鄂尔多斯盆地西缘南段银洞子地区构造变形机制及动力学成因分析OA

The Yindongzi area,located in the southern segment of the western margin of the Ordos Basin,is characterized by a strongly deformed thrust-nappe structural belt that exhibits pronounced lateral variations in structural architecture along strike.To date,research on the segmentation of tectonic deformation styles,the processes of multi-stage tectonic superposition and reworking,and the genetic mechanisms underlying deformation in this region remains limited.This study integrates 3D seismic data interpretation,balanced cross-section restoration,and discrete element numerical simulation to investigate the segmented deformation patterns in the Yindongzi area,reconstruct its multi-stage tectonic evolution,and identify the primary factors controlling thrust-nappe deformation.For the first time,we quantitatively reveal distinct deformation intensities across the northern,central,and southern segments of the Yindongzi area and validate the mechanism involving the selective inversion of pre-existing normal faults as the origin of the major thrust faults,which contrasts with earlier interpretations emphasizing neotectonic thrusting.The results indicate that the Yindongzi area is vertically partitioned by the Huianpu-Shajingzi fault into two structural systems:an intensely inverted thrust-nappe system in the hanging wall and an extensional fault system in the footwall that experienced weak or no inversion.The thrust-nappe system is dominated by west-dipping listric faults,including the Qinglongshan-Guyuan fault,Qinglongshan-Pingchuan fault,and Huianpu-Shajingzi fault,which control the development of imbricate thrust sheets,such as the Yindongzi and Shajingzi sheets.These sheets extend from the basin basement to the surface and constitute the primary deformation framework.In contrast,the extensional fault system,which exhibits only minor deformation,is confined to Ordovician and older strata.Since the termination of fault-depression subsidence in the Middle Ordovician,the Yindongzi area has undergone multiple phases of tectonic inversion.The Caledonian,Hercynian and Indosinian,orogenies produced several regional unconformities,with progressively increasing tectonic reworking intensity.The Yanshanian orogeny,in particular,generated compressive stresses nearly three times greater than those during the Caledonian,marking the critical stage during which the present-day structural configuration was finalized.Comprehensive analysis of stratigraphic architecture,tectono-sedimentary setting,and numerical simulations based on seismic profiles suggests that the current imbricate thrust geometry in the Yindongzi area resulted from the intense late-stage inversion of normal faults,such as the Qinglongshan-Pingchuan fault and Huianpu-Shajingzi fault:that were active during sedimentation from the Changcheng System to the Ordovician.The substantial inversion of these two structures accommodated most of the regional compressional displacement,thereby shielding pre-existing normal faults in the basin interior from significant compression and resulting in their low degree of reactivation.This mechanism may explain the relatively weak tectonic deformation observed within the basin interior.Overall,this study offers valuable insights into the complex deformation processes in the basin-mountain transition zone of the Ordos Basin and provides a useful reference for future hydrocarbon exploration in the region.