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).