To better understand the mechanisms of crustal exhumation related to tectonic extension, we report on the progressive doming and detachment faulting of the Cretaceous Liaonan metamorphic core complex (MCC). The detachment fault zone of Liaonan MCC is comprised of two branches, i.e., the Jinzhou detachment fault zone (JDFZ) and the poorly-researched Dongjiagou shear zone (DSZ). Thus, integrated structural, microstructural, quartz c-axis fabrics, and fluid inclusion analysis, and U-Pb on zircon dating were performed on mylonites along the DSZ. In contrast with the JDFZ that possesses characteristics of detachment fault zone, the DSZ encompasses Archean gneisses and Neoproterozoic meta-sedimentary rocks, between which exists an obvious metamorphic contrast forming a tectonic discontinuity contact (TDC). However, rocks from both sides of the TDC possess structures and fabrics for identical geometries and kinematics that are consistent with those along the JDFZ. Thermometric analysis of fluid inclusions from syn-tectonic quartz veins (630 °C, 470 °C, 350 °C) and quartz c-axis fabric from mylonites along the DSZ show that the shearing penetrates throughout the Archean to Neoproterozoic rocks. Dating of zircons from syn-kinematic granitic dikes from DSZ yields an age ca. 134 Ma, which is similar to the ages of early shearing along the JDFZ (ca. 133~134 Ma). The results imply that the shearing initiated in both JDFZ and DSZ at an early stage, then progressive shearing continued, and finally developed the detachment faulting along the JDFZ. Based on the timing and processes of the regional extension, a geodynamic model of MCC’s is proposed.