Late Jurassic-Early Cretaceous granitoid magmatism in Eastern Qinling, central-eastern China: SHRIMP zircon U-Pb ages and tectonic implications

The Eastern Qinling region, located in the southern margin of the North China Craton, is characterised by widespread granitoid intrusions. Precise geochronological constraints on the age and timing of these intrusions are lacking. In this paper, we report SHRIMP zircon U-Pb ages of 12 representative granitoid plutons, together with one syenite stock, dolerite, diorite and granitic dykes in Eastern Qinling. The results revealed two main magmatic events, which occurred in the Late Jurassic-Early Cretaceous (158 ± 3 to 136 ± 2 Ma) and the Early Cretaceous (134 ± 1 to 108 ± 2 Ma), respectively. The granitoids formed in the early magmatic event are similar in composition and are characterised by a mantle source mixed with variable amounts of crustal components, whereas those resulting from the late-stage magmatism show characters of I-, S- and A-types granite and coexist with coeval dolerite dykes and syenite stocks. A similar magmatic age distribution is also recognised in other belts or regions in East China, and even in other parts of the East Eurasian continental margin. This suggests that the Jurassic-Early Cretaceous magmatism was associated with the subduction of the Izanagi plate at a shallow angle or flat-slab subduction beneath the eastern China continent, whereas the Early Cretaceous magmatism was related to lithospheric thinning, asthenospheric upwelling and partial melting of the lower crust, induced by a change in Izanagi plate motion parallel to the continent margin.