Quaternary basalts from Longgang in the North China Craton: petrologenesis and characteristics of the mantle source

The geochemistry of Quaternary volcanic rocks from Longgang provides important constraints on the petrogenesis of continental alkali basalts and characteristics of mantle source in the eastern North China Craton. Longgang Quaternary basalts are alkali affinities and characterized by OIB-like REE and trace elements patterns. Longgang basalts show slight depleted Sr-Nd isotopic compositions ( (81) Sr/(16) Sr = 0. 7044 similar to 0. 7048, epsilon(Nd) = 0. 6 similar to 2. 1) and Dupal-like Pb isotopic compositions ((206) Pb/(204) Pb = 17. 734 similar to 18. 194, Pb-207/(204) Pb = 15. 553 similar to 15. 594, (208) Pb/(204) Pb = 38. 322 similar to 38. 707). These integrated geochemical and isotopic signatures consist with mantle mixing between MORB-like asthenospheric mantle, isotopically enriched EM I -type subcontinental lithospheric mantle and fluid/melt derived from subducted slab, indicating some degree interaction between lithosphere and asthenosphere and influence of subduction of the Pacific plate. The existing of multiple end-members in the magma source suggests that there might be several factors which affect the process of the lithospheric thinning or replacement in this region.