Determination of Zhu-Qiong movement: The enlightenment from tectonic and sedimentary characteristics of Fushan Sag, Beibuwan Basin

Abstract: The understanding of tectonic activity in the north basins of South China Sea has long been controversial. It is especially difficult for researchers to hold identical views in the problem of the determination of the Zhu-Qiong movement. Based on the research on the dynamic setting in the South China Sea and its surrounding basin, the authors believe that the Zhu-Qiong movement was a great extensional tectonic activity between Eocene and Oligocene, and it could be divided two episodes according to the dynamics in different stages. Fushan Sag is located in the southeast corner of Beibuwan Basin, which is one of the northern basins of the South China Sea. The sag’s tectonic and sedimentary characteristics show that there existed two backgrounds of extensional structure during the Zhu-Qiong movement, corresponding respectively to two episodes of Zhu-Qiong movement. In addition, according to the characteristics of the change of sedimentary rate as well as the time of the formation of faults which controlled sedimentation and distribution of multi-phase faults, it is held that the activity of the first episode of Zhu-Qiong movement occurred in Early-Middle Eocene (54Ma-39.4Ma). Its dynamics mechanism was that the West Pacific plate drew back in subduction caused by SE-trending mantle flow under the subduction of Indian plate beneath Eurasian plate. And the activity of the second episode of Zhu-Qiong movement took place in Late Eocene to Oligocene (39.4Ma-25.5Ma). The dynamics mechanism of this stage was different from that of the previous phase, and the extensional effect of Hainan mantle plume action on the lithospheric bottom led to the tectonic activity in this episode.