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

Abstract：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 to15km according to length balance of Cenozoic bottom, and the depth involved in contractive deformation ranges from 20km to 26km 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.