Large spatial and temporal variations in Himalayan denudation

Abstract

In the last decade growing interest has emerged in quantifying the spatial and temporal variations in mountain building. Until recently, insufficient data have been available to attempt such a task at the scale of large orogens such as the Himalaya. The Himalaya accommodates ongoing convergence between India and Eurasia and is a focal point for studying orogen evolution and hypothesized interactions between tectonics and climate. Here we integrate 1126 published bedrock mineral cooling ages with a transient 1D Monte-Carlo thermal–kinematic erosion model to quantify the denudation histories along ~2700km of the Himalaya. The model free parameter is a temporally variable denudation rate from 50Ma to present. Thermophysical material properties and boundary conditions were tuned to individual study areas. Monte-Carlo simulations were conducted to identify the range of denudation histories that can reproduce the observed cooling ages. Results indicate large temporal and spatial variations in denudation and these are resolvable across different tectonic units of the Himalaya. More specifically, across >1000km of the southern Greater Himalaya denudation rates were highest (~1.5–3mm/yr) between ~10 and 2Ma and lower (0.5–2.6mm/yr) over the last 2My. These differences are best determined in the NW-Himalaya. In contrast to this, across the ~2500km length of the northern Greater Himalaya denudation rates vary over length scales of ~300–1700km. Slower denudation (<1mm/yr) occurred between 10 and 4Ma followed by a large increase (1.2–2.6mm/yr) in the last ~4Ma. We find that only the southern Greater Himalayan Sequence clearly supports a continuous co-evolution of tectonics, climate and denudation. Results from the higher elevation northern Greater Himalaya suggest either tectonic driven variations in denudation due to a ramp-flat geometry in the main décollement and/or recent glacially enhanced denudation.