准噶尔盆地西北缘构造演化与扇体形成和分布

准噶尔盆地西北缘经历了多次(期)不同性质的构造演化。在新生代以后,表现出(类)前陆盆地性质,伴随区域构造运动发生强烈的碰撞挤压、冲断作用。断裂活动具有明显的推覆性质,产生了与断裂带平行的褶皱构造。西北缘逆掩断裂普遍具有同生活动性质,对扇体的形成有明显的控制作用。主要表现为冲断作用持续发生,上、下盘地形相差悬殊,自冲断席上剥蚀下来的碎屑物堆积于断崖根部而形成各类扇体(冲积扇、扇三角洲和水下扇等),阶梯式逆冲断裂则形成多级扇体。研究表明,从二叠纪到侏罗纪构造活动逐渐减弱,扇体规模逐渐变小;在平面上由于构造活动的位移,导致了扇体的迁移。总体来看,百口泉-夏子街地区活动性最强,延续时间最长,形成的扇体规模较大、叠置程度高、迁移明显;车拐-克拉玛依地区活动性较弱,形成的扇体规模小、叠置程度差、迁移小。

Tectonic evolution and development and distribution of fans on northwestern edge of Junggar Basin

The northwestern edge of Junggar Basin experienced multiphase tectonic movements of different natures, and it appeared as a foreland basin since Cenozoic. Extensive collision, compression and thrusting occurred along with regional tectonic movement, and faulting apparently had the nature of overthrusting, resulting in fold structures to be in parallel with the fracture zone. The overthrust faults were commonly syngenetic and controlled obviously the development of fans. Thrusting occurred continuously, so topographies on the hanging walls were greatly different from those on the footwalls. Clastics denuded from the thrust sheets accumulated on the foot of fault scarps, leading to the formation of various fans (alluvial fan, fan delta and submarine fan, etc.). Step thrust faults led to the formation of multistage fans. Tectonic activities attenuated gradually from Permian to Jurassic and the sizes of fans decreased gradually. Lateral displacement of tectonic activities resulted in the migration of fans. As a whole, the strongest and longest tectonic activities occurred in Baikouquan-Xiazijie area, hence the fans in that area would be relatively large, highly superimposed and largely migrated; while those in Cheguai-Karamay area were relatively weak, so the fans would be small, poorly superimposed and shortly migrated.