THE TECTONIC EVOLUTION OF THE CENTRAL ANDEAN PLATEAU AND GEODYNAMIC IMPLICATIONS FOR THE GROWTH OF PLATEAUS (Invited Presentation)

Current end-member models for the geodynamic evolution of orogenic plateaus predict (1) slow-and-steady rise during crustal shortening and ablative subduction (i.e., continuous removal) of the lower lithosphere, or (2) rapid surface uplift following shortening, associated with punctuated removal of dense lower lithosphere and/or lower crustal flow. We will review results from a recent multidisciplinary study of the modern lithospheric structure, geologic evolution, and surface uplift history of the Central Andean Plateau to evaluate the geodynamic processes that have formed the Plateau. Comparison of the timing, magnitude, and distribution of shortening and surface uplift, in combination with other geologic evidence, highlights the pulsed nature of plateau growth. We will discuss specific regions and time periods that show evidence for end-member geodynamic processes. In particular, the crustal thickening history of the central Altiplano and Eastern Cordillera indicates that modern crustal thickness is thinner than predicted crustal thicknesses, requiring the loss of crustal material by punctuated removal of dense lower lithosphere and/or crustal flow. Both the latest Oligocene-early Miocene and late Miocene-Pliocene rapid surface uplift events in this region correspond with time periods when crustal thicknesses exceeded the modern thickness. In contrast, the crustal thickening history of the northern Altiplano and Eastern Cordillera predict thinner than modern crustal thickness in this region, requiring crustal flow into this region, likely from the central Eastern Cordillera and Altiplano. The late Miocene-Pliocene rapid surface uplift of the northern Plateau corresponds with the timing of rapid crustal thickening as recorded in trace element ratios in arc magmatism, further implicating crustal flow in generating rapid surface uplift and the modern crustal thickness in this region. Integrative studies of the Central Andean Plateau indicate that gradual crustal thickening and weakening of the lower lithosphere promotes pulsed surface uplift events in plateau regions associated with both convective removal of the lower lithosphere and lower crustal flow.