Abstract
The South Dabashan arcuate tectonic belt located at the northern margin of the Yangtze Block in South China, which primarily comprises a series of northwestern (NW)-trending foreland fold-and-thrust belts (FTBs), is useful for determining the intracontinental orogeny processes of the Yangtze Block. In this study, we integrated the latest pre-stack depth migration of three- and two-dimensional seismic profiles, drill hole, and outcrop data to explore the structural geometric and kinematic features of the west segment of the South Dabashan FTB. This belt is characterized by multi-level detachment structures due to the presence of three predominant sets of weak layers: the Lower Triassic Jialingjiang Formation gypsum interval, Silurian mudstone beds, and Cambrian shale beds. The belt is accordingly subdivided vertically into three structural deformation systems. The upper system appears above the Jialingjiang Formation gypsum layer and exhibits Jura-type folds, which were formed by alternating anticlines and synclines that are parallel to each other. The middle system comprises Silurian shale as the base and Jialingjiang Formation gypsum interval as the passive roof and exhibits NW-striking imbricate thrusts. The lower system is bounded by Cambrian and Silurian detachment layers, forming a duplex structure. The Sinian and Proterozoic basements below the Cambrian were not involved in deformation. The west segment of the South Dabashan FTB underwent four periods of tectonic evolution: Late Jurassic to Early Cretaceous, Late Cretaceous, Paleogene, and Neogene to Quaternary. The deformation was propagated southward in imbricate style, resulting in the passive uplifting of the overlying strata. Based on the magnetotelluric and deep seismic profile, the tectonic processes of the west segment of the South Dabashan FTB are inferred to be primarily controlled by the Yangtze Block northward subduction under the Qinling Orogenic Belt and the pro-wedge multi-level thrusting during the Late Jurassic to Cretaceous.
Highlights
Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China, 3 Exploration Branch, SINOPEC, Chengdu, China, 4 SINOPEC Exploration and Production Research Institute, Beijing, China
In the upper structural deformation sandwiched between the three anticlines, while the syncline between the Zhuyuzhen anticline and the Liba anticline is split by faults, forming secondary anticlines and synclines. This indicates that the NE–SW-trending tectonic compression occurred again after the formation of the main fold, which resulted in the stratigraphic offset of the upper structural deformation system
Multiple sets of detachment layers developed in the northern margin of the Yangtze Block (YZB) formed three main structural deformation systems with different depths during the intracontinental orogeny processes in the South Dabashan fold-and-thrust belts (FTBs)
Summary
Convergence of North and South China Block, after the closure of the Paleo-Tethys since the Triassic (Dong et al, 2013). In the west segment of the South Dabashan FTB, the Jialingjiang Formation gypsum detachment layer exhibits disordered reflection, and the thickness of deformed strata varies from 100 to 1,500 m (Figures 5–8). This indicates that the NE–SW-trending tectonic compression occurred again after the formation of the main fold, which resulted in the stratigraphic offset of the upper structural deformation system These synclines and anticlines are gradually uplifted from the southwest to the northeast under the control of a series of thrust faults that developed in the detachment layer with different depths (Figure 5B). The deep structural deformation system in the Southern Dabashan Belt has the Cambrian detachment layer as the floor fault and the Silurian detachment layer as the roof fault, forming a duplex structure, but it only extends below the Zhuyuzhen anticline, and the FIGURE 9 | Tectonic restoration of seismic profile DBS06_L1023. The upper structural deformation system mainly developed the lowamplitude fold related to the faults with small fault displacement (Figure 12)
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