Detrital zircon ages and Hf isotopes of the early Paleozoic flysch sequence in the Chinese Altai,NW China: New constrains on depositional age,provenance and tectonic evolution |
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| Authors: | Xiaoping Long Chao Yuan Min Sun Wenjiao Xiao Guochun Zhao Yujing Wang Keda Cai Xiaoping Xia Liewen Xie |
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| Institution: | 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 10069, China;3. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;4. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Laboratory of Isotope Thermochronology, State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China;3. Xinjiang Research Center for Mineral Resources, Urumqi 830011, China;1. College of Earth Sciences, Jilin University, Changchun 130061, China;2. Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;3. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China |
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| Abstract: | Subduction–accretion complexes occur widely in the Central Asian Orogenic Belt (CAOB). Due to the scarcity of fossils, the depositional timing of the Habahe flysch sequence of the subduction–accretion complex in the Chinese Altai is poorly constrained, which gave rise to much controversy in understanding the time of the basement and the tectonic evolution of the Chinese Altai. U–Pb dating of detrital zircons from the Habahe sequence in the northwestern Chinese Altai reveals a young zircon population with a mean 206Pb/238U age around 438 Ma which, together with a mean 206Pb/238U age of 411 ± 5 Ma for the overlying rhyolite of the Dongxileke Formation, brackets the time of deposition of the sequence between early Silurian and early Devonian. The age of the Dongxileke rhyolite also indicates that the overlying Baihaba Formation possibly began to be deposited in the early Devonian, though U–Pb dating of detrital zircons from this formation gave a maximum depositional age of ～ 438 Ma. The youngest detrital zircons and metamorphic grains of the Habahe sequence reveal different provenance to the sequence in the east. The youngest and metamorphic zircon grains, with early Paleozoic, Neoproterozoic and pre-Neoproterozoic populations, suggest a multi-source for the Habahe sequence. The predominantly early Paleozoic zircons, characterized by concentric zoning, high Th/U ratios and euhedral shapes, imply that the sediments of the sequence were mostly derived from a proximal magmatic source. Based on the age patterns of the Neoproterozoic and pre-Neoproterozoic populations, the Tuva–Mongol Massif, along with adjacent island arcs and metamorphic belts, may be an alternative source region for the Habahe sequence. In view of new geochemical and chronological data for granitoids and advancement in the study of regional metamorphism in the Chinese Altai, we suggest a tectonic model of subduction beneath a huge subduction–accretion complex for the evolution of the Chinese Altai in the early Paleozoic. |
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