鄂尔多斯盆地基底演化及其对盖层控制作用

基底演化过程与其上覆沉积盖层的发展密切相关,因而可以通过盖层与基底的构造格局对比分析来推断基底演化的主要阶段,并进一步讨论盆地基底演化与盖层变形之间的相互作用。研究发现,鄂尔多斯盆地基底演化与自身结构和受力方式均有密切关系,同时对盖层变形有重要控制作用。早古生代在南北向洋-陆碰撞背景下,基底受自身组成结构制约在盆地内部发育了北东向隆坳相间的构造格局,晚古生代受南北向陆-陆碰撞的影响而在早期北东向展布的隆坳构造基础上叠加了南北向的中央古隆起,由于此时厚度较小,盖层的整体格局与局部形态都受控于基底的构造格局。至中生代燕山期,盆地受到了东西向挤压作用,基底内部形态基本保持不变,盆地基底边缘有明显的垂向活动,具体表现为东升西降;此时盖层发育已较为完整,因此更多地体现了相对孤立演化的特征,但其“跷跷板”式的运动总体上仍受到基底边缘升降活动的控制。

Basement evolution of the Ordos Basin and its constraint on cap rock

Since basement evolution has a close relationship with the caprock development, the process of basement evolution of the Ordos Basin and its constraint on caprock can be revealed by comparison between tectonic patterns of caprock series and those of the basement. Our research shows that the basement evolution of Ordos Basin was related to its structure and deformational history, and played an important role in controlling the distortion of the caprock. Under the setting of NS ocean-continent collision in the early Paleozoic, the basement, restricted by its inherited structure, developed NE-trending patterns of apophyses alternating with depressions. Moreover, in the late Paleozoic, a NS-trending center apophysis was superposed on the former NE trend structure patterns by the effect of continent-continent collision. Meanwhile, because the caprock was not thick, its configuration was completely controlled by basement evolution. When it came to the Yanshanian during the Mesozoic, the Ordos Basin underwent EW-trending extrusion, during which the style of the basement remained unaltered. However, the west and east margins of the Ordos Basin experienced distinct vertical movements, with the east margin uplifting and the west margin subsiding. At this time, the cap rocks were well developed and showed characteristics of relatively isolated evolution, although their teeterboard-style of movement was overall under the control of the eastern uplift and western subsidence of the basement.