Abstract:

 In this paper, the fine interpretations of seismic profiles in the central Longmen Mountains have been accomplished with the application of faultrelated folding geometry principles. Our studies found that there are multidetachment layers with different structural deformation in the mountain front belts. Among them, the deep detachment, which is below the PreCambrian Formation at the depth of (19±2) km, developed the duplex structures and superimposed wedges. The structural wedges are one of the most important structural styles in this area. The deep structural wedge model in section A was formed by superposition of breakbackward style and slipped more than 455 km. In contrast, structural wedge model in section B was formed by superposition of breakforward style and slipped only 166 km. Besides, the upper faults and strata were uplifted and folded because of the motion of the structural wedges. The largest vertical uplift of strata in the A and B section are 8 km and 3 km relative to the Western Sichuan Basin, respectively. The Superimposed wedges strike along the Longmen Mountains with zonal distribution in plan, having different sizes and geometric shapes. Our analysis indicated that they were formed during the Himalayan periods. Meanwhile, through the quantitative geometric and kinematic analysis, it is indicated that the forward modeling of wedges is in coincidence with the seismic sectional characteristics. The formation of the wedges had its own mechanism which is unclear yet. Owing to the special location, the structural characteristics and the genesis, the study of the formation of the wedges could provide the constraints on the dynamical mechanism of uplifting in the southeast margin of the QinghaiTibet Plateau.

Key words: seismic profiles, detachment fault, faultrelated fold, structural wedges, geometric model, kinematics, central Longmen Mountains