# Geochronology and geochemistry of Cenozoic magmatism in the north-western Ecuadorian Andes: the role of crustal thickness

J. Iglesias, C. Witt, O. Poma, O. Bruguier, D. Bosch, V. Bosse, M. Zattin, Monique Seyler, M.J. Hernández, F. Chanier, et al.

<figure><img src="image_1.png" /></figure>

► To cite this version:

J. Iglesias, C. Witt, O. Poma, O. Bruguier, D. Bosch, et al. Geochronology and geochemistry of Cenozoic magmatism in the north-western Ecuadorian Andes: the role of crustal thickness. Lithos, 2025, 514-515, pp.108159. 10.1016/j.lithos.2025.108159. hal-05403912

HAL Id: hal-05403912

https://hal.science/hal-05403912v1

Submitted on 8 Dec 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

# Geochronology and geochemistry of Cenozoic magmatism in the north-western Ecuadorian Andes: the role of crustal thickness

<figure><img src="image_4.png" /></figure>

Check for
updates

J. Iglesias<sup>a,b,*</sup>, C. Witt<sup>a</sup>, O. Poma<sup>c</sup>, O. Bruguier<sup>d</sup>, D. Bosch<sup>d</sup>, V. Bosse<sup>e</sup>, M. Zattin<sup>b</sup>, M. Seyler<sup>a</sup>, M.J. Hernández<sup>f</sup>, F. Chanier<sup>a</sup>, O. Averbuch<sup>a</sup>

## ARTICLE INFO

### Keywords:

- Northern Andes

- Magmatism

- Crustal thickness

- Zircon geochemistry

- Pressure sensitive minerals

## ABSTRACT

The Ecuadorian Cenozoic arc developed over autochthonous continental and accreted oceanic terrains. We reconstruct the tectono-magmatic evolution of the northernmost part of this arc using a comprehensive, multi-proxy approach that incorporates whole-rock chemistry and zircon petrochronology, including U-Pb geochronology, trace element geochemistry, and Hf-O isotopic analysis. Our results reveal two distinct magmatic periods at 41–16 Ma and 14–7 Ma. The older period is characterized by tonalitic rocks that exhibit trace element ratios, δ¹⁸O values (6.4–3 ‰), and εHf values (+17 – +12) in zircons that are indicative of highly juvenile sources, while the younger period comprises granodioritic rocks derived from a more enriched reservoir (δ¹⁸O: 8.2–5.8 ‰ and εHf: +13 – +7). The older magmas formed within the amphibole stability field in a moderately thick crust (~ 35 km), while the younger magmas were generated within the garnet stability field in thickened crust (~60 km). The transition from intermediate crustal thickness and juvenile settings to a thicker crust and more enriched settings occurred at around 14 Ma. This shift was most likely related to the arrival of the young (and buoyant) Nazca plate at the South American margin, which would have resulted in the shallowing of the subduction angle, increased compressional stresses, and facilitated melting of an evolved oceanic crust. This study highlights the utility of zircon petrochronology in unraveling the crustal-scale evolution of Cordilleran arcs, providing valuable insights into the dynamic processes that control continental growth and orogeny.

## 1. Introduction

Continental arcs form through subduction-related magmatism interacting with continental lithosphere, as well as accreted oceanic or transitional crustal domains (e.g., Ducea et al., 2015a, 2015b). The chemical composition, spatial extent, and location of these continental arcs are controlled by the relationship between slab-related processes (external) and processes occurring within the arc system (internal), such as crustal tectonic thickening, thrust belt shortening, and subduction-related accretion and erosion processes (Chapman and Ducea, 2019; DeCelles et al., 2009; Ducea et al., 2015b). Continental arcs are primary sites of intermediate magmatism; the composition of these magmas

results from the interaction of multiple reservoirs, including the mantle wedge, the continental crust, and slab fluids associated with magma formation, ascent, and differentiation (Farner and Lee, 2017; Jones et al., 2015; Turner and Langmuir, 2015a).

There is a strong, global correlation between elevation and crustal thickness in non-cratonic regions: over long wavelengths (>10 km) and timescales (>10 ky), higher elevations are primarily controlled by isostasy (Lee et al., 2015). At subduction zones, plate convergence leads to the shortening of the upper crust via thrusting both behind and in front of the arc, and, in some cases, by the underthrusting of the lower continental lithosphere beneath the arc. Both processes result in increased crustal thickness and are typically associated with shallow

<footnote><sup>a</sup> Lille University, Centre National de la Recherche Scientifique (CNRS), Littoral Côte d'Opale University, Institut de Recherche pour le Développement (IRD), UMR 8187, LOG, Laboratoire d'Océanologie et de Géosciences, F 59000 Lille, France</footnote>

<footnote><sup>b</sup> University of Padova, Geosciences Department, Via Giotto 1, 35137 Padova, Italy</footnote>

<footnote><sup>c</sup> Sociedad Minera Liga de Oro S.A. Somilor, Machala, Ecuador</footnote>

<footnote><sup>d</sup> University of Montpellier, CNRS, Géosciences Montpellier, 34095 Montpellier, France</footnote>

<footnote><sup>e</sup> Magmas and Volcanoes Laboratory, Université Clermont Auvergne, CNRS, IRD, OPGC, F-63000 Clermont-Ferrand, France</footnote>

<footnote><sup>f</sup> Departamento de Geología, Escuela Politécnica Nacional, Ladrón de Guevara E11 - 253, Quito, Ecuador</footnote>

<footnote>* Corresponding author at: Lille University, Centre National de la Recherche Scientifique (CNRS), Littoral Côte d'Opale University, Institut de Recherche pour le Développement (IRD), UMR 8187, LOG, Laboratoire d'Océanologie et de Géosciences, F 59000 Lille, France.

E-mail address: jorge.iglesiasflores@univ-lille.fr (J. Iglesias).</footnote>
angle subduction (DeCelles et al., 2009; Ducea et al., 2015b; Horton, 2018). Magmatic underplating is also considered a significant contributor to crustal thickening (Chiaradia, 2009; Garzione et al., 2008; Stirling et al., 2023). Conversely, retreating slab dynamics (i.e., roll-back) induce extensional strain, leading to crustal thinning (e.g., Horton, 2018; Lallemand et al., 2005).

Despite its oceanic nature, the crustal root in Ecuador is notably thick (Jaillard, 2022; Koch et al., 2021), while the average elevation of the Ecuadorian Andes is relatively low compared to southern Peru and Bolivia. Several studies suggest that lithospheric thickness plays a significant role in arc magma composition by controlling the extent of mantle melting (e.g., Chiaradia, 2015; Farner and Lee, 2017; Turner and Langmuir, 2015b). It is now widely accepted that the majority of geochemical diversity in arcs is generated at greater depths, especially near the base of the crust, through melting, assimilation, storage, and homogenization (MASH) processes (Hildreth and Moorbath, 1988). In addition, the extension of magmatic pathways during ascent through the crust (from its segregation and extraction in deep zones), also has a strong effect on differentiation processes, ultimately leading to the formation of more evolved magmas (e.g., Chiaradia, 2021; Farner and Lee, 2017).

Changes in crustal thickness have been studied using several approaches in subduction settings, including 1) whole rock (WR) geochemistry (e.g., Sr/Y; La/Yb; Chiaradia, 2015; Profeta et al., 2015; Sundell et al., 2021) and 2) zircon geochemistry (e.g., Eu/Eu*%; Sm/Yb; Ce/Y; Sundell et al., 2022; Tang et al., 2024). The latter has received increasing attention in recent years, due to the ubiquity, refractory nature, and chemical resistance of zircons. In particular, zircon analysis provides deeper insights than WR into the mechanisms and interaction between the deep crust and the mantle and, potentially, the subsequent ascent of magma through the crust. Both approaches rely on the presence or absence of pressure-sensitive mineral phases (mostly garnet, plagioclase, and amphibole) to infer the magma fractionation depth, which, assuming that fractionation occurs within the crust, provides a minimum crustal thickness.

Zircons preserve the initial ¹⁷⁶Hf/¹⁷⁷Hf isotopic composition of the magmatic reservoir at the time of crystallization (Reiners et al., 2017; Roberts and Spencer, 2015). Furthermore, the isotopic composition of oxygen in zircons can help identify the reservoirs (i.e., crust, mantle, and slab fluids) involved in magma genesis (Bindeman, 2008). Zircons in equilibrium with mantle-derived melts span a narrow range of δ¹⁸O values (5.3 ± 0.6 ‰) (Valley et al., 2005). Higher δ¹⁸O values (> 5.3 ± 0.6 ‰) are indicative of intracrustal melting (Bindeman, 2008; Valley et al., 2005), while lower δ¹⁸O values (< 5.3 ± 0.6 ‰) are indicative of sources of low δ¹⁸O in the mantle or interactions with hydrothermally altered crust (Bindeman, 2008; Monani and Valley, 2001; Valley et al., 2005). Coupling the analysis of radiogenic isotopes (e.g., Hf) with stable isotopes (e.g., O) allows researchers to differentiate between evolved (crustal) and juvenile (mantle-derived) isotopic signatures (e.g., Hawkesworth and Kemp, 2006; Kemp et al., 2007).

Zircon trace element (TE) concentrations, such as U, Th, Hf, Y, Yb, Ce, Eu, Nb, and Ti, as well as their ratios (e.g., U/Yb, Th/Yb, Th/U, Eu/Eu*, LREE/HREE, Yb/Gd), can provide valuable insights into the characteristics of the parent melt, magmatic differentiation processes, mineral fractionation (e.g., plagioclase, amphibole, titanite), crustal thickness, and crystallization temperature (e.g., Bell and Kirkpatrick, 2021; Belousova et al., 2002; Claiborne et al., 2010; Grimes et al., 2007, 2015; Kydonakis et al., 2014; Sundell et al., 2022; Watson and Harrison, 2005). When coupled with U-Pb ages and isotopic signatures (e.g., eHf and δ¹⁸O), the zircon TE record provides a remarkable window into the spatial and temporal variability of magmatic processes and their associated reservoirs. It also serves as an excellent tracer of the tectonic environment in which the arc was emplaced (Attia et al., 2020; Jara et al., 2021; Jones et al., 2015).

The Andes are the largest active subduction system and host one of the most geologically diverse Cenozoic continental arcs in the world. In

central and northern Ecuador (southern Northern Andes), Cenozoic magmatism was emplaced in oceanic (transitional) crust associated with an oceanic plateau and island arc system that accreted against the continental margin about 75–70 Ma ago (George et al., 2021; Jaillard, 2022; Vallejo et al., 2009; Witt et al., 2023). Throughout the Cenozoic, significant intermediate to acidic magmatism developed in these accretionary terrains, establishing geochemical trends indicative of progressive crustal thickening (Chiaradia, 2009; Schütte et al., 2010a). This trend was interrupted by episodic periods of extension and crustal thinning (George et al., 2021; Witt et al., 2023), highlighting the complexity of this arc system. Consequently, the Ecuadorian Andes provide an excellent natural laboratory to test innovative zircon-based geochemical constraints and their links to crustal thickness and, more broadly, compare the characteristics of settings associated with shallow and deep fractionation.

