Tectonic significance and geodynamic processes of large-scale Early Cretaceous granitoid magmatic events in the southern Great Xing'an Range, North China
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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 130-120Ma. Dioritic suite including diorite, tonalite, and granodiorite shows variable zircon eHf(t) of +1.4 to+11.8 and d18O values of +5.7 to +6.9‰, while granitic suite consisting of monzogranite, syenogranite, and granite porphyry also records variable zircon eHf(t) of -0.9 to +15.0 and d18O values of +6.3 to +8.1‰, suggesting crustal melting by preexisting crustal source with important recycled supracrustal components including fluids. Furthermore, these rocks show variable whole-rock d7Li values (-0.6 to +12.1‰), 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.
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