Abstract:  The southern subsag of the Baiyun sag-Liwan sag is a passive margins basin, located in the Pearl River Mouth basin, northern South China Sea. Its geological background is complex and it has experienced many periods of stretching and subsidence. The tectonic evolution from the Eocene to the Miocene includes rifting and downwarping, forming a multi-level sedimentary structure. In this study, tectonic-thermal modelling is used to recover the tectonic subsidence history and basement heat flow history, so as to explore the geodynamic background of the basin evolution. This study selected 19 seismic lines (7 east-west, 12 north-south), established 380 simulation Wells, carried out tectono-thermal modelling, and recovered the tectonic subsidence history and tectono-thermal evolution history of southern subsag of the Baiyun sag-Liwan sag. It is found that there are two periods of rapid subsidence in southern subsag of the Baiyun sag-Liwan sag since Eocene, which occurred in Eocene (47.8-33.9 Ma) and Miocene (23.0-13.8 Ma), and their tectonic subsidence has significant differences between east-west and north-south. Meanwhile, the basement heat flow experienced two significant increases, the first time in the Eocene, the basement heat flow rapidly increased to about 86 mW/m2. The second time in the Miocene, the basement heat flow reached the highest value at 13.8 Ma, and reached 125 mW/m2 in the southern Liwan sag. The results show that the subsidence and heat flow characteristics of southern subsag of the Baiyun sag-Liwan sag are closely related to its tectonic evolution.

Key words: tectono-thermal modelling, tectonic subsidence, basement heat flow, southern subsag of Baiyun sag-Liwan sag, Pearl River Mouth basin