Nanpanjiang basin: A window on the tectonic development of south China during Triassic assembly of the southeastern and eastern Asia |
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| Institution: | 1. Paleontological institute, University of Zürich, Karl Schmid-Strasse 4, 8006 Zürich, Switzerland;2. BCG Parc de la Rouvraie 28, 1018 Lausanne, Switzerland;3. Institute of Earth Surface Dynamics, University of Lausanne, Géopolis, 1015 Lausanne, Switzerland;4. Department of Earth Sciences, University of Geneva, 13 rue des Maraîchers, 1205 Geneva, Switzerland;5. Guangxi Bureau of Geology and Mineral Resources, Jiangzheng Road 1, 530023 Nanning, China;1. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Wuhan Institute of Geology and Mineral Resources, China Geological Survey, Wuhan 430223, China |
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| Abstract: | As the largest siliciclastic sink in the South China block, the Triassic Nanpanjiang basin is generally thought of as a foreland basin related to Indosinian collision between the South China and Indochina blocks. Our basin analysis, spanning an eight years period, provides details of Lopingian to Middle Triassic stratigraphic fill and tectonic subsidence of the basin. Field observation and sedimentological analyses reveal that the basin was not filled by a monotonous turbidite system and suggest instead the development of five primary depositional units constituted by deep-water turbidite systems, mass-transport deposits, condensed drapes, shallow-water isolated carbonate platforms, and volcano-volcaniclastic rocks. The stratigraphic completeness of the basin, the coexistence of widespread but localized carbonate platforms within axially filled deep-water basin, tectonically generated cyclothems of transverse mass-transport deposits along intrabasinal faults and basin fill of extrusive rocks of bimodal composition together apparently call in question the claim that crustal shortening prevailed during the Late Permian to pre-Norian Triassic. Patterns of basin fill, differential tectonic subsidence and very high subsidence rate of the region adjacent to master fault are more closely match the pattern expected for extensional to transtensional basin in a back-arc setting. The crustal extension in the southwestern South China was not consistent with hypothesized Indosinian collision between South China and Indochina blocks, but more likely developed in response to northwestward subduction of the paleo-Pacific plate. Our results, combined with regional considerations, lead to a new model for the Triassic tectonic evolution of South China during Triassic assembly of the southeastern and eastern Asia. |
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| Keywords: | Basin fill Tectonic subsidence Triassic turbidites Nanpanjiang basin South China block |
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