Geochemistry of the Guadalupian - Lopingian Carbonate Rocks from the NE Sichuan Basin, China: Implications for Paleo-oceanic Environment and Provenance

Abstract

Abstract The Dongwu Movement (including the eruption of the Emeishan Large Igneous Province (ELIP) ) , as the last part of the Hercynian cycle in the Yangtze region is an essential event between the Guadalupian and Lopingian, which has significant implications for the Paleo-oceanic environment and Paleoclimate of the area. To study the changes in the sedimentary environment in the Guadalupian and Lopingian, the Zhenba section was selected to analyze trace elements and rare earth elements. Trace elements and rare earth elements indicate that in the Guadalupian, the limestone samples had prominent typical shallow-water seawater deposition characteristics and were less affected by terrigenous detritus, which was an arid oxidation environment (Sr/Cu ranges from 4 to 1381; Rb/Sr value is low; δCe<1, Ceanom<-0.1; Er/Nd ranges from 0.1 to 0.27; Y/Ho ranges from 44 to 72), while in the Lopingian, the limestone samples were more affected by terrigenous detritus, which was a humid climate with the weak oxidation-reduction environment (Sr/Cu ranges from 1 to 656; Rb/Sr value is high; δCe tends to 1, Ceanom greater than and close to -0.1; Er/Nd<0.1; Y/Ho ranges from 26 to 44). The geochemical diagrams of TiO2-Al2O3, Al2O3-REE, La-Th-Sc, Th-Co-Zr/10, Th-Sc-Zr/10 and 87Sr/ 86Sr of the sample indicate that the terrigenous detrites of the sample should mainly come from the South Qinling active continental margin, rather than the weathering of Emeishan basalt. Acid bentonite should come from the Paleo-Tethys island arc or the island arc formed by the subduction of the South China Plate to the North China Plate, rather than ELIP. These evidences support the view that the North China Plate may have collided with the South China Plate in the middle to late Wujiaping.