广西百色盆地构造-热演化初步研究

百色盆地是一个典型的第三纪走滑拉分盆地,印度板块与欧亚板块碰撞造山造成右江断裂带先左行(距今20~50 Ma)后右行(距今20 Ma以来)是盆地形成较确定的构造背景。盆地分田东、头塘和莲塘3个坳陷,那笔和那葛2个隆起。坳陷形成于NW向左行左阶排列断列的重叠、错列处,而隆起形成于NW向左行右阶排裂断裂的重叠、错列处。其构造演化分为六吜—洞均前拉盆期、那读—建都岭拉分期和建都岭末—第四系后拉分期3个主要构造阶段,每个阶段具有明显不同的特征。通过盆地有机质镜质体反射率、磷灰石裂变径迹和流体包裹体综合研究表明,百色盆地的热演化程度总体较低。仅那读组生油岩达到低熟,极少数为成熟,其它生油岩层未成熟。盆地热演化总的规律是:从距今大约55 Ma开始,古地温随着坳陷沉降和沉积而逐步增加,并于距今大约25~35 Ma达到最大值。然后随着地壳缓慢抬升,地层温度逐渐变冷。热演化程度低是控制百色盆地油气远景较差的主要原因。 

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.