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).