# Noble gas magmatic signature of the Andean Northern Volcanic Zone from fluid inclusions in minerals

J. Lages, A.L. Rizzo, A. Aiuppa, Pablo Samaniego, J.L. Le Pennec, J.A.

Ceballos, P.A. Narváez, Yves Moussallam, Philipson Bani, C. Ian Schipper, et al.

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To cite this version:

J. Lages, A.L. Rizzo, A. Aiuppa, Pablo Samaniego, J.L. Le Pennec, et al. Noble gas magmatic signature of the Andean Northern Volcanic Zone from fluid inclusions in minerals. Chemical Geology, 2021, 559, pp.119966. 10.1016/j.chemgeo.2020.119966. hal-03881757

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1 **Noble gas magmatic signature of the Andean Northern Volcanic Zone from**
2 **fluid inclusions in minerals**

3 J. Lages a,*, A.L. Rizzo b, A. Aiuppa a,b, P. Samaniego c, J.L. Le Pennec c, J.A. Ceballos e, P.A.

4 Narváez f, Y. Moussallam c,d, P. Bani c, C. Ian Schipper g, S. Hidalgo h, V. Gaglio a, E. Alberti a
5 and A. Sandoval-Velasquez a

6

7 Author's affiliations:

8 a Dipartimento DiSTeM, Università degli Studi di Palermo, Palermo, Italy

9 b Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy

10 c Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, Clermont-Ferrand, France

11 d Lamont-Doherty Earth Observatory, Columbia University, New York, USA

12 e Servicio Geológico Colombiano - Observatório Vulcanológico y Sismológico de Manizales, Colombia

13 f Servicio Geológico Colombiano, Observatório Vulcanológico y Sismológico de Pasto, Colombia

14 g School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand

15 h Instituto Geofísico - Escuela Politécnica Nacional, Quito, Ecuador

16

17 * Corresponding author: Joao Lages; joaopedro.nogueiralages@unipa.it
18 Abstract

Trace volatile elements like He are key for understanding the mantle source signature of magmas and to better constrain the relative roles of subduction and crustal processes to the variability of along-arc chemical and isotopic signatures of magmatic fluids. Here we report on noble gas abundances and isotopic data of Fluid Inclusions (FIs) in eruptive products and/or fumarolic gases from the Colombia-Ecuador segment of Andean Northern Volcanic Zone (NVZ). FIs in olivine phenocrysts from Ecuador (El Reventador, Cotopaxi and Tungurahua) yield air-normalized corrected ³He/⁴He ratios of 7.0-7.4 Rᴀ, within the MORB range (8±1 Rᴀ). With exception of the Cotopaxi lavas (opx<<Oliv.), these are indistinguishable of those obtained for their cogenetic orthopyroxene pairs and of gas emissions previously reported in literature. Olivine phenocrysts from Nevado del Ruiz fissure lavas also yield the highest ³He/⁴He (8.5±0.3 Rᴀ) for this volcanic system, which is in the range of fumarolic gases for Galeras (previously reported as high as 8.8 Rᴀ and here measured to a maximum of 8.3±0.1 Rᴀ). Our dataset highlights disparities between isotope signatures of eruptive products from Ecuador (avg. ~7.2 Rᴀ) and those reported for the Colombian portion of the NVZ (avg. ~8.5 Rᴀ). Previous studies on the geochemistry of erupted products put in evidence significant along-arc variations ascribed either to the involvement of different slab components, or to variable depths of evolution of arc magmas within the continental crust. However, the same variation is not discernible in the signature of noble gases, especially helium, from FIs and gas emissions analyzed in this study, with little inter-variation between Cotopaxi, Reventador and Tungurahua (all within 0.2 Rᴀ from the Ecuador average of 7.2) and Galeras and Nevado del Ruiz, whose maximum values differ by ~0.3 Rᴀ. We therefore suggest a homogenous MORB-like ³He/⁴He signature for the mantle wedge beneath this arc segment, whereby along-arc variations in crustal thickness (from <35 km at the northernmost part of the segment to ≥50 km at the Ecuadorian arc segment) may factor largely into the variability recorded on our data set. The first CO₂/³He ratios obtained in FIs from Andean rocks support the hypothesis of increasing crustal contamination from Colombia to Ecuador, concomitant with increasing crustal thicknesses under the respective arc regions.

