Tectonic Deformation of the Western Qilian Shan in Response to the North–South Crustal Shortening and Sinistral Strike-Slip of the Altyn Tagh Fault Inferred From Geomorphologic Data

Zhidan Chen,Rui Liu,Wenbin Xu,N V Koronovsky,An Li

doi:10.3389/feart.2022.808935

Abstract

The tectonic deformation of a series of NWW-trending compressional band-shaped mountains and fault zones in the Qilian Shan, northeastern Tibet, plays an important role in absorbing the north–south crustal shortening of the Tibetan Plateau and accommodating the sinistral strike-slip of the Altyn Tagh fault. However, the deformation pattern of these mountains and fault zones in response to crustal shortening and sinistral strike-slip remains to be investigated. In this study, we present the slope map and swath profiles of the western Qilian Shan extracted from high-resolution digital elevation model (DEM) data and the fluvial geomorphologic characteristics of the Baiyang river in the northwestern Qilian Shan. Our data indicate that the crustal uplift of the northern Qilian Shan is stronger than that of the central and southern ranges of the Qilian Shan because of the high-terrain relief and stronger erosion. In addition, the deformed terraces of the Baiyang river documented the activity of NWW-trending faults in the western Qilian Shan. Based on the longitudinal profiles and ages of the deformed river terraces, the vertical slip rates of the Changma, Yumen, and Bainan faults in the western Qilian Shan since ∼60 ka were constrained to be 0.31 ± 0.06, 0.33 ± 0.02, and 0.24 ± 0.02 mm/a, respectively. Based on the comparison with previous studies, we noticed that the rate of the vertical slip since the Late Quaternary of the northern Qilian fault of 1.5–2 mm/a is significantly higher than that of the Changma fault of 0.3–0.6 mm/a, which matches the terrain relief in the Qilian Shan and demonstrates that the northern Qilian Shan has been rising faster than its southern ranges. From the slip rates of the NWW-trending faults in the western Qilian Shan, we suggest that the crustal shortening is widely distributed in the NWW-trending compressional orogenic belts and fault zones across the Qilian Shan, among which the northern Qilian Shan and its frontal thrust system absorb the greatest shortening amount, whereas strike-slip faults within the Qilian Shan accommodate most of the sinistral strike-slip of the Altyn Tagh fault.

Highlights

The collision and post-collisional convergence between India and Eurasia have caused crustal shortening and thickening and led to the generation of the magnificent mountain ranges of the Himalayas and Tibetan Plateau (Molnar and Tapponnier, 1975; England and Houseman, 1986; Harrison et al, 1992; Yin and Harrison, 2000)
The geomorphologic characteristics of the Baiyang river derived from the slope map and swath profiles of the western Qilian Shan based on digital elevation model (DEM) data suggest that the river erosion in the northern Qilian Shan is more intense than that in the central Qilian Shan and the terrain relief reaches a maximum in the northern Qilian Shan
The topographic slope map and two swath profiles of the western Qilian Shan extracted from high-resolution DEM data show that the terrain relief in the northern Qilian Shan is significantly higher than that in the central and southern Qilian Shan

Summary

Introduction

The collision and post-collisional convergence between India and Eurasia have caused crustal shortening and thickening and led to the generation of the magnificent mountain ranges of the Himalayas and Tibetan Plateau (Molnar and Tapponnier, 1975; England and Houseman, 1986; Harrison et al, 1992; Yin and Harrison, 2000). Since the onset of the Indo-Asian collision at 65–50 Ma, the Himalayan–Tibetan orogen has absorbed at least 1,400 km of crustal shortening (Yin and Harrison, 2000; Ding et al, 2017), which have been transformed into the rapid uplift of mountains (e.g., Harrison et al, 1992; Wang et al, 2014), thrusting and strike-slip of faults (e.g., Molnar and Tapponnier, 1975; Zhang et al, 2004), lateral extrusion of blocks (e.g., Tapponnier and Molnar, 1976; Hodges et al, 2001), and shrinking and extinction of basins (e.g., Wang et al, 2014; Ding et al, 2017). Its enormous size makes it a non-negligible part of studies of the tectonic deformation of the plateau (Figure 1B)

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Discussion

Conclusion