STRUCTURAL SIGNIFICANCE OF BRINK SAGS IN THE BOHAI BAY BASIN

According to the structural characteristics of brink sags in the Bohai Bay Basin,the formation and evolvement of the basin show the characteristics of passive rift basins,which are provided with inheritance,multi-direction extension and rotation strike-slip.In co-ordination with the structural characteristics of host sags,the rift-subsidence which occurred in Cenozoic in the background of area stress actions and fault-block movements in the Bohai Bay Basin is summarized in this paper.Together with the northward extension caused by the unbalance of fault blocks moving northward,the northern plate extended north-westward inner due to the difference of movement between speed and distance from the east to the west of the plate.During the differential movement of fault-blocks tilting and extending process,the Tan-Lu fault belt adjusted in the strike-slip process and made shearing stress release effectively.At the same time,a series of strike-slip sags were formed along the fault belt.The formation model of the Bohai Bay Basin can be summed up as:the crust extension-the crust rift and extension as well as the sub-geosphere viscoelasticity rheid becoming thinner-the mantle uplift-the mantle plume invasion and melting-(the crust rise and erosion)-the thermal subsidence.