The Bolivian Altiplano, in the Central Andes of South America, is part of the second largest high plateau on Earth. It is an elongate region of subdued relief, similar to 1.2 x 10(5) km(2) and similar to 4 km above sea level, bounded by the Eastern Cordillera and volcanic are (Western Cordillera). Here the crust is up to similar to 75 km thick. We describe the Cenozoic geological evolution of this region, using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure. Crustal shortening and magmatic addition and, locally, sedimentation are the main mechanisms of Cenozoic crustal thickening, leading to nearly 4 km of surface uplift since the Paleocene. Addition of mafic melts appears to be a first-order mechanism of Cenozoic crustal growth, contributing similar to 40% of the crustal thickening beneath the volcanic are. Removal of the basal part of the lithosphere may have caused two episodes of widespread are and behind-are mafic volcanism, at similar to 23 Ma and 0 - similar to 5 Ma, contributing to the surface uplift. The Altiplano originated as sedimentary basin, several hundred kilometers wide, between the proto-Western Cordillera and a narrow zone of uplift (proto-Eastern Cordillera) farther east. The latter zone formed by inversion of the center of a wide lacustrine or marine Cretaceous Paleocene basin close to sea-level at similar to 45 Ma. A thickness' of 2-4 km of Paleogene continental clastics accumulated in the proto-Altiplano basin. Subsequently, in the Oligocene, we estimate that this region and the western margin of the Eastern Cordillera were tectonically shortened similar to 22% (similar to 65 km), resulting in similar to 9 km of average crustal thickening. The Altiprano basin was rejuvenated at similar to 25 Ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting Eastern and Western Cordilleras. Between similar to 25 and 5 Ma, folding and thrusting in the western margin of the Eastern Cordillera migrated westward into the center of the Altiplano basin, essentially terminating deposition, except in local subbasins, and accommodating similar to 13% (similar to 30 km) of shortening and an estimated similar to 7 km of average crustal thickening. Subsequently, there has been strike-slip deformation and limited local thrusting (< 5 km of shortening). Geomorphological and geochronological evidence for 1.5-2 km of surface uplift of this region since the Late Miocene suggests similar to 14 km of lower crustal thickening beneath an essentially rigid ''lid'', and can be explained by similar to 100-150 km of underthrusting of the Brazilian shield and adjacent regions beneath the eastern margin of the Central Andes. The present subdued relief in the Altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin.
