Vertical tectonics of a Neoarchean gneiss dome in the eastern North China Craton

Archean gneiss domes are a very common structure in old cratons, these are different from the structural patterns in the post-Archean linear orogenic belts related to subduction and collision. There are two tectonic models in Archean tectonics: horizontal tectonism and vertical tectonism. The formation mechanisms of Archean gneiss domes are still debated. Here we present data from the Anziling gneiss dome, a typical gneiss dome structure from the eastern North China Craton, which was formed dominantly by vertical tectonism during Neoarchean times (2554-2452 Ma). The Anziling gneiss dome is located in the east of Shuangshanzi, East Heibei Province and consists of the Anziling gneiss (a diopside-monzonitic gneiss) in the center outwards surrounded by the Jiguanshan gneiss (hornblende-plagioclase gneiss) and the Niuxinshan gneiss (trondhjemitic gneiss), together showing an irregular elliptical shape with a NE-ward extending tail on the surface. But in the cross-section, it represents a deflective dome, both north-western and south-eastern limbs dip approximately to the west. The dome suffered inhomogeneous ductile shear deformation, much stronger with more displacement in the north-western half (especially close to the margin) than that in the eastern half. The core area shows only a relatively weak deformation. Therefore, we suggest that the Anziling gneiss dome was formed by the TTG (trondhjemite, tonalite, granodiorite) pluton rising obliquely up towards the east by diapirism in the first stage, followed by sub-horizontal emplacement towards the north and then to the north-east associated with clockwise rotation in the second stage. The Anziling gneiss dome and its neighbouring Shuangshanzi shear zone were formed simultaneously, indicating that the Anziling gneiss dome was driven by both gravitational forces and magma diapirism.