Early Cretaceous granodiorite and its mafic enclaves from the Shuiyu area (Southern North China Craton): implications for crust–mantle interaction

Abstract

ABSTRACT The Early Cretaceous granitoids are widely distributed in the southern North China Craton (NCC), petrogenesis of these rocks is critical to understanding the implications for the Early Cretaceous geological evolution at the southern margin of the NCC. This paper presents detailed zircon LA-ICP-MS U-Pb ages, geochemistry, in-situ zircon Hf isotope for the granodiorite and its mafic microgranular enclaves (MMEs) from the Shuiyu area, southern NCC. The granodiorite and its MMEs have identical zircon U-Pb ages (~130 Ma). Field and petrological observations, such as ellipsoidal shapes, partly diffusive contact to the host rocks, erosion and resorption textures in amphibole, combined with their low SiO2 content, high Mg# values and negative εHf(t) values (−13 to −18), suggest the MMEs were derived from enriched lithospheric mantle. The host granodiorite displays moderate SiO2 contents, high Sr/Y (44 to 113) and La/Yb (25 to 38) ratios, and low zircon Hf isotopes (−10 to −23), suggesting they were from primary magmas generated by partial melting of the ancient thickened lower continental crust of the North China Craton. The petrogenesis of Early Cretaceous intrusions and its MMEs in southern NCC geodynamically interpreted as resulting from the break-off of the subducted Yangtze Craton slab, associated with the upwelling of asthenospheric mantle material, which provided the necessary heat and triggered the partial melting of the enriched lithospheric mantle beneath the southern NCC, producing primary mafic magma. Then, the mafic magma underplated and caused partial melting of a thickened region of the lower continental crust in the southern NCC.