Late Miocene high and rapid surface uplift and its erosional response in the Andes of central Chile (33°-35°S)

We address the question of the late Cenozoic geomorphological evolution of the central Chile Andes (33 degrees-35 degrees S), using uplift markers, river incision, previous and new ages of volcanic bodies, and new fission track ages. The uplift markers consist of relicts of high elevated peneplains that evidence > 2 km of regional surface uplift lasting similar to 2 Ma with variable amount along an E-W transect. The eastern Coastal Cordillera was uplifted 1.5-2.1 km at 33-34 degrees S and < 1 km at 35 degrees S, the western Principal Cordillera was uplifted similar to 2 km, and the central eastern Principal Cordillera was uplifted > 2.5 at 33 degrees 45'S and similar to 1.5 km at 34 degrees 30'S. Erosional response to uplift was characterized by the retreat of a sharp knickpoint with celerities between 10 and 40 mm a(-1). Extrapolation using a stream power law shows that uplift began shortly before 4 Ma or at 10.5-4.6 Ma (7.6 Ma central age) depending on the morphostructural units involved. The first alternative implies simultaneous uplift of the continental margin. The second model (the most reliable one) implies that the uplift affected together the eastern Coastal Cordillera and the Principal Cordillera, while the rest of the western fore arc subsided. This regional uplift can be mostly balanced by crustal thickening resulting from coeval shortening related to the out-of-sequence thrusting event in the Principal Cordillera and the uplift of the Frontal Cordillera. Simultaneously, emplacement of the southern edge of the flat slab subduction zone might have partially contributed to this uplift event.