Basin evolution in response to flat subduction in the Altiplano

This contribution assesses models for basin formation in the Altiplano. New magnetostratigraphy, palynology, and 40Ar/39Ar and U-Pb geochronology from the central Corque Syncline demonstrate that the 7.4 km-thick section was deposited between 36.7 and 18.7 Ma. The base of the section post-dates exhumation in both the Western and Eastern cordilleras, precluding deposition in a classic retroarc foreland basin setting. Rotated paleomagnetic vectors indicate counterclockwise rotation of 0.8°/Myr since the early Oligocene. Detrital zircon provenance data confirm previous interpretations of Eocene–early Oligocene derivation from the Western Cordillera and a subsequent switch to an Eastern Cordilleran source. Flexural modeling indicates that loads consistent with paleoelevation estimates cannot account for all subsidence. Rather, the timing and magnitude of subsidence is consistent with Eocene emplacement and Oligocene–early Miocene resteepening of a flat slab. Integration of the magmatic, basin, and deformation history provides a coherent model of the effects of flat subduction on the overriding plate. In this model flat subduction controlled basin formation in the upper plate, with subsidence enhanced in front of the zone of flat subduction but reduced over the crest of the flat slab. We conclude that the Altiplano was conditioned for plateau formation by Eocene–Oligocene flat subduction. Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts Supplementary material:https://doi.org/10.6084/m9.figshare.c.5664345