蒙古国早–中侏罗世含煤盆地分布及构造背景和地层

Distribution, tectonic settings and strata of Early-Middle Jurassic coal-bearing basins in Mongolia

蒙古国早–中侏罗世的主控构造是蒙古–鄂霍次克洋的消减闭合,其北地区发育弧后张裂盆地,其南的拼合大陆内的古缝合线被该消减造山运动激活而发生陆内造山。内蒙的3个陆内造山的磨拉石盆地均延入蒙古境内,故蒙古东部磨拉石盆地的发育与内蒙有相似的几何学和运动学特征。概述了各盆地的代表性地层,尽管其岩性和含煤性有明显差别,但因受制于同一个造山作用,沉积记录都以砾岩开始,都为向上变细的序列,且煤层均赋存于地层柱的中部,据此可把盆地演化分为成煤前、成煤和成煤后3个阶段。成煤阶段大煤田的形成受构造(堆积空间)和气候(成煤物质供应)的双重控制。

The key structure during Early-Middle Jurassic in Mongolia is subduction and closure of the Mongo-lia-Okhotsk ocean. To the north of the ocean there develops a group of back-arc extensional basins, whereas to the south of the ocean there exists an amalgamation continent, where the fossil geosutures are rejuvenated by the sub-duction orogeny and inland orogeny occurs. In Inner Mongolia of China, there develop three molasse basins related to the inland orogeny, all of these basins stretch into Mongolia, so that the molasse basins in eastern Mongolia have the same geometric and kinematic features as that in Inner Mongolia. The typical stratigraphic columns in the above-mentioned four basins are briefly illustrated. Although there are distinct lithologic and coaly characters con-strained by the same orogeny, the sedimentary records show some similarities in all of the basins, such as thick conglomerates in the basal part, a upward-fining succession, and the coal seams in the middle part of the column, etc. Based on the similarities, the evolution of Early-Middle Jurassic basins can be divided into three stages, namely, the pre-coal-forming stage, coal-forming stage and post coal-forming stage. The creation of economic coal fields are controlled by the structure （depositing space ） and climate （supplies of mother substance of coal ） in the coal-forming stage.