U-Pb Dating And Hf Isotopic Compositions Of Detrital Zircons In The Tongtian River's Sediments In SongPan-Ganzi Block Of China

The rivers clastic sediments detrital zircon use microanalysis,such as the U-Pb dating,Lu-Hf analysis and trace element,it has been one of the most effective method to exploring the origin and evolution of continental crust.In this paper,detrital zircon U-Pb dating and Hf isotopic compositions in rivers' sediments are used to explore tectonic evolution of related blocks.The paper collected 21 samples of sediments from the Tongtian River.Through zircon U-Pb dating and Hf isotopic compositions as well as chemical characteristics of major and trace elements in the sediments,the conclusions have been drawn as follws.?1?The SiO₂ content of all samples is above 60%,which show the same contents between the south and north branches and lower content for the mainstream.The REE distribution patterns of all samples are basically the same as that of the upper crust,with the characteristics of enriched LREE and flatten HREE and intermediate Eu negative anomalies??Eu=0.57-0.71?.Primitive mantle normalized trace element polts show typical characteristics of the upper crust.?2?The south of Tongtian River sediments with long distance carrying,the mafic component is lower;while river sediments form north and east of Tongtian River are near source area and the moving distance is short,which leads to high mafic component.?3?The zircon U-Pb ages of the sediments of the Tongtian River are mainly distributed as : the proportion of zircons in Paleoproterozoic?1600²500 Ma?and Neoproterozoic?541¹000 Ma?is large,respectively consisting of about 26%,24 %;Followed by the early Paleozoic and Late Paleozoic,Paleogene zircon is concentrated in the southern section.The differences in the Cretaceous and Jurassic ages are related to the general absence of the Jurassic and Cretaceous strata in the Songpan-Ganzi block,and the ancient basins exist near the source of the Chumaer River.?4?Hf isotope depletion mantle model age distribution range is 0.38⁴.36 Ga.There are three significant age peaks,which are respectively 0.9¹.5 Ga,1.5².3 Ga and 2.3³.2 Ga,indicating the existence of the least three crustal hyperplasia events.?5?The Tongtian River minerial sources are mainly from three blocks: Songpan-Ganzi block,North Qiangtang block and East Kunlun block.The ratio of the minerial sources fromthree blocks is 5:3:2.North Qiangtang may provide more sources on the stages of 0⁸00 Ma and 2000³000 Ma,while Songpan-Ganzi block provide more at the age of 800²000 Ma.