral stretching lineations (L 1). D 1 fabrics were reworked by following D 2 deformation. Associated with D 2 was the development of NW-verging asymmetric folds and accompanying thrust faults. Both D 1 and D 2 resulted from crustal thickening and coherent with prograde and peak metamorphism. D 2 deformation was followed by transpressional dextral shearing (D 3), 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 (D 4), a near E-W trending high strain belt across the Hengshan Complex. D 5 deformation is characterized by F 5 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. © 2007 Elsevier Ltd. All rights reserved.