渤海湾盆地黄骅坳陷新生代伸展量的时空分布特征

Characteristics of extension amounts and their temporal and spatial distribution of the Cenozoic of Huanghua Depression in Bohai Bay Basin

以渤海湾盆地黄骅坳陷22条区域地震剖面的构造解释为基础,利用平衡剖面技术计算了不同位置剖面的伸展量、伸展率和伸展系数,并分析了伸展量的时空分布规律。研究表明,黄骅坳陷新生代具有幕式伸展的特点,而且伸展量的时空分布极不均匀。空间上,伸展量主要是由盆地主边界断层伸展位移造成的,主边界断层位移较大处的伸展量也相应较大;时间上,水平伸展运动可以分为始新世、渐新世和新近纪3个时期,其中,始新世伸展主要发生在盆地南部,渐新世发生在中北部,新近纪伸展量较小,主要发生在中部。伸展量时空分布是受盆地构造变形、构造演化控制的。始新世,NNE向沧东断层的伸展位移是控制盆地伸展变形的主要因素,且沧东断层在盆地南区的伸展位移量较大。渐新世,NNE向沧东断层在盆地中北区的伸展位移量相对较大,同时盆地内部NNE向基底断层的右旋走滑诱导的NE向基底正断层对盆地伸展变形做出贡献。新近纪,盆地在后裂陷的热沉降过程中NNE向基底断层仍然有右旋走滑位移,致使盆地中部发育NE向盖层正断层。

Based on the interpretation results of the structural characteristics of 22 seismic profiles of Huanghua Depression in Bohai Bay Basin, the amount of extension, the extensional coefficient and the extensional ratio have been calculated by technique of balanced geological cross-sections, moreover, the spatial and temporal distribution of the extension amounts has been analyzed in this paper. The results show that Huanghua Depression was characterized by episodic evolution in the Cenozoic, and also the tem- poral and spatial distribution of extension amount of this depression was very uneven. On one side, the extension amount in space was mainly caused by the stretching displacement of the main basin boundaryfaults. The extension amount was correspondingly larger where the stretching displacement of the main ba- sin boundary faults was bigger. On the other side, the main extensional period can be divided into three periods which are the Eocene, the Oligocene and the Neogene. Among them, the extension in Eocene occurred mainly in the southern part of the basin while the one in the Oligocene occurred in the north-cen- tral part. And also, the extension amount in the Neogene was smaller and mainly occurred in the central. The temporal and spatial distribution of extension amount was controlled by basin tectonic deformation and tectonic evolution. In the Eocene, the stretching displacement of NNE trending Cangdong fault was the main factor that controlled the basin extensional deformation and the amount of the stretching displacement was larger in the southern area of the basin. In the Oligocene, the amount of the stretching displacement was relatively large in the north-central part. At the same time the NE trending basement normal fault which was induced by dextral strike-slip of the NNE trending basement fault in inner basin contributed a lot to the basin extension. In the Neogene, the NNE trending basement fault still had dextral strike-slip dis- placement when the basin was in the thermal subsidence process after the basin rift. It was the reason which caused the NE trending normal fault in the cover rock in the central part of the basin.