Timing and processes of late Mesozoic mid-lower-crustal extension in continental NE Asia and implications for the tectonic setting of the destruction of the North China Craton: Mainly constrained by zircon U-Pb ages from metamorphic core complexes

Late Mesozoic large-scale crustal extension occurred across the northeastern section of continental Asia, and metamorphic core complexes (MCCs) are the major features in this region. This paper presents new zircon U-Pb and Ar-Ar ages of biotite and hornblende for pre- or syn- (mylonitized) and post-kinematic (unmylonitized) intrusions from these MCCs, and attempts to determine the timing of initiation, duration and termination of the mid-lower-crustal ductile extension by integrating with geochronological data from previous studies. These MCCs have similar 40Ar/39Ar biotite and hornblende ages (130 to 110 Ma, mainly from 130 to 120 Ma), which are interpreted as the cooling ages and represent the timing of the late-stage formation of the MCCs. Zircon U-Pb ages for syn- to post-kinematic intrusions from some MCCs suggest that the mid-lower-crustal extension probably initiated at ca. 150-145 Ma with a peak occurring 145-130 Ma and continued to 130-120 Ma, which is older than that suggested by 40Ar/39Ar ages by 10-20 Ma. The early ductile extension most likely initiated in Mongolia and northern China during the Late Jurassic (150-145 Ma) at a deeper level, then propagated southwards (140-130 Ma), and finally developed throughout the entire continental NE Asia (130-120 Ma). Based on the timing and processes of the extension, a geodynamic model and tectonic setting of the destruction of the North China Craton (NCC) are proposed. (C) 2012 Elsevier B.V. All rights reserved.