鄂尔多斯西缘褶皱—逆冲断层带的构造特征和找气前景

野外地质观察和地震反射剖面分析表明,鄂尔多斯西缘褶皱山系和覆盖地区发育北东、北西向褶皱和西倾东冲的逆冲断层,组成褶皱—逆冲断层带。按其构造特征可归纳为以下六种类型: 1.褶皱—逆冲断层型 以桌子山褶皱—逆冲断层带为代表,构造特征为轴面西倾的不对称背向斜,逆冲断层发生在背斜陡翼上。 2.褶皱—逆冲推覆型 以小松山逆冲断层和推覆体为代表,构造特征为断面西倾东冲的逆冲断层,其上盘呈弧形突出,覆盖在下盘年轻的褶皱地层之上。 3.褶皱—犁式逆冲断层型 其典型地区是大、小罗山至马家滩地区,断面西倾东冲,上陡下缓呈犁式和坐椅式。 4.同沉积逆冲断层型 以铁克苏庙逆冲断层和其控制发育的深凹陷为代表。 5.同生基底正断层反转逆冲型 以西来蜂逆冲断层和北西向“河西系”逆冲断层为代表。 6.反向逆断层型 以断面东倾高角度呈叠瓦状错列的横山堡地区为代表。 初步认为,鄂尔多斯西缘褶皱—逆冲断层带的区域背景与A-俯冲作用有关的逆冲断层带有较大的差异,它们是在克拉通内地壳拆离作用的产物,其逆冲—推覆规模和缩短程度比A-俯冲带低, 鄂尔多斯西缘褶皱—逆冲断层的形成主要受侧向挤压力的控制。其形成方式有:(1)由于纵弯作用,先形成褶皱后产生逆冲断层。(2)受侧向挤压沿早期正断层逆转形成逆冲断层?

Structural Features and Gas Prospect of the Fold-thrust Belt in the western Margin of Ordos Basin

The structural features of the fold-thrust belt in the western margin of Or-!os basin can be classified as follows. (1) Fold-thrust type in the Zuozi Shan range. (2) Fold-thrust and nappe type in the Xiao Song mountain.(3)Fold-listric thrust type in the Majiatan area. (4)Syndepositional thrust type in the Tiekesumiao area. (5)Syngenetic reverse thrust type controlled by preexisting aormal faults in the Luoshan area of the southeastern Huolan mountain. (6)Higli angle imbricate antithetic revcrsa fault type in the Hengshanbao area, The fold-thrust bslt was forme] by lateral compression resulting from cru-stal decoupling, which is proved by simulation experiments in laboratory and by analysis of photoelastic model. In the area studied, the strata of Palaeozoic era, especially Carboniferous system, are fayourable for gas generation. Sandstones of Permian system are suitable for gas reservoir and mudstones for cap rock. So the rock seris mentioned above may serve as a good source-reservoir-cap rock assemblage. Because of the most part of tha region was disturbed violently by fold-thrusts, the gas fields were destroyed.Based on the study of preservation condition of the area, the author proposes that the upper Palaeozoic strata in Majiatan and in the eastern Hengshanbao area may be hopeful for gas exploration, while regions beneath the Xiaosong mountain nappe and localities in the east and southeast side of the Tiekesumiao deep depression may also be an exciting area for gas prospecting,