Geochemical characteristics and provenance analysis of Lower Jurassic Badaowan Formation in Changji area of Xinjiang,China

Based on the field survey of Lower Jurassic Badaowan Formation(Fm.)in Changji area of Xinjiang,China,the authors studied the sedimentary environment and provenance characteristics using the analyses of stratigraphic profiles,sedimentary structures,petrography,zircon U-Pb chronology and geochemistry.The results show that Badaowan Fm.deposited in fluvial to swamp shallow-deep-lacustrine sedimentary facies deposition.Contents of Sr and ratios of Sr/Cu,Sr/Ba,Th/U,SiO2/Al2O3,V/(V+Ni),V/Cr,and Cu/Zn together indicate that Badaowan Fm.was deposited in an oxygen-poor transitional freshwater environment,under humid climatic conditions.Geochemical characteristics and Q-F-L,Qm-E-Lt,Th-Co-Zr/10,La-Th-Sc,and Th-Sc-Zr/10 discrimination diagrams indicate that the tectonic setting of the source area was a continental island arc environment.Lithological composition,Th/U ratios,and Co/Th-La/Sc,La/Th-Hf,and La/Yb-REE discrimination diagrams show that the source rocks of Badaowan Fm.were upper-crust felsic volcanic rocks.U-Pb dating of detrital zircons yields ages of 1542.3±15.0 to 232.9±3.3 Ma and mostly in the ranges of 470-410 and 370-280 Ma.A comparison of these ages with the age data from different blocks of crystalline rock in Tianshan Mountains area reveals that the sedimentary rocks in the Badaowan Fm.were sourced predominantly from the central and subordinately from the southern Tianshan Mountains during Early Jurassic.