Geochemical Characteristics And Petrogenesis Of Early Cretaceous Granitoids In Wuchagou Region Of Central Great Xing'an Range

The Great Xing'an Range is located in the Central Asian Orogenic Belt,which is characterized by the occurance of widespread Mesozoic igneous rocks.With the application of the technology of the LA-ICPMS and the research of the granitoids,a lot of data had been obtained.However,the research of the Late Mesozoic magmatism is poor,which restricted our understanding of the Late Mesozoic tectonic setting of the Great Xing'an Range.We undertake the geochemical and geochronological studies on late Mesozoic granitoids from the Wuchagou area in the central Great Xing'an Range,aiming to determine their emplacement ages and petrogenesis and further constraint the Late Mesozoic tectonic setting of the Great Xing'an Range.Zircons from seven representative samples are euhedral–subhedral,display oscillatory growth zoning,and have Th/U values of 0.63–1.84,indicating a magmatic origin.LA–ICP–MS zircon U–Pb age data indicate that these granitoids formed during the Early Cretaceous with the ages of 134~127Ma.These granitoids are characterized by high silica(SiO2 =65.21%~78.43%),total alkali concentrations(K2O+Na2O=6.77%~9.66%),low concentrations of CaO(0.10%~2.55%),MgO(0.07%~1.30%),and P2O5(0.01%~0.20%),with A/CNK and ?Eu values of 0.94~1.51 and 0.21~0.93,respectively.They are also enriched in large-ion lithophile elements(e.g.Rb,Th,U)and depleted in high field elements(e.g.Nb,Ta,Ti,and P),indicating that they can genetically be ascribed to high-K calc-alkaline I-type granitoids.The positive ?Hf(t)values(+4.9 to +8.4)of the Early Cretaceous granites and their corresponding Hf two-stage model ages of 654 Ma to 874 Ma indicate that the parental magma was derived from partial melting of Neoproterozioc juvenile crustal material.Considering the regional geological investigations and temporal–spatial distribution of the coeval igneous rocks,the authors considered that the the formation of Early Cretaceous granites in the Wuchagou area was related to the subduction of Paleo-Pacific plate.