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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<inf>1</inf>-D<inf>5</inf>). The D<inf>1</inf> episode formed small isoclinal folds (F<inf>1</inf>), penetrative axial planar foliations (S<inf>1</inf>) and mineral stretching lineations (L<inf>1</inf>). D<inf>1</inf> fabrics were reworked by following D<inf>2</inf> deformation. Associated with D<inf>2</inf> was the development of NW-verging asymmetric folds and accompanying thrust faults. Both D<inf>1</inf> and D<inf>2</inf> resulted from crustal thickening and coherent with prograde and peak metamorphism. D<inf>2</inf> deformation was followed by transpressional dextral shearing (D<inf>3</inf>), 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<inf>4</inf>), a near E-W trending high strain belt across the Hengshan Complex. D<inf>5</inf> deformation is characterized by F<inf>5</inf> 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.