东海盆地西湖凹陷构造样式及其演化

Structural Framework and Evolution of Xihu Sag in East China Sea Basin

西湖凹陷是经历多期构造作用的白垩—第三纪盆地。多期裂陷和反转构造作用的叠加导致了相对复杂的构造格架样式和盆地地质结构。凹陷总体上具有东西分带,南北分块的构造格局。裂陷期的同沉积断裂组成了多种复合的构造样式:西部斜坡带主要发育断阶、地堑和地垒构造;中央洼陷带则以复合"Y"字型、羽状和似花状断裂组合为主;东缘断阶带主要发育"Y"字型、梳状和羽状组合。坳陷反转期,早期的同沉积断裂发生了不同程度的逆冲反转,形成了多种复合的构造样式,例如反冲叠瓦扇构造、后断叠瓦式逆冲构造等叠合构造样式。从盆地的构造样式出发,探讨了盆地的形成演化和构造-沉积充填过程对有利圈闭带发育分布的控制作用,对富生烃凹陷油气预测具有重要指导意义。

Xihu sag is a Cretaceous-Tertiary basin which experienced multi-episodic tectonism. Complicated tectonic styles and geological structures were generated by multi-episodic rifting and inversion. Zonation in latitudinal direction and blocking in longitudinal direction is the main feature of the Xihu sag. Faults developed in synrift phases formed several structural styles： the fault terraces, grabens and horsts were generated in the western slope belt; fracture assemblages in the central depression belt were the complex Y-type fractures, feather fractures and flower-like fractures; while in the eastern fault terrace belt the Y-type fractures, comb-like fractures and feather fractures were generated during the phase of inverted tectonism. The synrift faults developed in early phase formed several structural styles, such as backwash imbricated structures and posthumous imbricated thrusting structures. Combined with tectonic styles analysis, the control effects of evolution of the basin and the process of sediment filling to trap development are discussed, which is an important guide to the petroleum prediction of hydrocarbon enriched sag.