Discovery of Volcanic Matter in the Upper Maokou Formation in Wumengshan Area and Its Geological Significance：Evidence of Early Activity of the Emeishan Mantle Plume

To deepen our understanding on the evolution of the Emeishan mantle column activity in the Wumengshan area of northeastern Yunnan, the isotopic chronology, zircon trace element, zircon Hf isotopes and dental spines of the middle and upper tuffs of the Maokou Formation in this area were investigated, the result shows that the zircon U-Pb age of the uppermost tuffs of the Maokou Formation is 268.7 ± 1.7 Ma, and the conodont found is Jinogondolella aserrata, which is a typical molecule of the Permian Guadalupian Wordian, corresponds to the zircon U-Pb age. The zircon trace element characteristics show that it is consistent with the Emeishan basalt and is a basal magmatic zircon, and it is in a continental arc-type tectonic setting with both the Emeishan flood basaltic tuffs, proving that it is homologous with the Emeishan flood basalt and may represent the volcanic activity before the large-scale eruption of the Emeishan Large Igneous Province. The average ε_Hf(t) of the 6 zircons is -5.7, indicating that the early volcanic activity of the Emeishan mantle plume was strongly influenced by the crust. The discovery of tuffaceous limestone in Maokou Formation indicates that the Emeishan mantle plume occurred in Wumengshan area in the Permian Guadalupian Wordian, which adds new evidence for the establishment of the Emeishan mantle plume model. .