Thermal and kinematic modeling of bedrock and detrital cooling ages in the central Himalaya

We introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens. Along a Trans‐Himalayan transect in central Nepal, we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern Himalayan topography. The model assumes a thermal steady state and utilizes a simple ramp‐and‐flat‐style decollement, representing the Main Himalayan Thrust. The model also assumes a topographic steady state, such that overthrusting is balanced by erosion to maintain a constant topographic profile. Erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface. To predict the detrital cooling‐age signal, we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite. Predicted cooling‐age distributions are compared with detrital 40 Ar/ 39 Ar muscovite data to assess varying tectonic and erosion scenarios. Such cooling‐age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate. The best fit model assigns 4–6 km Myr −1 of overthrusting (equivalent to as much as 1.5–2 km Myr −1 of vertical erosion) to the Asian plate. Although a trade‐off exists between ramp geometry along the decollement and the best fit rate, only a narrow range of ramp dips, decollement depths, and erosionally compensated overthrusting rates are compatible with the observed detrital ages.