43

Keywords Andean Volcanic Belt; Northern Volcanic Zone; fluid inclusions; noble gases; helium; crustal thickness;

46 **1. Introduction**

Due to their inert behavior and large isotope ratio variability among the different Earth's reservoirs, noble gases such as He, Ne and Ar are considered optimal tracers to constrain mantle geochemical features and the key processes that contribute to modifying deep magmatic sources (e.g., Gautheron and Moreira, 2002; Martelli et al., 2014; Rizzo et al., 2018). In addition, noble gases may help in evaluating the complex migration processes of magmatic fluids from the Earth's mantle to the atmosphere, hydrosphere and crust (e.g., Porcelli and Wasserburg, 1995a; Farley and Neroda, 1998; Ozima and Igarashi, 2000; Porcelli et al., 2001; van Keken et al., 2002; Ballentine et al., 2002; Moreira, 2013; Rizzo et al., 2015; Boudoire et al., 2018). These volatiles can be primordial in origin, trapped in the mantle since planetary accretion, produced in-situ, or they may be recycled into the mantle via material originally at the surface through subduction (e.g., Jackson et al., 2013; Kobayashi et al., 2017; Smye et al., 2017). Seismic tomography studies point out that oceanic plates can be subducted well below the 670 km discontinuity down to the core-mantle boundary (e.g., van der Hilst et al., 1997; Bijwaard and Spakman, 1998; Fukao et al., 2001). Additionally, numerical modelling of mantle convection patterns (van Keken and Ballentine, 1999) casts doubt upon the likelihood of maintaining a deep region of the mantle isolated over geological timescales. Noble gas
chemistry of magmatic fluids in volcanic arcs shows ³He/⁴He isotope variations ranging from 10.1 to 0.01 Rₐ (Hilton et al., 2002; Sano and Fischer, 2013). While ³He/⁴He ratios > 9.5 Rₐ (reported for example by Jean-Baptiste et al., 2016 for the Vanuatu arc) have been attributed to the contribution of the incipient plume at the westernmost edge of the Pacific super-plume (Montelli et al., 2006), ³He/⁴He ratios lower than Mid-Ocean Ridge Basalt (MORB, 8±1 Rₐ, Graham, 2002; Graham et al., 2014) have been interpreted as a result of either (i) the subducted slab component, including altered oceanic crust and oceanic sediments (Di Piazza et al., 2015; Robidoux et al., 2017; Battaglia et al., 2018); (ii) shallow-derived He resulting from interactions between the rising magma and the continental crust overlying the volcanic arc (Sano and Wakita, 1985a; Sano and Fischer, 2013); and/or (iii) the influence and nature of continental crust subducted beneath volcanic arcs (e.g., Southern Italy; Hilton et al., 2002; Martelli et al., 2014 and references therein).

To better determine the relative contributions of subduction-related parameters (e.g., convergence rate, slab dip, slab age, etc.) and crustal processes (crustal thickness and magma-residence time in the crust) to the observed along-arc ³He/⁴He variations, it is crucial to account for the space-time variability of available data so far reported in the literature for arc volcanism. Geographic controls on ³He/⁴He signatures have been assigned to either magma aging or interaction with surrounding country rock (e.g. Marty et al., 1989; Hilton et al., 1993a; Van Soest et al., 1998; Notsu et al., 2001; Hilton et al., 2002), especially in far-from-vent areas where degassing occurs less vigorously. Both processes can add a radiogenic helium component to mantle-derived melts and therefore decrease ³He/⁴He ratios (<<MORB), such as those observed in hydrothermal fluids. Also, it must be considered that the use of standard sampling techniques for noble gas extraction from high-temperature fumaroles (Sano et al., 1990; Giggenbach et al., 1993 and references therein) requires direct access to outpouring vents often located at hazardous volcanic areas. In other cases, surface manifestations of volcanic degassing are absent from quiescent stages of activity. Such scenarios make noble gas volcanic gas-based characterization of volcanic centers more difficult.

