Abstract
Abstract. The Himalayas stretch ∼3000 km along the Indo-Eurasian plate boundary. Along-strike variations in the fault geometry of the Main Himalayan Thrust (MHT) have given rise to significant variations in the topographic steepness, exhumation rate, and orographic precipitation along the Himalayan front. Over the past 2 decades, the rates and patterns of Himalayan denudation have been documented through numerous cosmogenic nuclide measurements in central and eastern Nepal, Bhutan, and northern India. To date, however, few denudation rates have been measured in Far Western Nepal, a ∼300 km wide region near the center of the Himalayan arc, which presents a significant gap in our understanding of Himalayan denudation. Here we report new catchment-averaged millennial-scale denudation rates inferred from cosmogenic 10Be in fluvial quartz at seven sites in Far Western Nepal. The inferred denudation rates range from 385±31 t km−2 yr−1 (0.15±0.01 mm yr−1) to 8737±2908 t km−2 yr−1 (3.3±1.1 mm yr−1) and, in combination with our analyses of channel topography, are broadly consistent with previously published relationships between catchment-averaged denudation rates and normalized channel steepness across the Himalaya. These data show that the denudation rate patterns in Far Western Nepal are consistent with those observed in central and eastern Nepal. The denudation rate estimates from Far Western Nepal show a weak correlation with catchment-averaged specific stream power, consistent with a Himalaya-wide compilation of previously published stream power values. Together, these observations are consistent with a dependence of denudation rate on both tectonic and climatic forcings, and they represent a first step toward filling an important gap in denudation rate measurements in Far Western Nepal.
Highlights
The denudation of tectonically active mountain belts is controlled by feedbacks between tectonics, climate, and topography (e.g., Willett, 1999; Hilley and Strecker, 2004; Whipple and Meade, 2006; Roe and Brandon, 2011)
In Earth’s largest mountain belt, the Himalaya, some studies suggest that denudation is strongly controlled by climate (Clift et al, 2008; Gabet et al, 2008; Hirschmiller et al, 2014; Hodges et al, 2004; Huntington et al, 2006; Olen et al, 2015; Thiede et al, 2004; Vannay et al, 2004; Wobus et al, 2003), while others suggest it is dominantly controlled by tectonic forcings (Burbank et al, 2003; Godard et al, 2014; Scherler et al, 2014; Olen et al, 2015), and yet others suggest that the relative strength of climatic and tectonic controls vary along strike with climate and crustal structure (Harvey et al, 2015; Olen et al, 2016; van der Beek et al, 2016)
We report new basin-averaged denudation rate measurements inferred from cosmogenic 10Be in stream sediment in Far Western Nepal to better understand denudation rate patterns in this segment of the Himalaya
Summary
The denudation of tectonically active mountain belts is controlled by feedbacks between tectonics, climate, and topography (e.g., Willett, 1999; Hilley and Strecker, 2004; Whipple and Meade, 2006; Roe and Brandon, 2011). There is, a significant gap in denudation rate measurements in Far Western Nepal, which spans a ∼ 300 km region near the center of the Himalayan arc (Fig. 1). The only millennialscale denudation rates that have been measured in Far Western Nepal are in the Karnali River basin and are based on cosmogenic nuclide measurements in samples collected near the range front (Lupker et al, 2012). Van der Beek et al (2016), for example, noted that many of their thermochronometric sampling sites were only accessible on foot This has hindered efforts to test hypotheses about feedbacks between climate, tectonics, and topography across this portion of the Himalaya
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