Millennial-scale denudation rates in the Himalaya of Far Western Nepal

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 catchmentaveraged 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±0.01mmyr-1) to 8737±2908 t km-2 yr-1 (3.3±1.1mmyr-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.