Geochemical characteristics and tectonic significance of Early Jurassic Quemo Co Formation inWoruoshan area, north Qiangtang basin

Early Jurassic Quemo Co Formation is very important for studying the sedimentary evolution form the late Triassic to the early Jurassic in Qiangtang basin. Geochemistry and provenance characteristics of sandstones in the Quemo Co Formation of Woruo Mmountain area were studied by analyzing the selected major element and trace element compositions. The results suggest that the sandstone deposited in the chasmic stage of the passive continental margin. The sandstones are the lithic sandstone which mainly consist of K-feldspar, plagioclase, illite, chlorite and quartz. The chemical index of weathering (CIW), the chemical index of alteration (CIA) parameters and the A-CN-K plot of the sandstones suggest that weathering of the elastic constituents has been intense in the area, the elastic constituents of sandstones underwent K-metasomatisim during weathering processes, illite replaced feldspar and perhaps the original kaolinite in the feldspar. The index of compositional variability (ICV) suggests that some sandstones contain first cycle materials The A-CN-K diagram indicates that a high average plagioclase-to-K-feldspar ratio in the provenance, varying from granodiorite to granite. The REE characteristics suggest only one source of acid igneous rock for the sandstones in this area.