珠江口盆地形成机制与油气地质

珠江口盆地位于南海北部陆缘地壳强烈薄化带之上，各坳陷的凹陷结构、构造变形样式、裂后沉降均存在显著差异，不同于陆内典型断陷盆地。裂陷期凹陷结构由珠一坳陷典型箕状断陷向珠二坳陷的断-拗复合型和珠四坳陷的岩浆底辟改造型断拗转换，控凹断层的结构样式由单组高角度犁式断层向多组断层构成的大型拆离断裂系统转换，湖盆由早到晚、由北向南断控作用减弱而拗陷作用增强，分隔性减弱而岩浆底辟的改造增强；裂后沉降具有阶段性和分带差异性，早期以整个盆地的缓慢沉降为主，约27.2 Ma进入差异沉降阶段，以陆缘外侧珠四坳陷的强烈沉降为主要特征，约23 Ma强烈沉降区域向北扩展至珠二坳陷，裂后的差异沉降形成了浅水与深水沉积环境，并控制了珠海组和珠江组-韩江组两大陆架坡折带的发育。珠江口盆地分带差异演化与其陆缘地壳的强烈伸展-薄化-破裂过程有关，初始岩石圈结构的差异、薄化过程中地壳流变性质的转换、岩浆底辟作用的参与共同控制了凹陷结构的分带差异；破裂过程中扩张脊向南的跃迁、裂陷期地壳薄化程度的差异共同控制了裂后沉降的阶段性和分带差异性，从而具有不同的构造-热演化史。珠江口盆地的分带差异演化，使得凹陷的结构、沉积充填、热演化史等基础石油地质条件均有所不同，必然导致其成藏规律和勘探策略的差异。

Formation mechanism and petroleum geology of Pearl River Mouth Basin

The Pearl River Mouth Basin is located above the strong thinning belt of continental margin crust in the northern South China Sea. There are significant differences in the depression structure, tectonic deformation pattern and post-crack settlement of each depression, which is different from the intracontinental typical fault basin. The depression structure during rifting period was transformed from the typical dustpan-like fault depression in Zhu-1 depression to the composite fault depression in Zhu-2 depression and the fault depression transformed by magmatic diapirism in Zhu-4 depression. The structural pattern of the depression-controlled fault was converted from the single-group high-angle plough-shaped fault to a large-scale detached fault system composed of multiple groups of faults. The lake basin has the fault control effect weakened from early to late and from north to south, while the depression effect was enhanced, showing the weakened separation and the enhanced transformation by magmatic diapirism. The post-crack settlement presented phased and zonal differences. In the early stage, the whole basin was dominant by slow subsidence, and entered the differential subsidence stage in about 27.2 Ma. The Zhu-4 depression on the outer continental margin was dominant by strong subsidence, and in about 23 Ma, the strong subsidence area extended northward to the Zhu-2 depression. The post-crack differential settlement led to shallow-water and deep-water sedimentary environments, controlling the development of two slope-break zones, i.e., Zhuhai Formation and Zhujiang Formation-Hanjiang Formation. The differential evolution of zoning in the Pearl River Mouth Basin was related to the strong extension-thinning-rupture process of the continental margin crust. During the differentiation and thinning process of the initial lithospheric structure, the transformation of crustal rheological properties and the participation of magmatic diapirism jointly controlled the zoning difference of depression structure. During the rupture process, the southward transition of extensional ridge and the difference in thinning degree of the crust during rifting period jointly controlled the phased and zonal differences of the post-crack settlement, thus forming a different tectonic-thermal evolution history. The zoning differential evolution of the Pearl River Mouth Basin resulted in different basic petroleum geological conditions of depression, such as the structure, sedimentary filling and thermal evolution history, which will inevitably lead to the differences in its accumulation laws and exploration strategies.