Structural Features and Evolution of the Northwestern Sichuan Basin: Insights From Discrete Numerical Simulations

Abstract

The northwestern Sichuan Basin has experienced Meso-Cenozoic intracontinental compressional tectonic processes and formed multi-detachment stratigraphic distribution of foreland basins and fold-thrust belts, which have caused complicated structural deformations in the deep buried layers. Rapid uplift with accelerated erosion and two sets of detachments in the Lower Triassic and Lower Cambrian controlled the multilevel deformation structure. We conducted discrete numerical simulations with double weak detachments and erosion under extrusion conditions in order to examine the mechanics and kinematics of the frontalpiedmont zones of the NW Sichuan Basin. The following findings were made. (1) With continuous compression, the weak detachments promoted the decoupled and ladder-like deformation of the thrust belt, where the deformation above the slip layer extended further than it did below it. Rapid uplift and erosion at the thrust front contributed to the formation of a passive roof fault and a monocline in the upper layer, a series of forward and backward thin-skinned thrust-buried structures in the middle layer sandwiched between two weak detachments and stacking structures in the lower layer. (2) Erosion effectively prevents the deformation from propagating above the upper detachment, but can advance a horizontal transition in the deformation style generated within the middle brittle layer: from oblique and tight fault propagation folds to symmetrical, wide, and gentle detachment folds. (3) The model results consistent with tectonic deformation in the NW Sichuan Basin indicate a possible evolutionary mechanism under compression. There is hierarchical deformation of uncoordinated contraction controlled by the Lower Triassic and Early Cambrian weak layers, with the characteristics of the shallow monocline, the middle thin-skinned thrusts, and the deeper basement-involved folds. Continuous compression contributed a sequential pattern of steps as a whole, from the frontalpiedmont zones to the foreland basin, autochthonous stacking thrusts, and the huge buried structure in the NW Sichuan Basin. During the Himalayan period, syntectonic erosion along with the uplifted thrust front maintained the development of a passive-roof duplex and a huge forward buried structure.

Effects of Salt Thickness on the Structural Deformation of Foreland Fold-and-Thrust Belt in the Kuqa Depression, Tarim Basin: Insights From Discrete Element Models

“…Both the regional geological structure analysis and the structural simulation experiments show that if there is a regional distribution of salt rock as an important décollement layer in the fold orogenic belt and its foreland basin, the strata will undergo obvious structural stratification deformation in the vertical direction (Figures 5, 6) (Wang et al, 2010;Yin et al, 2011;Xu et al, 2012;Wu et al, 2014;Yang, 2017;Neng et al, 2018;Li, 2019;Li et al, 2020;Sun et al, 2021;Xu et al, 2021). The results of these experiments well reflect the regional structural characteristics of the northern margin of the western Kuqa Depression (Figure 8).…”

“…The discrete element method (DEM) has been applied to the study of geological and geophysical problems in recent decades (Hardy et al, 2009;Yin et al, 2009;Liu et al, 2015;Morgan, 2015;Botter et al, 2016;Buiter et al, 2016;Morgan and Bangs, 2017;Li, 2019;Li et al, 2020;Xu et al, 2021). A full, detailed description of the theory behind this modeling approach and its application to geological problems is given by Morgan (2015) and Li C. et al (2017Li C. et al ( , 2018Li C. et al ( , 2021, Li (2019).…”

“…They were calibrated through a series of repose angles and two-dimensional biaxial tests based on the method presented by Li, (2019; and Morgan (2015). In numerical simulations, a local damping coefficient, which was the one most commonly used (Potyondy and Cundall, 2004;Itasca Consulting Group 2008;Kozicki and Donzé, 2008;O'Sullivan, 2011;Scholtès and Donzé, 2013;Weatherley et al, 2014;Zhao, 2015;Li, 2019;Xu et al, 2021), was added to damp the reflected waves from the boundary of the particle and to avoid buildup of kinetic energy in the closed system (Itasca Consulting Group 2008;Li, 2019). The meaning of the other parameters in Tables 1 and 2 was given by Morgan (2015) and Li (2019).…”

Influence of preexisting structures on salt structures in the Kuqa Depression, Tarim Basin, Western China: Insights from seismic data and numerical simulations

“…In contrast, the thick‐skinned imbricate thrust fault system has been forming under a compressive environment since the late Miocene. This interpretation scheme is determined by the comprehensive analysis of the structural and sedimentary evolution, structural modelling, structural quantitative calculation and balanced cross‐section restoration (Gao, 2020; He et al., 2023; Li et al., 2016; Wang et al., 2017; Wu et al., 2014; Xu et al., 2021; Yin et al., 2011). Previous studies (Guo et al., 2010; Qi et al., 2009; Yang et al., 2018) have suggested that the high‐angle basement‐involved faults are regional extensional faults that developed in the Jurassic–Early Cretaceous extensional environment also support this interpretation scheme.…”

Geochemical Characteristics and Origin of Formation Water From the Upper Triassic Xujiahe Tight Sandstone in the Xiaoquan-Fenggu Structural Belt, Western Sichuan Depression, China

“…The western Sichuan Depression is located in the western part of the Sichuan Basin in China. It was developed based on the foreland basins in the western Sichuan Basin starting in the Late Triassic and represents the most developed area of continental natural gas in the Sichuan Basin (Xu et al, 2021). The western Sichuan Depression is a long strip zone extending in a NE-SW direction, and it is divided into north, middle, and south sections by the Mianzhu-Fenggu line and the Dayi-Chengdu line.…”