In addition to the spatial ³He/⁴He variability around individual volcanoes, temporal He isotope changes have been commonly reported in many active volcanoes (Sano and Fischer, 2013). Several studies exist of temporal fluctuations of ³He/⁴He ratios, correlating well with changes in volcanic activity. These include Mt. Etna (Caracausi et al., 2003; Rizzo et al., 2006; Paonita et al., 2012, 2016) and Stromboli, in Italy (Capasso et al., 2005; Rizzo et al., 2009, 2015a), at Mount Ontake, in Japan (Sano et al., 2015), Santorini, in Greece (Rizzo et al., 2015b), and at Turrialba, in Costa Rica (Rizzo et al., 2016). Such phenomena attest to the fact that He isotope signatures measured at the surface might be affected by processes happening deep in the magma chamber, including the input of new magma as volcanic activity escalates.

Because of spatial/temporal variability, and due to the fact that some arc volcanoes remain unsampled to date, mostly due to their remoteness and inaccessibility, arc-scale noble gas compositional catalogues (Hilton et al., 2002; Sano and Fischer, 2013) remain biased by the incomplete and heterogeneous data set available. Nonetheless, global reviews (Hilton et al. (2002), Sano and Fischer (2013), Oppenheimer et al. (2014) and Mason et al. (2017) provide convincing evidence for arc-scale correlations between isotope tracers and slab/crustal processes.

Despite the high density and intense activity of NVZ volcanoes, few studies exist up to date dealing with their noble gas isotope signature (Hilton et al., 2002). High temperature (>300°C) fumarole data have only been reported for Galeras (Sano and Williams, 1996; Sano et al., 1997). These provide an opportunity to sample volatiles released directly from magma at depth. Lower temperature emissions (e.g., bubbling hot springs), located on the flanks of volcanoes, allow for the sampling of noble gases released through
hydrothermal systems. The overall dominance of low temperature noble gas data for NVZ volcanoes led Hilton et al. (2002) to estimate ³He/⁴He averages for Colombia and Ecuador of 5.66±2.41 and 3.22±0.98, respectively. These are far below the expected MORB range (8±1). This study focus on improving the current dataset for the Northern Volcanic Zone, by reporting on new noble gas data from fluid inclusion analysis in olivine and pyroxene phenocrysts from five of the most active volcanoes in the entire Andean Volcanic Arc, Tungurahua, El Reventador and Cotopaxi in Ecuador, and Galeras and Nevado del Ruiz in Colombia. These data are integrated with the first measurements of CO₂ concentration (CO₂/³He ratios) in fluid inclusions (FIs) from Andean rocks to further constrain the geochemical features of the magmatic source underlying these volcanic centers. Finally, our investigation provides new information on the processes governing the variations in noble gas compositions along the Northern Volcanic Zone.

## 2. Geodynamic and geological setting

The Andes are a continental volcanic arc formed by the subduction of the 12-20 Ma old Nazca plate slab (Jarrard, 1986) beneath the South American plate, occurring at a rate of about 50-70 mm/yr (Trenkamp et al., 2002; Nocquet et al., 2014). This volcanic chain extends for over 7000 km along the western margin of South America and volcanism there occurs in four separate regions: the Northern (NVZ), Central (CVZ), and Southern (SVZ) volcanic zones, as a result of the subduction of the Nazca plate; and the Austral (AVZ) volcanic zone originating on the convergent plate boundary between the Antarctic plate and the continental South American plate (Fig. 1A). The Colombian segment of the NVZ is defined by a narrow volcanic arc (Fig. 1B) located above the Benioff zone that clearly defines a steep subduction slab (Ojeda and Havskov, 2001) exhibiting lateral variations in the dip angle, from ~20°-35° north of the Carnegie Ridge (Pennington, 1981) to ~25° beneath Ecuador (Guillier et al., 2001; Kendrick et al., 2003; Yepes et al., 2016; Fig. 1C). This change in dip angle underneath Ecuador causes the volcanic arc to widen and split into three segments, the frontal arc (Western cordillera), the main arc (Eastern Cordillera) and the back-arc dominated by dacitic, andesitic and shoshonitic products, respectively (Hall et al., 2008; Hall and Mothes, 2008; Hidalgo et al., 2012; Ancellin et al., 2017). The documented along-arc variations in subduction parameters (e.g., Syracuse et al., 2010) and in the chemical/isotopic signature of the eruptive volcanites (e.g., Ancellin et al. 2017) make the Andes, and in particular the NVZ, a unique geodynamic setting to test for the influence of varying subduction geometries and thermal regimes on the noble gas fluid signature along the arc.

