Rapid late Miocene rise of the Bolivian Altiplano: Evidence for removal of mantle lithosphere

The oxygen isotopic compositions of carbonates deposited in the northern Altiplano demonstrate a rapid change in late Miocene time, which we attribute to an increase in elevation. Rainfall samples over an elevation transect adjacent to the Altiplano of northern Bolivia display a systematic decrease in mean annual δ¹⁸O values and define a local δ¹⁸O vs. altitude gradient [R. Gonfiantini, M.-A. Roche, J.-C. Olivry, J.-C. Fontes, G.M. Zuppi, The altitude effect on the isotopic composition of tropical rains, Chem. Geol. 181 (2001) 147-167.], which we apply to paleo-meteoric water values determined from carbonates. Age constraints from magnetostragraphy and paleoelevation estimates suggest surface uplift of ∼2.5 to 3.5 km occurred between ∼10.3 Ma and 6.8 ± 0.4 Ma, when the Altiplano rose to its current elevation. Only the removal of dense eclogitic lower crust and mantle lithosphere can generate a change of this magnitude and rapidity. This change coincides with an ∼30% decrease in the rate of convergence between the South America and Nazca plates and the propagation of deformation into the eastern Subandean zone, which we infer to have resulted from the increase in the force per unit length applied by the elevated Andean plateau to the surrounding lowlands.