Stepwise Widening of the Central Andes—The Role of the Lower Crust

The outward growth of many orogens occurs through pulsed migration the strain front. During Cenozoic shortening central Andes, front abruptly migrated ∼400 km eastward across Altiplano, isolating plateau interior from major deformation. In contrast to traditional critical wedge model that focuses on shallow crust deformation, our lithosphere-scale numerical models show ductile lower plays a key role in dynamics orogen. As orogen grows upward, flows and causes stepwise expansion landward-migrating step length strain-front increases with decreasing crustal strength. Topographically, weaker promotes formation smooth underthrusting stronger foreland lithosphere. Our results indicate seemly unrelated physiography, deep-lithosphere structure, plateau-wide Altiplano may all be result weak crust.