Controls on the Shape and Kinematics Mountain Belts: Insights from Distinct Element Modeling

The flat surface of orogenic plateaus requires a weak detachment at the base of the crust that prevents the formation of large-wavelength topography in the centre of the orogen and decouples the deformation of crust and mantle. We use numerical distinct-element simulations of plateau orogeny to show that the mass flux across the lateral tips of this detachment controls the shape and kinematics of the plateau flanks. If the mass flux is directed towards the plateau, e.g. foreland crust moves into the detached section, it forms a low-slope, small-taper flank. If the mass flux is directed outward, thrusting towards the foreland generates a steep-slope, large-taper flank. The mass flux itself is controlled by the shear strength distribution at the base of the crust. Application of this concept to the Andes gives clear constraints for the lower crustal shear strength during the formation of the Altiplano–Puna plateau. The simple particle model thus enabled us to decipher the first order controls on the evolution of convergent plateau orogens.