3-D Structural Model of the Hejiaying Area, Northeastern Sichuan Basin: Constraint from High-resolution Swath 3-D Seismic Data

The Fangdoushan structural belt in the northeastern Sichuan Basin is characterized by typical thin-skinned multi-level detachment structures. It is an ideal area for addressing the deformation mechanism in the intra-continental tectonics of South China. Regional detachment layers, delineation of structural styles of different structural layers, and the spatial coupling among the different structural layers are still of controversial. Thus, quantitative analysis of spatial combination features and differences of different structural layers is the key to understand mechanism of multi-layer detachment in the study area. Using digital elevation model, outcrop data, and high-resolution swath 3D seismic data, we construct 3D structural model of Hejiaying area, northern part of Fangdoushan anticline, discuss the differential deformation characteristics of different structural layers and their controlling factors under the multi-layer detachment.

The regional detachment layers control the structural style of the fold-thrust structure which is decoupled vertically to form four sets of structural layers: base, deep, middle and shallow levels. It develops regional detachment layers in Middle and Lower Cambrian gypsum layer, Lower Silurian mudstone layer, and Lower Triassic gypsum layer. Interpretation of seismic sections indicates that the base level forms a structural wedge in the shallow metamorphic Banxi Group. Deep level is controlled by Cambrian and Silurian detachment layers, forming low-amplitude anticlines; Middle level is controlled by Silurian detachment layer, forming high-angle brittle thrusts. Shallow level is characterized by gypsum-bearing detachment in the Lower Triassic. Differences in the combination of mechanical stratigraphy and shortening in different structural layers determine the differences in structural styles. Weak layers transmit displacement with larger shortening distance and stronger deformation. The superimposed deformation of different structural layers controls uplift in the Hejiaying area.