Exhumation of metamorphic core complexes through progressive doming and detachment faulting: insights from the Cretaceous Liaonan metamorphic core complex, eastern North China craton

38 To better understand the mechanisms of crustal exhumation related to tectonic 39 extension, we report on the progressive doming and detachment faulting of the 40 Cretaceous Liaonan metamorphic core complex (MCC). The detachment fault zone of 41 Liaonan MCC is comprised of two branches, i.e., the Jinzhou detachment fault zone 42 (JDFZ) and the poorly-researched Dongjiagou shear zone (DSZ). Thus, integrated 43 structural, microstructural, quartz c-axis fabrics, and fluid inclusion analysis, and 44 U-Pb on zircon dating were performed on mylonites along the DSZ. In contrast with 45 the JDFZ that possesses characteristics of detachment fault zone, the DSZ 46 encompasses Archean gneisses and Neoproterozoic meta-sedimentary rocks, between 47 which exists an obvious metamorphic contrast forming a tectonic discontinuity 48 contact (TDC). However, rocks from both sides of the TDC possess structures and 49 fabrics for identical geometries and kinematics that are consistent with those along the 50 JDFZ. Thermometric analysis of fluid inclusions from syn-tectonic quartz veins 51 (630 °C, 470 °C, 350 °C) and quartz c-axis fabric from mylonites along the DSZ 52 show that the shearing penetrates throughout the Archean to Neoproterozoic rocks. 53 Dating of zircons from syn-kinematic granitic dikes from DSZ yields an age ca. 134 54 Ma, which is similar to the ages of early shearing along the JDFZ (ca. 133~134 Ma). 55 The results imply that the shearing initiated in both JDFZ and DSZ at an early stage, 56 then progressive shearing continued, and finally developed the detachment faulting 57 along the JDFZ. Based on the timing and processes of the regional extension, a 58 geodynamic model of MCC’s is proposed. 59