塔里木盆地库车坳陷收缩构造变形模型若干问题的讨论

The interpretation models and discussion on the contractive structure deformation of Kuqa Depression, Tarim Basin

塔里木盆地库车坳陷中、新生界表现出以逆冲断层、纵弯褶皱为基本结构要素的收缩构造变形特征。本文依据地质-地球物理勘探资料,建立了"薄皮收缩构造"和"分层收缩构造"两种模型,讨论了不同构造变形模型的几何结构、收缩变形量、构造动力学机制等方面的差异,并认为"分层收缩构造模型"更为合理。"分层收缩构造模型"强调塔里木克拉通与南天山之间的侧向挤压,中、新生界受岩层能干性影响而发生分层收缩构造变形,新生界以伴生有破冲断层的滑脱褶皱变形为主,中生界以逆冲断层及相关褶皱变形为主,深层发育基底卷入的逆冲断层和断块构造,但是不同层次的收缩变形量基本保持一致。按照平衡剖面原理测算库车坳陷新生界的收缩量为12～15 km,卷入收缩构造变形的深度在山前应该为20～26 km,因此部分逆冲断层应该切割到盆地基底中。尽管变形强度总体上是自深而浅、自造山带向前陆逐渐减弱,作为浅层强变形的秋里塔格构造带的深层也可能发育一定程度的收缩构造变形,构成深层的油气圈闭。

The basic characteristics of structural deformation in Kuqa Depression of, Tarim Basin is contractive structural deformation, owing to the development of a lot of thrusts and buckling folds in Mesozoic and Cenozoic strata. This paper establishes two types of model for interpreting the contractive structural deformation in Kuqa Depression based on the structural features interpreted from geological outcrop, seismic data, well-log and CEMP （Continuous Electromagnetic Profile） data, and discusses their differences in geometry, shortening extent and dynamics. One model is the ＂skin-contractive deformation＂, a typical ＂A-type＂ subduction model. The other is the ＂delaminate contractive deformation＂, in which both the sedimentary cover and the basement of the depression are involved in contractive deformation in respective styles, with no real regional detachment fault developed. The ＂delaminate contractive deformation＂ is considered to be more reasonable so far as the data and theoretical concepts are concerned. The model emphasizes that Cenozoic, Mesozoic and basement decoupled under lateral pressure between Tarim craton and South Tianshan Mountain affected by the capability of the strata, Cenozoic was dominated by detachment folds with break thrusts, Mesozoic was dominated by thrusts with related folds, and the basement was dominated by thrusts and faulted blocks. The shortening extents at the bottom of Cenozoic, the upper of Mesozoic and the basement of the depression are basically identical. The shortening extent ranges from 12km to15krn according to length balance of Cenozoic bottom, and the depth involved in contractive deformation ranges from 20kin to 26kin in the front of South Tianshan Mountain according to excess area of Mesozoic in sectional plane. Therefore, the basement of the depression is uplifted in the north and is involved in the thrust. Although the intensity of contractive deformation gradually decreases from mountain to foreland and from the shallow part to the depth in theory, the Mesozoic and basement under the salt rock of Eocene in Qiulitag structural zone might still be involved in contractive structure deformation owing to a tight- closed anticline at the shallower level. The structure is trapped at the deeper level