Tectonic History of the Andes and Sub-Andean Zones: Implications for the Development of the Amazon Drainage Basin

The Andes and the Amazon River have been neighbouring geographical and geological features for at least the past 10 million years. However, the nature of the interactions between them remains unclear. The western margin of South America has been convergent since ~100 Ma, but only during the last 30 million years has there been an adjacent subduction orogen of the extent observed today. Instead, the configuration of the Amazon River evolved from 11 Ma and has remained largely unchanged at least for the past 6 million years. In this chapter we review the available data on the history of deformation, palaeoelevation and exhumation of the northern Central Andes, Northern Andes and adjacent sub-Andean basins in order to compare these data sets with the evolution of the Amazon drainage basin. The available data are far too scarce to propose definitive patterns, but do allow us to pose testable hypotheses on the interaction between the Andes, evolution of sub-Andean zones and the Amazon River. Deformation in the Andes began prior to the establishment of the modern Amazon drainage network and patterns. Although the modern Amazon is very young it appears to be closely related to the development of the Andes. This interrelated history of Amazon River and Andes is inferred from the acceleration in the denudation rates of the Eastern Cordillera, which coincides with the moment that Andean palaeoelevations became significant and began to constitute an orographic barrier and trap to moisture-bearing winds. However, this acceleration could also be related to the development of a denser drainage network in the Andean headwaters. All these factors, together with the presence of orogenperpendicular basement highs, may have prompted a greater and more focused water and sediment influx towards the Amazon lowlands, producing a river directed to its present-day delta plains in the Atlantic Ocean. As previously proposed, the synchronous development of intense deformation in the sub-Andean basins appears to be related to changing mechanical conditions in the foreland sedimentary wedge that prompted deformation to migrate to the lowlands.