As the northern boundary of the North Dabie complex unit, the motion of the Xiaotian-Mozitan shear zone (XMSZ) in Early Cretaceous can be used to understand evolution of the North Dabie dome. For obtaining deformation time of the XMSZ, this paper used LA-ICP MS zircon U-Pb geochronology to study 4 undeformed intrusions from Xiaotian-Mozitan ductile shear zone based on detailed field survey. Detailed geochronological data show that these intrusions formed between 130-120 Ma. Therefore, a conclusion can be drawn that the ductile shear zone in XMSZ formed in the earliest Early Cretaceous associating with structural evidences. The XMSZ initiated as the same flat-lying ductile detachment shear zone at a deeper crustal level. Development of the flat-lying detachment shear zone was associated with lower crustal lateral flow under gravitational collapse in the earliest Early Cretaceous, and the detachment shear zone represents upper boundary of the lower crustal flow. The following large-scale magmatic intrusion and resultant buoyancy increase led to exhumation of the North Dabie dome and warping of the detachment shear zone. The present geometry of the detachment shear zones was caused by the inhomogeneous exhumation of the dome. The evolution of the XMSZ demonstrates that the North Dabie dome is a metamorphic core complex developed in the Dabie orogenic belt during post-orogenic extension.