Structural analysis and numerical modeling of multi-stage tectonic deformation in the Ziliujing anticline, SW Sichuan Basin, China: Implications for deformation propagation in salt-bearing fold-and-thrust belts

Investigating the multi-stage tectonic evolution of fold-and-thrust belts (FTBs) remains a significant challenge. In particular, the evolution of its internal structures and the mechanisms that govern deformation propagation require further research. This study focuses on the Ziliujing anticline located in the southwestern Sichuan Basin, China. It provides an in-depth analysis of the structural development and evolution of the frontal zone of the SW Sichuan FTB, which has propagated from the southeast to the northwest. Through detailed interpretation of seismic reflection profiles and quantitative area-depth-strain (ADS) analysis, we have identified three distinct stages of tectonic shortening corresponding to the Caledonian, Indosinian, and Yanshan-Himalayan orogenic periods. These findings are consistent with the established history of regional tectonic evolution. Furthermore, discrete-element numerical simulations demonstrate that the pinch-out of the basal décollement exerts a significant influence fault development and the formation of overlying fold patterns during multi-stage tectonic deformation. During the initial phase, deformation progressively propagates forward until it reaches the tip of the décollement, where subsequent deformation becomes predominantly localized. The decoupling effect induced by the intermediate décollement facilitates the continued forward propagation of underlying deformation. These insights contribute to a deeper understanding of the multi-stage compressional deformation of salt-bearing fold-thrust belts and the critical factors governing the propagation of deformation from mountain ranges to basins.