海拉尔盆地乌尔逊凹陷中的伸展断层转折褶皱分析

Extensional Fault-Bend Folding in Urxun Sag,Hailaer Basin

乌尔逊凹陷是海拉尔盆地中部的一个典型中新生代陆相箕状断陷。本文在阐明海拉尔盆地的构造特征及其演化过程的基础上,通过详细分析乌南次凹断陷期原型盆地的构造几何学特征,认为其断层上盘存在明显的膝折变形,符合伸展断层转折褶皱理论的应用前提。运用该理论对乌南次凹断陷期原型盆地进行了正演模拟,恢复了乌南次凹断陷期构造的发育过程。研究表明,乌南次凹断陷期原型盆地的发展演化经历了四个阶段:张裂孕育阶段、初始张裂阶段、强烈拉张阶段和稳定张裂阶段,不同构造变形阶段的褶皱样式、沉积厚度和水平伸展量存在明显差异,总的水平伸展量为3.42km。

Urxun Sag in the middle Hailaer Basin is a typical Meso-Cenozoic terrestrial half-graben.In this paper,we firstly illustrate the structural features and evolution of the Hailaer Basin and then analyze the structural geometric characteristics of the seismic reflection profile across the rifting-period prototype basin of the southern Urxun sub-sag.The kink-bands in the hanging- wall are proved to be extensional fault-bend folds.Thus further modeling about the rifting-period prototype basin of the southern Urxun sub-sag can be done to playback the development process of its rifting-period structure with the extensional fault-bend folding theory.The research shows that the evolution of the rifting-period prototype basin of the southern Urxun sub-sag can be divided into four phases：the pre-faulting phase,the initial faulting phase,the intense faulting phase and the stable faulting phase. In fact,its different evolutional phases have different sedimentary thicknesses,different folding styles and different horizontal extensions.Its total extension turns out to be 3.42 km.