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Construction of age frequencies of provenances on the eastern side of the Yinggehai Basin:Studies of LA-ICP-MS U-Pb ages of detrital zircons from six modern rivers,western Hainan,China

WANG Ce;LIANG Xinquan;ZHOU Yun;FU Jiangang;JIANG Ying;DONG Chaoge;XIE Yuhong;TONG Chuanxin;PEI Jianxiang;LIU Ping;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences;University of Chinese Academy of Sciences;CNOOC China Ltd.Zhanjiang;China University of Geosciences(Wuhan);  
U-Pb dating of detrital zircons from sands along main rivers in western Hainan was carried out by using cathodoluminescence(CL)imaging and LA-ICP-MS microdomain analysis of 700 grains,and 644 valid data were obtained.The studies reveal that(1)the zircon age characteristics of the six rivers are of two markedly different groups:the samples from Zhubi Jiang,Changhua Jiang,Beili He and Ganen He in the north mainly display Hercynian-Indosinian ages(236 257Ma),while the Wanglou and Ningyuan rivers in the south show Late Yanshanian ages(ca.99Ma),which are consistent with the ages of igneous rocks distributed along those rivers,reflecting that the sediments are controlled and influenced by the source areas;that(2)the zircon ages from the six rivers are scattered ranging from 86 Ma to 1600 Ma,but mainly concentrated in a range of 80 300 Ma,with three main peaks of ca.254 Ma,ca.238 Ma and ca.99 Ma and two secondary peaks at 159 Ma and 1400 1600 Ma.The ca.254 Ma event in Hainan Island is different from the inland South China Block in that it is an important Permian magmatic event closely related with the closure,subduction and collision of the Paleo-Tethys Ocean.The peak of ca.238 Ma also indicates an important magmatic event in Hainan Island.Hainan had turned into a post-orogenic extensional environment since 245 Ma and forming a series of Triassic I-type and A-type granites from south to north.The Permian and Triassic granites might result from the same continuous evolution event.The detrital zircon ages of ca.99 Ma can be matched with those of the Tonganling-Niulaling basaltic andesite-rhyolite,Tunchang adakite as well as the Shilu granodiorite,indicating that it might be affected by the westward subduction of the Paleo-Pacific plate;that(3)the major age spectrum of the western Hainan is quite different from that of the Red River in northernVietnam in that it is characterized by the Yanshanian ages(ca.99Ma)but lack of the Himalayan ages(22-55Ma)corresponding to the tectonic-magmatic-metamorphic events in the Red River Fault Zone and the older zircon ages.
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