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Differential Tectonic Deformation and Controlling Factors on Deep and Shallow Strata in the Kelasu Structural Belt, Kuqa Depression, Northwest China


The Kelasu structural belt, located in the transitional zone between the Kuqa depression and southern Tianshan thrust belt, has distinctive structural deformation because of its special stress environment. Based on the latest seismic and drilling data, we present a new seismic interpretation schemes on Kelasu tectonic zone, and analyze the differential geometric characteristics, evolution process, formation mechanism and controlling factors between the deep and shallow strata. The results show that the deep structural deformation of Kelasu region can be divided into the inversion fault system formed by tectonic inversion of basement-involved normal faults, and the newborn cover-decollement thrust imbricate fault system that developed in the footwall of major fault. While the shallow structural deformation belongs to fold-related fault, which has experienced multi-stage evolutions including the fault-propagation fold triggered by growth of basement-involved fault, the drape fold induced by differential compaction, the flexural fold induced by strong compression and the formation of thrust fault. The deep basement-involved fault system develops in continuous extensional environment from Jurassic to Paleogene, while the cover-detachment imbricate fault system and shallow tectonic deformation are mainly formed in the compressional tectonic environment from Miocene to Quaternary. The deep deformation mechanism is controlled by special tectonic location and changeable stress field of basin-mountain transition belt in different geological periods. However, the shallow structural deformation is affected by many factors, such as the resurrection of basement-involved fault, differential loading, salt diapirism, enhancement of extrusion stress and the topographic height difference of Northern monoclinal structural belt, and the main controlling factor varies with different evolution stages. The structural deformations of deep and shallow strata in Kelasu tectonic belt are different from its adjacent area, which is related to the different propagation distances and styles of tectonic stress between deep and shallow strata from Kelasu structural belt to foreland region.