北部湾盆地福山凹陷古近系双层结构形成机制

以北部湾盆地区域构造分析为基础, 在福山凹陷构造活动性研究的基础上探讨了福山凹陷形成的动力学机制, 分析了凹陷东部地区古近系地层中双层结构的形成机制问题.研究认为: 福山凹陷在平面上受红河断裂的左行走滑和海南隆起顺时针旋转的双重作用, 流三段沉积期凹陷在旋转-拉分作用下发生强烈的水平伸展, 为东部地区下构造层中的反向断层提供动力源, 海南隆起的快速隆升作用形成了上构造层中的重力滑动生长断层, 渐新统早期在流二段泥岩中发育的火成岩侵入体在凹陷的东部地区形成一道天然屏障, 最终形成双层结构.结果表明, 双层结构形成过程可划分为裂陷雏形期、下构造层伸展断裂期、中部塑性层发育期、上构造层形成期以及双层结构定形期5个主要阶段. 

Genetic Mechanism of Double-Layer Structure in Paleogene of Fushan Sag,Beibu Gulf Basin

Based on the regional tectonic analysis of Beibu Gulf basin, in this paper, the tectonic activities of Fushan sag is studied, the dynamic formation mechanism of the sag is discussed, and the formation mechanism of double-layer structure in Paleogene strata of the eastern area is analyzed. It is regarded that Fushan sag was under the dual effect of sinistral strike-slip of Red River fault and clockwise rotation of Hainan uplift. During the deposition period of the third member of Liushagang Formation (Els₃), intense horizontal extension occurred during the rotation and pull-apart of the sag, which provided dynamic source for the antithetic faults of the lower tectonic layer in the eastern area. The rapid uplift of Hainan uplift led to the formation of gravity slumping growth faults in the upper tectonic layer. In the Early Oligocene, the intrusive igneous rocks in the second member of Liushagang Formation (Els₂) formed a natural barrier. Finally, there formed the double-layer structure. The forming process of the double-layer can be divided into five major stages as follows: rifting embryonic period, extending faulted period of the lower tectonic layer, development period of middle plastic layer, formation period of tectonic system, and finalizing period of double-layer structure.