木里煤田沉降史与控煤构造特征研究

Subsidence history and coal-controlled structure characteristics in Muri coalfield

木里煤田位于中祁连断隆带,是祁连山含煤区的主体,盆地构造演化与中生代以来整个祁连地区构造事件紧密相关。依据区域地质调查成果、煤田地质勘查报告以及钻孔等资料,采用回剥技术分析了研究区中生代以来的沉降史及构造演化特征。沉降史模拟结果表明:侏罗纪缓慢沉降,至早白垩世快速大幅沉降,燕山运动导致晚白垩世整体隆升,转为抬升剥蚀阶段;古近纪以来,受青藏高原隆升的影响而快速隆升剥蚀,随后新近纪以来又快速沉降;构造运动形成的差异性升降是沉降-隆升及煤系遭受改造的主要原因。研究区控煤构造及煤系赋存特征表现为,煤系形成之后受断裂控制呈不对称向斜或单斜状,分布于逆冲断裂下盘;向斜核部及较缓翼地层受构造破坏较小,煤系赋存稳定,为有利的赋煤区。

Muri coalfield is located in the middle part of the Qilian faulted uplift zone,also is the main part of Qi Lian-shan coal-bearing district,the structural evolution of Muri basin is closely related to the tectonic event in Qilian district. According to regional geological survey,drillhole and geological survey report of Muri coalfield,we analyzed the subsidence history by back-stripping method and tectonic evolution characteristics. The simulated results showed that subsiding slowly in Jurassic period then rapidly with larger subsidence scope in Early Cretaceous Epoch,uplifting and denudating Late Cretaceous by the Yanshan tectonic movement,uplifting rapidly and denudating in Paleogene according to Tibetan plateau uplift,subsiding rapidly in neogene epoch. With comparison and analysis of the fold,coal-controlled structure and sedimentary characteristics,coal occurrence regularity was controlled by fault,the coal measures were preserved well in downthrown side of thrust fault,which take on the feature of uniclinal stratum and asymmetric syncline,while coal measures were preserved in syncline and low-angle flankwith less damage and buried depth of coalbed becoming helpful to coalmining.