Multistage crust-mantle interactions during the destruction of the North China Craton: age and composition of the Early Cretaceous intrusions in the Jiaodong Peninsula

In situ Zircon U-Pb ages and Hf-isotopes, whole-rock major- and trace elements, and Sr-Nd isotopic compositions of the Liudusi and Taiboding intrusions in the Jiaodong Peninsula (eastern China) are presented to trace their petrogenesis and relationships to lithosphere evolution. The Liudusi complex, which consists of biotite-bearing gabbro and quartz monzonite, formed at ca 115Ma. The rocks show shoshonitic alkaline affinities and have crust-like trace-element compositions, superchondritic Zr/Hf and Nb/Ta, but low Rb/Sr and high Ba/Rb ratios, coupled with high initial ⁸⁷Sr/⁸⁶Sr, and negative ε_Nd(t) (-15.9) and ε_Hf(t) (-17.8 to -16.4). The data suggest that the complex was derived from an amphibole-bearing spinel to garnet lherzolitic mantle which is tectonically affiliated to the southeastern margin of the North China Craton (NCC). The parental magma may have experienced fractionation of olivine, clinopyroxene, apatite and Fe-Ti oxides. The Taiboding porphyritic K-feldspar granites (ca 118Ma) with high SiO₂ (72.7-73.7wt.%) are metaluminous with Nb/Ta ratios (10.7-12.4) similar to that of the average continental crust. They also have highly negative zircon ε_Hf(t) (-21.8 to -19.3), low ε_Nd(t) (-17.5 to -15.2) and initial ⁸⁷Sr/⁸⁶Sr of 0.70874-0.70883, suggesting that they were dominantly derived from partial melting of the ancient NCC lower crust but with contributions from the mantle. The Liudusi and Taiboding intrusions reflect complex processes involving partial melting of the lithospheric mantle that was modified by a subducted continental crust, lower crust anatexis induced by basaltic underplating, and subsequent magma hybridization in an extensional regime associated with a considerable thinning of the lithosphere in the eastern NCC during the Early Cretaceous. Multistage crust-mantle interactions including (1) lithospheric mantle modification, induced by subduction of the continental crust which would make the lithospheric mantle more susceptible to weakening, melting and thinning; (2) basaltic underplating, which would lead to the reworking and replacement of the lower crust, and (3) hybridization of mantle- and crustal-derived magmas that reflects further exchange of energy and material between the reactivated lithospheric mantle and the deep crust, can be identified from the generation of the two intrusions. These processes played important roles in the destruction of the eastern NCC lithosphere, especially along near-suture areas.