Tectonic Uplift Variations along the Danghe Nan Shan Constrained by Fluvial Geomorphic Indices

Graphical abstract

0 INTRODUCTION

The Qilian Mountain Belt, at the forefront of the Tibetan Plateau’s expansion, offers key insights into the plateau’s tectonic deformation (Zuza et al., 2018; Zheng et al., 2010; Zhang et al., 2004; Tapponnier et al., 2001; Meyer et al., 1998). The northwest-trending mountain ranges in the Qilian Shan (“Shan” means “Mountain” in Chinese) have significantly influenced this deformation (Zheng et al., 2013). While much research has focused on the slip rates of major boundary fault systems like the Altyn Tagh, North Qilian, and Haiyuan faults, quantitative studies on internal faults within the orogenic belt, such as the Danghe Nan Shan thrust fault, Daxue Shan fault, and Changma fault, remain insufficient. Understanding the deformation characteristics of these internal faults is crucial for comprehending the region’s tectonic deformation.

The Danghe Nan Shan, situated in the northwestern portion of the Qilian Shan, exhibits geomorphic features indicative of differential tectonic activity. The range is characterized by deeply incised river valleys, asymmetric drainage patterns, and active fault segments that control regional topographic evolution (Wang et al., 2019; Zuza et al., 2018). However, the degree of spatial variability in uplift and its driving mechanisms requires further investigation. Understanding these variations is essential for reconstructing the neotectonic evolution of the region and assessing associated seismic hazards.

High-resolution digital elevation models (DEMs) have become essential for extracting topographic indices that reflect fault activity (Bian et al., 2025; Wang D et al., 2024; Zhou et al., 2022; Wang Y Z et al., 2018; Kirby and Whipple, 2012). This study utilizes SRTM 30 m data (Farr and Kobrick, 2000) to analyze the standard stream steepness index (k_sn) and river knickpoints. The k_sn effectively reveals spatial variations in erosion/uplift rates (Wang and He, 2020; Gallen and Wegmann, 2017;Wobus et al., 2006,2003; Kirby et al., 2003; Whipple and Tucker, 2002). while river knickpoints provide insight into temporal variations (Wang et al., 2018; Kirby and Whipple, 2012; Whipple, 2004).

This study integrates knickpoint and k_sn analysis to illustrate the tectonic deformation of thrust faults on both sides of the Danghe Nan Shan, enhancing our understanding of the interplay between tectonic processes and surface dynamics in the northeastern Tibetan Plateau and the region's landscape evolution.

1 RELATIONSHIP AMONG k_sn, KNICKPOINTS AND UPLIFT RATE

The stream power model incorporates erosion rate and geomorphic parameters. Under steady-state conditions, erosion, and uplift rates are equal, establishing a relationship between k_sn and uplift rate (Howard, 1994; Howard and Kerby, 1983).

k_{sn}={\left(\frac{U}{K}\right)}^{\frac{\mathrm{1}}{n}}(1)

k_{sn}=(\frac{S}{A^{\theta }})(2)

In Equation 1, k_sn represents the river channel steepness index, U is the uplift rate, K denotes bedrock erodibility, and n is the slope exponent (generally set to 0.45) (Wobus et al., 2006; Kirby et al., 2003; Whipple and Tucker, 2002; Snyder et al., 2000). Thus, k_sn reflects the relative intensity of the uplift rate. Further studies indicate k_sn is also valuable for assessing transient rock uplift rates in dynamic systems (Ma et al., 2021;Wang et al., 2019,2017; Pan et al., 2015). In Equation 2, S is the slope, A is the drainage area, and θ is a constant (typically 0.4 to 0.6) representing the relationship between drainage area and erosion rate (Wobus et al., 2003); in this study, θ is 0.45.

