TRANSFER ZONES AND DIFFERENCES IN INTRA-PLATE DEFORMATION IN GREAT QIKOU SAG OF THE BOHAI BAY BASIN

Based on the newly acquired high-resolution 3D seismic data, we analyzed the transfer zones and their bearing on differences in intra-plate deformation in the Great Qikou Sag of the Bohai Bay Basin. The transfer zones in the Great Qikou Sag can be subdivided into three orders: (1) The first-order N—S-trending major transfer zones from west to east, i.e. the East Kongdian Transfer Zone, the Coastal Transfer Zone, and the Yangerzhuang Transfer Zone, corresponding to three basement-involved strike-slip faults, respectively. The three zones play an important role in reconciling the differences in structural styles of the west and east sides of the Great Qikou Sag. (2) The three second-order transfer zones roughly in E—W trending, including the Hangu, Haihe-Xingang, and Qizhong transfer zones, corresponding to the three subbasin-controlling faults from north to south, respectively. They play a role in adjusting the differences between the south, the middle, and the north parts of the Huanghua Depression. (3) The third-order transfer zones are generally perpendicular to its master fault, with the function to transmit the extension among faults. The origin of transfer zones in the Great Qikou Sag varies. The master boundary faults control over the basement-involved structures and differentiation of Cenozoic extension. The existence and development of different transfer zones in the Great Qikou Sag may cause different deformation in different periods and different faulted-blocks in the Huanghua Depression, resulting in differences in structural styles of the different parts of the Great Qikou Sag. For examples the Huanghua Depression is influenced by the roll-back subduction of the Pacific Plate and the collision between the Indian Plate and the Eurasian Plate. The depression is under a dextral transtensional stress field in the Cenozoic, resulting in rifting during the early evolutionary period, and pull-apart faulting during the later evolutionary period. Its principal regional stress underwent clockwise rotation in Cenozoic, from the NWW—SEE-trending extension during the Kongdian- Shasi period to the NW—SE-trending extension during the Shasan-Dongying period, and near N—S-trending extension during the Neogene. Such an evolutionary process can be used to successfully explain the development and evolution of the pull-apart Great Qikou Sag.