福建含煤区逆冲推覆构造的类型及其对煤炭赋存的影响

福建省含煤区主要分布在闽西南坳陷带,区内出露的煤系地层主要为中二叠统童子岩组。区内煤系地层普遍发育有逆冲推覆构造。从逆冲推覆构造的断层性质、对煤系地层的控制作用不同,可分为3种类型。即:基底逆冲推覆构造、层间逆冲推覆构造、盖层逆冲推覆构造。基底逆冲推覆构造主要造成煤系地层下伏的老地层逆冲推覆至煤系地层之上。在地表上,表现为煤系地层被大面积的逆冲推覆体所掩盖,给地质找煤增加难度;层间逆冲推覆构造主要造成煤系地层之间的大面积重复,空间上煤系地层厚度大增,相应单平方面积的煤炭资源赋存量大幅增加;盖层逆冲推覆构造主要造成煤系地层推覆至煤系上覆地层之上,煤系地层作为相对运动的断层上盘,在运动过程中造成煤系地层支离破碎,从而大大降低了勘探价值。从形成机制分析,3类逆冲推覆构造形成的规模不一。基底逆冲推覆构造不论在深度、广度、力度上都表现的最为宏大,分布最为广泛。基底逆冲推覆构造的产生,彻底改变了福建煤系地层的赋存状态;层间逆冲推覆构造规模一般只有矿区规模;盖层逆冲推覆构造的规模最小。从有利于地质找煤角度分析,应着重加强基底逆冲推覆体下找煤研究。

Types of thrust-nappe tectonics and their effects on coal reserves in Fujian coal-bearing area

Fujian coal-bearing area is mainly located in the depression region of southwestern Fujian Province,in which the exposed coal-bearing stratum principally consists of the middle Permian Tongziyan Formation.The thrust-nappe tectonics are widely developed in coal-bearing stratum,and could be classified into three types according to the characteristics of the fault and their impacts on coal-bearing stratum:basement thrust-nappe tectonics,interlayer thrust-nappe tectonics and cover thrust-nappe tectonics.In the basement thrust-nappe tectonics,old stratums thrust up over coal-bearing stratum,manifesting the covering of the thrust-nappe above coal-bearing stratum in a large scale on the ground and increasing the difficulty in investigation.By largely repeating of coal-bearing stratum and effectively thicken them,the interlayer thrust-nappe tectonics significantly increase the coal reserves per square area.On the contrary,as the upper wall of the cover thrust-nappe tectonics,coal-bearing stratum trend to be fragmented during the relative tectonic movement,definitely,then reduce the development value.Distinguished forming mechanisms contribute to distinct scales of those thrust-nappe tectonics.The basement thrust-nappe tectonics are the most widely distributed in depth,breadth and dynamics,and they completely change the abundance of coal resource in Fujian Province.The interlayer thrust-nappe tectonics are usually identified just within the mining area,while the size of cover thrust-nappe tectonics are even more limited.To draw a conclusion,it is necessary to carry out farther research on the exploration of coal resources underlying the basement thrust nappe.