Permian radiolarians, chert and basalt from the Daxinshan Formation in Lancangjiang belt of southwestern Yunnan, China

The stratigraphical sequences composed of chert and basalt were found in the Daxin-shan area of Simao and the Manbie area of Jinghong, southwestern Yunnan. The Middle Permian to ealiest Late Permian radiolarians, such as Follicucullus and Pseudoalbaillella, have been identified from the chert. The chert from the Manbie area of Jinghong is characterized by high SiO2 content (over 92%), large ratios of MnO/TiO2 (2.15) and low ratios of AI/(AI+Fe+Mn) (≤0.1) and Ce/Ce*(0.4), which indicate that the chert was deposited in pelagic basin. The chert from the Dax-inshan area of Simao, however, is characterized by low SiO2 content, low ratios of MnO/TiO2 (0.27) and high ratios of Al/(Al+Fe+Mn) (0.49) and Ce/Ce*(0.88), which imply that the chert was deposited in continental margin basin. The basalts from the both areas belong to tholeiite series, and the chemical compositions of their major, rare earth and trace elements show the characteristics of MORB. These results evidence that there are volcanic rocks and che