Temporal and Spatial Distribution of Tectonic Subsidence and Discussion on Formation Mechanism of Anomalous Post-Rift Tectonic Subsidence in the Qiongdongnan Basin

To investigate the temporal and spatial distribution of tectonic subsidence and the formation mechanism of anomalous post-rift tectonic subsidence in the Qiongdongnan basin,we calculated the tectonic subsidence history of sixty-eight wells by back stripping method.Then fifteen representative wells were chosen to estimate stretching strain rate using inverse theory and to calculate stretching factors.The results suggest that the extent of tectonic subsidence in the center and southern depressions is greater than that in northern depression.Tectonic subsidence rate that varied with time can be summarized as "locally quick-holisticly slow-locally quick"followed by gradually decreasing in the post-rift period and attained its minimum during 15.5-10.5 Ma,but it started to increase again since 10.5-5.5 Ma.Anomalous post-rift tectonic subsidence is more obvious in both east and west than in the north of the Qiongdongnan basin and the extent in center depressions increases from west to east.In time scale,the post-rift subsidence increases with time,and the process can be summarized as quick-slow-quick multiple stages.Our results suggest that the quick subsidence in the early post-rift stage likely resulted from the diversity of stretching during the rift period,and the quick tectonic subsidence since Later Miocene was likely caused by magmatic activities.