RESEARCH ON THE TECTONO-THERMAL EVOLUTION OF THE BAISE BASIN, GUANGXI PROVINCE

Baise basin is a typical strike-slip and pull-apart basin that was formed in the Tertiary Period. It is the tectonic background and main reason why the Baise Basin was formed. The collision of the India Plate and the Eurasian Plate made the Youjiang fracture belt left-handed strike slip(20-50 Ma ago) first, then right-handed strike slip (20 Ma till now). The basin includes three depressions (the Tiandong Depression, the Toutang Depression and the Liantang Depression) and two uplifts (the Nabi Uplift and the Nage Uplift). The three depressions were formed in the places where the left stage stagger NW fractures turning left overlapped and arrayed, and the two uplifts were formed in the places where the left stage stagger NW fractures turning left overlapped and arrayed. The three main periods of tectonic evolution includes the Liuniu-Dongjun pull-apart period, the Nadu-jianduling pull-apart period, and the Late Jiandu-ling-Quaternary epi-pull-apart period. Each period had its own apparently different characteristics. Although the scale of the basin is small, there are better oil source rocks and the conditions of reservoirs and cover rocks. The main problem about influencing oil-gas formation is that the degree of thermal evolution is lower. The thermal evolution of the Baise Basin was modelled based on vitrinite reflectance R_o, apatite fission tracks and fluid inclusions. The modelling results showed that the gradient of thermal evolution was lower. the Nadu Formation is the only oil-generating strata with low maturity. The oil-generating strata of the rest formations are not mature. The basic characteristics of thermal evolution in the basin were that paleotemperature increased with the subsidence and sedimentation of the Tiandong Depression from 55 Ma ago first, and achieved the highest during 25-30Ma ago, then decreased gradually with the slow lifting of the crust. The low thermal evolution of the basin is one of the most important factors resulting in poor prospective oil-gas.