2.2 Subduction of the Carnegie Ridge
The aseismic Carnegie Ridge is 200 km wide and rises up to 2 km above the surrounding ocean floor (Fig. 1); it is one of the most prominent bathymetric highs intercepting the South American trench. The oblique subduction of the Carnegie Ridge in Ecuador (Fig. 1) is linked with coastal surface and rock uplift (Pedoja et al., 2006), strike-slip faulting (Fig. 2; e.g., Egbue and Kellogg, 2010; Baize et al., 2015; Alvarado et al., 2016), changes in magmatism, and the extrusion of the North Andean Sliver coeval with the opening of the Gulf of Guayaquil. However, the timing of onset of Carnegie Ridge subduction is controversial. Spikings et al. (2000, 2001, 2004) suggested an early onset of ridge subduction at 15-10 Ma based on the exhumation history of the Eastern Cordillera. Pilger (1984) suggested that the ridge collided at 15 Ma based on a plate-kinematic reconstruction. Using a refined plate-kinematic reconstruction, Daly (1989) suggested a late Miocene (~8 Ma) onset of ridge subduction, which was thought to be in agreement with the timing of arc widening and migration (e.g., Gutscher et al., 1999). Studies based on the timing of submarine canyon incision, marine terrace uplift, and variation in the spatial distribution and chemistry of magmatism have proposed an onset at ~5 Ma (Barberi et al., 1988; Collot et al., 2019; Pedoja et al., 2006; Bourdon et al., 2003). Finally, a Pleistocene onset of ridge subduction was suggested based on plate-kinematic reconstructions (Londsdale and Klitgord, 1978), a shift toward adakitic arc volcanics at 1.5 Ma (Samaniego et al., 2005), coastal uplift and stratigraphy of marine terraces (Cantalamessa and Di Celma, 2004), and accelerated subsidence and sedimentation rates in the Gulf of Guayaquil. The latter process was associated with accelerated escape of the North Andean Sliver and the geometry of shelf depocenters (e.g., Witt et al., 2006; Hernández et al., 2020).