This study focuses on the northernmost section of the Ecuadorian arc, which has the greatest crustal thicknesses (60–65 km; Koch et al., 2021). This study aims to contribute to our understanding of the spatial distribution, petrography, geochronology, chemical evolution, and reservoir characterization of the Santiago (41–31 Ma) and Apuela (23–7 Ma) batholiths (henceforth referred to as SB and AB, respectively), alongside other minor igneous occurrences. Additionally, we evaluate widely used whole-rock crustal thickness markers and test several zircon-based crustal thickness proxies. These data allow us to propose a geodynamic model that explores the mechanisms and rates of orogenic exhumation.

## 2. Geodynamic and geological framework

The Northern Andes (encompassing the Andes of Ecuador, Colombia, and Venezuela) are characterized by the accretion of oceanic lithosphere either during a single Late Cretaceous event (Luzieux et al., 2006; Vallejo et al., 2009) or multiple Late Cretaceous–Eocene accretion events (Jaillard, 2022; Kerr et al., 2002). In addition to differences in timing, these models imply distinct tectonic processes: the single-event model involves westward subduction followed by collision, leading to ophiolitic obduction (i.e., oceanic crust over continental crust). In contrast, the multiple-event model involves successive collisions and subduction jams caused by the arrival of buoyant oceanic plateaus, resulting in the stacking of oceanic crust beneath oceanic crust (see Jaillard, 2022 for details). In Ecuador, the main relics of the accreted crust can be observed along the Western Cordillera (WC), which consists mainly of poorly dated Late Cretaceous oceanic plateau basalts, ultramafic rocks, and other submarine arc sequences (e.g., Hughes and Pilatasig, 2002; Jaillard, 2022; Kerr et al., 2002; Vallejo et al., 2009).

The Ecuadorian Cenozoic arc formed from the eastward subduction of the Farallon and Nazca plates beneath the South American Plate (Fig. 1). The Nazca plate separated from the Farallon plate around 25 Ma and arrived at the Ecuadorian margin around 15 Ma (Meschede and Barckhausen, 2001). The Cenozoic arc is highly segmented and is emplaced within accreted oceanic crust to the north and continental crust to the south of a suture zone defined by the Calacali-Pujili Paltanga Fault Zone (CPPF; Fig. 1). The magmatic arc was emplaced following these accretion event(s) by at least ~60 Ma, as evidenced by the ubiquitous presence of magmatic zircons in the detrital record (George et al., 2021; Witt et al., 2023) and Paleocene intrusions in southern Ecuador (e.g., the San Lucas pluton). However, direct evidence for in situ ~55–45 Ma magmatic activity remains sparse.

Several models for arc evolution have been proposed, including: 1) different isotopic signatures correlated with different oceanic/continental assimilants at depth (Schütte, 2009); 2) a ~ 9 Ma change in reservoir signatures from a MORB-type mantle to adakitic-like signatures as a result of crustal thickening driven by a change in the tectonic setting due to the onset of the subduction of the Carnegie ridge (Chiaradia et al., 2004); 3) a Late Oligocene–Early Miocene arc magmatic flare-up associated with accelerating and less oblique
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** Geodynamic sketch of Ecuador, highlighting the location of the study area (indicated by the square) detailed in Fig. 2. Major intrusive bodies are labeled as follows: S-Santiago, AApuela, D-Domo, T-Telimbela, B-Balzapamba, C-Chaucha, G-Gaby. WC-Western Cordillera, EC-Eastern Cordillera.</figcaption></figure>

subduction (Schütte et al., 2010aa); 4) the development of adakitic-like signatures younger than ~40 Ma in the Macuchi Arc formed by mantle-derived melts that evolved in the lower mid-crustal sections of a thickened, juvenile (accreted) crust (Chiaradia, 2009); 5) slab roll-back and trenchward migration of the arc from continental to accreted crust at ~40 Ma (George et al., 2021), and 6) possible periods of intense magmatism at ~60 and ~43 Ma, with various reservoir signatures related to the melting of both crustal materials and enriched mantle sources as well as a trend towards less enriched magmas between 30 and 10 Ma, most likely related to the emplacement of the arc in the continental crust in southern Ecuador (Witt et al., 2023).

The study area lies within the Naranjal Block (NB; Boland et al., 2000), located near the junction of the forearc and the WC in northern

Ecuador (Fig. 1). The coastal forearc is primarily composed of mostly siliciclastic Cenozoic sedimentary deposits that overlie the accreted plateau oceanic crust (Aizprua et al., 2020; Hernández et al., 2024; Luzieux et al., 2006). The NB is in faulted contact with the Pallatanga block and is crossed by the Mulaute shear zone (Fig. 2; Boland et al., 2000). There are two major intrusive batholiths in the study area (Fig. 2). The SB is primarily composed of tonalites that have been dated between 44 and 35 Ma using K-Ar dating on hornblende and biotites (Boland et al., 2000). In contrast, the AB consists of quartz-diorites and has been dated between 23 and 7 Ma using K-Ar dating on hornblende and biotite as well as U/Pb dating on zircon (Fig. 2; Boland et al., 2000; Schütte et al., 2010a, 2010b; Díaz Castro et al., 2025; Margirier et al., 2023; this work). Both batholiths are hosted within poorly dated
<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Geological map of northwestern Ecuador (refer to Fig. 1 for location), showing sample locations and ages (in Ma) determined in this study. Previously reported ages from Boland et al. (2000), Díaz Castro et al. (2025), Schütte et al. (2010a) and Margirier et al. (2023) are also included. The Mulaute Shear Zone (MSZ) is indicated. Ages are color-coded as follows: orange (41–16 Ma), blue (14–9 Ma), and green (7–9 Ma).</figcaption></figure>

volcanoclastic units of the Rio Cala and sequences of the Macuchi Island arc (Boland et al., 2000). Geochemically, the SB is calc-alkaline metal-uminous while the AB is calcic-metaluminous (Boland et al., 2000). The NB hosts two of the most significant mineral deposit discoveries in Ecuador over the last 20 years: the Eocene Cascabel porphyry Cu-Au and the late Miocene Llurimagua (Junín) porphyry Cu-Mo deposits (Chiaradia et al., 2004; Schütte et al., 2012) are hosted by the SB and the AB, respectively.

## 3. Analytical basis and description of methods

A total of 24 samples were collected from the western part of the AB as well as from intrusive bodies to the east of the SB. Sampling locations are indicated in Fig. 2 and Table 1. These locations were selected for their accessibility and suitability for sampling, and in most cases represent areas of mining interest.

### 3.1. Whole-rock major and trace elements

Whole-rock geochemical analyses were conducted on 23 samples using the lithium metaborate/tetraborate fusion technique. Major

element oxides in the resulting diluted solutions were measured using inductively coupled plasma atomic emission spectrometry (ICP-AES), while trace and rare-earth elements were measured using inductively coupled plasma mass spectrometry (ICP-MS) at the MSALABS laboratory (Langley, Canada). Additional details, including fusion parameters and detection limits are provided in the Supplementary Information. Geochemical data were processed using the R programming language and the Geochemical Data Toolkit (GCDkit) software (Janoušek et al., 2016).

### 3.2. U-Pb dating

Zircon separation was performed at the University of Lille, France following a standard density and magnetic separation procedure (Malusà and Fitzgerald, 2019; and references therein). Zircon grains were handpicked under binocular microscopes, mounted on epoxy resin, and polished to reveal the center of each crystal. The internal structures of each zircon crystal were examined, and appropriate dating zones were selected using cathodoluminescence imaging (see Supplementary Fig. 1 for representative images). In situ laser ablation multi-collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)
<table><caption>**Table 1**
Sample Location and description.</caption><thead><tr><th>Sample</th><th>Latitude</th><th>Longitude</th><th>Lithology</th><th>Age</th><th></th></tr></thead><tbody><tr><td>NB-03</td><td>0.350</td><td>-78.746</td><td>Granodiorite</td><td>37.8 ±<br>0.51 Ma (n<br>= 13)</td><td>206Pb/238<br>U Mean</td></tr><tr><td>NB-04</td><td>0.834</td><td>-78.143</td><td>Quartzodiorite</td><td>11.07 ±<br>0.4 Ma (n<br>= 10)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-05</td><td>0.839</td><td>-78.149</td><td>Dacitic<br>Porphyry</td><td>10.94 ±<br>0.12 Ma (n<br>= 9)</td><td>206Pb/238<br>U Mean</td></tr><tr><td>NB-11</td><td>0.764</td><td>-78.129</td><td>Dacitic<br>Porphyry</td><td>9.1 ± 0.24<br>Ma (n =<br>11)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-13</td><td>0.766</td><td>-78.131</td><td>Diorite</td><td>13.7 ± 0.3<br>Ma (n = 8)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-16</td><td>0.837</td><td>-78.147</td><td>Dacitic<br>Porphyry</td><td>10.97 ±<br>0.19 Ma<br>(n = 10)</td><td>Concordia</td></tr><tr><td>NB-18</td><td>0.302</td><td>-78.772</td><td>Diorite</td><td>31.5 ±<br>0.88 Ma<br>(n = 8)</td><td>206Pb/238<br>U Mean</td></tr><tr><td>NB-19</td><td>0.306</td><td>-78.773</td><td>Dioritic<br>Porphyry</td><td>32.27 ±<br>0.97 Ma<br>(n = 7)</td><td>Concordia</td></tr><tr><td>NB-20</td><td>0.888</td><td>-78.141</td><td>Andesitic<br>Porphyry</td><td>8.11 ±<br>0.28 Ma (n<br>= 12)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-21</td><td>0.889</td><td>-78.143</td><td>Dacitic<br>Porphyry</td><td>7.69 ±<br>0.29 Ma<br>(n = 10)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-22</td><td>0.892</td><td>-78.144</td><td>Quartzodiorite</td><td>7.84 ±<br>0.18 Ma<br>(n = 12)</td><td>Concordia</td></tr><tr><td>NB-24</td><td>0.907</td><td>-78.178</td><td>Andesitic<br>Porphyry</td><td>7.75 ±<br>0.18 Ma<br>(n = 12)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-27</td><td>0.309</td><td>-78.772</td><td>Diorite</td><td>0.56 Ma<br>(n = 9)</td><td>Concordia</td></tr><tr><td>NB-28</td><td>0.310</td><td>-78.773</td><td>Dioritic<br>Porphyry</td><td>32.12 ±<br>0.75 Ma<br>(n = 8)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-29</td><td>0.310</td><td>-78.773</td><td>Granodiorite</td><td>32.45 ±<br>0.69 Ma<br>(n = 10)</td><td>Concordia</td></tr><tr><td>NB-30</td><td>0.328</td><td>-78.750</td><td>Granodiorite</td><td>36.57 ±<br>0.39 Ma<br>(n = 12)</td><td>Concordia</td></tr><tr><td>NB-37</td><td>0.869</td><td>-78.198</td><td>Dioritic<br>Porphyry</td><td>31.32 ±<br>0.81 Ma (n<br>= 6)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-41</td><td>0.823</td><td>-78.387</td><td>Granodiorite<br>Hb-</td><td>40.59 ±<br>0.52 Ma<br>(n = 13)</td><td>Lower<br>Intercepts</td></tr><tr><td>NB-57</td><td>0.7791</td><td>-78.3357</td><td>Quartzodiorite<br>Hb-</td><td>38.2 ± 2.1<br>Ma (n = 9)</td><td>Concordia</td></tr><tr><td>NB-60</td><td>0.7804</td><td>-78.3355</td><td>Quartzodiorite<br>Hb-</td><td>38.2 ± 2<br>Ma (n =<br>10)</td><td>Concordia</td></tr><tr><td>NB-63</td><td>0.3280</td><td>-78.7502</td><td>Quartzodiorite</td><td>36.2 ± 1.6<br>Ma (n =<br>10)</td><td>Concordia</td></tr><tr><td>NB-64</td><td>0.2219</td><td>-78.6510</td><td>Granodiorite</td><td>15.89 ±<br>0.86 Ma<br>(n = 10)</td><td>Concordia</td></tr><tr><td>NB-65</td><td>0.2700</td><td>-78.7857</td><td>Quartzodiorite</td><td>39.3 ±<br>0.49 Ma<br>(n = 3)</td><td>206Pb/238<br>U Mean</td></tr><tr><td>NB-66</td><td>0.2715</td><td>-78.7858</td><td>Quartzodiorite</td><td>38.8 ± 0.7<br>Ma (n =<br>10)</td><td>206Pb/238<br>U Mean</td></tr></tbody></table>

