The Dadu River in the eastern Tibetan Plateau has the potential to record transient variations of tectonic uplift since the Late Cenozoic. In this study, we extracted bedrock channels of the Dadu River drainage basin from the 30 m ASTER digital elevation model. The longitudinal river profiles were then analyzed, and three generations of knickpoints were recognized via the slope area method. By solving the analytical solution of the linear transient stream power incision model, we determined a Late Cenozoic history of regional tectonic uplift. The results reveal slow pre–middle Miocene uplift rates (<0.1 mm/a) and then increased gradually to 0.33 ± 0.03 mm/a since 12–15 Ma until present. This increase of uplift rate from bedrock channel inversion is consistent with the regional findings of low‐temperature themochronology, emphasizing the potential and significance to utilize channel profiles to infer the tectonic uplift history.

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The Tibetan Plateau (TP), with average elevation of >4,000 m and lateral extent over 2,500,000 km 2 , forms not only the most giant topographical feature in SW China but the highest plateau on the earth (Liu-Zeng et al., 2008). The elevations of the plateau increase through time, as a response to the Cenozoic collision and convergence of the India-Eurasia plates, exerting primary control on large-scale fault system, topographic framework, and regional and global atmospheric circulation (Yin & Harrison, 2000). Thus, the plateau has long been a popular natural laboratory for understanding the feedbacks between continental deformation, landscape evolution, and climate change (Yuan et al., 2013). The long wavelength topography of the plateau remnants changes over a very long wavelength in the SE part, with elevations decreasing gradually from the inner highland of ∼5,000-∼500 m over a horizontal distance of ∼1,500 km (Clark & Royden, 2000; Figure 1). This makes the SE plateau distinctly different from those steep margins between the TP with for example Tarim and Sichuan basins (Clark & Royden, 2000).Since decades, numerous models have been proposed to explain how the SE plateau grows, most of which are focused on the roles of lower-crustal flow and/or upper-crustal shortening (Royden et al., 1997;Tapponnier et al., 2001). The former owed crustal thickening to be driven by a flux of low-viscosity Newtonian fluid through a lower-crustal channel and predicted rapid topographic growth from 10 to 15 Ma to present.

Cenozoic extension of the Qinling range-Weihe Graben system has occurred in response to the uplift and growth of the Tibetan Plateau. Rapid exhumation of the northern Qinling range since the late Miocene is also regarded as resulting from the eastward expansion of the northeast part of Tibet. Tectonic evidence of this in the landscape remains unclear, but the fluvial system can provide a sensitive proxy record of tectonic forcing through space and over time scales of 105–107 a. Here, we present a study of channel profiles in the northern Qinling range, which forms a footwall highland separated from the southern Weihe Graben by active normal faults. We identify a population of knickpoints that separate river profiles with a gentle upstream gradient from steeper downstream reaches. Above the knickpoints, steepness indices increase from the central part towards the west and east, whereas channel steepness shows its highest values in the Huaxian-Huayin section. We observed no systematic changes of channel steepness pattern as a function of rock resistance, drainage area, or channel concavity. Correlation analysis between channel steepness and basin elevation and relief documents the control of tectonic forcing on regional topography. While bearing no relation to geological outcrop boundaries, the knickpoints show a strong correlation between retreat distance, catchment area, and river length. We infer that the knickpoints formed in response to an increase in mountain uplift rates and retreated as a kinematic wave. Under linear slope exponent n, we calibrated channel erodibility K~1.00±0.44×10−6 m0.1/a and derived knickpoint ages of 5.59±1.80 Ma. Combining the ages of onset of active faulting and mountain growth in the NE Tibetan Plateau (8–10 Ma, e.g., Liupan Shan, Jishi Shan, and eastern segments of the Haiyuan and Kunlun faults) and in the southwest Qinling range (9–4 Ma), we conclude that growth of the NE Tibetan Plateau began in the mid-Miocene time and expanded eastwards to the Qinling range-Weihe Graben during the late Miocene and early Pliocene.

Abstract. The long profile of rivers is shaped by the tectonic history that acted on the landscape. Faster uplift produces steeper channel segments, and knickpoints form in response to changes in the tectonic uplift rates. However, when the fluvial incision depends non-linearly on the river slope, as commonly expressed with a slope exponent of n≠1, the links between tectonic uplift rates and channel profile are complicated by channel dynamics that consume and form river segments. These non-linear dynamics hinder formal attempts to associate the form of channel profiles with the tectonic uplift history. Here, we derive an analytic model that explores a subset of the emergent non-linear dynamics relating to consuming channel segments and merging knickpoints. We find a criterion for knickpoint preservation and merging, and we develop a forward analytic model that resolves knickpoints and long profile evolution before and after knickpoint merging. We further develop a linear inverse scheme to infer tectonic uplift history from river profiles when all knickpoints are preserved. Application of the inverse scheme is demonstrated over the main trunks of the Dadu River basin that drains portions of the east Tibetan Plateau. The model infers two significant changes in the relative uplift rate history since the late Miocene that are compatible with low-temperature thermochronology. The analytic derivation and associated models provide a new framework to explore the links between tectonic uplift history and river profile evolution when the erosion rate and local slopes are non-linearly related.