U-Pb Isotope Geochronology of Syntectonic Granites from Hainan Island, South China: Constraints on Tectonic Evolution of
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U-Pb Isotope Geochronology of Syntectonic Granites from Hainan Island, South China: Constraints on Tectonic Evolution of the Eastern Paleo-Tethys Ocean ZHOU Yang1), 2), YAN Yi1), LIU Hailing3), *, CAI Jianxin3), ZHOU Mengfei4), ZHANG Xinchang1), WANG Yin2), 5), and SHEN Baoyun6) 1) Key Laboratory of Ocean and Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China 2) University of Chinese Academy of Sciences, Beijing 100049, China 3) South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China 4) Institute of Porous Flow and Fluid Mechanics, Chinese Academy of Sciences, Langfang 065007, China 5) SKL, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 6) School of Electromechanical Engineering, Guangdong University of Technology, Guangzhou 510006, China (Received October 10, 2019; revised May 3, 2020; accepted June 4, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract Since the recognition of the Indosinian orogeny in northern Vietnam, Triassic orogens have been widely identified around the western and southwestern boundaries of the South China block. The paleo-Tethys sutures stretch from west to southeast, from Jinshajiang-Ailaoshan via NE Vietnam to Hainan Island; these sutures exhibit and develop voluminous Permian – early Triassic magmatism and numerous high-strain shear zones. As ophiolites related to the paleo-Tethys are lacking on Hainan Island, the eastward extension of the Indosinian orogeny and subduction and closure time of the paleo-Tethys Ocean on Hainan Island remain controversial. Here, an integrated kinematic and geochronological study has been conducted on two shear zones, called the Xiaomei and Mangsan shear zones. U-Pb zircon dating yields an age of early Triassic (252 – 251 Myr) for Xiaomei syntectonic granites which formed in the same tectonic setting and presented the similar nanoparticles to the Indosinian granites from Ailaoshan ductile shear zone, including the strawberry-like and flower-like nanoparticles. The NE-trending Mangsan shear zone represented by the gneissic granites with middle Permian ages (264 – 262 Myr) formed in the same tectonic setting as the Wuzhi-shan granites that were proposed as I-type granites. These middle Permian gneissic granites with arc affinity may represent an arc setting related to the NW subduction of the paleo-Tethys. The analyses reveal that granites with late Triassic ages (235 – 232 Myr) in the Xiaomei shear zone have the characteristics of A-type granites. The late Triassic extensional events on Hainan Island may be related to the subduction of the paleo-Pacific Plate beneath the East Asian continent. Key words
Indosinian orogeny; Hainan Island; Xiaomei shear zone; Mangsan shear zone; syntectonic granites; paleo-Tethys
1 Introduction Hainan Island is located in the zone of convergence among the Philippine Plate, South China continent and Indochina block (Fig.1a). This island consists
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