| The China offshore area is a petroliferous enrichment zone in East Asia,along which various types of sedimentary basin were developed.Since the Cenozoic it has been under the influence of interaction between ocean and continent plates as well as geodynamic processes.Temporal-spatial differences of basin structure determine the differences of hydrocarbon enrichment in China offshore region,so the key to hydrocarbon exploration in China offshore basins is to reveal the temporal-spatial differences and formation mechanism of them,which is significant for clarifying the epicontinental tectonic evolution of East Asia.Based on integrated application of the latest exploration data,this dissertation takes the Bohai Sea basin(intracontinental rift),the East China Sea basin(epicontinental back-arc rift),the Beibu Gulf basin(passive margin rift)and the Yinggehai basin(strike-slip pull-apart basin)as the key anatomy object.Through the meticulous description of fault systems and basin structures,the spatial variations among those basins were clarified;through the quantitative characterization of fault activity and the restoration of balanced sections,the differences in the evolution of different basins are revealed;through the 4D-geodynamic simulation,the history of plate subduction and mantle convection is recovered as well as the deep dynamic processes of different basins.On this basis,combined with the systematic analysis of the basement structure development and regional tectonic setting,the controlling factors of the tectonic differences of Cenozoic basins offshore China are discussed.The results show as below:The tectonic framework varies a lot among different basins offshore China.Cenozoic offshore basins have experienced a transition from initial rifting to differential rifting,which controlled the evolution of different basins with their own tectonic characteristics.The whole Bohai Sea basin is distributed in NNE direction and cut by NW direction fault,leading the basin to be divided into northern and southern segments.And the structural style indicates the superposition effect of strike-slip and extension.The Bohai basin has experienced from "strong extensional and weak strike-slip" rifting stage to "strong strike-slip and weak extensional" rifting stage,and the stage of the Neogene strike-slip depression.There are obvious differences in the ratio of strike-slip and extensional effects in different periods.The East China Sea basin is controlled by NNE-trending faults with obvious differences between the east and west.The rifting center of East China Sea basin was located in the western sub-basin during the Late Mesozoic to Paleocene,then migrated to the eastern sub-basin during the Eocene.The rifting evolution of the East China Sea basin was characterized by the migration from west to east.The Beibu Gulf basin has experienced a rift stage dominated by NE-,NNE-and nearly EW-directed faults,which embodies a transformation rift process.Yinggehai basin has experienced the rifting evolution stage of weak strike-slip during early to middle Eocene and strong strike-slip pull-apart from late Eocene to Oligocene,and the depression superimposed with dextral strikeslip stage in Neogene,which shows that the continuous strike-slip controls the basin evolution.In response to the transformation of the deep structures in the East Asia continental margin,the geodynamic processes of different basins offshore China are obviously different.In the early Paleogene,the entire East Asian continental margin was significantly influenced by the subduction of the Indian plate and the Izanagi plate,and the whole East Asian continental margin had a uniform mantle wedge structure,and the mantle flow field was bidirectional convergence,strong in the west and weak in the east.After the subduction of the IzanagiPacific mid-ocean ridge,the geodynamic processes of different basins are obviously different.The asthenosphere mantle flows rapidly from east to west in the Bohai basin due to the sink of the Izanagi and the subduction of Middle Pacific Ridge.The deep mantle flow in the East China Sea basin was obviously controlled by the Pacific and Philippine plates.At 40 Ma from now,in the front of the Pacific subduction zone,the mantle flow has the characteristics of annular flow and the local upwelling is obvious.The subduction wedging of the Philippines plate at 20 Ma causes the mantle velocity to decrease obviously.The Beibu Gulf basin is controlled by the Pacific plate and the Izanagi plate,and the mantle upwelling is obvious.At the same time,the proto South China Sea subduction drives the mantle to flow southward.The mantle beneath the Yinggehai Basin is mainly horizontal flowing.Basement structure,geodynamic process and regional dominant factors are the key factors controlling the tectonic differences of Cenozoic basins offshore China.The basement structures of basins are obviously different from north to south,and a series of suture zones or transition zones with different properties are developed,which leads to the development of different basins in the continental margin of East Asia.Different regional controlling factors control the evolution of different basins offshore China.Mantle upwelling caused by the dehydration of the back margin of the Izanagi residual plate and the dextral strike-slip of the Tanlu fault zone are the two dynamic sources,which controlled the formation of the "strike-slip and extension" composite basin in the Bohai basin.The joint effect of the Pacific and Philippine plates causing the mantle upwelling led to the rift migration in the East China Sea basin.The subduction and extinction of the proto South China Sea driven by plate reconstruction resulted in the clockwise shift of regional extensional stress,which determined the NE-NEE-EW rift transition of the Beibu Gulf basin.The Yinggehai basin experienced a strong strike-slip pull-apart effect due to the large-scale sinistral motion of the Red River fault zone caused by the strong collision between the India and Eurasia plates. |
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