东营凹陷伸展断弯褶皱的构造几何学分析

STRUCTURAL GEOMETRIC ANALYSES ON THE EXTENSIONAL FAULT-BEND FOLD IN THE DONGYING DEPRESSION

东营凹陷是渤海湾盆地南部一个典型的中新生代半地堑盆地。本文通过对横穿东营凹陷的地震反射剖面进行精细的构造解析,发现这个半地堑盆地的伸展构造具有明显的膝折变形特征,基本上符合伸展断弯褶皱模型。由此运用伸展断弯褶皱理论,同时按照平衡剖面原理,详细恢复了东营凹陷伸展构造的发育过程。经过对盆地内部构造变形的反复拟合和测算,我们确定了东营凹陷伸展断弯褶皱的构造几何学特征及其运动学过程,揭示出东营凹陷各主要裂谷阶段的地壳水平伸展量,并且将其中的背斜解释为上凹与上凸断层转折组合所形成的一个伸展背斜构造。同时采用构造几何学方法推断在白垩纪末期该地区曾经历过大约1750m厚的剥蚀作用,总伸展量可达25km。

The Dongying depression is a typical Mesozoic-Cenozoic half-graben in the Bohai Bay Basin. In this paper we present the results of a fine structural geometric analyses of the seismic reflection profiles across the Dongying depression, where half-graben structures display the features of kink-band deformation and extensional fault-bend fold. In our work we focused on the possibility of using theories of extensional fault-bend fold and balanced cross-section, restored the kinematic processes of the extensional structures in the Dongying depression. The results of our study show that this approach is appropriate for （ 1 ） evaluating the crustal extensional amount in major stages, （2） interpreting the forming of the extensional anticline, and （3） deducing that this basin experienced the erosion of about 1,750 m in the end of Cretaceous.