Provenance Analysis And Tectonic Setting Of The Late Triassic-Middle Jurassic In Eastern Guangdong Basin

The Eastern Guangdong Basin is located in the southwestern margin of the Cathaysian Plate,the intersection of Tethys tectonic domain and Pacific tectonic domain.Its sedimentary evolution,magmatic activity and tectonic characteristics record the basic information of Mesozoic tectonic evolution in South C hina.Based on the field geological survey and U-Pb chronological analysis of clastic zircons in the Late Triassic-Jurassic strata of Daxi Town,Zijin Huangcun and Huizhai Town,Eastern Guangdong Basin,this paper reveals the sedimentary and sediment source characteristics of the basin,and then discusses its tectonic background.The Lantang Group of Early Jurassic in Daxizhen area of Xinfeng is divided into three subgroups from bottom to top: the lower subgroup shows the trend of argillaceous debris to medium-fine sandstone from bottom to top,and various sedimentary facies assemblages,including massive mudstone,siltstone,distal bar or estuarine bar facies,distributary channel facies,etc.,constitute the characteristics of the change from shallow sea or pre-delta sedimentary system to delta front sedimentary system.The middle subgroup is characterized by sand-mud interbedding,and its stratigraphic lithology,sedimentary structure and sedimentary facies combination constitute the front delta-delta front sedimentary system;the upper subgroup develops horizontal and trough cross-bedding sedimentary structures,which may reflect mouth bar and distributary channel facies,and pre-delta to delta plain sedimentary system.The U-Pb dating of the zircons shows that the youngest age of the group is 186+3.2 Ma,and the youngest age of the clastic zircons of the overlying strata samples is 169.3+2.5 Ma and 169.4+1.5 Ma,respectively.The oldest sedimentary age of the group is about 169 Ma,belonging to the Middle Jurassic and mainly continental deposits.The characteristics of clastic zircon age groups of Jurassic strata in Xinfeng Daxizhen,Zijin Huangcun and Jiexi Huizhai Town of Eastern Guangdong Basin are 220 Ma-337 Ma,373 Ma-451 Ma,800 Ma,1800 Ma in the Early Jurassic,212 Ma-254 Ma,371 Ma-435 Ma and 1740 Ma-1897 Ma in the Middle Jurassic.The provenance analysis shows that the early Jurassic provenances in the study area of the eastern Guangdong Basin mainly come from the southwestern margin of the Yangtze Plate,Hainan Island and the widely distributed Caledonian and Indosinian magmatic activities and metamorphism areas;the middle Jurassic provenances in the basin mainly come from the northeastern Fujian Province and southwestern Zhejiang uplift areas in the northeastern direction of the eastern Guangdong Basin,the possible magmatic arcs(uplift areas)in the eastern part and the possible magmatic arcs(uplift areas The Indosinian and early Yanshanian magmatic active areas are widely distributed.The characteristics and differences of clastic zircon age groups in the early and middle Jurassic,as well as the variation of source area distribution,reflect the transformation of tectonic dynamic system in South China from Tethyan to Pacific tectonic domains,with a time limit of about 169 Ma.Its tectonic setting is the early Yanshanian magmatic activity and crustal uplift induced by the subduction of the Middle Jurassic Pacific to the East Asian continent,which affected the sedimentary process of the Eastern Guangdong Basin.