关键词: 下扬子区, 断陷盆地, 伸展构造, 基底断裂, 成盆机制

Abstract:

In an effort to further advance our understanding of the characteristics and dynamics of the Cenozoic fault basins in the Lower Yangtze region, we characterize the geological structures and formation mechanism of the fault basins by the interpretations of the seismic, drilling and geological data. Based on the regional cross sections perpendicular to the axis of the basins and their comparisons in time and space, we found that the scale of the basins gradually expanded from the land to the sea, and the rifting sequences increased in the thickness, and that the structures became more complex. All of these facts show us that the extensional amount and intension of the basins gradually increase from the west to the east. Constrained by the approximately wedge geometry of the Lower Yangtze block and boundary condition of the eastern lateral extrusion, the block approaches to expand in the southnorth direction, which could reactivate the preexisting faults of the preCenozoic basement, and then induced regional rifting process and basin subsidence, suggesting that the formation of the fault basins in the Lower Yangtze region was constrained by the two basic factors: the basement and the stress. The Cenozoic extension in the Lower Yangtze region and the dextral movement of the TanLu fault are all the geological responses to the tectonic deformation of the Lower Yangtze block, which can be explained well by the subduction of the Pacific Plate.

Key words: Lower Yangtze region, fault basin, extensional structure, basement fault, formation mechanism