THE EVOLUTION OF THE ALTIPLANO-PUNA PLATEAU OF THE CENTRAL ANDES

The enigma of continental plateaus formed in the absence of continenta l collision is embodied by the Altiplano-Puna, which stretches for 180 0 km along the Central Andes and attains a width of 350-400 km. The pl ateau correlates spatially and temporally with Andean are magmatism, b ut it was uplifted primarily because of crustal thickening produced by horizontal shortening of a thermally softened lithosphere. Nonetheles s, known shortening at the surface accounts for only 70-80% of the obs erved crustal thickening, suggesting that magmatic addition and other processes such as lithospheric thinning, upper mantle hydration, or te ctonic underplating may contribute significantly to thickening. Uplift in the region of the Altiplano began around 25 Ma, coincident with in creased convergence rate and inferred shallowing of subduction; uplift in the Puna commenced 5-10 million years later.