Age and composition of the Rushan intrusive complex in the northern Sulu orogen, eastern China: petrogenesis and lithospheric mantle evolution

AbstractZircon U–Pb age, whole-rock elemental and Sr–Nd isotopic data are presented for the Rushan intrusive complex from the northern Sulu orogen, China. The intrusion, emplaced at c. 111 Ma, consists mainly of biotite-bearing gabbro and pyroxene-bearing diorite. The rocks are high-K calc-alkaline in major elements, and enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), depleted in high field strength elements (HFSE), and possess narrow ranges of initial 87Sr/86Sr (0.70746–0.70827) and ɛNd(t) (−12.37 to −8.26). The complex is interpreted to originate from decompression melting of spinel-facies cratonic mantle that was metasomatized by the subducted Yangtze crustal materials and the melts experienced fractionation of olivine, clinopyroxene, apatite and Fe–Ti oxides. The Rushan complex is similar in composition to other Early Cretaceous mafic-intermediate complexes from the southern margin of the North China Craton, such as the Fangcheng basalts and Yinan gabbros, implying the mantle source of the Rushan intrusion is tectonically affiliated to the southern wedge of the Craton. We infer that the Rushan complex formed in an extensional regime corresponding to the asthenosphere upwelling during gradual erosion and replacement of the cratonic mantle by the fertile lithosphere beneath the eastern North China Craton.