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• Xiongpo structure is a superimposed deep fault-bend fold and shallow structural wedge. • Xiongpo structure is accommodated a horizontal shortening rate of 0.2 mm/yr. • LMS front is partitioned low shortening rates (<0.5 mm/yr) on individual structures. Cenozoic crustal shortening across the Longmen Shan (LMS) fold-and-thrust belt records the eastward growth of the Tibetan Plateau. Although the structural geometries of individual structures in the region have been studied, the kinematics and rates of deformation across these structures remain unclear. In this study, we construct a geological cross section to derive the subsurface structural architecture of the Xiongpo structure in the LMS piedmont using one seismic reflection profile, and data from two boreholes. The structure displays a superimposed deep fault-bend fold and shallow structural wedge with three splay thrust faults. Using two-dimensional kinematic models, based on fault-bend folding algorithm, we reconstruct three episodes of upper crustal shortening, with 7.0 ± 0.3 km of total shortening. Combining with previously published low-temperature thermochronology data, we further estimate that the structure has experienced an average shortening rate of ∼ 0.2 mm/yr since 40–25 Ma. We infer that the structure acted as the deformation front of the LMS fold-and-thrust belt between 40 and 25 Ma and 15–10 Ma driven by the eastward growth of the Tibetan Plateau. Finally, we review the shortening rates of other five structures within the LMS piedmont, and find that these six structures (including the Xiongpo structure) individually have undergone an average shortening rate < 0.5 mm/yr on each fault, suggesting that strain is partitioned along several structures within the LMS fold-and-thrust belt. We also show that the southern LMS piedmont has absorbed more upper crustal shortening than the central LMS, ∼0.5–0.7 mm/yr, since ∼2.6 Ma. [ABSTRACT FROM AUTHOR]

Abstract: Eastern Tibet is an important example of oblique convergence and associated strain partitioning, as suggested by recent 2‐D and 3‐D structural interpretations, yet the nature and evolution of oblique strain partitioning of this region remain poorly known. Here we use seismic reflection profiles, borehole data, and field investigations in the Longmen Shan piedmont to determine the subsurface structural architecture, and we observe several nearly N‐S striking thrusts and reactivation of NE striking preexisting faults. We interpret that this behavior is due to a regional principal compressional stress oriented in the E‐W direction, oblique to the NE striking Longmen Shan. Using the records of fault activity and related Late Pliocene and Quaternary foreland sediments and growth strata, as well as the coseismic rupture of the 2008 Mw 7.9 Wenchuan earthquake, we demonstrate that the Longmen Shan has experienced E‐W crustal shortening and oblique motion since ~5–2 Ma. We present two strain partitioning models arising from oblique thrusting in eastern Tibet and suggest that the eastward extrusion from Tibet is mainly accommodated on the strike‐slip Longriba fault and the dip‐slip Longmen Shan‐Min Shan fault zones. These results enhance our understanding of the tectonic relationship between the Songpan‐Ganzi terrane and the Sichuan basin and provide additional constraints for studies of the geodynamic response of eastern Tibet to the ongoing India‐Eurasia collision. [ABSTRACT FROM AUTHOR]

• A 3D fault morphology model of the RFBR was constructed for the southern LMS. • The geometrical irregularity of the RFBR induced segmentation of thrusting. • Fractured duplex over the geometrical bump contributed to the presence of seismic gap. A 3D fault morphology model has been constructed from seismic profiles covering the piedmont of the southern Longmen Shan (LMS), eastern margin of the Tibetan Plateau. It reveals a spatial correlation between an ∼3.5 km-high geometrical bump on the range front blind ramp (RFBR) and the gap between the 2008 M w 7.9 Wenchuan and 2013 M w 6.6 Lushan earthquakes. Sandbox modeling is then used to probe the effects of the geometrical irregularity of the RFBR on fault behaviors and the LMS range front deformation. Sand wedges are designed to thrust over artificial blind ramps, analogous to the thrusting of the LMS orogenic wedge toward the Sichuan Basin through the RFBR. The experiments reproduce the first-order deformation features presented in the southern LMS range front, confirming that along-strike geometrical variations of the RFBR have induced the segmentation of both fault motion and the range front deformation. Their results also suggest that the gap between the Wenchuan and Lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the RFBR. Additionally, there is a duplex structure occurring in the hanging wall of the geometrical bump, which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly (low seismic velocity) underneath the seismic gap. It is likely that this fractured body protected the gap from the ruptures of the Wenchuan and Lushan earthquakes. [ABSTRACT FROM AUTHOR]

Previous studies have proposed that the Eastern Tibetan Plateau underwent ∼E–W oblique crustal shortening, due to the eastward extrusion of the plateau since ∼5–2 Ma to present. However, the effects of the oblique thrusting on the three-dimensional (3D) fold morphology and kinematics in the front of the Longmen Shan fold-and-thrust belt are still poorly understood. We use 3D seismic data to produce five 3D geometric models and compare our results with structural models of the Yanjinggou anticline in the Longmen Shan fold-and-thrust belt, to investigate the effects of oblique thrusting on 3D fold evolution. The results show that regional oblique thrusting occurred within the LMS fold-and-thrust belt, resulting in rotation and a curved structural morphology, and suggest that this process may be applicable globally to both small- and regional-scale structures, as well as larger-scale orogenic belts in obliquely convergent settings. • The effects of oblique thrusting on 3D fold geometry and kinematics are investigated. • The Yanjinggou anticline developed as a trishear fault-propagation fold with 1.2 km shortening. • The Yanjinggou anticline was affected by oblique thrusting at an angle of 55°. Three-dimensional (3D) subsurface seismic data acquisition and modeling are rarely undertaken; consequently, the complex effects of oblique thrusting on the 3D morphology and kinematics of folds are still poorly understood. We use 3D seismic data to produce five 3D geometric models and compare our results with structural models of the Yanjinggou anticline in the Longmen Shan fold-and-thrust belt, to investigate the effects of oblique thrusting on 3D fold evolution. 3D geometric modeling results reveal that oblique thrusting may cause fold asymmetry, vertical axis rotation, and a curved fold axis. 3D seismic interpretations and structural modeling suggest that the Yanjinggou anticline developed as a trishear fault-propagation fold and experienced a maximum shortening amount of 1.2 ± 0.1 km. The 3D structural and geometric models are consistent with paleomagnetic results, suggesting that the anticline was affected by oblique thrusting at an angle of 55° above a listric thrust fault with three fault ramps (19°, 30°, and 40°), causing the fold to rotate and develop a curved morphology. The integrated method used in this study to investigate the effects of oblique thrusting on 3D fold morphology and kinematics can be applied to regional oblique thrusting in the Longmen Shan and other fold-and-thrust belts worldwide. [ABSTRACT FROM AUTHOR]