The Structure, Evolusion And Regional Tectonic Implications Of Queshan Metamorphic Core Complex In Eastern Jiaodong Peninsula

The North China Craton(NCC) has suffered large scale lithosphere thinning during the late Mesozoic, and an important characteristic of it is the development of metamorphic core complex(mcc). Queshan mcc is a significant example of crust extension along the Jiaobei terrain in esatern NCC in this period.The mcc is a typical Cordilerran type core complexe which is constituted by 3-layered archtechture. The upper plate consists of weakly deformed half-graben basin and some lower Proterozoic Jingshan group formation; The lower plate is composed by high-grade metamorphic complexes of Jiaodong group, and plutonic bodies(Queshan pluton and Yuangezhuang pluton) associated with; Both plates are separated by a master detachment fault comprising mylonitic rocks. A series of brittle fault with NNE extending superimposed on and destructed the mcc. The petrology, geometry, kinematics, macro- and micro- structure and crystallographic preferred orientation of quartz show that the detachment fault zone experienced a progressive deformation and metamorphic processes from amphibole facies to greenschist facies, until the surface. It also indicates the lower plate rocks gradually transformed from a deep to a shallow crust level under the nearly NWW-SEE regional extensional mechanism. The finite strain of quartz and kinematic vorticity numbers in tectonite from the detachment fault zone show the shear type of the master detachment fault zone with exhumation change from pure shear dominated to simple dominated and the strain increased as a whole. Based on the discussion about the geochronology of superposed basin and intrusion the lower plate, we infer the age of the queshan mcc formed is 135-113Ma. According to the analysis of the characteristics and formation age of extentional teconics developed in Jiaodong-Liaodong peninsula, we infer that the extention of Jiaodong-Liaodong early Cretaceous extensional provinces occured during early Cretaceous went through two stages.and the middle-lower crust flow is the dominant factor of extentional tectonics-forming.