The Forma-tion Age of Baoban Group in Hainan Island and its Tectonic Significance
The Baoban Group is the oldest Precambrian crystalline basement discovered on Hainan Island to date,having undergone multiple tectonothermal events,making it an important carrier for studying the geotec-tonic attributes and block division of the Hainan(Hainan Island)Block.On the basis of summarizing the pre-vious research results,this paper conducts a new study on the zircon U-Pb geochronology through SHRIMP and LA-ICP-MS of migmatite and later intrusive granites and mafic rocks in the Baoban Group in the Baoban area of Dongfang city,Hainan Island to determine the formation age of the Baoban complex,the tectonother-mal events it has undergone,and its tectonic significance.According to the characteristics of rock combina-tions,the Baoban Group can be further divided into the Gezhencun Formation and the Ewenling Formation,both of which are intruded by later granitic and basic magmas and together constitute the Baoban complex.Zircon geochronology results indicate that the Gezhencun Formation was formed between 1480～1440 Ma,the Ewenling Formation was formed between 1460～1430 Ma,the gneissic granite intrusion occurred be-tween 1450～1430 Ma,and the mafic intruded later between 1425～1410 Ma.During the early to middle Mesoproterozoic,it underwent multiple tectono-thermal events including granite intrusion,migmatite,and mafic rock intrusion,while in the late Mesoproterozoic to early Neoproterozoic,it experienced tectono-ther-mal events related to the convergence on the Rodinia supercontinent.Regional block comparison analysis shows that the Hainan Block shares a similar Precambrian crystalline basement composition and multiple tec-tono-thermal event records with the Kontum Block of Vietnam,indicating an obvious affinity between them.
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