A knickpoint represents a distinct break in the slope along a river’s longitudinal profile. Once formed, it migrates upstream, altering the channel’s gradient in response to various geological and geomorphic processes. In tectonically driven knickpoint migration, k_sn increases downstream, resulting in a higher k_sn value compared to the upstream segment. In contrast, non-tectonic knickpoints generally exhibit irregular k_sn distributions without a systematic trend (Pavano et al., 2016; Yang and Simoes, 1998). However, in the Danghe Nan Shan area, non-tectonic knickpoints display elevated k_sn values upstream. Consequently, the downstream k_sn reflects the contemporary uplift of the associated fault. Nevertheless, if the downstream section is dominated by sediment deposition, the k_sn value may be lower than upstream, potentially leading to an underestimation of the relative magnitude of uplift.

Based on the above illustration, this study uniformly chose 25 rivers from both the north and south sides of the Danghe Nan Shan to investigate the uplift rate in the area (Figure 2a). Rivers were chosen from basins adjacent to the watershed on both sides of the Danghe Nan Shan. The TopoToolbox package (Schwanghart and Scherler, 2014) was used to extract k_sn values and knickpoints, with k_sn calculated using Equation 2. Knickpoints were classified as tectonic (upstream k_sn smaller than downstream k_sn) or non-tectonic (upstream k_sn larger than downstream k_sn).

2 SPATIAL VARIATION IN UPLIFT RATES

Our analysis reveals that k_sn values on the northern flank are significantly higher than those on the southern flank (Figure 2a), indicating a greater uplift rate in the northern region. Furthermore, the k_sn values on both the northern and southern flanks exhibit spatial variability along the fault strike, likely influenced by differential tectonic activity and lithologic controls (Figure 2a). Notably, on the northern flank, the northwestern segment displays distinctly elevated k_sn values, suggesting localized regions of intensified uplift, potentially linked to variations in uplift rates and crustal deformation processes.

The elevation trend of tectonic knickpoints along the northern flank of the Danghe Nan Shan closely corresponds to that of the active fault, with an elevation difference ranging from 600 to 1 600 m (Figure 2b). Similarly, on the southern flank, the elevation trend of tectonic knickpoints aligns with the trends of three active faults, with elevation differences varying between 200 and 600 m (Figure 2c). These observations indicate that the formation of tectonic knickpoints is directly influenced by fault activity, and the downstream k_sn of these knickpoints serves as a proxy for the current uplift rate of the associated faults. Additionally, variations in downstream k_sn values provide further insights into uplift heterogeneity along the fault strike, enabling segmentation of the flanks based on differential uplift characteristics.

On the northern flank, the average downstream k_sn values for segments I and II are 195.2 m⁰·⁹ and 121.6 m⁰·⁹, respectively. In contrast, no tectonic knickpoints are observed in segment III, where the average k_sn for river channels is 78.5 m⁰·⁹ (Figure 2d). These values suggest a relative uplift rate hierarchy of U_I > U_II > U_III. On the southern flank, only segments II and III contain rivers with tectonic knickpoints, exhibiting average k_sn values of 104.7 m⁰·⁹ and 73.3 m⁰·⁹, respectively. The average k_sn values for segments I, IV, and V are 49.3 m⁰·⁹, 91.5 m⁰·⁹, and 59.6 m⁰·⁹, respectively. Notably, although segment IV lacks tectonic knickpoints, its average k_sn is comparable to the downstream k_sn observed in segment II. This suggests the possibility that knickpoints in segment IV have migrated upstream and have disappeared at the divide. Despite this, the similar k_sn values between segments II and IV imply comparable uplift rates, leading to the inferred uplift rate hierarchy on the southern flank: U_II = U_IV > U_III > U_I = U_V. These results highlight the spatial variability of tectonic uplift in the Danghe Nan Shan.

Previous studies targeting the northern Danghe Nan Shan thrust system have provided localized assessments of its structural geometry and kinematic behavior (Shao et al., 2023; Xu et al., 2021; van der Woerd et al., 2001; Meyer et al., 1998). Quantitative rate constraints exist for distinct segments: Shao et al. (2023) reported a vertical uplift rate of 1.4 ± 0.4 mm/a and a shortening rate of 0.8 ± 0.2 mm/a at the western terminus, while Xu et al. (2021) estimated rates of 0.6 ± 0.2 mm/a (uplift) and 0.8 ± 0.2 mm/a (shortening) in an eastern segment. The results indicate apparent uniformity in shortening rates but suggest a significant eastward gradient decrease in the rate of vertical uplift along the thrust. This result is consistent with the findings observed by k_sn (Figure 2d), which typically indicates an uplift rate on the order of 10³ to 10⁵ years (Wang et al., 2023).

