Detrital zircon U-Pb-Hf isotopes and provenance of Late Neoproterozoic and Early Paleozoic sediments of the Simao and Baoshan blocks,SW China: Implications for Proto-Tethys and Paleo-Tethys evolution and Gondwana reconstruction |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;3. Earth Sciences, Earth Studies Building C02, School of Environment and Rural Science, University of New England, Armidale, NSW 2351, Australia;1. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. School of Ocean Sciences, China University of Geosciences, Beijing 100083, China;1. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. The Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 102206, China;3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, 510460, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Cenozoic Geoscience Editing, Hobart, TAS, 7005, Australia;4. Department of Earth Sciences, Sun Yat-sen University, West Xinggang Road 135, Guangzhou, 510275, China;5. Centre of Excellence in Ore Deposits (CODES), University of Tasmania, TAS 7005, Australia;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Department of Geological Sciences, 241 Williamson Hall, University of Florida, Gainesville, FL 32611, United States;4. School of Earth Science, Guilin University of Technology, Guilin 541004, China;5. Department of Geology, Hanoi University of Science, 334 Nguyen Trai Street, Hanoi, Viet Nam |
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| Abstract: | Early Paleozoic evolution of the northern Gondwana margin is interpreted from integrated in situ U-Pb and Hf-isotope analyses on detrital zircons that constrain depositional ages and provenance of the Lancang Group, previously assigned to the Simao Block, and the Mengtong and Mengdingjie groups of the Baoshan Block. A meta-felsic volcanic rock from the Mengtong Group yields a weighted mean 206Pb/238U age of 462 ± 2 Ma. The depositional age for the previously inferred Neoproterozoic Lancang and Mengtong groups is re-interpreted as Early Paleozoic based on youngest detrital zircons and meta-volcanic age. Detrital U-Pb zircon analyses from the Baoshan Block define three distinctive age peaks at older Grenvillian (1200–1060 Ma), younger Grenvillian (~ 960 Ma) and Pan-African (650–500 Ma), with εHf(t) values for each group similar to coeval detrital zircons from western Australia and northern India. This suggests that the Baoshan Block was situated in the transitional zone between northeast Greater India and northwest Australia on the Gondwana margin and received detritus from both these cratons. The Lancang Group yields a very similar detrital zircon age spectrum to that of the Baoshan Block but contrasts with that for the Simao Block. This suggests that the Lancang Group is underlain by a separate Lancang Block. Similar detrital zircon age spectra suggest that the Baoshan Block and the Lancang Block share common sources and that they were situated close to one another along the northern margin of East Gondwana during the Early Paleozoic. The new detrital zircon data in combination with previously published data for East Gondwana margin blocks suggests the Early Paleozoic Proto-Tethys represents a narrow ocean basin separating an “Asian Hun superterrane” (North China, South China, Tarim, Indochina and North Qiangtang blocks) from the northern margin of Gondwana during the Late Neoproterozoic-Early Paleozoic. The Proto-Tethys closed in the Silurian at ca. 440–420 Ma when this “Asian Hun superterrane” collided with the northern Gondwana margin. Subsequently, the Lancang Block is interpreted to have separated from the Baoshan Block during the Early Devonian when the Paleo-Tethys opened as a back-arc basin. |
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