was carried out on 20 samples at the Geosciences Laboratory in Montpellier, France (e.g., Bruguier et al., 2017; Genge et al., 2025). Four other samples were analyzed using LA-ICP-MS at the Magmas and Volcans Laboratory in Clermont Ferrand, France. All data acquisition parameters are provided in the Supplementary information. Concordia diagrams were generated using Isoplot R (Vermeesch, 2018). All diagrams are presented in Supplementary Fig. 2.

### 3.3. εHf and δ¹⁸O systematics

In situ Lu-Hf isotope analyses were performed at the Geosciences Montpellier Laboratory, University of Montpellier-France (AETE-ISO regional facility of the OSU OREME) using a Thermo Finnigan Neptune+ multi-collector-inductively coupled mass spectrometer (MC-ICP-MS) coupled with a Photon-Machine Analyte G2 excimer laser. To ensure data quality and reproducibility, the following reference materials were analyzed at the start of the session and after approximately every 15 samples: 91500 (¹⁷⁶Hf/¹⁷⁷Hf = 0.282315; Blichert-Toft, 2008); Plesovice (¹⁷⁶Hf/¹⁷⁷Hf = 0.282482; Sláma et al., 2008); GJ-1 (¹⁷⁶Hf/¹⁷⁷Hf = 0.282000; Morel et al., 2008). Zircon initial εHf values and ¹⁷⁶Hf/¹⁷⁷Hf ratios were calculated using the ¹⁷⁶Lu decay constant of 1.87 × 10⁻¹¹ yr⁻¹ (Söderlund et al., 2004), ¹⁷⁶Hf/¹⁷⁷Hf<sub>CHUR</sub> = 0.282785, and ¹⁷⁶Lu/¹⁷⁷Hf<sub>CHUR</sub> = 0.0336 parameters from Bouvier et al. (2008). Additional technical information can be found in the Supplementary Information.

Oxygen isotope analyses were performed at the Centre de Recherches Pétrographiques et Géochimiques (CRPG), Université de Lorraine, Nancy, France. Analyses were conducted with a Cameca IMS1270 in FC/ FC detection mode using a Cs⁺ primary ion beam with a 2.5 nA intensity and 10 kV acceleration. The instrument was calibrated for instrumental mass fractionation using the 91,500-zircon reference material, which exhibits raw δ¹⁸O values ranging from 7.08 ‰ to 7.34 ‰ (SMOW).

### 3.4. Trace-elements in Zircon

Zircon trace element concentrations were determined by LA-ICP-MS at Geosciences Montpellier Laboratory, University of Montpellier, France. The measurement parameters were a laser spot diameter of 30 µm, a repetition rate of 4 Hz, and a fluence of 6.8 J/cm². The spots were placed as close as possible to the sites where U-Pb dating had already been conducted to obtain readings that were in good agreement with the obtained U-Pb ages and trace element measurements. NIST 612 synthetic glass and the G91500 zircon standard were used as reference materials, while element concentrations were normalized to SiO₂ and calculated using Glitter 4.0 software.

## 4. Results

### 4.1. Zircon U-Pb dating

Zircon U-Pb dating was performed on 24 samples, identifying four distinct periods: Eocene (40.6 ± 0.52 to 36.2 ± 1.6 Ma; 8 samples), Oligocene (32.5 ± 0.69 to 31.3 ± 0.81 Ma; 6 samples), early Miocene (15.9 ± 0.86 to 13.6 ± 0.12 Ma; 2 samples), and late Miocene (11.07 ± 0.4 to 7.7 ± 0.29 Ma; 8 samples). No filtering of the highest and lowest concordant dates was applied when calculating the concordia or weighted mean ages. Errors in age calculations, both quantitative and graphical (e.g., error bars, ellipses), are reported at 95 % confidence intervals (2σ).

Concordia ages were determined for samples NB-63, NB-60, NB-57, NB-30, NB-16, and NB-22 and presented on Wetherill diagrams. The weighted mean ages were computed based on ²⁰⁶Pb/²³⁸U dates for samples with discordant analyses, which included NB-66, NB-65, NB-64, NB-29, NB-27, NB-5, and NB-3, as well as those with lower intercept ages, which included NB-41, NB-37, NB-28, NB-24, NB-21, NB-20, NB-13, NB-11, and NB-4. These results are presented on both concordia
and inverse concordia diagrams, allowing for the interpretation of discordance and age distribution across the sample set. Complete zircon U-Pb data are presented in Table 2 and Table 2.1 in the Supplementary Data. Representative analyses for each period are shown in Fig. 3. Remarkably, only one sub-concordant inherited zircon at 604 Ma was observed during U-Pb dating in a total of 253 analyzed grains (Table 2; Supplementary Data).

## 4.2. Petrographic characteristics and whole-rock major and trace element concentrations

A total of 21 samples were analyzed for major and trace elements, while an additional 2 samples were analyzed exclusively for trace elements. The full results are presented in Table 3 in the Supplementary Data. The sample set is primarily composed of tonalitic and granodioritic rocks (Fig. 4A). Tonalites dominate the 41–16 Ma and 14–9 Ma intervals, while the younger samples were mostly comprised of granodiorites (Fig. 4A). The tonalites and granodiorites exhibited relatively homogeneous, medium-grained, hypidiomorphic textures

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Representative zircon concordia and inverse concordia diagrams showing the $^{206}$Pb/$^{238}$U dates of the analyzed zircons, with 2σ (two-sigma) error margins. Weighted mean age plots for the $^{206}$Pb/$^{238}$U dates are also included.</figcaption></figure>
(Supplementary Fig. 3A). A few samples display porphyritic textures, characterized by phenocrysts embedded in a fine-grained matrix. The major mineral phases in all rock types were quartz (20–40 %), plagioclase (oligoclase–andesine; 60–40 %) and magnesio-hornblende; biotite (up to 10 %) and K-feldspar (up to 5 %) occur sporadically. Magnetite, titanite, epidote, fluorapatite, and zircon are the main accessory minerals. Amphibole occurs as euhedral, occasionally poikilitic crystals that enclose plagioclase and quartz; in general, the abundance of this mineral decreases as the magmas transitioned from tonalites to granodiorites, forming about 7–10 % in the 41–16 Ma group, 5–8 % in the 14–9 Ma group, (with a few values up to 18 %, usually in association with the biotite; Supplementary Fig. 3), and 9–10 % in the 9–7 Ma group. When present, biotite forms euhedral crystals or is co-crystallized with amphibole (Supplementary Fig. 3). Magnetite, apatite, and zircon are each present in abundances of less than 2 %, either interstitial to other minerals or enclosed in quartz, plagioclase, and amphibole. A few hornblende-rich samples contain up to 2.5 % coarse magnetite crystals that commonly enclose fluorapatite. Titanite (± epidote) occurs along amphibole rims or in association with biotite (Supplementary Fig. 3).

In terms of the major oxides (Supplementary Fig. 4), the chemical compositions of the samples are indicative of calc-alkaline, medium-K rocks. The older rocks are andesitic to dacitic (recalculated volatile-free 60.4–73.3 wt% SiO₂) while the two younger groups display more restricted compositions within the dacitic–rhyodacitic fields (65.9–74.4 wt% SiO₂); in addition, the younger samples exhibit higher Na₂O enrichment at similar SiO₂ levels. Plots of major oxides vs. SiO₂ content show that, despite some variations, especially in the Fe₂O₃ and P₂O₅ contents, all samples follow calc-alkaline trends (Supplementary Fig. 4). The variations in the AFM diagram are also typical of a calc-alkaline trend (Fig. 4B).

Chondrite normalized REE values are relatively distinct between the older and younger samples (Fig. 4C). The Eocene-Oligocene rocks are characterized by variable, null to moderate enrichments in LREE relative to HREE (La/N/YbN = 0.96–4.32) as well as flat MREE–HREE sections (Sm/N/YbN = 0.99–1.98). In contrast, the Miocene rocks are more strongly depleted in HREE, with La/N/YbN = 13.30–19.07 for the 14–9 Ma group and La/N/YbN = 7.04–9.68 for the 9–7 Ma group. The MREE–HREE slopes are also more pronounced in the 14–9 Ma rocks (Sm/N/YbN = 5.80–8.37) than in the youngest rocks (Sm/N/YbN = 3.26–3.44). However, the LREE enrichments relative to the MREEs are rather low and relatively similar in all samples (La/N/SmN = 1.01–2.79). A primitive mantle-normalized multi-element diagram (Fig. 4D) shows that, relative to the adjacent REEs, the samples from all three periods are strongly enriched in K and Sr as well as the most incompatible large ion lithophile elements (LILEs), such as Cs, Rb, and Ba. The samples are also depleted in high field strength elements (HFSEs) such as Nb, Ti, and P. These characteristics are typical of arc magmatism. The older and younger rocks can also be distinguished by variations in their La, Yb, and La/Yb and Gd/Yb ratios relative to their SiO₂ contents (Fig. 4E, F, G, H). Although these ratios remain relatively constant during differentiation for the 41–16 Ma rocks, they progressively decrease by a factor of ~4 with decreasing SiO₂ for the younger rocks. Sr/Y ratios for the older rocks vary between 8 and 44, with no correlation with the ages or the SiO₂ content (Fig. 5). In contrast, Sr/Y ratios range between ~80 and 135 for the 14–9 Ma interval, and between 49 and 78 for the youngest rocks. Similar patterns are observed in the (La/Yb)N ratios, with values between 13 and 20 for the 14–9 Ma interval and between ~7–10 for the youngest rocks (Fig. 5).

