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.