Reactivation mechanism of pre-existing faults in multiphase extensional setting: A case study of Enping 17 sag, Pearl River Mouth Basin

        The Enping 17 sag (EP17) is located in the northern part of the Pearl River Mouth Basin, and the Cenozoic boundary faults with complex-trending have been developed. The genetic mechanism of the boundary faults is still unclear, which limits the understanding of the structural evolution of the sag in the study area. Using high-quality three-dimensional seismic data, through seismic interpretation, throw-distance (T-x) plots, physical experiment and tectonic evolution sections, the geometric characteristics, activity and genesis of boundary faults are analyzed, and the reactivation mechanism of pre-existing faults and the evolution process of sags are discussed. The results show that the EP17 boundary fault is curved, and there are differences between the north and south sides: the north is dominated by NE-trending faults, accompanied by nearly ENE-trending faults, with slope-flat type and four-stage rolling anticline on the seismic profile; the south is a near NS-trending fault with shovel-type and two-stage rolling anticline. The selective reactivation of NE-trending and near NS-trending pre-existing faults in the Cenozoic controlled the evolution of the sag. The Enping 17 sag has undergone multiphase extension, and the extension direction rotates from NW-SE to N-S clockwise. The early Eocene NE-trending and near NS-trending pre-existing faults are reactivated at the same time, forming a strong extension zone at the fault tips, resulting in a rapid link between the north and south faults. These group of faults continued to be active during the Middle Eocene, and a new ENE-trending fault was formed in the north. The NE-and ENE-trending faults in the northern part of the Late Eocene continued to move, controlling the migration of the sedimentary center to the northern sag.