Deformation characteristics and genesis of the Waziyu metamorphic core complex in western Liaoning of China

Abstract

The Waziyu metamorphic core complex is situated at the eastern end of the Yanshan tectonic belt. The NNE-striking detachment ductile shear zone in the core complex lies between the Archean metamorphic basement and Fuxin-Yixian rift basin, dips NW gently, and shows corrugation folds. Exposure structures, microstructures, and quartz C-axis fabrics all indicate top-to-the WNW sense of shear, i.e., ca. 285°, for the shear zone. Estimates of the deformation temperatures (ca. 550−250°C) demonstrate its mid-crustal origination and progressive deformation from deep to shallow levels. The northern segment of the shear zone shows relatively weak exhumation with exposures of low-temperature mylonites whereas its middle and southern segments have more intense uplifting with exposures of high-temperature mylonites. Biotite and muscovite 40Ar/39Ar ages, U-Pb dating results of zircon from dikes and plutons as well as formation ages of the supra-detachment basin all suggest the formation time of 135–100 Ma for the core complex. The formation was also associated with syntectonic emplacement of the Early Cretaceous Shishan pluton. The western margin of the core complex was truncated by the Sunjiawan-Shaohuyingzi brittle normal fault when it uplifted to shallow crust levels, and finally exhumed to near-surface levels. The core complex was developed by the rolling-hinge model under WNW-ESE extension during the Early Cretaceous peak destruction of the North China Craton. Ductile flow did not appear in the lower plate, therefore not supporting the low-crust gravitational collapse.