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Large-scale strike-slip faults often develop in the collisional and accretionary orogenic belts around the world. The Central Asian Orogenic Belt (CAOB) contains numerous strike-slip faults and provides opportunities to decipher the relative movements among different components. Here, we report new data from the ENE-trending Yabrai dextral ductile shear zone in the Alxa region (NW China) of the southernmost CAOB. We performed field mapping, structural analysis, and muscovite 40Ar/39Ar dating to constrain the geometries, kinematics and timing of the shear zone. The Yabrai shear zone crops out for more than 150 km, and the kinematic indicators from the outcrops, microstructures, and quartz c-axis fabrics suggest a consistent dextral shear motion. The microstructures and EBSD results indicate intermediate-to low-temperature deformation (∼300–530 °C). Muscovite 40Ar/39Ar dating from mylonitic samples yield ages of 254–251 Ma, which imply that the shear zone was active in the Late Permian. The displacement of Yabrai shear zone is estimated to be ca. 30 km. An integration of spatiotemporal patterns of shear zones and regional aeromagnetic data suggests that a giant "S–C"-type shear system occurred in the Alxa region in the Late Permian. Based on this work and previous studies, a crustal-scale strike-slip system of late Paleozoic is developed between the CAOB and the southern cratons. It formed in a transcurrent regime after the closure of the Paleo-Asian Ocean, which was a response to the deformation of the whole CAOB in the end of late Paleozoic. • The Yabrai shear zone is a dextral ductile shear zone formed in the Late Permian. • A giant "S–C"-type shear pattern developed in the Alxa region in the end of the Paleozoic. • The shear system in the Alxa belongs to a transcurrent system along the southern CAOB. [ABSTRACT FROM AUTHOR]

The development of normal faults is controlled by many factors, among which mechanical layers or pre-existing fabrics play an important role in the growth of normal faults. It is widely accepted that normal faults are rarely continuous surfaces but are zones composed of fault segments, heterogeneously distributed fault rocks of various compositions, slip bands, blocks and other deformation elements. Listric normal faults, particularly those developed in metamorphic crystalline rocks or preexisting fabric-developed basements, may be composed of subparallel faults in cross-sections, linked by extensional duplex structures. Here, we choose a listric rift-bounding fault rooted in foliation developed basements, the Langshan normal fault in the northwest corner of the Ordos Block, to conduct an outcrop analysis of fault geometry and linkage behavior from cross-sectional views. The Langshan normal fault zone is composed of mixed regions of high- and low-angle segments linked by duplex structures at various scales. Mylonitic foliations play a significant role in the formation of fault segments and the evolution of the listric fault zones. Lines of evidence show that small en echelon faults initiated from preexisting foliations. Local stress perturbation between overstepping faults results in the formation of duplex structures and displays a high fracture density, which serve to the coalesce of fault segments. Consequently, the progressive localization of strain onto a large listric fault is achieved by progressive development of extensional duplexing among fault segments in cross-sections. These extensional duplexes imply a scale-invariant property, based on which we can extrapolate this pattern occurs on larger scales and is verified by seismic data. The case of Langshan piedmont fault demonstrates the possibility of a listric fault being formed by subparallel planner faults and highlights the effects of preexisting fabrics on the evolution of listric faults, especially in basement fabrics developed regions along the fault. Image 1 • The Langshan normal fault shows segmentation in map and cross-section views. • The basement foliations play a significant role in the development of normal faults. • Extensional duplex structures display a scale-invariant property. • Listric normal faults can be formed via extensional duplexing. [ABSTRACT FROM AUTHOR]

A new type of structural association comprising periclinal folds is present in thick-bedded calcareous mudstones and siltstones of the Early Cretaceous Hekou Group in the Lanzhou Basin, NW China. The periclinal fold system consists of meso-scale, open anticlines and synclines with fold axial trends in two perpendicular orientations (NE-SW and NW-SE) and two sets of conjugate thrust faults that form intersections in the same two orientations. Folded and faulted layers of the periclinal fold system are not sedimentary bedding surfaces but sub-parallel curviplanar foliations formed by compaction of the original strata soon after deposition. Many folded curviplanar foliations connect with the unfolded, conjugate thrust faults, indicating that faulting was active during and/or soon after folding. The NE-SW and NW-SE-trending fold axes and fault planes indicate bilateral, subhorizontal contraction acting simultaneously during the formation of the periclinal fold system. In some cases, converging slickenlines on curviplanar foliation planes within anticline cores point to localized isotropic contraction probably caused by scaping fluids and increased hydrostatic pressure. Similarities with the better-known polygonal fault system include development in fine-grained sediments and layer boundness, whereas main differences are a dominance of contractional faults in the periclinal fold system versus extensional faults in the polygonal fault system and a higher consolidation of sediments needed for the development of the periclinal fold system. This study suggests that collision between the Lhasa and Qiangtang Blocks combined with oblique convergence and subsequent collision along the southeastern margin of the Eurasian plate following compaction-related volume loss of fine-grained sediments led to the formation of the periclinal fold system in the Hekou Group in the Late Cretaceous. • A type of structural association named as "Periclinal Fold System" is first reported. • The Periclinal Fold System develops in thick-bedded mudstones and siltstones. • Compaction fabrics are folded in the Periclinal Fold System, but not bedding planes. • The Periclinal Fold System is formed in the constrictional setting. [ABSTRACT FROM AUTHOR]