Sedimentology,U-Pb Detrital Zircon Ages And Tectonic Implications Of Zhayao Formation,Liaodong Peninsula,China

The Mesozoic Eastern North China Craton,especially the Liaodong peninsula,has been studied extensively with major concerns on the magmatic and/or metamorphic rocks.However,sporadically outcrops of the Mesozoic sedimentary sequences in Liaodong peninsula were not yet well understood.To fill this gap in respect of sedimentary rocks,the Zhayao Formation of Middle Jurassic from Liaodong Peninsula was chosen.The basin of Zhayao Formation has not been precisely constrained with many questions,including sedimentary sequence,age constraints,corresponded basin nature and its tectonic implication for the Liaodong peninsula.This thesis reports a new identified geological section with well outcropped Zhayao Formation in the Wafangdian area,and sedimentary sequence and zircon U-Pb age constraints.The results of petrographical studies exhibit that the sedimentary sequence of Zhayao Formation was deposited on a cratonic/continental environment and also indicate source rock.The sedimentary sequence majorly composed of sandstone with thin beds of shale.Three samples of detrital zircons have been processed and characterized by three major groups of U-Pb ages;first 2.9-2.1 Ga,in which huge number of zircon yield ages ranging from 2.6-2.4 Ga,second 2.0-1.6 Ga,the major population of zircon lies in 1.7-1.9 Ga and,third 450-250 Ma,which has major concentration of zircons in the range of 400-300 Ma.The structure styles of the region were investigated through extensive field works which reflect N-S trend of compressive forces and almost EW orientation of deformation.These results are consistent with the impact of collision between NCC and SCB during Middle Jurassic.Conclusively,this thesis suggests that the Zhayao Formation basin was formed due to continuous compressional forces exerted by collisional boundary between NCC and SCB,which shaped the Zhayao Formation?s basin.Although,this collisional boundary was far away from this basin but its impact was severe and continuous which caused the formation of cratonic/continental basin,the supply of sediments to the Zhayao Formation?s basin was from uplifted basement which was uplifted in response to active tectonical forces.