六盘山盆地形成和改造历史及构造应力场演化

六盘山盆地夹于鄂尔多斯地块、青藏地块和阿拉善地块之间,在中国大地构造体系中处于独特的构造位置。基于野外变形分析与断层滑动矢量构造应力场反演,初步确定了六盘山盆地形成与构造演化历史。结果表明,六盘山盆地主要经历了早白垩世成盆过程和后期改造过程2个大的阶段。早白垩世早期,受到区域近E-W向引张应力作用而发生断陷,盆内沉积了一套巨厚的河湖相六盘山群;早白垩世晚期在NW-SE向挤压下,断陷盆地发生构造反转,局部地区褶皱回返,六盘山群发生不同程度的断裂和褶皱变形,继而盆地开始了长期的隆升剥蚀作用。晚新生代,受到印度—欧亚大陆碰撞产生的远程效应,六盘山盆地先后经历了NE-SW向和近E-W向挤压应力作用,盆地发生了强烈的褶皱和断裂变形,六盘山快速隆起。六盘山盆地构造应力场演化历史不仅为研究周缘地块的运动学和动力学提供构造地质依据,也对盆地油气勘探具有指导意义。

Formation and modification history of the Liupanshan basin on the southwestern margin of the Ordos block and tectonic stress field evolution

Sandwiched between the Ordos block and the Alxa and Qinghai-Tibet blocks, the Liupanshan basin is situated in a special tectonic location in the tectonic system of China. Based on the field analysis of deformation and stress field inversion from fault slip data, the formation and tectonic evolution history of the Liupanshan basin has been preliminarily established. The results show that the basin mainly experienced the stage of basin formation and the stage of modification in the late stage. During the earliest Cretaceous, under the nearly E-W extensional stress, the basin was downfaulted and a very thick fluvial-lacustrine sequence of the Liupanshan Group was deposited in the basin. Near the end of the Early Cretaceous, under the NW-SE compression, the Liupanshan basin was inversed with in fold inversion occurring in some places, and the Liupanshan Group underwent faulting and deformation to different degrees. Then the basin began the long-continued uplift and erosion history. During the late Cenozoic, under the far-field effects caused by India-Eurasia collision, the Liupanshan basin was strongly folded and faulted due to NE-SW compression and then due to E-W compressions and Liupanshan was uplifted rapidly. The evolutionary history of the Liupanshan basin and change in stress regimes during the Early Cretaceous provide constraints on the geodynamics of block interaction in this area and are of importance for oil and gas exploration.