南天山褶皱冲断带西段变形空间差异性及控制因素

新生代早期印度板块与欧亚板块持续碰撞汇聚导致欧亚板块内部发生大规模的陆内变形,天山造山带再次隆升,并向塔里木盆地大规模逆掩推覆,形成了现今南天山褶皱冲断带,其变形表现出明显的空间差异性。本文以南天山褶皱冲断带西段为研究对象,通过对不同构造带的地震剖面解释、运用平衡剖面技术恢复出各演化阶段发育过程并计算出相应的变形量,分析本区构造带的空间差异性及其控制因素。通过分析认为南天山褶皱冲断带西段可以进一步划分为巴什布拉克构造段,乌恰-阿图什-喀什构造段和柯坪西缘构造段。其中,巴什布拉克构造段变形特征主要呈一系列对冲构造和背驮盆地样式。乌恰-阿图什-喀什构造段变形特征表现为深、浅两个层次:深部发育堆垛构造和构造楔,浅部发育断层传播褶皱和逆冲断层改造的褶皱带。柯坪西缘构造段变形更加强烈,也表现为深、浅两个层次:深部发育堆垛构造,堆垛程度更大,浅部也发育断层传播褶皱和逆冲断层改造的褶皱带以及反冲断层系。结合该研究区的地质概况进一步分析,本文认为南天山褶皱冲断带西段构造变形的差异性可能与新生代以来帕米尔块体向北推进、塔拉斯-费尔干纳右行走滑断裂的活动、先存断裂的活化与韧性滑脱层的影响有关。

Spatial variation and controlling factors of deformation in the western segment of the southern Tianshan fold-thrust belt

The continuous collision and convergence of the Indian and the Eurasian plates initiated during the early Cenozoic resulted in large-scale intra-continental deformation within the Eurasian plate. This event reactivated the Tian Shan orogenic belts, which propagated the thrust toward the Tarim basin, forming the present southern Tian Shan fold-thrust belts with significant spatial variation in deformation along the strike of the belts. In this paper, we analyze the spatial variation of deformation and its possible controlling factors based on the seismic profile interpretation and balanced cross-sections across the structural belts. This study suggests that the western segment of the southern Tian Shan fold-thrust belts can be subdivided into the Bashibu lake segment, the Wuqia-Atushi-Kashi segment, and the west Keping segment. Among them, a series of double-thrust structures and back-load basins were mainly developed in the Bashibu lake tectonic segment. The deformation characteristics of the Wuqia-Atushi-Kashi tectonic section were manifested in two levels: stacking structure and tectonic wedge developed in the deep part, and fault-propagating folds and fold belts reconstructed by southward thrust faults developed in the shallow part. The deformation of west Keping was more intense and also manifested in two levels: stacking structure developed in the deep part, fault-propagating folds, fold belts reconstructed by southward thrust faults and recoiling structural system developed in the shallow part. Based on the geology of the study area, it is concluded that the strata deformation variation in the western section of the southern Tian Shan fold-thrust belts may be related to the northward advance of the Pamir block since the Cenozoic era, the activity of the Taras-Fergana right strike-slip fault, the influence of the activation of preexisting faults and ductile slippage.