Subduction-related metasomatism of the lithospheric mantle beneath the southeastern North China Craton: Evidence from mafic to intermediate dykes in the northern Sulu orogen

Abstract

The widespread mafic to intermediate dykes in the northern Sulu orogen provide important constrains on mantle source characteristics and geodynamic setting. Here we present LA-ICPMS zircon U–Pb ages which indicate that the dykes were emplaced during Early Cretaceous (~113–108Ma). The rocks show SiO2 in the range of 46.2 to 59.5wt.% and alkalic and shoshonitic affinity with high concentrations of MgO (up to 7.6wt.%), Cr (up to 422ppm) and Ni (up to 307ppm). They are enriched in light rare earth elements LREE (La, Ce, Pr, Nd, Sm and Eu) and large ion lithophile elements (LILE, Rb, Sr, Ba, U and Th) and show strong depletion in high field strength elements (HFSE, Nb, Ta, Ti and P). The dykes possess uniformly high (87Sr/86Sr)i (0.70824–0.70983), low εNd(t) (−14.0 to −17.4) and (206Pb/204Pb)i (16.66–17.02) and negative εHf(t) (−23.5 to −13.7). Our results suggest that the source magma did not undergo any significant crustal contamination during ascent. The systematic variation trends between MgO and major and trace elements suggest fractionation of olivine and clinopyroxene. The highly enriched mantle source for these rocks might have involved melts derived from the subducted lower crust of Yangtze Craton that metasomatized the ancient lithospheric mantle of the North China Craton.