Early Cretaceous potassic volcanic rocks from the northern margin of the Sulu orogenic belt, Shandong Province, eastern China: Constraints on petrogenesis and crust–mantle interaction

Abstract

A major and trace element, Sr–Nd–Hf isotope, and zircon U–Pb geochronology study was conducted on Early Cretaceous volcanic rocks from the northern margin of the Sulu orogenic belt in Shandong Province, eastern China. These results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of crust–mantle interaction. The rocks comprise high‐K basaltic andesite, shoshonites, latites, high‐K dacites, and high‐K rhyolites. U–Pb zircon dating of four representative samples of latite, two high‐K dacites, and high‐K rhyolite indicates that these rocks formed from 126 to 122 Ma. The volcanic rocks are characterized by high K2O (2.04–6.70 wt.%) and total alkalis (Na2O + K2O; 5.3–10.9 wt.%) that plot within the field for shoshonitic rocks. All the rocks are enriched in light rare earth and large‐ion lithophile elements (e.g., Rb, Th, U, and K) and are depleted in high‐field‐strength elements (e.g., Nb, Ta, and Ti). The rocks have high initial 87Sr/86Sr ratios (0.706760–0.708898), low εNd(t) values (−19.5 to −12.5), and negative εHf(t) values (−31.3 to −19.7), similar to the Early Cretaceous Jiaodong mafic dikes and intermediate–mafic volcanic rocks. These geochemical and isotopic characteristics indicate that the volcanic rocks formed through simultaneous fractional crystallization and crustal assimilation of a basaltic magma derived from metasomatized mantle. The metasomatized mantle source might have been produced by the recycling of subducted Yangtze Craton crust into the ancient lithospheric mantle of the North China Craton.