The Late Mesozoic Tectonic Transition Of The Eastern Part Of North China Craton

The Liaodong Peninsula developed a large scale Jurassic-Cretaceous magmatic rocks and a series of Cretaceous extensional structures.The lower plates of the Cretaceous Jinzhou, Dongjiagou, Wanfu and Dayingzi detachment faults, in the Liaodong Peninsula, experienced a progressive deformation and metamorphic process from higher facies amphibolite facies to lower greenschist facies, i.e., these detachment faults underwent a gradual exhumation history from lower/middle to shallow crust levels. On the basis of our geochronological results of granitic intrusions or dykes from the lower plate of Liaonan and Wanfu mcc’s and previous dating ages, we present that the detachment faulting of the Jinzhou and Dayingzi detachment faults initiated at ca.135Ma and terminated at ca.113Ma or 106Ma.120Ma is the initiation of Wanfu detachment faulting. And also we reveal that there are two stages of exhumation of the four detachment faults, i.e., a long and progressive cooling/exhumation history for the lower plate of the Jinzhou, Dongjiagou and Dayingzi detachment faults (135- 120Ma), and a short, simple one for the lower plate of the Wanfu detachment fault (120-106Ma).Nine granites from the lower plate of Liaonan Metamorhphic core coemplex in the Liaodong Peninsula, using zircon U-Pb LA-ICP-MS dating, were dated 185Ma to 154Ma, which show that Jurassic is an important period of magmatism in the Liaodong Peninsula and the major intruding time is 185-154Ma. Previeous geochronological results of Cretaceous magmatism display 135-106Ma is also an important period.Geochemistry of Jurassic samples corresponds to I-type granites with adakitic and arc-like signatures which mainly experienced fractional crystallization and weakly partial melting of crust. On the basis of tectonic-magmatic discrimination diagrams, we conclude that the tectonic setting of North China Craton during Jurassic (ca.185-154Ma) was associated with Izanagi palte subduction and crustal thickening; however, Cretaceous granites (ca.135-106Ma) are post-orogenic, related to crust extension and lithospheric thinning. We use the geochronological and geochemical results to reconstruct the regional plate tectonics and the transition from compression to extension during the Late Jurassic-Early Cretaceous, ca.154-135Ma.