库车坳陷克拉苏构造带盐上和盐下构造变形差异及其控制因素分析

Differential Tectonic Deformation of Subsalt and Suprasalt Strata in Kuqa Depression and Their Controlling Factors

克拉苏构造带位于库车坳陷与南天山盆山过渡带,特殊的受力环境使其构造变形机制具有特殊性。依据最新的地震和钻井资料,并结合前人研究成果,建立了克拉苏构造带新的地震解释方案,并据此分析该地区盐上、盐下层构造变形几何形态、演化过程、形成机制等方面的差异及其控制因素。结果表明:克拉苏构造带盐下层构造变形可分为两部分,包括由基底卷入的高角度正断层后期挤压形成的反转断裂系统,以及主断裂下盘发育的次生盖层滑脱逆冲叠瓦断裂系统。盐上层构造变形为褶皱相关断层,其演化经历了基底断裂向上传递形成传播褶皱、差异压实作用诱发底辟褶皱、以及褶皱核部在持续挤压作用下形成破冲断层等多个阶段。盐下层基底卷入断裂系统形成于侏罗纪盆山过渡带伸展环境,而叠瓦式盖层滑脱断裂系统和盐上层构造变形主要形成于中新世-第四纪的挤压构造环境。盆山过渡带特殊的构造部位及在不同地质时期应力场的转换控制了盐下层构造变形机制,而盐上层构造变形受到基底断裂复活、差异沉积负荷、膏盐岩底辟上涌、挤压应力增强以及北部山前地形高差等众多因素影响,且不同演化阶段主控因素有所差异。克拉苏构造带盐下、盐上层变形机制和毗邻区带相比有较大差异,这与其特殊的构造位置以及构造应力在盐下和盐上地层向前陆方向传递的方式和距离不同等因素有关。

The Kelasu structural belt,located in the transitional zone between the Kuqa Depression and the southern Tianshan thrust belt,has a distinctive deformation mechanism because of its special stress environment.Based on the latest drilling data and research results,this paper established a new seismic interpretation scheme for the Kelasu structural belt,and analyzed the geometric characteristics,evolution process,formation mechanism and their controlling factors for the suprasalt and subsalt layers of the Kelasu region.The results showed that the subsalt structural deformation of the Kelasu structural belt can be divided into inversion fault system formed by the inversion of high angle basement-involved normal faults and the secondary cover-decollement thrust imbricate fault system that developed in the footwall of major fault.The suprasalt structural deformation belongs to fold-related faults,which experienced multi-stage structural evolution including the fault-propagation fold triggered by the stress transfer of basement-involved fault,the diapir fold induced by differential compaction,the flexural fold induced by strong compression and the formation of thrust fault.The subsalt basement-involved fault system formed in the extensional environment of the basin-mountain transition belt in the Jurassic,while the cover layer detachment imbricate fault system and suprasalt tectonic deformation mainly formed in the compressional tectonic environment from Miocene to Quaternary.The subsalt tectonic deformation mechanism is controlled by the special tectonic location and different stress field in different geological periods of the basin-mountain transition belt.However,the suprasalt structural deformation is affected by many factors,such as the resurrection of basement-involved faults,differential loading,the salt diapirism,the enhancement of extrusion stress and the topographic height difference of the northern monoclinal structural belt,and the main control factors differ in different evolution stages.The deformation mechanism of subsalt and suprasalt strata of the Kelasu structural belt is different from that of the adjacent structural belt,which is related to its special tectonic location and the different propagation distance and style of tectonic stress from the Kelasu structural belt to the foreland region in the deep and shallow strata.