Initiation and origin of dextral deformation at Mid-Eocene in the western Bohai Bay Basin, East China

Abstract

The Cenozoic back-arc rift basins along the continental margin of East Asia are featured by both extensional and dextral deformation systems. Here we investigate the timing and interaction of these two types of systems, based on seismic data, stratigraphic isopach maps and drilling data in the Jizhong Depression in the northwestern Bohai Bay Basin (BBB), East China. The results show the rifting was initiated as early as the Eocene while the dextral deformation did not occur until ca. 42 Ma. The Jizhong Depression changed from a simple rift basin with boundary faults to the west to a geometrically more complex dextral transtensional basin at ca. 42 Ma. This event was roughly concordant with the initial dextral slip on the Tan-Lu Fault lying at the eastern BBB, and together they transformed the BBB into a complex pull-apart rift basin. The tectonic reorganization of the BBB was probably the response to the change from an orthogonal to an oblique subduction of the Pacific Plate beneath East Asia at that time.