2.1 Cenozoic tectonics and exhumation history of the Ecuadorian Andes
The Ecuadorian Andes constitute a bivergent orogen with active thrusting at the western flank of the Western Cordillera (Eguez et al., 2003; Jaillard et al., 2004; Jaillard et al., 2005) and in the Subandes in the east (Baby et al., 2013). Currently, transpression dominates this region, which causes the northward extrusion of the North Andean Sliver along the dextral Puna-Pallatanga-Cosanga fault system (e.g., Alvarado et al., 2016).
The Western and Eastern cordilleras are separated by the Interandean Valley (Fig. 2), which is filled with Cenozoic volcanic and sedimentary rocks (e.g., Hungerbühler et al., 2002). The Western Cordillera is characterized by a high-elevation (3500 m), low-relief surface capped by Quaternary volcano-sedimentary deposits and Quaternary volcanoes. The western flank of the Western Cordillera is incised by ~2-km-deep valleys exposing Oligocene and Miocene intrusions (31 to 7 Ma; Schütte et al., 2010) and Cretaceous and Paleogene volcano-sedimentary rocks. None of the existing thermochronological data (e.g., Spikings et al., 2005; Winkler et al., 2005; Fig. 2A) has resolved the most recent exhumation history of the Western Cordillera that was associated with topographic growth and valley incision on its western flank. Thermochronological data from the Western and Eastern cordilleras record cooling phases at ~65-55 and 43-30 Ma that were associated with Cenozoic accretion events and changes in plate kinematics that led to exhumation (e.g., Spikings et al., 2001). Thermochronological data from the Eastern Cordillera also record several exhumation phases from 15 Ma to the present that have been linked to the onset of ridge subduction and the subduction of a bathymetric high along the subducting ridge (Spikings et al., 2000; 2001; 2004; 2010).