Geochemistry and geochronology of Upper Triassic sedimentary rocks from the south of the Dabie Orogen: Implications for the paleoenvironment, provenance and tectonic setting

The formation and evolution of the foreland basin in the south of the Dabie Orogen are both closely related to the uplift of the orogenic belt. However, the Late Triassic paleoenvironment and the provenance of the sediments in the foreland basin remain controversial. Nine samples from the Upper Triassic Puqi Group of the foreland basin were analysed for whole-rock major and trace elements and three sandstone samples were selected for zircon dating by U-Pb laser ablation inductively coupled plasma mass spectrometry. The concentrations of some major (e.g., CaO and Na2O) and trace (e.g., Rb, Sr and Ba) elements varied over a large range and showed different degrees of depletion. A series of major and trace element indicators, as well as the patterns of the rare earth elements, suggested derivation from felsic igneous rocks. The Late Triassic experienced fluctuations between cold warm climates, as indicated by the chemical weathering index ranging from 51.33 to 88.65. The CaO/(FeO + CaO), Rb/Sr and Ba/K ratios indicated that the paleosalinity changed from high to low. The Fe2O3/FeO, U/Th, V/Cr and Ni/Co ratios indicated an oxidizing sedimentary environment. The cathodoluminescence images, Th/U ratios and rare earth elements patterns of the detrital zircons all indicated a magmatic origin. Three samples showed significant peak ages of 224, 440, 748, 1870 and 2492 Ma, corresponding to the development of the Dabie Orogen. Our comprehensive analyses suggest that the Upper Triassic Puqi Group was formed by deposition during continental-continental collision. The Dabie Orogen was exhumed in the Late Triassic and supplied detrital sediments to the foreland basin. Based on zircon U-Pb dating and whole-rock major and trace element analyses, this study identifies Triassic magmatic zircons in the Late Triassic Puqi Group of the Dabie Orogen foreland basin, indicating a provenance from the Dabie Orogen and highlighting drastic paleoclimate changes in the region.image