Tectono-thermal modelling of Baiyun Sag, Pearl River Mouth Basin, since Cenozoic

摘要

The Pearl River Mouth Basin (PRMB) is a key area for marine oil and gas exploration in China, and the Baiyun Sag is the largest Cenozoic depression in PRMB. With complete Cenozoic strata and abundant drilling and seismic data, Baiyun sag is an ideal region for tectono-thermal modelling. In this paper, based on the multi-phase extensional model, tectono-thermal modelling is performed along six seismic profiles in Baiyun Sag to reveal the temporal and spatial differences of the thermal evolution, which can provide evidence for the evolution mechanism of PRMB and deep geodynamic process. The modelling results show that Baiyun Sag has undergone two phases of extension. The first phase (47.8～33.9 Ma) had started since the Eocene. The center and west part of Baiyun Sag have high tensile degree. The rapid rise of basal heat flow reached 80 mW·m~(-2); the second phase (23～13.8 Ma) tension occurred in the Miocene, the tension was stronger in the south and center of Baiyun Sag. The basal heat flow of the center reached the ～100 mW·m~(-2) at 13.8 Ma, and then decreased slowly and reached a steady state gradually. In general view, the stretch factor is large in the west and small in the east, large in the center and small in the margin. In the first phase, the stretch factor is large in the north, but in the second phase, the stretch factor is large in the south. The first phase was controlled by the strong extension during the rifting period. And the reactivation of extension and the "lower crustal flow" caused by the high velocity layer could be the main reason of the second phase (the post-breakup abnormal subsidence).