## 3. Petrological and eruptive background

In volcanic arc segments such as the Ecuador-Colombia magmas inherit their compositional signatures from multiple sources, including: (i) the dehydration/partial melting of the subducting sediments/oceanic crust; (ii) the mantle wedge; and (iii) the overlying continental crust (Hickey et al., 1986; Hildreth and Moorbath, 1988; Tatsumi, 1989; Stern 2002). Andean magmas range considerably in composition and the prevailing andesites attest for the severe processing of primary melts along the arc. In fact, experiments (Nicholls and Ringwood, 1972; Mysen et al., 1974) and analysis of natural samples (Reubi and Blundy, 2009) both show that andesites mainly form as the product of differentiation processes such as fractional crystallization, coupled with crustal assimilation and magma mixing (Grove et al., 2003; Kelemen et al., 2014; Schmidt and Jagoutz, 2017). On the other hand, recent studies highlight the fact that primitive arc magmas are intrinsically heterogeneous (Turner et al., 2016; Schmidt and Jagoutz, 2017), an important member of this family being the so-called magnesian andesites that are considered as direct by-products of mantle melting (e.g., Grove et al., 2003) and that are regularly found along the Ecuadorian volcanic arc (e.g. Samaniego et al., 2010). These processes not only impart chemical and textural signatures on the
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resulting eruptive products (Panter et al., 1997; Schiano et al., 2010; Garrison et al., 2011; Lee and Bachmann, 2014), but can also alter to various degrees the isotope signature of deep magmatic fluids.

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## 3.1 The colombian arc segment (CAS)

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### 3.1.1 Nevado del Ruiz

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The Nevado del Ruiz Volcanic Complex (CVNR) is located in the department of Caldas, near the northern end of the NVZ. Its history can be subdivided into four main eruptive phases, culminating in the Second Ruiz Eruptive Stage that included effusive-to explosive activity (Thouret et al., 1990). Over the past 11 ka, the volcano has erupted andesitic to dacitic magmas (about 40% dacites and 60% andesites; Vatin-Pérignon et al., 1990). Despite the complex eruptive history of Nevado del Ruiz, its geochemical evolution suggests a common magmatic source over time (see Vatin-Pérignon et al., 1990). In this study, we focused on the fissure lavas of *La Esperanza*, located in the northernmost sector of the volcanic complex. This segment is believed to be structurally controlled by the *Villamaría-Termales* fault system, which possibly provided the linear fractures through which these lavas were erupted (Martinez et al., 2014). Due to its stratigraphic position and moderate glacial processing, the age of this unit has been estimated at ~0,035 – 0,045 Ma. The presence of olivine microphenocrysts within microcrystalline-microlytic to moderately intergranular textures, clearly distinguishes these lavas from the majority of the eruptive periods of the volcanic complex that exhibit lower fractions of mafic minerals (25-45% overall in CVNR products; Vatin-Pérignon et al., 1990; Martínez et al., 2014).