A comparison of uplift rates derived from k_sn with fault geometry in the Danghe Nan Shan region indicates that hanging walls associated with single fault strands exhibit higher uplift rates than those associated with multiple fault strands. Specifically, along the northern flank, segment I, characterized by a single-strand thrust, is associated with a higher uplift rate compared to segment II, which comprises double-strand thrust faults and shows a lower uplift rate (Figure 3). A similar spatial pattern is evident along the southern flank, where segment IV (single-strand fault) exhibits a greater uplift rate than segment III (multiple fault strands) (Figure 3). These observed variations in uplift rate are hypothesized to be primarily attributable to differences in fault dip angles (Figures 3b, 3c, 3d). Steeper dip angles, generally associated with single faults as depicted schematically in the kinematic model (Figure 3e), are expected to yield a larger vertical component of uplift for a given magnitude of horizontal shortening. However, additional factors likely influence local uplift rates, including probable strain partitioning onto adjacent fault systems. For instance, the reduced uplift rate observed in southern segment I may be explained by significant deformation accommodation along a strike-slip fault within that segment. Similarly, lower uplift rates in segments III and V could result from the transfer of substantial deformation to an eastern strike-slip fault system (Figure 3a; Zheng et al., 2013). Collectively, these observations suggest that geomorphic analyses based on metrics like k_sn can effectively delineate spatial variations in uplift rates along active thrust systems and may provide valuable indirect constraints on subsurface fault geometry and regional strain distribution.

References

[1] Bian, S., Tan, X. B., Zuza, A. V., et al., 2025. How Does the Newly-Formed Drainage Divide Migrate after a River Capture Event? Earth and Planetary Science Letters, 651: 119165. https://doi.org/10.1016/j.epsl.2024.119165

[2] Farr, T. G., Kobrick, M., 2000. Shuttle Radar Topography Mission Produces a Wealth of Data. Eos, Transactions American Geophysical Union, 81(48): 583–585. https://doi.org/10.1029/EO081i048p00583

[3] Gallen, S. F., Wegmann, K. W., 2017. River Profile Response to Normal Fault Growth and Linkage: an Example from the Hellenic Forearc of South-Central Crete, Greece. Earth Surface Dynamics, 5(1): 161–186. https://doi.org/10.5194/esurf-5-161-2017

[4] Howard, A. D., Kerby, G., 1983. Channel Changes in Badlands. Geological Society of America Bulletin, 94(6): 739–752. https://doi.org/10.1130/0016-7606(1983)94<739:CCIB>2.0.CO;2

[5] Howard, A. D., 1994. A Detachment-Limited Model of Drainage Basin Evolution. Water Resources Research, 30(7): 2261–2285. https://doi.org/10.1029/94WR00757

[6] Kirby, E., Whipple, K. X., Tang, W. Q., et al., 2003. Distribution of Active Rock Uplift along the Eastern Margin of the Tibetan Plateau: Inferences from Bedrock Channel Longitudinal Profiles. Journal of Geophysical Research: Solid Earth, 108(B4): 24. https://doi.org/10.1029/2001JB000861

[7] Kirby, E., Whipple, K. X., 2012. Expression of Active Tectonics in Erosional Landscapes. Journal of Structural Geology, 44: 54–75. https://doi.org/10.1016/j.jsg.2012.07.009

[8] Ma, Y., Zheng, D. W., Zhang, H. P., et al., 2021. Plio-Pleistocene Establishment of Irtysh River in Junggar, Northwest China: Implications for Siberian-Arctic River System Evolution and Resulting Climate Impact. Geophysical Research Letters, 48(12): e2021GL093217. https://doi.org/10.1029/2021GL093217

