The Louzidian normal fault near Chifeng, Inner Mongolia: Master fault of aquasi-metamorphic core complex

A special metamorphic core complex underlain by a low-angle strike-slip duc tile shear zone is present near Chifeng in eastern Inner Mongolia, northern China. The geology of the study area is similar to that of several Cordill eran metamorphic core complexes, but contrasts in significant ways as well. A major ESE-dipping normal fault, the Louzidian Range frontal fault, forme d during Late Cretaceous extension. This fault separates a crystalline foot wall locally containing mylonitic basement gneisses and granitic rocks (0 t o >3 km thick) from a non-metamorphic hanging wall that is distended by nor mal faults. However, the shear sense of the underlying mylonitic shear zone , a low-angle strike-slip zone, is not compatible with the Louzidian fault. It may be related to a pre-Cretaceous regional sinistral strike-slip event rather than the Late Cretaceous regional crustal extension common througho ut eastern China. Pre-existing mylonitic fabric anisotropy appears to have controlled the development of the Louzidian normal fault. Chloritic breccia s locally developed along the fault indicate that it cut deeply into the cr ust of northern China.