Evidence of structural transformation in the eastern part of the Altyn Tagh Fault, northern margin of the Tibetan Plateau, China, based on the kinematics and shortening rate of the Hongliuxia region

Abstract

(a) Blocks distributed surround the Tibetan Plateau. (b) Active tectonics in the northeastern Tibetan Plateau. The black rectangle within the inset shows the study area. The thick grey line shows the block boundary. Blue arrows show the global positioning system (GPS) velocity with respect to the Eurasian Plate, and the green arrows represent the GPS velocity with respect to GAB. (c) Deformation rates of these faults and folds in the compressional stepover of the eastern ATF. JTF: Jinta Fault, HLF: Helishan Fault, LSF: Longshoushan Fault, NQLF: North Qilian Shan Fault, SS: sinistral strike-slip rate, Sh: shortening rate, V: vertical rate, HLX Fo.: Hongliuxia thrust-fold belt, HSG Anti.: Huoshaogou Anticline, NKTF: North Kuantanshan Fault, LJM Anti.: Laojunmiao Anticline, and BYF: Baiyang Fault. • Shortening rate of the Hongliuxia region was 0.7 ± 0.2 mm/yr in Late Pleistocene. • Hongliuxia region showed more N–S shortening than the W–E strike-slip. • Stepover was formed between the eastern Altyn Tagh fault and Jinta-Nanshan fault. The Altyn Tagh Fault (ATF) and the North Qilian Shan Fault, as the northern margin of the Tibetan Plateau, have always been the focus of attention while developing a propagation model of the plateau. However, rocks in the North Qilian Shan Fault are intensely deformed and understanding the deformation history is difficult. The ATF and North Qilian Shan Fault have propagated into the Hexi Corridor and led to a series of new faults and folds. Based on simple kinematics and insignificant deformations of these new faults and folds, the geological process can be easily understood. The Hongliuxia region, which represents a positive flower structure in the easternmost part of the ATF, is the binding transformation site between the ATF and North Qilian Shan Fault. In this study, the kinematics of the Hongliuxia region was determined based on structural profiling and fault surveys. The shortening rate (0.7 ± 0.2 mm/yr) was estimated from the deformation and 10 Be exposure age of fluvial terraces. We found that the ATF might be connected to the Jinta-Nanshan Fault by a compressional stepover on the northern part of the Yumen Basin, which transforms into a series of compressional ridges, including the Hongliuxia thrust-fold belt, Huoshaogou Anticline, and North Heishan Fault. We infer that the ATF and the Longshoushan Fault, which serve as boundary faults, might be linked by multiple compressional stepovers. The gradual changes of the striking angles by compressional stepovers indicated the transformation from strike-slip to compressional structures and these changes caused the two boundary faults (ATF and Longshoushan Fault) to jointly undergo crustal deformation associated with the northward propagation of the Tibetan Plateau. This study can advance our understanding of the relationship between ATF and the Qilian Shan thrust fault system.