The age and tectonic environment of Carboniferous volcanic-sedimentary strata in Changning-Menglian zone, Western Yunnan Province

A large area of Carboniferous volcanic-sedimentary strata is exposed in the Changning-Menglian junction.The precise determination of its age and the identification of the paleo-tectonic environment are of great significance for understanding and restoration of Changning-Menglian zone and evolution of the Eastern Paleotethys Ocean.The detailed field geological survey and profile surveying indicate that the contact between basalt and carbonate rock is conformity.A detailed microfacies analysis was carried out on carbonate rocks, and four types of microfacies were identified, granular bioclastic limestone (MF1), spherulitic mud particles bioclastic limestone (MF2), oolitic limestone (MF3) and coral clastic reef limestone (MF4), indicating that the main carbonate rock was formed in a shallow-water high-energy environment under a warmer tropical-subtropical palaeoclimate background.Zircon U-Pb dating of the tuff interbeded between carbonate rock and basalt yields the average age of 351.7±2.5 Ma, indicating that the eruption of basalt was in the Early Carboniferous.This set of volcanic-sedimentary rocks include basalt, reef limestone, tuff, etc.with OIB-type geochemical characteristics, and its tectonic environment is defined as ocean island-seamount, which is an important part of oceanic crust fragments in the Sanjiang orogen and records important information about the tectonic evolution of the Paleo-Tethys oceanic basin and the formation process of the orogenic belt.