Late Palaeozoic and early Mesozoic tectonic and palaeogeographic evolution of central China: evidence from U-Pb and Lu-Hf isotope systematics of detrital zircons from the western Qinling region

The western Qinling region of central China is situated centrally in the Kunlun, Qilian, Qinling, Longmenshan, and Songpan-Ganzi orogens. Late Palaeozoic and Early Mesozoic sediments deposited here may provide keys to understanding the tectonic evolution of the Palaeo-Tethys and collision of the North China and Yangtze Cratons. We conducted in situ U-Pb and Lu-Hf isotope analyses of 568 detrital zircons collected from Upper Palaeozoic to Mesozoic sandstones in the central Qinling block, Taohe depression, and Bailongjiang block in western Qinling to constrain the sources of these sandstones. Our results reveal that the Bailongjiang block has affinities with the Yangtze Craton, from which it may have been rifted. Therefore, the Palaeo-Tethyan Animaqen suture between the two cratons lies north of the Bailongjiang block. We identified the North China Craton as the main source for Triassic flysch in central China. It is possible that the Bailongjiang block could have blocked detritus shed from the North China Craton into the main depositional basins in the Songpan-Ganzi area. The dominance of 300-200 Ma detrital zircons of metamorphic origin in Lower Jurassic sandstones indicates that the Dabie-Qinling orogen was elevated during Early Jurassic time. In addition, our Lu-Hf isotopic results also reveal that Phanerozoic igneous rocks in central China were mostly products of crustal reworking with insignificant formation of juvenile crust.