Tectonic significance and geodynamic processes of large-scale Early Cretaceous granitoid magmatic events in the southern Great Xing'an Range, North China

摘要

The origin and geodynamic evolution of peak Early Cretaceous magmatism in the southern Great Xing'an Range, North China, have long been controversial. Here we report new U-Pb zircon ages (141-129Ma) of a suite of dioritic-granitic rocks from central Inner Mongolia, far from the sutures or plate boundaries of the Paleo-Pacific and Mongol-Okhotsk oceans, thus delineating an Early Cretaceous intracontinental magmatic province, which had a peak activity at 130-120 Ma. Dioritic suite including diorite, tonalite, and granodiorite shows variable zircon epsilon(Hf)(t) of +1.4 to +11.8 and delta O-18 values of +5.7 to +6.9%, while granitic suite consisting of monzogranite, syenogranite, and granite porphyry also records variable zircon epsilon(Hf)(t) of -0.9 to +15.0 and delta O-18 values of +6.3 to +8.1 parts per thousand suggesting crustal melting by preexisting crustal source with important recycled supracrustal components including fluids. Furthermore, these rocks show variable whole-rock delta(7) Li values (-0.6 to +12.1 parts per thousand), indicating fluids played an important role in magma source. We propose a deep-sourced water-fluxed melting scenario by ancient hydrous slabs inherited from the Paleo-Asian Ocean that were trapped in the deep interior, thus releasing aqueous fluids to melt the lithospheric mantle and produce water-rich mafic magmas. These mafic magmas were underplated into crust where they promoted water-fluxed partial melting to generate the large-scale Early Cretaceous magmatism in the southern Great Xing'an Range. Such melting due to fluxing of aqueous fluids was probably operating as a widespread process responsible for the Early Cretaceous dramatically tectonomagmatic events and evolution of continental crust in NE Asia.