Abstract:

In North China the upper crust is dominated by brittle deformation and lower crust is characterized by ductile extension. However these two styles of different deformation have the same extensional direction and the similar extension amount, which resulted in the development of a regional detachment layer along the top of the middle crust in North China due to differential movement between the upper and lower crust. The detachment structure has controlled the development of the basin-range pattern and the basement of North China Block. The tectonics in this region is produced by thin-skinned extension in the brittle upper crust.The stair-shape detachment layer in North China Block is distributed continuously at depth 12-22 km (mostly at 15-18 km). Eleven detached units (or regions) can be identified. Brittle faulting mainly occurs in the upper crust. The locations of the faulted blocks, configuration and their deformation manners are dictated jointly by occurrence of the ramp-flat detachment, cutoff lines perpendicular to the detachment and accommodation faults parallel to the detachment. Three primary axes of the rifted-depression, two main cutoff lines and three main accommodating faults have been recognized.

Key words: crust, extension regime, detachment layer, ductile deformation, brittle deformation, North China