Abstract
The salt layer is critical for the structural deformation in the salt-bearing fold-and-thrust system, which not only acts as the efficient décollement layer but also flows to form salt tectonics. Kuqa Depression has a well-preserved thin-skinned fold-and-thrust system with the salt layer as the décollement. To investigate the effects of salt thickness on the structural deformation in the Kuqa Depression, three discrete element models with different salt thicknesses were constructed. The experiment without salt was controlled by several basal décollement dominant faults, forming several imbricate sheets. The experiments with salt developed the decoupled deformation with the salt layer as the upper décollement (subsalt, intrasalt, and suprasalt), significantly similar to the Kuqa Depression along the northern margin of Tarim Basin. Basal décollement dominant imbricated thrusts formed at the subsalt units, while the monoclinal structure formed at the suprasalt units. The decoupled deformation was also observed in the tectonic deformation graphics, distortional strain fields, and max shear stress fields. However, the salt layer was thickened in the thick salt model, and the salt thickness of the thin salt model varied slightly because the thin salt weakened the flowability of the salt. The lower max shear stress zone was easily formed in the distribution region of salt under the action of compression stress, which is conducive to the flow convergence of salt and the crumpled deformation of interlayer in salt. The results are well consistent with the natural characteristics of structural deformation in the Kuqa Depression. Our modeling result concerns the structural characteristics and evolution of salt-related structures and the effects of salt thickness on the structural deformation in the compressional stress field, which might be helpful for the investigations of salt-related structures in other salt-bearing fold-and-thrust belts.
Highlights
The Kuqa Depression is a peripheral foreland basin placed at the southern piedmont of Tianshan Orogen, Northwest China (Figure 1)
Based on three simulation experiments, we focused on the internal relationship between the experimental results and structural deformation characteristics in the northern margin of the Kuqa area, e.g., the formation of the "accommodative space" in the salt strata and the crumpled deformation of the dolomite interbed in the Kelasu structural belt
The experiments with salt developed the decoupled deformation with the salt layer as the upper décollement, significantly similar to the Kuqa Depression in the northern margin of Tarim Basin
Summary
The Kuqa Depression is a peripheral foreland basin placed at the southern piedmont of Tianshan Orogen, Northwest China (Figure 1). As one of the most important hydrocarbonbearing evaporite basins in China (Yu et al, 2014; Feng et al, 2018; Song et al, 2019), numerous salt-related structures were widely developed in the Kuqa Depression, especially in the Kelasu structural belt with obvious topographic relief features and obvious structural deformation features (Tang et al, 2004; Wu et al, 2014; Yu et al, 2014; Wu et al, 2015a; Zhao and Wang, 2016; Wang et al, 2017; Neng et al, 2018). How did differential thickness distribution of these two salt layers influence the structural deformation in the western and eastern depression? How did differential thickness distribution of these two salt layers influence the structural deformation in the western and eastern depression? It is worthy of further research to explore the influence of the differential thickness of rock salt on the structural evolution, especially from the perspective of experimental simulation
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