塔里木盆地库车前陆冲断带多滑脱层构造变形特征

Tectonic deformation characteristics of multi-detachment beds in Kuqa foreland thrust belt,Tarim Basin

目前对膏盐岩、煤系地层等多套滑脱层在挤压构造活动中的构造变形特征、变形机理及控制因素的研究相对薄弱。利用高精度三维地震资料、钻井资料,建立了塔里木盆地库车前陆冲断带西段、中段和东段的挤压型多滑脱层构造变形样式,结合数值模拟和构造演化,系统分析了库车前陆冲断带多滑脱层构造变形特征、控制因素及变形机理。以膏盐岩和煤系地层为界,纵向上划分为盐上层、盐层、盐下层、煤层和煤下层等五大构造层。分析认为,库车前陆冲断带经历了晚海西—印支期、燕山期、喜马拉雅期等多期构造活动,晚海西—印支期形成的古冲断构造控制了中生界沉积格局,膏盐岩、煤系地层等滑脱层与古隆起分布差异共同控制着分层构造变形,古隆起控制滑脱层分布及冲断带规模,膏盐岩控制浅层及盐下逆冲构造,煤系地层控制冲断带前缘及煤下逆冲构造。盐上层以盖层滑脱为主,盐下发育叠瓦逆冲构造,膏盐岩塑性流动形成盐丘、盐枕、盐刺穿等构造,煤层揉皱变形,煤上地层剪切逆冲,煤下层滑脱逆冲,具有“多期滑脱、复合变形、垂向叠置”的特征。煤系地层既是烃源岩又是盖层和滑脱层,整个中生界在构造挤压过程中发生同轴变形,煤系地层下方的逆冲断裂具有成排成带的特征,煤下层滑脱逆冲断裂简单,构造更加宽缓,油气勘探潜力较大。

At present,the study on the tectonic deformation characteristics,deformation mechanism and controlling factors of multiple sets of detachment layers such as salt rock and coal measure strata during compressive tectonic activity is relatively weak.In this paper,based on high-precision 3D seismic data and drilling data,the multi-detachment tectonic deformation patterns of the western,middle and eastern sections of Kuqa foreland thrust belt are established.Combined with numerical simulation and tectonic evolution,the characteristics,controlling factors and deformation mechanism of the multi-detachment tectonic deformation of Kuqa foreland thrust belt are systematically analyzed.It is divided into five structural layers:upper salt layer,salt layer,lower salt layer,coal layer and lower coal layer.The analysis shows that the Kuqa foreland thrust belt has experienced multiple tectonic activities such as late Hercysian-Indosinian,Yanshanian and Alpine,and the paleothrust structure formed in the late Hercysian-Indosinian controlled the Mesozoic sedimentary pattern.The distribution difference between the detachment layer of the salt rock and coal measure strata and the paleo-uplift jointly controlled the stratified tectonic deformation,and the paleo-uplift controlled the distribution of the detachment layer and the scale of the thrust belt.Salt rock controls shallow and subsalt thrust structures,and coal measure strata controls thrust belt front and subcoal thrust structures.The salt layer is dominated by cap slippage,the imbricated thrust structure is developed under the salt,the salt dome,salt pillow and salt puncture are formed by the plastic flow of the salt rock,the coal seam crumples and deforms,the coal layer shear thrust and the coal layer slippage thrust are characterized by“integral extrusion,multi-layer slippage,vertical superposition and stratified deformation”.The coal measure strata are not only the source rock,but also the cap layer and the slip layer.The whole Mesozoic strata have coaxial deformation in the process of tectonic compression.The thrust fault below the coal measure strata has the characteristics of a row of belts,and the slip thrust fault in the coal layer is simple,the structure is wider and slower,and the oil and gas exploration potential is larger.