鄂尔多斯盆地叠合演化及构造对成煤作用的控制

Ordos Basin superposed evolution and structural controls of coal forming activities

鄂尔多斯盆地是多期成煤盆地叠合改造形成的构造盆地。石炭纪、二叠纪、三叠纪和侏罗纪成煤盆地的沉积演化过程具有一定差异,但煤炭资源形成的时空规律具有高度相似性。大地构造背景转换过程控制聚煤期,石炭纪、二叠纪含煤岩系形成于加里东—海西构造运动转换过程,三叠纪和侏罗纪含煤岩系形成于印支—燕山转换过程。沉积作用转换区域控制成煤区,在近海型盆地中,成煤区位于向陆一侧的河-海沉积作用转换区域。在内陆湖泊型盆地中,成煤区位于围绕湖心呈环带状分布的河-湖沉积作用转换区域。燕山及以后的构造运动控制了含煤岩系的形变方式和煤炭资源赋存状态。鄂尔多斯成煤盆地后期改造的显著特点是西部逆冲,东部隆起,南部和北部隆升和断陷共生。盆地西缘发育近南北向逆冲推覆构造,导致侏罗纪含煤岩系大面积剥蚀,造成石炭纪、二叠纪含煤岩系剥蚀、重复、褶皱和断裂。东部发生大面积隆起,石炭纪、二叠纪和侏罗纪含煤岩系遭受大范围剥蚀。盆地内部形成向北西缓倾的斜坡和南北向延伸的向斜,使晚古生代、三叠纪、侏罗纪煤炭资源得到保存。南部和北部边缘相继发生先抬升后断陷,形成了银川—河套断陷和汾渭断陷,构成了鄂尔多斯盆地含煤岩系的南北边界。构造背景和沉积作用转换是控制煤炭资源形成的重要地质条件,在大地构造运动界面上覆岩系中,寻找沉积体系转换区域是战略性找煤的有效途径。

The Ordos Basin is a tectonic basin formed by the superposition and transformation of multi-stage coal-accumulating basins.While the sedimentary evolution processes of Permo-Carboniferous,Triassic and Jurassic were different from one another,the time-space laws of coal resource formation in each period were very similar.The coal-accumulating period was controlled by the conversion process of tectonic structure.Permo-Carboniferous coal was formed in the conversion process of Caledonian-Hercynian tectonic movement,whereas Triassic and Jurassic coal was formed in the conversion process of Indochina-Yanshan tectonic movement.The coal-accumulating area was controlled by the conversion area of sedimentation.In offshoretype basin,the coal-accumulating area was found in the landside conversion area of river-lake sedimentation.In inland-lake-type basin,the coal-accumulating area had a ring-shaped distribution of conversion areas of riverlake sedimentation around the basin center.The deformation mode and occurrence state of coal resource were controlled by tectonic movement in the Yanshan period and later.The remarkable characteristics of the later transformation in the Ordos Basin were the thrust nappe structure in the west,the uplift in the east,and the concurrence of uplift and fault depression structures in the south and north.The thrust nappe developed in the west side of the Ordos Basin,not only did it cause large area erosion of Triassic and Jurassic coal but also repetition,fold and fracture of Permo-Carboniferous coal.The large area uplift developed in the east side of the Ordos Basin caused large area erosions of Permo-Carboniferous and Jurassic.The northwestward slope and extended northern syncline formed in this basin saved the coal resource of Late Paleozoic,Triassic and Jurassic.Uplift followed by fault depression in the south and north side of the Ordos Basin formed two fault depressions named Yinchuan-Hetao and Fenwei,which became the southern and northern boundaries of the Ordos Basin.The tectonic structure and conversion of sedimentation were important geological conditions in forming coal resources.Therefore,finding conversion areas amongst overlying rocks at the interface of tectonic movement is an effective strategy in coal finding explorations.