准噶尔盆地乌夏前陆冲断带沉降史与沉积响应研究

Subsidence and sedimentary response of Wuxia foreland thrust belt in the northwestern margin of Junggar basin

针对前陆冲断带的特殊构造位置及沉积特征的复杂性,本文在地层剥蚀厚度恢复和层序划分的基础上,通过对准噶尔盆地西缘乌夏前陆冲断带沉降史分析,在海西运动晚期准噶尔地块与西伯利亚板块发生碰撞挤压,形成一系列冲断推覆构造,前缘岩石圈挠曲下陷发育周缘前陆盆地,并夹杂大规模的短暂伸展火山喷发活动,接受了巨厚的二叠系沉积层序;随着板块俯冲在二叠纪末的逐渐消亡,三叠纪进入印支期陆内坳陷继承性挤压活动阶段,周边受南北向挤压和左旋构造应力场影响,前陆冲断带古断裂再次逆冲,哈拉阿拉特山急剧抬升,后缘和什托洛盖盆地形成;进入侏罗纪-白垩纪(燕山运动早中期),为陆内坳陷的填充消亡阶段,但有继承性活动,构造活动强度较二叠纪大为减弱,在燕山运动Ⅲ幕晚期最终被覆盖定型。整个过程受地体碰撞和板内挤压影响,冲断带发生幕式构造活动,从而导致盆地沉降也发生幕式变化,而且冲断带每次挤压逆冲均导致相应的沉降和沉积物充填,并直接控制前陆盆地和陆内坳陷的沉积充填特征。

In view of unique geotectonic position and complex sedimentation of foreland thrust belts, this study analyzed subsidence history and sedimentary system distribution of the Wuxia foreland thrust belt in the western margin of the Junggar basin on the base of erosion thickness restoration and sequence division. The results reveal that collisional compression between Junggar block and Siberian block in the late stage of Hercynian movement resulted in the formation of a series of nappe structures. A peripheral foreland basin formed due to flexure and subsidence of the foreland lithosphere, accompanied by large-scale transient volcanic activities, resulting in deposition of a mass of Permian strata. With gradually perishing of plate subduction in the end of the Devonian, this area entered inherited compression activity stage of Indo-Sinian intracontinental depression in the Triassic. Affected by stress field of N-S compression and sinistral structure, paleo-fault zones revived to thrust up and Hala’ alate mountain uplifted sharply, forming the Heshituoluog basin on back of thrust belt. The Jurassic-Cretaceous period(early-mid-Yanshanian Movement) witnessed filling and perishing of the intracontinental depression, but still there existed inherited fault activities but in decreasing intensity of structural activity. Therefore, the intracontinental basin got into the shape at the third episode of the Yanshanian movement. The Wuxia area had been undergoing plate collision and intracontinental compression through all the courses, during which episodic thrusting activities of the thrust belt caused basin subsiding episodically and correspondingly deposition and filling and directly controlled the depositional features of foreland basin and depression basin.