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Permian radiolarians,chert and basalt from the Daxinshan Formation in Lancangjiang belt of southwestern Yunnan,China |
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| Authors: | |
| Institution: | 1. Faculty of Earth Science, China University of Geosciences, Wuhan 430074, China 2. Institute of Geology and Dynamics of the Lithosphere, University of Goettingen, Goldschmidtstr. 3, D-37077 Goettingen, Germany 3. Yunnan Institute of Geological Sciences, Kunming 650011, China 4. Regional Geological and Mineral Resources Investigation Institute, Yunnan Geo-Exploration Bureau, Yuxi 653100, China |
| Abstract: | The stratigraphical sequences composed of chert and basalt were found in the Daxinshan 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 SiO2content (over 92%), large ratios of MnO/TiO2 (2.15) and low ratios of Al/(Al+Fe+Mn) (≤0.1) and Ce/Ce*(0.4), which indicate that the chert was deposited in pelagic basin. The chert from the Daxinshan 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 chert sequences representing pelagic basin and oceanic basin near continent. These sequences and the formerly reported island-arc volcanic rock sequences imply that the Daxinshan Formation in the Lancangjiang belt represents a sedimentary assemblage formed in active continental margin basin. |
| Keywords: | Permian chert basalt geochemistry Lancangjiang belt |
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