Detrital Provenance Of The Lower Mesozoic In The Eastern Guangdong Basin And Its Geodynamic Implication

At present,The Late Triassic-Early Jurassic geodynamic background of South China Block(SCB)keeps controversial.The Late Triassic-Early Jurassic Eastern Guangdong Basin locates at the southeastern margin of the SCB and its basin evolution,geochemical data,magmatic activities,detrital modes of sandstone,paleogeographic evolution and other aspects contain key geological records.In this study,detrital provenance and its geodynamic implications of the Upper Triassic-Lower Jurassic sequences of the Eastern Guangdong Basin are analyzed by means of modal analysis,detrital zircon LA-ICP-MS dating,paleogeographic analysis,geochemical analysis along with the reconstruction of paleoenvironment,paleocurrent data and regional magmatic activities.On the Q-F-L and Qm-F-Lt diagrams,most of the Late Triassic-Early Jurassic sandstones fall within continental block provenance,indicating there were a stable craton to provide its material.The dating results display the Late Triassic samples with seven age peaks,i.e.231 Ma,436 Ma,305 Ma,815 Ma,1853 Ma,2067 Ma and 2487 Ma,ranging from 206 Ma to 2544 Ma and the Early Jurassic with eight age peaks,i.e.196 Ma,247 Ma,320 Ma,432 Ma,770 Ma,1060 Ma,1820 Ma and 2430 Ma,ranging from 194 Ma to 3284 Ma.Provenance analysis suggests that the sediment sources of the Eastern Guangdong Basin are mainly from the north and northeast directions,resembling the Yongan Basin to the northeast and the Dongkeng Basin to the north and consistent with the Late Triassic-.Early Jurassic paleocurrent directions.The southeastern SCB occurred two large-scale transgression in the Late Triassic-Early Jurassic and formed a series of transitional coal-bearing basins.The results of paleogeographic analysis shows that the Late Triassic-Early Jurassic Eastern Guangdong Basin is N-E trending.The particle size in space is reduced from coarse to fine from western Fujian to eastern Guangdong and from southeastern Hunan to eastern Guangdong,indicating that the provenance comes from the north and northeast,consistent with the results of detrital zircon U-Pb dating.On the La-Th-Sc and Th-Sc-Zr/10 diagrams,most of the Late Triassic-Early Jurassic samples are plotted in continental arc or active continental margin,reflecting that SCB has been influenced by the subduction of the Paleo-Pacific plate.Integrated analysis of the petrology,sediment provenance,paleogeographic evolution and geochemical data reveals that the Late Triassic-Early Jurassic basins in the southeastern SCB,even though bear characteristics of passive continental margin,already received sediment supply probably from the uplifts in more northeastern region resulted from the northwesternward subduction of the Paleo-Pacific plate.