Post-Rift Faulting Migration, Transition and Dynamics in Zhu 1 Depression, Pearl River Mouth Basin

Abstract

A increasing number of studies on rift basin reveal that the post-rift evolution of rift is not solely dominated by thermal subsidence. Tectonic activity and deformation including fault reactivation is also active during the Post-rift stage. Zhu1 Depression (Pearl River Mouth Basin, northern margin of SCS) is characterized by active Post-rift faulting, which has great contributions to oil and gas migration and accumulation of the Neogene in this area. In this paper, post-rift fault system (more than 3200 faults) in Zhu1 Depression is studied by geometric and kinematic analysis method using high quality 3D seismic reflection data, which gives insights into the dynamics evolution of the post-rift stage. The analysis reveals two episodes of faulting in the post-rift stage, named Nanhai-phase faulting and Dongsha-phase faulting respectively. Transition of faults geometry and kinematics from Nanhai-phase to Dongsha-phase indicates a change of the dynamics. The peak time of fault activities has a migration both in Nanhai-phase faulting and Dongsha-phase faulting. The former migrates from S to N, and the later migrates from E to W. The two episodes of faulting are both mainly controlled by tensional stress, with a slight component of shear stress in Dongsha-phase. Regional extensional direction transforms from NNE10∼15°in Nanhai-phase faulting to NNE20∼25°in Dongsha-phase faulting, with 5∼10°clockwise rotation. The Nanhai-phase faulting is closely related to the sea-floor spreading of SCS, and the peak time of fault activity is consistent with the post-rift abnormal subsidence period. The Dongsha-phase faults form after the cease of the sea-floor spreading of SCS and fit well with the collision time between the Luzon Arc and the Eurasian Plate. Coincidently, direction of the regional intermediate principal strain (s2) during the Dongsha-phase faulting is consistent with the collision direction between the Luzon Arc and the Eurasian Plate. All these features together with the faulting migration direction confirm the conclusion that the Dongsha-phase faulting in Zhu1 Depression is the result of the collision between the Luzon Arc and the Eurasian Plate since middle Miocene.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016