### 4.3. εHf and δ¹⁸O in zircon

The εHf(t) values (Fig. 6 and Table 4; Supplementary Data) are indicative of a consistent trend of enrichment across all analyzed periods. In the 41–31 Ma interval, εHf(t) values range from +16.9 to +13.2. In contrast, εHf(t) values show a general decreasing trend in the Miocene, ranging from +13 to +7.4, interrupted by higher values around 12 Ma.

The δ¹⁸O values (Table 5; Supplementary Data) also exhibit an increasing supracontinental signature over time, from sub-mantelic values in the Eocene, transitioning to mantle-like values in the Oligocene, followed by values that plot above the mantle field in the Miocene.

### 4.4. Trace elements in zircon

All the analyzed zircons fall within the continental domain proposed by Grimes et al. (2007), with a marked increase in U/Yb ratios with increasing melt fractionation (Fig. 7A). The Th/U ratio serves as an indicator of zircon origin, with values <0.1 suggesting a metamorphic source and values >0.1 pointing to an igneous origin—either felsic (0.1–0.7) or mafic (>1.5) (Kirkland et al., 2015; and references therein). Th/U ratios ranging between 0.1 and 0.7, confirm an igneous origin with a felsic composition. The Th/U values cluster around ~0.5 in the Eocene-Oligocene and decrease to ~0.2 during the Miocene (Fig. 7B). REE patterns show the enrichment of HREE and the depletion of LREE, as well as negative Eu and positive Ce anomalies; these are all characteristic of igneous zircons (Supplementary Fig. 5). A slightly greater HREE depletion is observed in the Late Miocene compared to older samples.

The Eu/Eu* ratio (Fig. 8) exhibits two distinct increasing trends, rising from approximately 0.3 to 0.7 over time. The LREE/HREE ratio exhibits a sustained increase between 41 and 7 Ma, while the U/Yb ratio also shows a marked positive (enrichment) trend, with an older cluster (41–31 Ma) exhibiting a narrower range of values below 0.5 and a younger second cluster (16–8 Ma) exhibiting a broader range of values between 0.5 and 2.5. Furthermore, Ti-in-zircon temperatures (proposed as a thermometer by Watson and Harrison (2005) assuming an αTiO₂ > 0.5), show a slight decrease of crystallization temperatures from 650 to 800 °C between 41 and 31 Ma to 600–700 °C between 16 and 7 Ma.

The analysis of the trace element ratios (Eu/Eu* vs. Hf, Yb/Gd vs. Th/U, Yb/Gd vs. Hf) can provide insights into pressure-sensitive mineral fractionation (Bell and Kirkpatrick, 2021). Indeed, distinct trends emerged across different periods based on this analysis. For example, the lack of correlation between Eu/Eu* and Hf (Fig. 9A) suggests that plagioclase is not a dominant fractionating phase in any period. In contrast, the increase in the Yb/Gd ratio with increasing Hf and decreasing Th/U in the 41–16 Ma period is indicative of amphibole fractionation, a trend that is not observed in the younger periods (Fig. 9B, C). Finally, these ratios also provide insights into magmatic differentiation processes. Unlike the 41–16 Ma period, the 14–7 Ma period is characterized by a significant increase in magmatic water content (H₂O) as well as deeper melting and/or increased interaction with magmas generated at greater depths (Fig. 9D, E). Zircon trace element analyses are presented in Table 6 in the Supplementary Data.

## 5. Discussion

### 5.1. New chronologic insights for the Santiago and Apuela Batholiths

The new U-Pb (zircon) dataset presented in this study allows for a redefinition of the spatial distribution of magmatic bodies in the NB. Our study identified zircon U/Pb ages ranging from 40.6 to 38.1 Ma in the region east of the SB; ages ranging from 39.3 to 31.48 (late Paleogene) near the southwestern boundary of the AB, and ages ranging from 37.8 to 36.28 Ma in regions previously mapped as part of the AB (Fig. 2). Although whether these new ages redefine the extent of the SB remains uncertain, they clearly provide new insights into the spatial extent of Eocene magmatism in the NB.

Within the AB, our analysis reveals a single age of 15.63 ± 0.86 Ma, which is consistent with the hornblende K/Ar age of 16.5 Ma reported by Boland et al. (2000). Northeast of the NB, near the Colombian border, we obtained Miocene ages ranging from 13.7 to 7.69 Ma. Like the Eocene magmatism, while it is not clear whether these new ages redefine the extent of the AB, they certainly redefine the spatial extent of Miocene
<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Classification and selected geochemical characteristics for representative granitoids of this study. A) Normative Q'-ANOR diagram of Streckeisen and Le Maitre (1979). Q' = quartz/ (quartz +20 feldspars). 100 ANOR = 100.anorthite/ (orthoclase + anorthite). B) A-F-M plot of Irvine and Baragar (1971) showing the calc-alkaline nature of the studied samples. C) Primitive mantle normalized multi-element patterns. D) Chondrite normalized rare earth element diagram. Normalizing values of the primitive mantle and chondrite are from Sun and McDonough (1989). E) Variations of La vs. SiO2 (wt%). F) Variations of Yb vs. SiO2. G) Variations of La/Yb ratios vs. SiO2 (wt%). H) Variations of Gd/Yb ratios vs. SiO2 (wt%).</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Adakite discrimination diagrams. A) Sr/Y vs. Y, and B) (La/Yb) N vs. Yb N. Rejected data points, represented by empty circles, do not meet the filtering criteria (55–68 % SiO₂, 0–4 % MgO, and 0.05–0.2 % Rb/Sr) established in Profeta et al. (2015) for crustal thickness calculations.</figcaption></figure>

## magmatism in the NB.

The chronological dataset presented here provides a robust framework for the temporal distribution of magmatism in the NB, with two main periods of magmatic activity identified at 41–31 Ma and 16–7 Ma. Whether the gap between these two periods represents a true magmatic gap cannot be determined with the current dataset. Detrital zircons obtained near the NB spanning the ~31–16 Ma interval (e.g., sample NA-12 from Pepper et al., 2016) exhibit highly juvenile εHf(t) values above 13, which is atypical for the central Ecuadorian Andes (Fig. 6; George et al., 2021; Schütte, 2009; Witt et al., 2021). This suggests that these zircons may be sourced from granitoids emplaced in the NB. This evidence, combined with the U-Pb age of 23 Ma for the AB reported by Margirier et al. (2023), would explain the 31–16 Ma gap that has arisen due to a lack of in-situ dating. However, a recent study exploring the evolution of the continental arc in Colombia suggests that ~23 Ma granitoids observed in the southern WC may represent the first products of magmatism after an Oligocene-Miocene magmatic gap, related to highly oblique convergence (Botello et al., 2024 and references therein). Finally, it should be noted that only one inherited zircon was identified across all dated rocks, suggesting a lack of continental crust beneath the NB.

## 5.2. Enrichment trends

The 41–31 Ma magmatic interval is characterized by depleted mantle-like εHf(t) values (Fig. 6). Zircon δ¹⁸O measurements corroborate this observed trend in εHf(t) values. In the 41–16 Ma interval, sub-mantelic δ¹⁸O values, which are commonly linked to hydrothermally altered oceanic basement rocks, transitioned toward mantle-like δ¹⁸O values. In contrast, the 14–7 Ma interval is characterized by εHf(t) values that possessed moderately enriched signatures and δ¹⁸O values that exhibited slightly supracontinental signatures. Consequently, the εHf(t) and δ¹⁸O values, as well as other whole-rock and zircon trace element contents (e.g., Sr/Y, La/Yb_n, LREE/HREE, and U/Yb), present an enrichment trend from 41 to 7 Ma (Figs. 5, 6, and 8) that is strongly suggestive of progressive variations in the magmatic reservoirs.

The SB exhibits a more pronounced yet less widespread juvenile εHf(t) signature compared to rocks north and south of the NB. Specifically, slightly enriched signatures are observed in the Timbiqui Complex (Colombia), while more dispersed signatures are observed in the El Domo deposit (Fig. 6; Vallejo et al., 2016; Barbosa-Espitia et al., 2019). The isotopic signatures of the SB are the most primitive signatures observed in both the in situ and detrital record of the Cenozoic Ecuadorian arc (Pepper et al., 2016; Schütte et al., 2010b; Vallejo et al., 2016;
<figure><img src="image_10.png" /><figcaption>**Fig. 6.** Plots showing: A) εHf(t) vs. crystallization age, and B) δ¹⁸O vs. crystallization age for the studied zircons. Intrusive bodies are labeled as follows: A, Apuela; T, Telimbela; B, Balsapamba; C, Chaucha; G, Gaby.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Fig. 7.** Zircon discrimination diagrams. A) U/Yb vs. Hf, following by Grimes et al. (2007) and B) Th vs. U.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>Fig. 8. Trace elements ratios in zircon.</figcaption></figure>

Witt et al., 2023).

Barbosa-Espitia et al. (2019) proposed that depleted HREE, intermediate Sr/Y, and the absence of Eu anomalies in the intrusive rocks of the Timbiqui Complex in southern Colombia are indicative of a moderately mature arc, formed at mid-to-shallow crustal levels, with the assimilation of both sediment and deep mafic crust. In contrast, from 41 Ma onwards, the SB exhibits more juvenile εHf(t) signatures, with δ¹⁸O values typical of gabbroic reservoirs and whole-rock and zircon trace element contents that are characteristic of very immature magmatism (i. e., poorly evolved mantle-derived magmas). Despite these primitive signatures, the whole-rock and zircon trace elements in the SB suggest that the magmatic differentiation occurred in the amphibole stability field, with mid-crustal thickness estimates of about 35 km (see Section 5.3).

