Controls on the shape and kinematics of the Central Andean plateau flanks: Insights from numerical modeling T. Vietor * , O. Oncken GeoForschungsZentrum Potsdam, Germany Received 11 March 2005; received in revised form 31 May 2005; accepted 3 June 2005 Available online 11 July 2005 Editor: S. King Abstract 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. This study uses 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 pro-flank. If the mass flux is directed outward, thrusting towards the foreland generates a steep-slope, large-taper retro-flank. The mass flux itself is controlled by the shear strength distribution at the base of the crust. The two general types of orogenic flanks from three combinations that can be used to classify the evolution of plateau orogens in general. Application of this concept to the Andes allows to decode the lower crustal shear strength distribution during the formation of the Altiplano–Puna plateau. Their western slope is a retro-flank localized by the underlying oceanic subduction zone. On the eastern side a pro-flank accretes foreland crust, which is progressively decoupled from the moving mantle below. D 2005 Elsevier B.V. All rights reserved. Keywords: numerical models; plateaus; kinematics; Andes 1. Introduction Collisional orogens inherit the asymmetric kine- matic properties of the preceding subduction zone and evolve into asymmetric bivergent orogens [1]. The two flanks strongly differ in their kinematic and morphological evolution. The second largest orogen on earth, the Central Andean Altiplano–Puna plateau is the result of tectonic shortening in the vicinity of the convergent Peru–Chile margin but no continental collision is involved in this process and the orogen is exclusively built from upper-plate material [2–4]. However, similar to collisional orogens, the two wedge-shaped flanks that bound the central plateau region sharply differ in morphology and kinematic evolution (Fig. 1). While the western flank is steep and finite shortening is limited to a few kilometers 0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2005.06.004 * Corresponding author. E-mail address: tvietor@gfz-potsdam.de (T. Vietor). Earth and Planetary Science Letters 236 (2005) 814 – 827 www.elsevier.com/locate/epsl