Zircon U−Pb ages and Hf isotopic compositions of river sediments from the Gonghe Basin and implication on tectonics and evolution of the crust

To reveal the history of tectonic activity and crustal evolution in the sedimentary source area of the Gonghe Basin, U−Pb dating and Hf isotope analysis of detrital zircons in the floodplain sediments of the Qushian river and Xi river in the Gonghe Basin were analyzed by LA−MC−ICP−MS approach in this study. It was revealed that the U−Pb age of these detrital zircons can be divided into 5 groups: 309~172 Ma, 471~368 Ma, 943~737 Ma, 2368~1698 Ma, 2543~2453 Ma.According to the tectonic−magmatic events in the study area, it is concluded that the detrital sediments of the floodplains of the Qushian River and Xi River are provided by the Western Qinling block at different times. There are two main detrital zircon U−Pb ages, 236 Ma and 403 Ma, reflecting the geological record of the collision of blocks in different parts of the paleo and proto−Tethys oceans, induced strong magmatic events, and the emergence of rift valleys and neonatal ocean basins in the post−collision extension stage. The features of Hf isotopic composition revealed that the crust in the source area underwent a major accretion period at 2.7~1.3 Ga, and created 84% of the current crust. ε_Hf(t) value ranges between −14.7 and +15.0, Hf depleted mode age in the range of 3.6~0.24 Ga, indicating the presence of Paleoarchean ancient crust substance in the source area substrata. Since 0.5 Ga, the growth of the earth's crust has mainly been dominated by the recycling of ancient crust substance, and the growth of the crust has stopped at 0.28 Ga. Furthermore, using formula of recycling ratio, ratios between remelting and juvenile crust with age have been calculated.