Zircon U/Yb and LREE/HREE ratios also indicate significant evolution of the magmatic reservoirs between 41 and 7 Ma, with the most significant change occurring at ~14 Ma and peak values at 12 Ma (Fig. 8). These trends may reflect source enrichment via crustal assimilation/melt interaction, or HREE depletion due to fractionation or the presence of residual high-pressure minerals (e.g., garnet, amphibole) in the source, or a combination of both processes (see Section 5.3). Notably, these variations correlate with other enrichment trends (e.g., εHf(t), δ¹⁸O) and crustal thickness markers (see Section 5.3). Our dataset suggests a transition to adakite-like magmas, characterized by low Yb and Y contents, high Sr/Y and La/Yb ratios, and low Rb/Sr ratios (see Fig. 5 and Supplementary Fig. 6). This transition occurred at approximately 14 Ma, which is approximately 5 Ma later than previously proposed for central-southern Ecuador (Chiaradia et al., 2004). Furthermore, this ~14 Ma transition is unlikely to be due to the onset of the subduction of the Carnegie ridge as most estimates place its initiation at 6–2 Ma (Hernández et al., 2020; Margirier et al., 2023; Michaud et al., 2009; Witt et al., 2006). The enrichment of the magmatic reservoirs during the late Miocene via the addition of greater amounts of continental crust melts is also unlikely due to minor δ¹⁸O enrichment and the lack of inherited zircons across a total of 253 analyzed grains. The limited δ¹⁸O variation further reflects the low sensitivity of oxygen isotopes to minor crustal input, as the mantle's large oxygen reservoir

tends to buffer these signals. In contrast, a mass balance based on εHf, which is more sensitive to small crustal contributions, showed minimal sediment inputs, consistent with the subtle isotopic shifts observed in this study and with other Andean εHf-δ¹⁸O mixing models (e.g., Jones et al., 2015). Consequently, the most plausible scenario for the enrichment of the magmatic reservoirs involves the subduction of sediments associated with the arrival of the young Nazca plate (see also Section 5.3); this includes those likely resulting from subduction-erosion processes or through the melting of a more enriched oceanic lithosphere compared to the Eocene and Oligocene. The latter mechanism is similar to that proposed by Chiaradia (2009), who proposed that the enrichment of the magmatic reservoirs is the result of the interaction between mantle-derived magmas and the lower or intermediate sections of a thickened juvenile crust.

The majority of markers (e.g., U/Yb, LREE/HREE ratios) suggest a small decrease in enrichment ~9 Ma, indicating a change in magmatic reservoir conditions; however, it is difficult to determine whether this is a sustained depletion of the source or simply a minor drop in a global enrichment trend, as there is a lack of younger data in this area.

### 5.3. Crustal thickness constraints and estimates

Whole-rock Sr/Y and La/Yb ratios have been proposed as barometers of magmatic differentiation in intermediate to felsic rocks (SiO₂ between 55 and 68 %). These ratios are based on the differential partitioning of Sr, Y, La, and Yb in the fractioning mineral phases and melts (e.g., Chiaradia, 2015; Luffi and Ducea, 2022; Profeta et al., 2015). Estimates of magmatic fractionation depths are based on the pressure stability fields of plagioclase and garnet, which are diagnostic of thin and thick crust, respectively. In general, Sr is preferentially incorporated into the solid phase at low pressures (<1 GPa) where it strongly fractionates into plagioclase. However, at higher pressures (>1.2 GPa), where plagioclase is less abundant or even absent, Sr is more likely to partition into the liquid phase. Conversely, Y is incompatible at low pressures but becomes increasingly compatible at higher pressures, preferentially partitioning into garnet (and eventually amphibole). Consequently, a higher Sr/Y ratio may be indicative of higher differentiation pressures (or depths),
<figure><img src="image_13.png" /><figcaption>**Fig. 9.** Zircon Geochemistry showing: A, B, C) fractionation trends of plagioclase and amphibole; and D, E) discrimination diagrams illustrating magmatic differentiation processes.</figcaption></figure>

the presence of garnet at the source (e.g., Alonso-Perez et al., 2009), or alternatively the accumulation of Sr-rich plagioclase in lower crust (Brackman and Schwartz, 2022; Carty et al., 2021). A similar process controls the La/Yb ratio (and, consequently, the LREE/HREE ratio): Yb is more compatible with garnet and amphibole relative to La at higher pressures. Thus, a higher La/Yb ratio is also suggestive of crystallization or differentiation at higher pressures.

However, these barometers require cautious interpretation due to their dependance on tectonic settings and sensitivity to source characteristics, redox states, and magma mixing (Macpherson et al., 2006; Moyen, 2009; Richards and Kerrich, 2007). These complexities can decouple whole-rock compositions from true melt signatures, highlighting the need for complementary proxies such as mineral chemistry. In this study, we address this issue by focusing on zircon geochemistry, which, alongside whole rock data, reveals pronounced HREE fractionation in chondrite-normalized patterns. This strongly suggests that residual or fractionating garnet played a major role in depleting Yb and Y in the parental melts. Furthermore, the samples in this study lack the typical features of plagioclase-rich cumulates, such as high Al₂O₃ contents, positive Eu and Sr anomalies, and high modal plagioclase

abundance. For these reasons, we consider it more likely that the high values of these barometers are related to the presence of garnet.

Amphibole fractionation is favored at higher pressures and higher water contents (Davidson et al., 2007). Accordingly, as depth increases, magmatic differentiation is characterized by enhanced amphibole crystallization, with limited to absent plagioclase fractionation. At even higher pressures, garnet fractionation becomes dominant, which can mask amphibole signatures (Alonso-Perez et al., 2009; Ulmer, 2007).

Quantitative estimates using the method proposed by Sundell et al. (2021) suggest a crustal thickness of approximately 28 km during the 41–31 Ma period (average Sr/Y and La/Yb ratios of ~20 and ~2, respectively). The estimated crustal thicknesses increase around 14 Ma, reaching a maximum of around 60 km at 12 Ma (average Sr/Y ratio of ~95 and La/Yb ratio of ~16). During the 8–7 Ma period, the estimated crustal thicknesses decrease to approximately 50 km (average Sr/Y ~70 and La/Yb ~8), accompanied by a slight depletion of the reservoirs, as reflected in zircon geochemistry (e.g., decreasing U/Yb; see Section 5.2). In general, these estimates are consistent with the current crustal thickness of about 50 km in this part of the WC (Koch et al., 2021).

Additional evidence for crustal thickening at ~14 Ma is provided by
the low zircon LREE/HREE ratio (~0.03; Fig. 8), suggesting crystallization from melts under high-pressure conditions within the garnet stability zone. Other proxies for crustal growth in zircon show varying degrees of agreement, with certain proxies agreeing (e.g., Dy/Yb); roughly agreeing (e.g., Ce/Y), or disagreeing (e.g., Eu/Eu*) with these outcomes. It should be noted that Eu/Eu* ratios are also dependent on other parameters, such as oxidation, oxygen fugacity, and source composition (e.g., Yakymchuk et al., 2023).

Several other whole-rock and zircon geochemical characteristics further support the idea of magmatic evolution occurring within an intermediate to thick crust. Eu/Eu* in zircon does not exhibit a clear relationship with increased fractionation (i.e., Hf) (Fig. 9A), suggesting that magmatic evolution occurred primarily at middle to deep crustal levels, outside the plagioclase stability zone. Claiborne et al. (2010) suggest that the presence of amphibole in the host melt is evidenced by the increase of Yb/Gd in zircon as Hf increases and Th/U decreases; this pattern is particularly prevalent during the 41–16 Ma interval, suggesting that amphibole was a major fractionating phase during this period. Conversely, during the 14–7 Ma period, a relatively constant Yb/ Gd ratio (Fig. 9B, C) suggests that magmatic evolution occurred in zones where amphibole stability was not as dominant as that of garnet. The presence of garnet is further supported by the more significant fractionation of HREE during this period as well as the decreasing WR (La-Gd)/Yb ratios with differentiation (see Fig. 4E, F).

Zircon trace element ratios (Th/Yb vs. Eu/Eu*, U/Yb vs. Eu/Eu*; Bell and Kirkpatrick, 2021; Reimink et al., 2020) suggest that magmas were the result of deep melting of the crust during the 14–7 Ma period; this was accompanied by assimilation- fractional crystallization (AFC) processes and an increase in H₂O content compared to the 41–16 Ma period, as evidenced by the negative correlation between U/Yb and Eu/Eu* and the increase of Th/Yb with the increase of Eu/Eu* (see Fig. 9D, E). These findings are corroborated by Zircon Ti thermometry, which reveal lower crystallization temperatures for the Miocene granitoids, indicative of the evolution of melts under water-saturated conditions (Harrison et al., 2007). This process may have been driven by the consumption of hydrated minerals (e.g., amphibole) or increased interaction with slab fluids, as inferred in other settings (Grove et al., 2012).

5.4. Regional considerations and geodynamic implications

Crustal thickening can result from tectonic shortening, magmatic inflation, or underplating (Lee et al., 2015). Slab angle fluctuations are among the primary factors that control upper-plate strain and magmatism in subduction settings (Horton, 2018; Lallemand et al., 2005). In general terms, slab rollback, and its associated transition to higher subduction angles, leads to extensional upper-plate strain and a trenchward migration of magmatism, while shallowing subduction angles lead to compressional upper-plate strain and the landward migration of magmatism. These slab fluctuations, combined with internal orogenic processes (e.g., tectonic thickening and magmatic underplating), provide effective explanations for the evolution of upper-plate tectonics and magmatism in several Andean settings (Horton, 2018; Jara et al., 2021; Savignano et al., 2016).

Continental arcs are among the highest topographic features on Earth, and highlight the strong relationships between magmatism, crustal thickening, and the resulting topographic response. The thicker crust will generate a topographic response in an attempt to maintain an isostatic equilibrium with the underlying mantle (e.g., Farner and Lee, 2017; Lee et al., 2015). Currently, there are no pre-Quaternary estimates of paleoaltitude for the entire Ecuadorian Andes. However, studies focusing on Cenozoic magmatism have highlighted several periods of elevated crustal thickness. For example, the adakitic signatures of the Eocene Macuchi Arc have been interpreted as evidence of a thickened juvenile crust (Chiaradia, 2009), although ~42 Ma massive sulfide deposits in El domo deposit, located at the western foothills of the WC, are indicative of submarine conditions (Vallejo et al., 2016). This study

presents evidence that suggests: 1) a thickness estimate of about 35 km from 41 to 31 Ma, which corresponds to a paleoaltitude of about 1.5 km based on global relationships (Lee et al., 2015) as well as an oceanic crust density of 2.8 g/cm³ (Aizprua et al., 2020); and 2) a period of crustal thickness increase at 14–12 Ma, up to a mean of 60 km, accompanied by the enrichment of magmatic reservoirs. A crustal thickness of 60 km and a crustal density of 2.8 g/cm³ represent a mean altitude of ~4 km (Lee et al., 2015).