[9] Meyer, B., Tapponnier, P., Bourjot, L., et al., 1998. Crustal Thickening in Gansu-Qinghai, Lithospheric Mantle Subduction, and Oblique, Strike-Slip Controlled Growth of the Tibet Plateau. Geophysical Journal International, 135(1): 1–47. https://doi.org/10.1046/j.1365-246X.1998.00567.x

[10] Pan, B. T., Li, Q., Hu, X. F., et al., 2015. Bedrock Channels Response to Differential Rock Uplift in Eastern Qilian Mountain along the Northeastern Margin of the Tibetan Plateau. Journal of Asian Earth Sciences, 100: 1–19. https://doi.org/10.1016/j.jseaes.2014.12.009

[11] Pavano, F., Pazzaglia, F. J., Catalano, S., 2016. Knickpoints as Geomorphic Markers of Active tectonics: A Case Study from Northeastern Sicily (Southern Italy). Lithosphere, 8(6): 633–648. https://doi.org/10.1130/L577.1

[12] Schwanghart, W., Scherler, D., 2014. Short Communication: TopoToolbox 2 – MATLAB-Based Software for Topographic Analysis and Modeling in Earth Surface Sciences. Earth Surface Dynamics, 2(1): 1–7. https://doi.org/10.5194/esurf-2-1-2014

[13] Shao, Y. X., van der Woerd, J., Liu-Zeng, J., et al., 2023. Shortening Rates and Recurrence of Large Earthquakes from Folded and Uplifted Terraces in the Western Danghe Nan Shan Foreland, North Tibet. Journal of Geophysical Research: Solid Earth, 128(1): e2021JB023736. https://doi.org/10.1029/2021JB023736

[14] Snyder, N. P., Whipple, K. X., Tucker, G. E., et al., 2000. Landscape Response to Tectonic forcing: Digital Elevation Model Analysis of Stream Profiles in the Mendocino Triple Junction Region, Northern California. GSA Bulletin, 112(8): 1250–1263. https://doi.org/10.1130/0016-7606(2000)112<1250:LRTTFD>2.0.CO;2

[15] Tapponnier, P., Xu, Z. Q., Roger, F., et al., 2001. Oblique Stepwise Rise and Growth of the Tibet Plateau. Science, 294(5547): 1671–1677. https://doi.org/10.1126/science.105978

[16] van der Woerd, J., Xu, X. W., Li, H. B., et al., 2001. Rapid Active Thrusting along the Northwestern Range Front of the Tanghe Nan Shan (Western Gansu, China). Journal of Geophysical Research: Solid Earth, 106(B12): 30475–30504. https://doi.org/10.1029/2001JB000583

[17] Wang, D., Dong, Y. P., Xi, Z. P., et al., 2024. Evaluation of the Relative Tectonic Activity from the Faults in the Gengma-Lancang-Menghai Seismic Belt (Southwestern China). Journal of Earth Science, 35(1): 131–143. https://doi.org/10.1007/s12583-021-1565-1

[18] Wang, J. Y., He, Z. T., 2020. Responses of Stream Geomorphic Indices to Piedmont Fault Activity in the Daqingshan Area of China. Journal of Earth Science, 31(5): 978–987. https://doi.org/10.1007/s12583-020-1321-y

[19] Wang, W., Shao, Y. X., Zhang, J. Y., et al., 2023. Channel Profiles Reveal Fault Activity along the Longmen Shan, Eastern Tibetan Plateau. Remote Sensing, 15(19): 4721. https://doi.org/10.3390/rs15194721

[20] Wang, Y. Z., Zhang, H. P., Zheng, D. W., et al., 2018. River Longitudinal Profiles under Transient State and the Related Tectonic Signals. Quaternary Sciences, 38(1): 220–231 (in Chinese with English Abstract)

[21] Wang, Y. Z., Zhang, H. P., Zheng, D. W., et al., 2017. How a Stationary Knickpoint Is sustained: New Insights into the Formation of the Deep Yarlung Tsangpo Gorge. Geomorphology, 285: 28–43. https://doi.org/10.1016/j.geomorph.2017.02.005

