Channel Profile Response to Abrupt Increases in Mountain Uplift Rates: Implications for Late Miocene to Pliocene Acceleration of Intracontinental Extension in the Northern Qinling Range-Weihe Graben, Central China

Abstract

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.

Multi‐Stage Growth in the North Margin of the Qinling Orogen, Central China, Revealed by Both Low‐Temperature Thermochronology and River Profile Inversion

“…These data are mostly from steep catchments with mean slope above 20–25°, causing a low correlation between denudation rates with channel steepness and thus large variations in the calculated K values (Y. Z. Wang et al., 2020). Thus, it would be significant to study the spatial variations in the inversed histories (under a fixed K ), but not to only examine the influences of variable K values on inversed histories.…”

“…Wang et al. (2020b) divided the NQF into seven segments, based on the spatial pattern of channel steepness indices. Here, for each segment, we gathered the river profiles together to infer the temporary variations in the relative uplift rates.…”

“…Since the late Miocene, the normal throw of the NQF caused rapid mountain growth and rock exhumation in the footwall and subsidence and deposition in the adjacent Weihe Graben (Han et al., 2002; Meng, 2017), which has dictated the first‐order feature of the modern topography (Y. Z. Wang et al., 2020). The transverse rivers that originate from the north range are short but steep, which was suggested to contain transient signals of rapid fault throw (Shi et al., 2021; Y.…”

“…The transverse rivers that originate from the north range are short but steep, which was suggested to contain transient signals of rapid fault throw (Shi et al., 2021; Y. Z. Wang et al., 2020). These rivers flow to the Weihe Graben and then to the Yellow river.…”

“…Recently, detailed analysis on the modern landscape and catchment‐wide denudation erosion pattern in the north range has indicated strong dependence of modern topography on the late Cenozoic tectonic forcing (He et al., 2020; Shi et al., 2021; Y. Z. Wang et al., 2020). Questions, however, remain about the early and middle Cenozoic exhumation history in the north Qinling and the underlying geodynamics.…”