Thermochronological data, including apatite fission track and apatite (U-Th)/He dating, provide evidence of multiple Miocene-Pliocene phases of arc cooling in the WC (Margirier et al., 2023) as well as in moderately deep detrital rocks in the adjacent forearc (Brichau et al., 2021). The first phase reflects post-magmatic thermal relaxation following the emplacement of Miocene intrusions, evidenced by thermochronological data showing slow cooling rates (~15 °C/Myr) and minimal exhumation rates (<0.1 km/Myr) between 20 and 15 Ma. The second phase, which occurred at ~6–5 Ma in the NB (~7–6 Ma in the rest of the WC), at increased exhumation rates of ~0.5 km/Myr. This phase coincided with uplift along the Coastal Cordillera in the forearc as well as the onset of tectonically controlled crustal thickening and exhumation in the WC and is related to the onset of the subduction of the Carnegie Ridge (Margirier et al., 2023). The geochemical suggests that crustal thicknesses began to increase at ~9 Ma in the central parts of the WC (Chiaradia et al., 2004) and ~14 Ma in the NB (this work), at least 3–8 Ma before the arrival of the Carnegie Ridge into the subduction margin (best estimates at 6–5 Ma; see Hernández et al., 2024).

The increase in crustal thickness in the NB could have arisen from two potential mechanisms: 1) Andean compressional stresses associated with either regional overthrusting at mid-low crustal levels and eastward dipping reverse faults, such as those more specifically observed near the Andean piedmont in the WC (Hernández et al., 2024); and 2) magmatic underplating related to the successive build-up of magmatic arcs. Our data reveals that the increase of crustal thickness occurred relatively abruptly around 14–12 Ma: this suggests that compressional tectonic stresses are a more plausible mechanism for crustal thickening compared to long-term magmatic build-up. We also suggest that the crustal thickening in the NB is most likely linked to the arrival of newly formed, buoyant oceanic lithosphere from the Nazca plate beneath the South American margin at ~15–14 Ma (Hey, 1977; Meschede and Barckhausen, 2001). The relatively young and buoyant nature of the oceanic lithosphere would have reduced the subduction angle, leading to increased lithospheric coupling and compressive deformation of the upper plate. This interpretation is further supported by the contemporaneous uplift of the forearc margin (Hernández et al., 2020) and the onset of the first exhumation period in the WC (Margirier et al., 2023).

6. Conclusions

Whole-rock geochemistry, coupled with U-Pb geochronology, trace elements, and radiogenic and stable isotopes in zircon, provides an excellent framework for evaluating the Cenozoic tectono-magmatic evolution of the northernmost part of the Ecuadorian arc (Fig. 10). Magmatic rocks in the NB exhibit a compositional shift from basic tonalitic (41–16 Ma) to intermediate-acidic granodioritic magmas (14–7 Ma).

Both whole rock and zircon geochemistry suggest a greater contribution from enriched (i.e., evolved) reservoirs during the Miocene compared to the Eocene–Oligocene period. This is supported by an isotopic pull-down in $\epsilon$Hf values and $\delta^{18}\text{O}$ values (> 5.3 ‰) consistent with input from supracrustal altered materials during the Miocene.

The increased contribution of evolved materials may be due to the melting of a more evolved oceanic crust as a result of the underthrusting of oceanic plateau fragments or the occurrence of sediment subduction. The predominantly primary origin of zircons suggests that no continental crust was involved in magmatism during the 41–7 Ma interval, indicating that plateau accretion and underplating were the main
<figure><img src="image_14.png" /><figcaption>**Fig. 10.** Cartoons showing the proposed tectono-magmatic model, A) during the emplacement of the Santiago batholith, B) and during the emplacement of the Apuela batholith.</figcaption></figure>

mechanisms driving the crustal evolution of the WC as proposed by Jaillard (2022).

From the Eocene to the early Miocene (41–16 Ma), juvenile mantle signatures in εHf, δ¹⁸O, and zircon trace elements (U/Yb, Eu*/Eu, LREE/HREE) suggest that magmatic differentiation occurred in zones of increased amphibole stability, indicating interaction with an already thickened crust. Towards the late Miocene (11–7 Ma), evolved signatures in εHf and δ¹⁸O, coupled with zircon trace element trends, suggest magmatic evolution in high-pressure differentiation zones within the garnet stability field, indicative of significantly thickened crust. This evolutionary trend reflects fractionation in a thickening crust, with crustal thickness estimates of approximately 35 km at 41–16 Ma, which increased to 60–70 km at 14–9 Ma and 60–50 km at 9–7 Ma.

Our data shows that geochemical enrichment and crustal thickening peaked at around 12 Ma. This timing rules out any direct association between these trends and the subduction of the Carnegie Ridge, the onset of which would have been around 6–5 Ma based on best estimates. Instead, the observed thickening—and potentially the enrichment trend—appear to be related to the arrival of the more buoyant Nazca plate at the South American margin around 15–14 Ma, which would have resulted in a shallower subduction angle and the establishment of a more compressional setting in the northern part of the WC.

A reduction in geochemical enrichment and crustal thickness trends around 9 Ma is evident in all datasets, including whole-rock constraints (e.g., Sr/Y, La/Yb), zircon isotopes (δ¹⁸O, εHf) and zircon TE (U/Yb, LREE/HREE); this likely indicates a change in magmatic reservoir conditions. However, it is difficult to determine whether this represents a sustained depletion of the source or simply a minor drop in a broader enrichment trend, as no younger data are currently available for this area.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.lithos.2025.108159.

### CRediT authorship contribution statement

Hernández Salazar: Resources, Writing – review & editing.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgments

This work was supported by Cornerstone Capital Resources, the Institute National des Sciences de l'Univers (CNRS, France), the VINCI program of the Italian-French University, and the National Polytechnic School (Ecuador) through the PIEX-DG-IRD-23 External Project. Elizabeth Bell and an anonymous reviewer, as well as Associate Editor Greg Shellnutt, are kindly thanked for their detailed comments and criticisms that significantly improved our study.

### References

* Aizprua, C., Witt, C., Brönner, M., Johansen, S.E., Barba, D., Hernandez, M.J., 2020. Forearc Crustal Structure of Ecuador Revealed by Gravity and Aeromagnetic Anomalies and Their Geodynamic Implications. Lithosphere 2020, 2810692. https://doi.org/10.2113/2020/2810692.

* Alonso-Perez, R., Müntener, O., Ulmer, P., 2009. Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids. Contrib. Mineral. Petrol. 157, 541–558. https://doi.org/10.1007/s00410-008-0351-8.

* Attia, S., Cottle, J.M., Paterson, S.R., 2020. Erupted zircon record of continental crust formation during mantle driven arc flare-ups. Geology 48, 446–451. https://doi.org/10.1130/G46991.1.

* Barbosa-Espitia, Á.A., Kamenov, G.D., Foster, D.A., Restrepo-Moreno, S.A., Pardo-Trujillo, A., 2019. Contemporaneous Paleogene arc-magmatism within continental and accreted oceanic arc complexes in the northwestern Andes and Panama. Lithos 348–349, 105185. https://doi.org/10.1016/j.lithos.2019.105185.

* Bell, E.A., Kirkpatrick, H.M., 2021. Effects of crustal assimilation and magma mixing on zircon trace element relationships across the Peninsular Ranges Batholith. Chem. Geol. 586, 120616. https://doi.org/10.1016/j.chemgeo.2021.120616.

* Belousova, E., Griffin, W., O'Reilly, S.Y., Fisher, N., 2002. Igneous zircon: trace element composition as an indicator of source rock type. Contrib. Mineral. Petrol. 143, 602–622. https://doi.org/10.1007/s00410-002-0364-7.

* Bindeman, I., 2008. Oxygen Isotopes in Mantle and Crustal Magmas as Revealed by Single Crystal Analysis. Rev. Mineral. Geochem. 69, 445–478. https://doi.org/10.2138/rmg.2008.69.12.

* Blichert-Toft, J., 2008. The Hf isotopic composition of zircon reference material 91500. Chem. Geol. 253, 252–257. https://doi.org/10.1016/j.chemgeo.2008.05.014.

* Boland, M., Pilatasig, L., Ibadango, E., McCourt, W., Aspden, J., Hughes, R., & Beate, B. (2000). Geology of the Western Cordillera of Ecuador between 0°00' and 1°00'N
(Stalyn Paucar, Ed.,2024). Report Number 10. Geological Information Mapping Programme. BGSCODIGEM/MEM.Boland, M.L., Pilatasig, L.F., Ibadango, F.C., McCourt, W.J., Aspden, J.A., Hughes, R.A., Beate, B., 2000. Geology of the Cordillera Occidental of Ecuador between 0° and 1°N. (No. 10), Proyecto de Desarrollo Minero y Control Ambiental. CODIGEM-BGS, 10, 118 pages.

Botello, G.E., Cardona, A., Siachoque, A., Jaramillo-Ríos, J.S., Zapata, S., Marulanda, U. M., Valencia, V., 2024. Early Miocene magmatism in the Western Cordillera of Colombia: implications for magma source and evolution. International Geology Review 1-26. https://doi.org/10.1080/00206814.2024.2403737.

Bouvier, A., Vervoort, J.D., Patchett, P.J., 2008. The Lu-Hf and Sm-Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth Planet. Sci. Lett. 273, 48-57. https://doi.org/10.1016/j.epsl.2008.06.010.

Brackman, A.J., Schwartz, J.J., 2022. The formation of high-Sr/Y plutons in cordillaran-arc crust by crystal accumulation and melt loss. Geosphere. https://doi.org/10.1130/GES024001.

Brichau, S., Reyes, P., Gautheron, C., Hernández, M.J., Michaud, F., Leisen, M., Vacherat, A., Saillard, M., Proust, J.N., O'Sullivan, P., 2021. First timing constraints on the Ecuadorian Coastal Cordillera exhumation: Geodynamic implications. J. S. Am. Earth Sci. 105, 103007. https://doi.org/10.1016/j.jsames.2020.103007.

Bruguier, O., Bosch, D., Caby, R., Vitale-Brovarone, A., Fernandez, L., Hammor, D., Laouar, R., Oubadi, A., Abdallah, N., Mechati, M., 2017. Age of UHP metamorphism in the Western Mediterranean: Insight from rutile and minute zircon inclusions in a diamond-bearing garnet megacryst (Edough Massif, NE Algeria). Earth Planet. Sci. Lett. 474, 215-225. https://doi.org/10.1016/j.epsl.2017.06.043.

Carty, K., Schwartz, J.J., Wiesenfeld, J., Klepeis, K.A., Stowell, H.H., Tulloch, A.J., Barnes, G.C., 2021. The Generation of Arc Andesites and DACites in the Lower Crust of a Cordillieran Arc, Fiordland, New Zealand. J. Petrol. 62, egab043. https://doi.org/10.1093/petrology/egab043.

Chapman, J.B., Ducea, M.N., 2019. The role of arc migration in Cordillieran orogenic cyclicity. Geology 47, 627-631. https://doi.org/10.1130/G46117.1.

