Early Cretaceous mafic dikes in the eastern North China Craton: implications for the effect of slab subduction on the mantle sources

The Early Cretaceous mafic dikes occur widely in the major gold districts of the eastern North China Craton (NCC), which are coeval and cospatial with many gold deposits, and these mantle-derived magmatic rocks provide a window to investigate the mantle compositions and metasomatism. Here, we present the Sr-Nd-Pb isotopic compositions of the Xiaoqinling mafic dikes and compare with regional geochemical and isotopic data for mafic dikes in Jiaodong, Xiaoqinling and interior of the NCC. The results indicate that the Early Cretaceous mafic dikes of Xiaoqinling and Jiaodong low-Ti group were derived from arc-like subcontinental lithospheric mantle (SCLM), that of Jiaodong high-Ti group were derived from OIB-like asthenospheric mantle, and that of the interior NCC were derived from both of lithospheric and asthenospheric mantle. Further, their mantle sources during Early Cretaceous were dominantly metasomatized by aqueous fluids derived from subduction slab as well as by limited melt and carbonate. Furthermore, the mantle beneath the Jiaodong low-Ti and Xiaoqinling is mainly characterized by EM2 type, whereas that of the interior NCC is mainly of EM1 type. Besides, the whole-rock Nd and zircon Hf isotopic compositions of these mafic dikes show clearly temporal and spatial variations with their ages of 145 ~ 110 Ma, reflecting that the mantle of the eastern NCC changed from the ancient IAB-like SCLM to juvenile OIB-like mantle through metasomatism. This process was controlled by the slab rollback of the paleo-Pacific plate during the extension.