Discrete-element numerical modeling of sub-salt structures in the Central Kelasu fold-thrust belt, Kuqa Depression, northwestern China

Abstract

Knowledge of the deformation history and dominant factors influencing the formation of sub-salt structures is necessary to understand the formation of sub-salt traps. In this study, the discrete-element method (DEM) is used to assess the deformation mechanism of sub-salt structures in the Central Kelasu fold-thrust belt of the Kuqa Depression. A series of DEM models of the Central Kelasu fold-thrust belt are constructed, the final deformation styles of the models are compared with the real structures in order to determine the fitting degree of each models, and the dominant factors influencing the formation of sub-salt structures are determined. A thin salt layer promotes the deformation in the sub-salt sequence. Salt sub-sags, basal uplifts, and pre-existing faults can also promote the deformation in the sub-salt sequence in the northern part of the models. Large deformations accumulate in pre-existing structures in the northern part of the models, and then subsequent deformations are also transmitted to the salt layer and supra-salt sequence; however, these deformations are hardly transmitted to the sub-salt sequence in the middle and southern parts of the models. Among the eight DEM models constructed in our research, the horizontal-stratum model without any initial structures showed the best fit to actual phenomena. Earlier simple structures of Mesozoic layers can be deformed into the current complex structures under compression effects in the late Himalayan period. By comparing with other regions and analyzing the deformation progress of the DEM model, the sub-salt structures in the Kuqa Depression are considered to be fold-accommodation fault structures.