Chiaradia, M., 2009. Adakite-like magmas from fractional crystallization and melting-assimilation of mafic lower crust (Eocene Macuchi arc, Western Cordillera, Ecuador). Geol. Chem. 265, 468-487. https://doi.org/10.1016/j.chemgeol.2009.05.014.

Chiaradia, M., 2015. Crustal thickness control on Sr/Y signatures of recent arc magmas: an Earth scale perspective. Sci. Rep. 5, 8115. https://doi.org/10.1038/srep08115.

Chiaradia, M., 2021. Zinc systematics quantify crustal thickness control on fractionating assemblages of arc magmas. Sci. Rep. 11, 14667. https://doi.org/10.1038/s41598-021-94290-6.

Chiaradia, M., Fontboté, L., Beate, B., 2004. Cenozoic continental arc magmatism and associated mineralization in Ecuador. Mineral. Deposita 39, 204-222. https://doi.org/10.1007/s00126-003-0397-5.

Claiborne, L.L., Miller, C.F., Wooden, J.L., 2010. Trace element composition of igneous zircon: a thermal and compositional record of the accumulation and evolution of a large silicic batholith, Spirit Mountain, Nevada. Contrib. Mineral. Petrol. 160, 511-531. https://doi.org/10.1007/s00410-010-0491-5.

Davidson, J., Turner, S., Handley, H., Mcpherson, C., Dosseto, A., 2007. Amphibole "sponge" in arc crust? Geology 35, 787. https://doi.org/10.1130/G23637A.1.

DeCelles, P.G., Ducea, M.N., Kapp, P., Zandt, G., 2009. Cyclicity in Cordillieran orogenic systems. Nat. Geosci. 2, 251-257. https://doi.org/10.1038/ngeo469.

Díaz Castro, C., Cooke, D.R., Belousov, I., Vaca, S., Garwin, S., Mather, N., Ward, J., Whistler, B., Creaser, R., 2025. The Cascabel Porphyry Cu-Au-Ag District, Northern Ecuador. Economic Geology 120, 335-362. https://doi.org/10.5382/econgeo.5147.

Ducea, M.N., Saleeby, J.B., Bergantz, G., 2015a. The Architecture, Chemistry, and Evolution of Continental Magmatic Arcs. Annu. Rev. Earth Planet. Sci. 43, 299-331. https://doi.org/10.1146/annurev-earth-060614-105049.

Ducea, M.N., Saleeby, J.B., Bergantz, G., 2015b. The Architecture, Chemistry, and Evolution of Continental Magmatic Arcs. Annu. Rev. Earth Planet. Sci. 43, 299-331. https://doi.org/10.1146/annurev-earth-060614-105049.

Farner, M.J., Lee, C.-T.A., 2017. Effects of crustal thickness on magmatic differentiation in subduction zone volcanism: A global study. Earth Planet. Sci. Lett. 470, 96-107. https://doi.org/10.1016/j.epsl.2017.04.025.

Garzione, C.N., Hoke, G.D., Libarkin, J.C., Withers, S., MacFadden, B., Eiler, J., Ghosh, P., Mulch, A., 2008. Rise of the Andes. Science 320, 1304-1307. https://doi.org/10.1126/science.1148615.

Genge, M.C., Witt, C., Zattin, M., Bosch, D., Bruguier, O., Mazzoli, S., 2025. Are long-lasting isotope trends independent from slab dynamics, upper-plate stress regime and crustal thickness? Insights from central Patagonia. Earth Planet. Sci. Lett. 653, 119229. https://doi.org/10.1016/j.epsl.2025.119229.

George, S.W.M., Horton, B.K., Vallejo, C., Jackson, L.J., Gutierrez, E.G., 2021. Did accretion of the Caribbean oceanic plateau drive rapid crustal thickening in the northern Andes? Geology 49, 936-940. https://doi.org/10.1130/G48509.1.

Grimes, C.B., John, B.E., Kelemen, P.B., Mazdab, F.K., Wooden, J.L., Cheadle, M.J., Hanghej, K., Schwartz, J.J., 2007. Trace element chemistry of zircons from oceanic crust: A method for distinguishing detrital zircon provenance. Geology 35, 643. https://doi.org/10.1130/G23603A.1.

Grimes, C.B., Wooden, J.L., Cheadle, M.J., John, B.E., 2015. "Fingerprinting" tectono-magmatic provenance using trace elements in igneous zircon. Contrib. Mineral. Petrol. 170, 46. https://doi.org/10.1007/s00410-015-1199-3.

Grove, T.L., Till, C.B., Krawczynski, M.J., 2012. The Role of H2O in Subduction Zone Magmatism. Annu. Rev. Earth Planet. Sci. 40, 413-439. https://doi.org/10.1146/annurev-earth-042711-105310.

Harrison, T.M., Watson, E.B., Aikman, A.B., 2007. Temperature spectra of zircon crystallization in plutonic rocks. Geology 35, 635. https://doi.org/10.1130/G23505A.1.

Hawkesworth, C.J., Kemp, A.I.S., 2006. Using hafnium and oxygen isotopes in zircons to unravel the record of crustal evolution. Chem. Geol. 226, 144-162. https://doi.org/10.1016/j.chemgeol.2005.09.018.

Hernández, M.J., Michaud, F., Collot, J.-Y., Proust, J.-N., d'Acremont, E., 2020. Evolution of the Ecuador offshore nonaccretionary-type forearc basin and margin segmentation. Tectonophysics 781, 228374. https://doi.org/10.1016/j.tecto.2020.228374.

Hernández, M.J., Michaud, F., Collot, J.-Y., d'Acremont, E., Proust, J.-N., Barba, D., 2024. Evolution of the Manabí forearc basin in Ecuador: From the collision of Caribbean oceanic plateau to the build up of the Andes and Coastal Cordilleras. Tectonophysics 870, 230133. https://doi.org/10.1016/j.tecto.2023.230133.

Hey, R., 1977. Tectonic evolution of the Cocos-Nazca spreading center. Geol. Soc. Am. Bull. 88 (10), 1404-1420.

Hildreth, W., Moor bath, S., 1988. Crustal contributions to arc magmatism in the Andes of Central Chile.

Horton, B.K., 2018. Tectonic Regimes of the Central and Southern Andes: Responses to Variations in Plate Coupling During Subduction. Tectonics 37, 402-429. https://doi.org/10.1002/2017TC004624.

Hughes, R.A., Pilatasig, L.F., 2002. Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes. Tectonophysics 345, 29-48. https://doi.org/10.1016/S0040-1951(01)00205-0.

Jaillard, E., 2022. Late Cretaceous-Paleogene orogenic build-up of the Ecuadorian Andes: Review and discussion. Earth Sci. Rev. 230, 104033. https://doi.org/10.1016/j.earscirev.2022.104033.

Janousek, V., Moyen, J.-F., Martin, H., Erban, V., Farrow, C. (Eds.), 2016. Geochemical modelling of igneous processes - principles and recipes in R language: bringing the power of R to a geochemical community, Springer geochemistry. Springer, Berlin Heidelberg.

Jara, J.J., Barra, F., Reich, M., Leisen, M., Romero, R., Morata, D., 2021. Episodic construction of the early Andean Cordillera unravelled by zircon petrochronology. Nat. Commun. 12, 4930. https://doi.org/10.1038/s41467-021-25232-z.

Jones, R.E., Kirstein, L.A., Kasemann, S.A., Dhuime, B., Elliott, T., Livtak, V.D., Alonso, R., Hinton, R., 2015. Geodynamic controls on the contamination of Cenozoic arc magmas in the southern Central Andes: Insights from the O and Hf isotopic composition of zircon. Geochim. Cosmochim. Acta 164, 386-402. https://doi.org/10.1016/j.gca.2015.05.007.

Kemp, A.I.S., Hawkesworth, C.J., Foster, G.L., Paterson, B.A., Woodhead, J.D., Hergt, J. M., Gray, C.M., Whitehouse, M.J., 2007. Magmatic and Crustal Differentiation History of Granitic Rocks from Hf-O Isotopes in Zircon. Science 315, 980-983. https://doi.org/10.1126/science.1136154.

Kerr, A.C., Aspden, J.A., Tarney, J., Pilatasig, L.F., 2002. The nature and provenance of constrained oceanic terranes in western Ecuador: geochemical and tectonic constraints. J. Geol. Soc. Lond. 159, 577-594. https://doi.org/10.1144/0016-764901-151.

Kirkland, C.L., Smithies, R.H., Taylor, R.J.M., Evans, N., McDonald, B., 2015. Zircon Th/U ratios in magmatic environs. Lithos 212-215, 397-414. https://doi.org/10.1016/j.lithos.2014.11.021.

Koch, C.D., Delph, J., Beck, S.L., Lynner, C., Ruiz, M., Hernandez, S., Samaniego, P., Meltzer, A., Mothes, P., Hidalgo, S., 2021. Crustal thickness and magma storage beneath the Ecuadorian arc. J. S. Am. Earth Sci. 110, 103331. https://doi.org/10.1016/j.jsames.2021.103331.

Kydonakis, K., Kostopoulos, D., Poujol, M., Brun, J.-P., Papanikolaou, D., Paquette, J.-L., 2014. The dispersal of the Gondwana Super-fan System in the eastern Mediterranean: New insights from detrital zircon geochronology. Gondwana Res. 25, 1230-1241. https://doi.org/10.1016/j.gr.2013.05.009.

Lallemand, S., Heuret, A., Boutelier, D., 2005. On the relationships between slab dip, back-arc stress, upper plate absolute motion, and crustal nature in subduction zones. Geochem. Geophys. Geosyst. 6, 2005GC000917. https://doi.org/10.1029/2005GC000917.

Lee, C.-T.A., Thurner, S., Paterson, S., Cao, W., 2015. The rise and fall of continental arcs: Interplays between magmatism, uplift, weathering, and climate. Earth Planet. Sci. Lett. 425, 105-119. https://doi.org/10.1016/j.epsl.2015.05.045.

Luffi, P., Ducea, M.N., 2022. Chemical Mohometry: Assessing Crustal Thickness of Ancient Orogens Using Geochemical and Isotopic Data. Rev. Geophys. 60. https://doi.org/10.1029/2021RG000753.

Louieux, L.D.A., Heller, F., Spikings, R., Vallejo, C.F., Winkler, W., 2006. Origin and Cretaceous tectonic history of the coastal Ecuadorian forearc between 1°N and 3°S: Paleomagnetic, radiometric and fossil evidence. Earth Planet. Sci. Lett. 249, 400-414. https://doi.org/10.1016/j.epsl.2006.07.008.

Macpherson, C.G., Dreher, S.T., Thirlwall, M.F., 2006. Adakites without slab melting: High pressure differentiation of island arc magma, Mindanao, the Philippines. Earth Planet. Sci. Lett. 243, 581-593. https://doi.org/10.1016/j.epsl.2005.12.034.

