Very slow erosion rates and landscape preservation across the southwestern slope of the Ladakh Range, India

摘要

Erosion rates are key to quantifying the timescales over which different topographic and geomorphic domains develop in mountain landscapes. Geomorphic and terrestrial cosmogenic nuclide (TCN) methods were used to determine erosion rates of the arid, tectonically quiescent Ladakh Range, northern India. Five different geomorphic domains are identified and erosion rates are determined for three of the domains using TCN Be-10 concentrations. Along the range divide between 5600 and 5700m above sea level (asl), bedrock tors in the periglacial domain are eroding at 5.0 +/- 0.5 to 13.1 +/- 1.2 meters per million years (m/m.y.)., principally by frost shattering. At lower elevation in the unglaciated domain, erosion rates for tributary catchments vary between 0.8 +/- 0.1 and 2.0 +/- 0.3m/m.y. Bedrock along interfluvial ridge crests between 3900 and 5100m asl that separate these tributary catchments yield erosion rates <0.7 +/- 0.1m/m.y. and the dominant form of bedrock erosion is chemical weathering and grusification. Erosion rates are fastest where glaciers conditioned hillslopes above 5100m asl by over-steepening slopes and glacial debris is being evacuated by the fluvial network. For range divide tors, the long-term duration of the erosion rate is considered to be 40-120 ky. By evaluating measured Be-10 concentrations in tors along a model Be-10 production curve, an average of 24cm is lost instantaneously every 40 ky. Small (<4km(2)) unglaciated tributary catchments and their interfluve bedrock have received very little precipitation since 300ka and the long-term duration of their erosion rates is 300-750 ky and >850 ky, respectively. These results highlight the persistence of very slow erosion in different geomorphic domains across the southwestern slope of the Ladakh Range, which on the scale of the orogen records spatial changes in the locus of deformation and the development of an orogenic rain shadow north of the Greater Himalaya. Copyright (c) 2014 John Wiley & Sons, Ltd.