Late Mesozoic intracontinental deformation at the northern margin of the North China Craton: A case study from the Kalaqin massif, southeastern Inner Mongolia, China

Abstract

The East Asian continent underwent intense crustal shortening-thickening and following large-scale lithospheric extension in the late Mesozoic due to multiple plate convergence. How to respond to the multiple plate convergence in the North China Craton remains enigmatic. Here we undertaken structural measurements and fault kinematic analysis of the Kalaqin massif in the northern part of the North China Craton (NCC), together with new geochronological results, delineate two stages of intracontinental deformation in the area: (1) NE–SW-striking ductile sinistral shearing (Ds) at 150–135 Ma; and subsequent (2) NW–SE ductile–brittle extensional deformation (De) at 135–110 Ma. Based on electron-backscatter diffraction (EBSD) analysis of quartz c-axis fabric and the characteristics of dynamically recrystallized quartz and feldspar, we estimate that ductile deformation during Ds and De occurred at temperatures of 400–700 °C (i.e., greenschist–amphibolite facies conditions). Kinematic vorticity analysis shows that Ds deformation was characterized by vorticity values (Wk) of 0.72–0.87 (average = 0.793), corresponding to general shear with a dominant simple shear component. Somewhat lower vorticity values of 0.45–0.92 (average = 0.698) during De event indicate a dominant pure shear component. We suggest that Ds reflected the regional NE-striking sinistral shearing represented by the Tan-Lu Fault Zone. Combined with contemporaneous dextral transpression along the ~E–W-striking Chifeng–Kaiyuan Fault and Fengning–Longhua Fault, these structures constituted a regional conjugate strike-slip system in the northern edge of the NCC. Ds event was likely associated with the episode B of the Yanshanian movement, which might result from the subduction of the Paleo-Pacific plate beneath East Asia and the closure of the Mongol-Okhosk Ocean. The subsequent De represents the destruction of the NCC during the Early Cretaceous, which was likely influenced by the roll-back of the Paleo-Pacific plate and post-orogenic extensional collapse of the Mongol-Okhotsk belt.