Deep-level ductile detachment system in the Jiaobei terrain, eastern China: Deformation response of the overlying plate during the exhumation of Yangtze plate.
胶北地体中的深层次拆离构造:扬子板片折返的板上响应

Two large-scale deep-level ductile detachments are identified in the Precambrian basement of Jiaobei block, at the southeast end of North China Craton and nearing the northern Sulu ultrahigh pressure metamorphic belt, eastern China. They are respectively DF1 locating between Archean Jiaodong Group (JD) and Paleo-proterozoic Fenzishan Group (FZS) and DF2 between FZS or JD and Neo-proterozoic Penglai Group (PL). Microstructures and fabrics show the top-to-northwest shear sense and the fabric evolution of quartzite with temperature decreasing. The recrystallized deformation ages are restricted at 153±2Ma and 128.5±1.5Ma by SHRIMP U-Pb dating for mylonitic orthogneiss from DF1, which behalf respectively the forming age and reactive age of detachment. Combining with other extension structures, such as magmatism, sediments of Cretaceous Jiaolai basin and the ductile detachment confining Jiaolai basin (148Ma), we suggest that the large-scale deep-level ductile detachments with top-to-NW shear sense formed during the uplift (late exhumation) extension stage of UHP metamorphic rocks and is kind of intraplate deformed effect of overlying plate during continental deep-subduction of Yangtze plate.