库车坳陷中段基底断裂特征及其对盐构造变形的影响

Characteristics of basement faults in the middle section of Kuqa Depression and their influence on salt tectonic deformation

基底断裂对盐构造的形成演化过程有重要控制作用。针对库车坳陷盐构造最为发育的克拉苏构造带和秋里塔格构造带,运用最新的二维和三维地震资料解释方案,分析了基底断裂的几何学特征、形成过程,及其对后期盐构造变形的影响。结果表明:库车坳陷不同地区基底断裂和盐构造变形样式有较大不同;基底断裂几何样式的差异,是导致盐构造复杂多变的重要原因。基底断裂的活动一定程度上影响了原始盐层的沉积厚度,还控制了盐构造的发育位置和变形样式。物理模拟实验表明:基底断裂在后期变形中相对于无断裂区可优先活动,使盐下层构造变形的传播距离变大,而盐上层变形传播距离减小。此外基底断裂的活动还可促使断裂顶部盐上层的褶皱作用增强,并发育新的断层。有限元数值模拟实验表明:在构造挤压初期,即使是远离山前的秋里塔格构造带,基底断裂顶部也可出现明显的剪应力和应变增大区域,这是该地区盐构造规模宏大的重要原因。

The basement faults play an important role in the formation and evolution process of salt structures. Taking the Kelasu structural belt and Qiulitage structural belt where the most spectacular salt structure developed in the Kuqa Depression as examples, the geometric characteristics, formation mechanism and their influence on the salt structure deformation are analyzed by using the latest 2D and 3D seismic data. The results show that basement faults are widely developed in the Kuqa Depression, but their characteristics and formation mechanism are quite different in different structural zones. The difference in geometric styles of basement faults during later rejuvenation are important reasons for the complexity and variability of salt structural styles in different structural zones. The basement fault can not only control the sedimentary range of the original salt lake, the development location and scale of the salt diapir anticline,and the deformation style of the salt structure. The physical simulation experiment shows that the basements fault preferentially activate and absorbs some extrusion displacement in the later deformation, which increases the propagation distance of structural deformation in the subsalt strata, and decreases the propagation distance of deformation in the suprasalt layer. In addition,the activity of basement faults can also enhance the folding at the top of the fault and development of new faults in the supra-salt layer. The finite element numerical simulation experiment shows that in the early stage of tectonic compression, even in the Qiulitage structural belt far from the front of the mountain, there can be an obvious area of increasing shear stress and strain at the top of the basement fault, which is an important reason for the large scale of salt structure in this area.