[22] Wang, Y. Z., Zheng, D. W., Zhang, H. P., et al., 2019. The Distribution of Active Rock Uplift in the Interior of the Western Qilian Shan, NE Tibetan Plateau: Inference from Bedrock Channel Profiles. Tectonophysics, 759: 15–29. https://doi.org/10.1016/j.tecto.2019.04.001

[23] Whipple, K. X., Tucker, G. E., 2002. Implications of Sediment-Flux-Dependent River Incision Models for Landscape Evolution. Journal of Geophysical Research: Solid Earth, 107(B2): ETG3-1–ETG3-20. https://doi.org/10.1029/2000JB000044

[24] Whipple, K. X., 2004. Bedrock Rivers and the Geomorphology of Active Orogens. Annual Review of Earth and Planetary Sciences, 32: 151–185. https://doi.org/10.1146/annurev.earth.32.101802.120356

[25] Wobus, C., Whipple, K. X., Kirby, E., et al., 2006. Tectonics from Topography: Procedures, Promise, and Pitfalls. Special Paper of the Geological Society of America, 398: 55–74. https://doi.org/10.1130/2006.2398(04)

[26] Wobus, C. W., Hodges, K. V., Whipple, K. X., 2003. Has Focused Denudation Sustained Active Thrusting at the Himalayan Topographic Front? Geology, 31(10): 861–864. https://doi.org/10.1130/G19730.1

[27] Xu, Q., Hetzel, R., Hampel, A., et al., 2021. Slip Rate of the Danghe Nan Shan Thrust Fault from ¹⁰Be Exposure Dating of Folded River Terraces: Implications for the Strain Distribution in Northern Tibet. Tectonics, 40(4): e2020TC006584. https://doi.org/10.1029/2020TC006584

[28] Yang, C. T., Simoes, F. J., 1998. Simulation and Prediction of River Morphologic Changes Using GSTARS 2.0. In: Proceedings of the 3rd International Conference on Hydro-Science and -Engineering, Aug. 31-Sep. 3, 1998, Cottbus/Berlin. 1–8. http://www.sjrdotmdl.org/concept_model/phys-chem_model/documents/300001732.pdf

[29] Zhang, P.-Z., Shen, Z. K., Wang, M., et al., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9): 809–812. https://doi.org/10.1130/g20554.1

[30] Zheng, D. W., Clark, M. K., Zhang, P. Z., et al., 2010. Erosion, Fault Initiation and Topographic Growth of the North Qilian Shan (Northern Tibetan Plateau). Geosphere, 6(6): 937–941. https://doi.org/10.1130/GES00523.1

[31] Zheng, W. J., Zhang, P. Z., He, W. G., et al., 2013. Transformation of Displacement between Strike-Slip and Crustal Shortening in the Northern Margin of the Tibetan Plateau: Evidence from Decadal GPS Measurements and Late Quaternary Slip Rates on Faults. Tectonophysics, 584: 267–280. https://doi.org/10.1016/j.tecto.2012.01.006

[32] Zhou, C., Tan, X. B., Liu, Y. D., et al., 2022. Ongoing Westward Migration of Drainage Divides in Eastern Tibet, Quantified from Topographic Analysis. Geomorphology, 402: 108123. https://doi.org/10.1016/j.geomorph.2022.108123

[33] Zuza, A. V., Wu, C., Reith, R. C., et al., 2018. Tectonic Evolution of the Qilian Shan: An Early Paleozoic Orogen Reactivated in the Cenozoic. GSA Bulletin, 130(5/6): 881–925. https://doi.org/10.1130/B31721.1

Funding

the Second Tibetan Plateau Scientific Expedition and Research Program (STEP)(2019QZKK0901)

the State Key Laboratory of Earthquake Dynamics(LED2023B04)

the National Natural Science Foundation of China(42272242)

the National Natural Science Foundation of China(W2411033)

the National Natural Science Foundation of China(W2521003)

the Science and Technology Plan of Gansu Province(22JR11RA088)

RIGHTS & PERMISSIONS

China University of Geosciences (Wuhan) and Springer-Verlag GmbH Germany, Part of Springer Nature