The Lancang River Zone of southwestern Yunnan,China: A questionable location for the active continental margin of Paleotethys |
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| Institution: | 1. Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Ferrara, Italy;2. Faculty of Earth Science, Shahid Beheshti University, Tehran, Iran;1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;3. Department of Earth Sciences, Sun Yat-Sen University, Guangzhou 510275, China;4. CSIRO Earth Sciences and Resource Engineering, Bentley, WA 6102, Australia;5. Western Australian Argon Isotope Facility, Curtin University, WA 6845, Australia |
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| Abstract: | In an attempt to constrain a Late Paleozoic tectono-metamorphic event along the Lancang River Zone, fourteen samples were processed for K/Ar dating on fine mineral fractions and detrital muscovites from this zone in southwestern Yunnan, China. The samples include mica schists, mylonites and gneisses from the Proterozoic Lancang Group and phyllites from the western part of the Simao Basin. In addition, one Ar/Ar analysis was performed on separated phengites from a blueschist of the central part of the Lancang Group. The results reveal a considerable spread of ages; the tectonic evolution of the zone is constrained by the new data, which accentuate two temporally separate, but spatially overlapping events: (i) a Late Carboniferous high-P/low-T metamorphism related to an east-vergent, Late Paleozoic thrust belt, inverting a Devonian to Carboniferous marginal basin of the Yangtze-Platform, and (ii) an upper Permian and Triassic low-P/high-T belt caused by a post-orogenic stage of rifting with distinct petrological and geochemical similarities of the igneous rocks to the Emeishan Large Igneous Province. These results imply that no active continental margin accounts for the subduction of the Paleotethys main branch, proposed to be recorded either along the Lancang River or the Changning-Menglian Belt. |
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