南海北部大陆边缘新生代盆地构造演化及其对油气聚集的影响

The northern margin of South China Sea goes through the geological process from continental rift to passive continental margin during Cenozoic, and develops a lot of sedimentary basin on the continental shelf including Beibuwan, Yingehai, Qiangdongnan, Zhujiangkou basin and so on. Affected by the regional crust structure and dynamic process, the feature of tectonic evolution shows up a spatiotemporal differences between basin and basin, even tectonic units within basin. This project tried to draw out the objective law and spatiotemporal differences in basin structure and tectonic evolution during Cenozoic making use of seismic data, probe into the controlling factor which causes the spatiotemporal differences of tectonic evolution, and analyze the tectonic evolution exercised the influence on the hydrocarbon accumulation. The research content consists of 4 respects: (1) features of fault systems and fault activities of Cenozoic in northern margin of South China Sea; (2) comparative analysis of basin structure and tectonic evolution between basin and basin, tectonic units within basin in margin of South China Sea; (3) regional tectonic evolution and dynamics during Cenozoic in the northern margin of South China Sea; (4) the spatiotemporal differences in basin structure and tectonic evolution and what of the effect on the hydrocarbon accumulation in the northern margin of South China Sea. This project not only contribute to some key problem solving about the continental margin tectonic evolution of the northern margin of South China Sea, but also is a useful for evaluating the potentiality of petroleum resources in the research area.

南海北部新生代经历了从大陆裂谷到准被动大陆边缘的演化过程，发育有北部湾、莺歌海、琼东南、珠江口等大型含油气盆地。受区域地壳结构及构造动力学过程影响，南海北部盆地与盆地之间、盆地内部不同构造单元之间新生代构造-沉积演化的差异性十分明显。本项目旨在利用石油勘探资料分析南海北部新生代盆地构造演化的差异性及其控制因素，揭示盆地构造演化差异性对油气聚集的影响。研究内容包括：其一，南海北部大陆边缘区域断裂系统及其新生代构造活动的时空差异性；其二，南海北部新生代盆地结构特征及其时空差异性；其三，南海北部盆地构造演化及其动力学过程；其四，南海北部新生代盆地构造演化差异性对油气聚集的影响。该项目研究试图在理论上探讨南海北部大陆边缘构造演化及其动力学过程等科学问题，在应用上揭示南海北部新生代盆地构造演化的时空差异性对油气聚集的影响。

大量油气勘探资料证实发育在南海北部大陆边缘的珠江口、琼东南、北部湾等NE向新生代盆地均具有南北分带、东西分区和垂向分层的三维结构差异特征，NW向的莺歌海盆地也具有分带分层的结构。盆地主要发育NE向和NW向两组基底深大断裂，在盆地演化过程中控制着盆地分区分带的构造格局，不同区带盆地伸展断裂系统差异明显。在珠江口—琼东南盆地，两个NW向构造变换带连接并调节东西不同区段的伸展构造变形。自下而上，珠江口—琼东南盆地新生代层序可划分为裂陷构造层、断拗过渡构造层和陆阶-斜坡构造层（北部湾盆地不发育该构造层），断裂系统由NE向发生顺时针旋转为近EW向或NWW向。南海北部大陆边缘盆地经历断陷期（可细分为2~3幕）、断拗过渡期和裂后洋盆沉降期（北部湾盆地除外）等3期差异明显的构造演化阶段，不同区段构造演化具有明显的时空差异性。珠江口盆地的强烈裂陷时期（始新世）、裂陷结束时限（早渐新世）早于琼东南盆地（早渐新世和晚渐新世）。构造变形具有“早强晚弱、北强南弱、自北西向南东（由陆到海）逐渐增强、脆性（早）转向韧性（晚）、由上地壳（早）向下地壳（晚）甚至地幔渗透”的迁移演变规律。南海北部陆缘盆地沉降过程均可划为3幕，各盆地的沉降特征具有明显的时空差异性。珠江口—琼东南盆地沉降特征相似，北部湾盆地最早结束第二幕沉降，莺歌海盆地“幕式”特征最明显。这4盆地之间沉降的“幕式”共性特征是对南海扩张过程中的动力学过程的响应。盆地沉降规律平面特征与盆地分区分带的格局也有良好对应关系。盆地不同区段的伸展构造变形具有分层次、分区带、分时期的时空差异特征。多幕裂陷阶段，盆地伸展模式可能由纯剪切转变简单剪切。自北西向东南的地幔侧向流动可能是陆缘破裂形成盆岭式断陷结构的主动力源，而板块之间的相互作用是盆地裂陷演化过程中差异变形的被动力源。共发表标注本项目资助论文9篇。