Malusà, M.G., Fitzgerald, P.G. (Eds.), 2019. Fission-Track Thermochronology and its Application to Geology, Springer Textbooks in Earth Sciences, Geography and Environment. Springer International Publishing, Cham. https://doi.org/10.1007/978-3-319-89421-8.

Margirier, A., Strecker, M.R., Reiners, P.W., Thomson, S.N., Casado, I., George, S.W.M., Alvarado, A., 2023. Late Miocene Exhumation of the Western Cordillera, Ecuador, Driven by Increased Coupling Between the Subducting Carnegie Ridge and the South American Continent. Tectonics 42, e0222TC007344. https://doi.org/10.1029/2022TC007344.

Meschede, M., Barckhausen, U., 2001. The relationship of the Cocos and Carnegie ridges: age constraints from paleogeographic reconstructions. Int. J. Earth Sci. 90, 386-392. https://doi.org/10.1007/s005310000155.

Michaud, F., Witt, C., Royer, J.-Y., 2009. Influence of the subduction of the Carnegie volcanic ridge on Ecuadorian geology: Reality and fiction, in: Backbone of the
Americas: Shallow Subduction, Plateau Uplift, and Ridge and Terrane Collision. Geol. Soc. America. https://doi.org/10.1130/2009.1204(10).

Monani, S., Valley, J.W., 2001. Oxygen isotope ratios of zircon: magma genesis of low N18O granites from the British Tertiary Igneous Province, western Scotland. Earth Planet. Sci. Lett. 184 (2), 377-392.

Morel, M.L.A., Nebel, O., Nebel-Jacobsen, Y.J., Miller, J.S., Vroon, P.Z., 2008. Hafnium isotope characterization of the GJ-1 zircon reference material by solution and laser-ablation MC-ICPMS. Chem. Geol. 255, 231-235. https://doi.org/10.1016/j.chemgeo.2008.06.040.

Moyen, J.-F., 2009. High Sr/Y and La/Yb ratios: The meaning of the "adakitic signature". Lithos 112, 556-574. https://doi.org/10.1016/j.lithos.2009.04.001.

Pepper, M., Gehrels, G., Pullen, A., Ibanez-Mejia, M., Ward, K.M., Kapp, P., 2016. Magmatic history and crustal genesis of western South America: Constraints from U-Pb ages and Hf isotopes of detrital zircons in modern rivers. Geosphere 12, 1532-1555. https://doi.org/10.1130/GES01315.1.

Profeta, L., Ducea, M.N., Chapman, J.B., Paterson, S.R., Gonzales, S.M.H., Kirsch, M., Petrescu, L., DeCelles, P.G., 2015. Quantifying crustal thickness over time in magmatic arcs. Sci. Rep. 5, 17786. https://doi.org/10.1038/srep17786.

Reimink, J.R., Davies, J.H.F.L., Bauer, A.M., Chacko, T., 2020. A comparison between zircons from the Acasta Gneiss Complex and the Jack Hills region. Earth Planet. Sci. Lett. 531, 115975. https://doi.org/10.1016/j.epsl.2019.115975.

Reiners, P., Carlson, R., Renne, P., Cooper, K., Granger, D., Noah, M., Schoene, B., 2017. Rb-Sr, Sm-Nd, and Lu-Hf. In: Geochronology and Thermochronology, 9781118455852. Wiley, Hoboken, pp. 127-150.

Richards, J.P., Kerrich, R., 2007. Special Paper: Adakite-Like Rocks: Their Diverse Origins and Questionable Role in Metallogenesis. Econ. Geol. 102, 537-576. https://doi.org/10.2113/gsecongeo.102.4.537.

Roberts, N.M.W., Spencer, C.J., 2015. The zircon archive of continent formation through time. Geol. Soc. Lond. Spec. Publ. 389, 197-225. https://doi.org/10.1144/SP389.14.

Savignano, E., Mazzoli, S., Arce, M., Franchini, M., Gautheron, C., Paolini, M., Zattin, M., 2016. (Un)Coupled thrust belt-foreland deformation in the northern Patagonian Andes: New insights from the Esquel-Gaste sector (41°30'-43'S). Tectonics 35, 2636-2656. https://doi.org/10.1002/2016TC004225.

Schütte, P., 2009. Geochronology, geochemistry, and isotopic composition (Sr, Nd, Pb) of Tertiary porphyry systems in Ecuador. https://doi.org/10.13097/ARCHIVE-OUVERTE/UNIGE:6367.

Schütte, P., Chiaradia, M., Beate, B., 2010a. Geodynamic controls on Tertiary arc magmatism in Ecuador: Constraints from U-Pb zircon geochronology of Oligocene-Miocene intrusions and regional age distribution trends. Tectonophysics 489, 159-176. https://doi.org/10.1016/j.tecto.2010.04.015.

Schütte, P., Chiaradia, Massimo M., Beate, B., 2010b. Petrogenetic Evolution of Arc Magmatism Associated with Late Oligocene to Late Miocene Porphyry-Related Ore Deposits in Ecuador. Econ. Geol. 105, 1243-1270. https://doi.org/10.2113/econgeo.105.7.1243.

Schütte, P., Chiaradia, M., Barra, F., Villagómez, D., Beate, B., 2012. Metallogenic features of Miocene porphyry Cu and porphyry-related mineral deposits in Ecuador revealed by Re-OS, 40Ar/39Ar, and U-Pb geochronology. Mineral. Deposita 47, 383-410. https://doi.org/10.1007/s00126-011-0378-z.

Sláma, J., Košler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S.A., Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., Whitehouse, M.J., 2008. Plešovice zircon — A new natural reference material for U-Pb and Hf isotopic microanalysis. Chem. Geol. 249, 1-35. https://doi.org/10.1016/j.chemgeo.2007.11.005.

Söderlund, U., Patchett, P.J., Vervoort, J.D., Isachsen, C.E., 2004. The 176Lu decay constant determined by Lu-Hf and U-Pb isotope systematics of Precambrian mafic intrusions. Earth Planet. Sci. Lett. 219, 311-324. https://doi.org/10.1016/S0012-821X(04)00012-3.

Stirling, J.E., Denyszyn, S.W., Loucks, R.R., Kemp, A.I.S., Hammerli, J., Fiorentini, M.L., Vervoort, J.D., 2023. Formation of lower arc crust by magmatic underplating revealed by high-precision geochronology. Geology 51, 1101-1105. https://doi.org/10.1130/GES01315.1.

Sundell, K., Laskowski, A., Kapp, P., Ducea, M., Chapman, J., 2021. Jurassic to Neogene Quantitative Crustal Thickness Estimates in Southern Tibet. GSA Today 31, 4-10. https://doi.org/10.1130/GSATG461A.1.

Sundell, K., George, S.W.M., Carrapa, B., Gehrels, G.E., Ducea, M.N., Saylor, J.E., Pepper, M., 2022. Crustal Thickening of the Northern Central Andean Plateau Inferred From Trace Elements in Zircon. Geophys. Res. Lett. 49. https://doi.org/10.1029/2021GL096443.

Tang, M., Guo, Z., Cao, W., Chu, X., 2024. Revisiting zircon Eu anomaly as a proxy for crustal thickness: A case study of the Sierra Nevada Batholith. Earth Planet. Sci. Lett. 643, 118897. https://doi.org/10.1016/j.epsl.2024.118897.

Turner, S.J., Langmuir, C.H., 2015a. The global chemical systematics of arc front stratovolcanoes: Evaluating the role of crustal processes. Earth Planet. Sci. Lett. 422, 182-193. https://doi.org/10.1016/j.epsl.2015.03.056.

Turner, S.J., Langmuir, C.H., 2015b. What processes control the chemical compositions of arc front stratovolcanoes?: MODELS OF MAGMA GENESIS IN GLOBAL ARCS. Geochem. Geophys. Geosyst. 16, 1865-1893. https://doi.org/10.1002/2014GC005633.

Ulmer, P., 2007. Differentiation of mantle-derived calc-alkaline magmas at mid to lower crustal levels: experimental and petrologic constraints. Period. Mineral. 309-325. https://doi.org/10.2451/2007PM0030.

Vallejo, C., Winkler, W., Spikings, R.A., Luzieux, L., Heller, F., Bussy, F., 2009. Mode and timing of terrane accretion in the forearc of the Andes in Ecuador, in: Backbone of the Americas: Shallow Subduction, Plateau Uplift, and Ridge and Terrane Collision. Geol. Soc. America. https://doi.org/10.1130/2009.1204(09).

Vallejo, C., Soria, F., Tornos, F., Naranjo, G., Rosero, B., Salazar, F., Cochrane, R., 2016. Geology of El Domo deposit in central Ecuador: a VMS formed on top of an accreted margin. Mineral. Deposita 51, 389-409. https://doi.org/10.1007/s00126-015-0616-x.

Valley, J.W., Lackey, J.S., Cavosie, A.J., Clechenko, C.C., Spicuzza, M.J., Basei, M.A.S., Bindeman, I.N., Ferreira, V.P., Sial, A.N., King, E.M., Peck, W.H., Sinha, A.K., Wei, C. S., 2005. 4.4 billion years of crustal maturation: oxygen isotope ratios of magmatic zircon. Contrib. Mineral. Petrol. 150, 561-580. https://doi.org/10.1007/s00410-005-0025-8.

Vermeesch, P., 2018. IsoplotR: A free and open toolbox for geochronology. Geosci. Front. 9, 1479-1493. https://doi.org/10.1016/j.gsf.2018.04.001.

Watson, E.B., Harrison, T.M., 2005. Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth. Science 308, 841-844. https://doi.org/10.1126/science.1110873.

Witt, C., Bourgois, J., Michaud, F., Ordoñez, M., Jiménez, N., Bosson, M., 2006. Development of the Gulf of Guayaquil (Ecuador) during the Quaternary as an effect of the North Andean block tectonic escape. Tectonics 25, 2004TC001723. https://doi.org/10.1029/2004TC001723.

Witt, C., Bosch, D., Aízprua, C., Poujol, M., Chiaradia, Massimo, 2021. Geodynamic controls at the southernmost Northern Andes magmatic arc: Geochemical and geophysical evidence. In: Presented at the Réunion des Sciences de la Terre (RST 2021), Lyon, p. 195.

Witt, C., Poujol, M., Chiaradia, M., Villagomez, D., Seyler, M., Averbuch, O., Bouden, N., 2023. Geodynamic controls in the southernmost Northern Andes magmatic arc: Trace elements and Hf-O isotopic systematics in forearc detrital zircon. GSA Bull. https://doi.org/10.1130/B36510.1.

Yakymchuk, C., Holder, R.M., Kendrick, J., Moyen, J.-F., 2023. Europium anomalies in zircon: A signal of crustal depth? Earth Planet. Sci. Lett. 622, 118405. https://doi.org/10.1016/j.epsl.2023.118405.