1 Introduction
The topography and morphology of the Andes results from crustal
shortening and thickening associated with the convergence of the oceanic
Nazca Plate and the continental South American Plate as well as
superposed climate-driven surface processes. At the orogen-scale, slab
geometry, inherited heterogeneities, and lithospheric strength exert
first-order controls on deformation, uplift, and magmatic processes, and
thus topography of the upper plate (e.g., Isacks, 1988; Horton and
Fuentes, 2016; Rodriguez Piceda et al., 2022). At a more regional scale,
the presence of bathymetric highs on the downgoing Nazca Plate also
influences the tectono-magmatic and topographic evolution the overriding
plate (e.g., Barberi et al., 1988; Espurt et al., 2007; Wipf et al.,
2008; Georgieva et al., 2016). Several field studies relate Quaternary
coastal uplift, documented by uplifted marine terraces, to the
subduction of bathymetric highs such as sea mounts or aseismic ridges
(e.g., Macharé and Ortlieb, 1992; Gardner et al., 1992; Hsu, 1992;
Pedoja et al., 2006; Saillard et al., 2011; Freisleben et al., 2021). On
larger spatial scales, long-wavelength uplift of the Amazonian foreland
is thought to reflect basal shear and thickening of the lower crust
associated with the subduction of the Nazca Ridge underneath the Central
Andes (e.g., Espurt et al., 2010; Bishop et al., 2018). Modeling studies
suggest that subduction of bathymetric highs enhances upper-plate
deformation and promotes regional uplift that propagates away from the
trench when the subduction of a ridge initiates (e.g., Dominguez et al.,
2000; Gerya et al., 2009; Martinod et al., 2013). While the influence of
aseismic ridge subduction in the topographically low forearc and
foreland regions is reasonably well documented, the influence of ridge
subduction on the high-elevation regions of the northern Andes has
remained uncertain. Some authors suggest that the subduction of the
Nazca Ridge and subsequent slab flattening triggered regional uplift in
the Western Cordillera and the Subandes of northern Peru (e.g.,
Margirier et al., 2015; Bishop et al., 2018), but the relative
importance of ridge subduction versus the change in slab geometry is
unknown. Other studies relate uplift and exhumation of the Eastern
Cordillera in Ecuador and Colombia to ridge subduction (Spikings et al.,
2001, 2010; Spikings and Simpson, 2014); however, owing to shortening
phases unrelated to ridge subduction in the eastern side of the Andes
(e.g., Mégard, 1984; Sébrier et al., 1988), the link between exhumation
in this area and ridge subduction is not straightforward.
The oblique subduction of the aseismic Carnegie Ridge in Ecuador (Fig.
1) has strongly impacted the geological evolution of the northern Andes
by promoting strike-slip faulting and the northward motion of the North
Andean Sliver, reactivating inherited tectonic structures (e.g., Egbue
and Kellog, 2010; Schütt and Whipp, 2020), and driving changes in
magmatism (e.g., Barberi et al., 1988; Bourdon et al., 2003; Chiaradia
et al., 2020). Despite its importance for the evolution of the northern
Andes, neither the timing of ridge subduction nor its potential impact
on uplift and exhumation are well constrained. To unravel these
relationships, we present new geochronological and thermochronological
data from the previously sparsely dated Western Cordillera integrated
with structural information (e.g., Daly, 1989; Eguez et al., 2003),
geochemistry (e.g., Bourdon et al., 2003; George et al., 2020), and
existing thermochronological data (Spikings et al., 2000, 2001, 2004,
2010; Winkler et al., 2005) to decipher the effect of the onset of ridge
subduction, its timing, and the spatiotemporal patterns of exhumation
above the subducted portions of the Carnegie Ridge.