Abstract: A series of metamorphic core complexes developed around the Bohai Bay Basin recording the crustal stretching process of the eastern North China Craton since the Late Mesozoic. In order to reveal the characteristics of the metamorphic core complex developed in the basin, we selected the Xianxian High and southern Raoyang Sag as the study area. We determined the deformation characteristics of the Xianxian fault and its hanging wall through fine interpretation of the seismic and drilling data, and constructed the age and lithology of the strata developed on the Xianxian High using drilling data obtained from the southern Raoyang Sag. We discuss here the timing and genetic model of the Xianxian metamorphic core complex based on comprehensive consideration of its developmental characteristics and background in the North China Craton. Our study shows that (1) the curved Xianxian fault in the study area has the characteristics of the main detachment fault; (2) the southern Raoyang Sag, located in the hanging wall of the fault, shows residual Middle Proterozoic to Lower Paleozoic accompanied by numerous secondary faults with different dips in the sag; and (3) the Archean to Paleoproterozoic strata constitute the main part of the Xianxian High with lithology including hornblende, biotite monzonitic and localized granite gneisses. Overall, our results demonstrate that the Xianxian metamorphic core complex, formed in the Late Mesozoic (K1?), has the basic characteristics of a typical metamorphic core complex. It developed in the background of the large-scale lithospheric thinning of the eastern North China Craton and evolved in accordance with the rolling-hinge model.

Key words: extensional structures, metamorphic core complex, Xianxian High, Bohai Bay Basin