Geochemical and Sr-Nd-Pb isotopic compositions of mafic dikes from the Jiaodong Peninsula, China: evidence for vein-plus-peridotite melting in the lithospheric mantle

Major and trace elements and Sr-Nd-Pb isotope data are reported for Cretaceous mafic dikes from the Jiaodong Peninsula, eastern China. These dikes range from medium-K and high-K calc-alkaline to shoshonitic or ultrapotassic rocks, which are characterized by high MgO (Mg = 71-53) and Cr (177-1012 ppm) and low TiO2 (0.55-0.90 wt.%), total Fe2O3 (5.12-9.48 wt.%) and CaO (4.99-9.94 wt.%). Overall, they are enriched in the large ion lithophile elements (HFSE, e.g., Rb, Ba, Sr) and light rare earth elements (LREE), depleted in the high field strength elements (HFSE, e.g., Nb, Ti, P), and possess uniform initial Sr-87/Sr-86 (0.7094-0.7114) but relatively wide ranges of Nd[epsilon(Nd) (T)= -100.1- -17.0] and PB (Pb-206/(PB)-P-204 = 16.75-18.03) isotopic ratios, implying a magma origin from enriched but heterogeneous mantle sources. These geochemical and isotopic characteristics can be explained by the vein-plus-peridotite melting model, with amphibole- or phlogopite-bearing pyroxenite veins that reside in refractory lithospheric mantle beneath the North China Block. Such a vein-enriched mantle source formed by multiple metasomatic events, which we infer to have resulted from subduction-related processes that may have occurred in the Late Archean and Mesoproterozoic. The mafic dikes constitute a member of the widespread Mesozoic magmas emplaced in the North China Block as a result of regional lithospheric extension. (C) 2004 Elsevier B.V. All rights reserved.