The newly discovered Waziyu metamorphic core complex, Yiwulü Shan, western Liaoning Province, North China

The previously undiscovered Waziyu metamorphic core complex in the Yiwulu Shan, a mountain range in western Liaoning Province, consists of a master, west-dipping, low-angle normal fault, the Waziyu detachment, that separates a hanging wall of dominantly Early Cretaceous sedimentary and volcanic units from a footwall of mylonitic and non-mylonitic units. Exposures of the Waziyu detachment fault (previously called the Sunjiawan-Shaohuyingzi fault) along the western flank of the range have dips of 10～40° and excellent kinematic indicators that give consistent top-to the west-northwest sense of shear (ca. 290°). Mylonitic units in the footwall associated with Early Cretaceous crustal extension yield the same top-to the west-northwest sense of shear and are kinematically related to the Waziyu detachment fault. The timing of extension and metamorphic core complex development in the Yiwulu Shan is broadly constrained as Early Cretaceous (ca.127～116 Ma) by published and unpublished U-Pb geochronology,~(40)Ar/~(39)Ar thermochronology, and stratigraphic age determinations based upon biostratigraphy in the hanging wall supradetachment Fuxin basin. We have found no evidence for a symmetrical Yiwulu Shan mcc as reported in earlier literature. Recognition of the Waziyu mcc and its WNW-rooting detachment fault adds to our understanding of the extensional behavior of the North China crust. Future work in the Yiwulu Shan should include field-based structural studies to define the spatial extent of both the detachment fault and the kinematically related footwall mylonites, collection of additional samples for geo/thermochronology, and petrologic studies of the plutons within the range. We attribute formation of the Waziyu metamorphic core complex to collapse of an orogenically thickened crust that was facilitated by thermal weakening due to Early Cretaceous magmatism and paleo-Pacific plate boundary reorganization.