U-Pb Dating And Hf Isotopic Compositions Of Detrital Zircons In The Nuomin Rivers' Sediments From The Greater Khingan Range And Their Geological Implications

The Nuomin river is located in Northeast China,north of Greater Khingan Range,and in the eastern part of the Central Asian orogenic belt.During the Mesozoic era,it was influenced by the circum Pacific tectonic system and Mongolia jaw khotsk tectonic system,with complex tectonic activities and strong magmatism.Therefore,the Phanerozoic volcanic rocks in Greater Khingan Range area are mainly Mesozoic,in which a large number of volcanic rocks are distributed in the late Early Cretaceous.Sediments can record the information and evolution histories of their provenances' regional crust,and are ideal for uniform sampling of the crust in river drainage.Compared with the studies of the outcropped geological bodies,river detrital zircons can reflect the peak time and the intensity of the magmatic events within catchment.Thus,the research on the river detrital zircons is significant to explore the formation and evolution of the crust in a catchment.In recent years,detrital zircon u-p dating,Lu Hf isotope analysis and trace element analysis have become mature and effective geochemical analysis methods,which are mostly used to explore the tectonic evolution of continental crust.In this paper,through systematic study of geochemistry,zircon U-Pb dating and Hf isotopic on the Nuomin rivers' sediments in the Greater Khingan Range to discuss the occurrence time of magmatic events related to the sediments of the Nuomin river,and explore the tectonic evolution history of the related areas,the conclusions have been drawn as follows:(1)The main and trace elements of the flood plain sediments in the NOMIN River Basin are basically the same as the average composition of the continental upper crust,which can represent the average composition of the upper crust in the region;The abundances of Au,Hg,Sn,Pb,Mo and other ore-forming elements in the river sediments are obviously higher than the average values of the upper crust of the continent,indicating that these ore-forming elements in the basin have a good prospecting background.(2)Among the 98 zircons,73 grains have concordant U-Pb ages ranging from 137 Ma to125 Ma,with a peak age of 130 Ma.They are the products of Early Cretaceous magmatism.It is inferred that they were influenced by the subduction of the paleo Pacific plate.(3)The zircon Hf isotopic two-stage depleted mantle model ages range from 1.04 to 0.6Ga,which indicates that the early Cretaceous magmatism of the basin crust is mainly the product of the melting of the Neozoic Cenozoic crust,that is,the accretive crust was reformed in the late Mesozoic tectonic system during the expansion and reduction of the paleo Asian Ocean.