Abstract:
Three sets of sedimentary intercalations were systematically identified in Emeishan basalt in the Zhaotong area, Northeastern Yunnan for the first time, indicating that there were at least three long eruption intermissions during the main eruption period of Emeishan basalt.Taking the sedimentary intercalations as the subcycle division mark, the Emeishan basalt in the study area could be divided into four eruption subcycles.The existence of sedimentary intercalation provides a new key evidence for the episodic eruption of Emeishan basalt.The sedimentary intercalations between the third and fourth subcycles of Emeishan basalt in the study area have large sedimentary thickness and obvious sedimentary characteristics.In this work, the basaltic fine sandstone was selected for LA-ICP-MS dating, and the zircon U-Pb age was 261.6 ± 0.6 Ma.This age represents the time of the main eruption period of Emeishan basalt in the Zhaotong area, and defines the lower limit of the sedimentation time of the sedimentary intercalation.The eruption center and volcanic mechanism distribution of Emeishan basalt may be influenced and controlled by the deep faults in the region.The eruption form is multi-stage and multi-point eruption, while the sedimentary intercalations are developed in a small intermountain depression catchment basin formed by multi-point eruption of basalt.