Petrogenesis of the Mesozoic mafic dykes in the Jiaodong Peninsula: Implications for the evolution of the lithospheric mantle beneath the eastern North China Craton

Mafic dykes are generally formed in an extensional environment and can also indicate the characteristics of the mantle source region. Mesozoic mafic dykes are widely developed in the Jiaodong Peninsula and are closely associated with gold veins. Based on the geochronological and geochemical characteristics of regional mafic dykes, this study selects mafic dykes in typical gold deposit for detailed research. The geochronological study of mafic dykes in typical gold deposit reveals that the Mesozoic mafic dykes occurred from 136Ma to 103Ma. The mafic dykes have high levels of MgO, SiO2, Cr, Ni and Mg#, with K2O content of 1.93%~2.58% and Na2O content of 1.58%~2.96%, belonging to the high-K calcium alkaline-series basalt. The geochemical compositions of mafic dykes show that they were derived from the low-level partial melting of enriched lithospheric mantle in the spinel-garnet transition zone. Geochemical signatures of the mafic dykes, including enrichment in LILEs and depletion in HFSEs, reveal mantle source metasomatism by fluids from an ancient subducted slab. Comprehensive study of these dykes across the Jiaodong Peninsula implicates the Early Mesozoic westward subduction of the Paleo-Pacific Plate beneath the North China Craton as the primary event that enriched the lithospheric mantle through subduction-related metasomatism. Driven by a steepening subduction angle and retreat of the Paleo-Pacific Plate, along with a shift in the Izanagi Plate's motion, the region experienced significant extension during the Early Cretaceous. This extension facilitated lithospheric thinning and asthenospheric upwelling, which in turn caused underplating and partial melting of the lithospheric mantle, forming mafic dykes between approximately 136Ma and 103Ma. In conclusion, the Mesozoic lithospheric thinning in the eastern part of the North China Craton is a long-term thermal erosion event caused by the subduction and retreat of the Paleo-Pacific Plate.