准噶尔盆地南缘褶皱-冲断带变形特征及成因机制模拟

Deformation Feature and Genesis Simulation of Fold-and-Thrust Belts in the Southern Margin,Junggar Basin

准噶尔盆地南缘褶皱-冲断带发育于北天山和博格达山北侧的准噶尔盆地南部的山前地区,构造变形具有明显的横向分带、纵向分段、垂向分层特征,其主控因素在于挤压应力的作用方式和滑脱层的空间分布规律。西段受北天山斜向挤压应力作用影响,发育北西西向四排雁列式褶皱-冲断带,构造变形样式为基底卷入式厚皮构造和盖层滑脱式薄皮构造,变形过程受侏罗系煤层和白垩系、古近系高塑性泥岩层等多滑脱层控制。滑脱层及其上覆岩层厚度决定变形的强度和应力向前传递的远近程度,厚度越大,褶皱变形强度越大。东段受博格达山正向楔冲挤压应力作用影响,发育近东西向向北凸出的弧形基底卷入式褶皱-冲断带,滑脱构造不发育。根据构造变形特征和相似理论,利用沙箱模拟实验分别对正向挤压和15°、30°、45°等斜向挤压平面变形进行了模拟,结果表明正向挤压和15°斜向挤压是形成东段和西段变形特征的主控应力条件,并设计了斜向和正向挤压组合边界平面模拟实验进行了验证,合理地解释了东、西段构造变形的差异。利用双滑脱层剖面模型实验对西段四排褶皱-冲断带的演化过程进行了模拟再现。

The fold-and-thrust belts is situated in the southern margin of the Junggar Basin and the northern part of Tianshan and Bogeda Mountains, which can be divided into two structure segmentation from the west to the east. The main factors controlling the fold-and-thrust belts are attributed to the different direction of compressed stresses and thickness of decollement beds. The four fold-and-thrust belts developed in the western segment from declinate compression stress included the basement-involved and the decollement structure styles. Deformation evolution was related to Jurassic coal beds and Cretaceous and Eogene clay beds. The thickness of ductile beds controlled the de- formation intensity and transmission distance. The more thickness is, the more intensive deformation is. The base- ment-involved fold-and-thrust belts developed at the eastern segment in the southern margin of the Junggar Basin, lack of decollement structure, generated from stress coming from the Bogeda Mountain wedge thrusting vertically. Based on deformation characteristics and theory of similarity, several plain and profile sand-box experiments were devised to simulate deformation compressed from different directions. Simulation results illustrate that the vertical compression and the declinate compression with 15°angle between stress and boundary were responsible for the deformation differenciation between the western segment and the eastern segment. The evolution of four fold-and-thrust belts was simulated and reappeared by a double decollement model.