蒙古国西部早–中侏罗世含煤盆地的演化和后期改造—以希奈金斯盆地为例<br> Evolution and Later Reformation of Early-Middle Jurassic Coal-Bearing Basins in Western Mongolia—A Case Study from the Shinejinst Basin

Abstract

因基底构造、同造山应力场和区域演化的不同，蒙古东、西两部早–中侏罗世含煤盆地有不同的几何学和运动学特征。控制中带磨拉石盆地西段发育的是两条近北西向的压扭性断裂带，与蒙古–鄂霍次克缝合线西段的走向一致。近北西向断裂由北西西–近东西向的斜冲段和北西向的斜冲–走滑段组成，前者的前锋断层控制了下盘的含煤盆地发育。这些控盆断裂向北(东)斜冲，成盆动力来自中国西部特提斯洋早侏罗世末闭合和嗣后的碰撞产生的向北推挤。希奈金斯盆地演化可分为三个阶段，后期经历了四期改造。西部寻找下–中侏罗统大煤田的方向是希奈金斯盆地南次盆类型的构造盆地；其主要特征，一是成煤期盆地发育受北西西–近东西向斜冲断层及近北东向左行剪切断层控制，二是早白垩世的拉张事件中处于正断层的上盘，三是新生代隆升时位于山前或山麓地区。 Owing to variation of the basement structures, syn-orogenic stress fields and regional tectonic evolution, the Early-Middle Jurassic coal-bearing basins in western Mongoliashow different geometric and kinematic features from the simultaneous molasse basins in easternMongolia. The west segment of the Mongolia-Okhotsk suture is a NW- striking transfer zone, which constraints two transpressional fracture belts developing in western Mongolia. The tran- spressional fracture consists of the oblique thrust with NWW- to nearly E-W-striking, and the NW-orientated oblique thrust-strike slipping fault. The front fault of the oblique thrust controls a coal-forming basin in its lower plate. The ba- sin-controlling fault thrusts north(east)wards, with the basin dynamics resulting from a northward push-compression caused by closure of Tethyan ocean in the end of Early Jurassic in western China and followed continent-continent col- lision. The evolution of the Shinejinst Basin can be divided into three stages, which experiences four episodes of refor- mation after its reversion. The coal-search direction for the Lower-Middle Jurassic large coal fields in western Mongo- lia should be a kind of the South Sub-Basin of Shinejinst Basin, which could be indicated by three characters: 1) the basin-controlling faults being NWW- to nearly E-W-striking oblique thrust as well as NE-striking sinistral shearing fault, 2) to be situated at upper side of normal fault in Early Cretaceous extension, and 3) to be located along the piedmont belt of thrust or foothill of range in the Cenozoic uplifting.