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### 3.1.2 Galeras

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The Galeras Volcanic Complex (GVC) is located approximately 60 km north of the Colombia-Ecuador border. Over the past 1 Ma it has been characterized by caldera-forming eruptions, followed by the construction of new active cones that produced lavas and pyroclastic flows, ranging from basaltic-andesites to dacites (Calvache and Williams, 1997a and b). Its Holocene active cone lies on the eastern side of the volcanic complex and produced the basaltic-andesite products analyzed in this study. These were interpreted as possible fissure lavas (Calvache, 1990) that extend for an average length of 1.8 km and are located ~3-4 km away from the Galeras central crater. Plagioclase and pyroxene are the main mineral phases in these lavas, but fresh olivine is common (Calvache, 1990). Considering the location of the lava flow outcrops, Calvache (1990) argued that these lavas may have erupted with a high effusion rate in order to travel such long distances. Their well-preserved morphology suggests an approximate age between the pyroclastic flow deposits of 1100 y BP and the major eruption of 1866 CE (Calvache, 1990).

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## 3.2 The ecuadorian arc segment (EAS)

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### 3.2.1 El Reventador

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Although geographically located in the Ecuadorian back-arc, El Reventador displays a typical Main Arc geochemistry. A large sector collapse around 19,000 y BP left a prominent 4 km-wide volcanic collapse scar (Aguilera et al., 1988). Since then, a young, symmetrical, 1 km-high volcanic cone has grown to be one of the most active volcanoes in the Ecuadorian Andes. After 26 years of quiescence, the volcano initiated a new period of intense volcanic activity starting with a sub-Plinian event in November 3, 2002, rapidly followed by two lava flows effusively emplaced over a two-month period after the reactivation of the system (Samaniego et al., 2008). Petrological analysis of products from the 2002 eruption suggests that there was a single pre-eruptive reservoir with a top at 8 ± 2 km and a base at 11 ± 2 km (Ridolfi et al., 2008;
Samaniego et al., 2008). The same authors reported on the geochemical and mineralogical characteristics of the 2002 and later-emplaced 2004-2005 lava flows with overall silica contents ranging 56-59 wt.%. In this study we analyzed the 2009 lava flows consisting of medium-high K basaltic andesites to andesites, that display similar compositions to those reported for the initial 2002 eruptive products (porphyritic, ~25 – 30 vol.% phenocrysts in pyroclastic blocks and ~40 vol.% in lava flows), with a mineral assemblage composed of plagioclase, clinopyroxene, orthopyroxene, amphibole, magnetite, with scarce olivine (Samaniego et al., 2008).

### 3.3.2 Cotopaxi

Cotopaxi, a stratovolcano located ~60 km south of Quito, on the Main Arc, has exhibited a history of bimodal volcanism, where rhyolitic and andesitic magmas erupt in quick succession, apparently from the same vent, displaying very limited intermingling (Hall and Mothes, 2008). Each eruption cycle has been characterized by a similar eruptive pattern, involving plinian scoria or pumice tephra falls, scoria or pumice pyroclastic flows, blocky-lava flows, and widespread debris flows. From the end of the Colorado Canyon episode 4,000 years ago until the present, Cotopaxi has experienced a continuous series of periodic eruptions, all of which have involved andesitic magmas, with 57–62% SiO₂ (Hall and Mothes, 2008, Pistolesi et al., 2011) and phenocryst assemblages that include plagioclase, orthopyroxene, clinopyroxene, magnetite, and rare olivine. The younger products of Cotopaxi IIB comprise a series of andesitic scoria falls, lava flows and a single rhyolite eruption. In the lavas from Cotopaxi IIB olivine is occasionally present in trace amounts, but increases up to 2% (Hall and Mothes, 2008) in the youngest rocks analyzed in this study.

### 3.3.3 Tungurahua

Tungurahua is a stratovolcano located in central Ecuador on the Main Arc. Historical records (Martinez, 1932) and chronological data of the eruptive products of Tungurahua (Hall et al., 1999; Le Pennec et al., 2008) reveal that regional tephra fallouts, blocky lava flows, pyroclastic flows and related debris flows (such as the 1100 y BP analyzed in this study), characterized most eruptions in recent times. A recurrence rate of at least one pyroclastic flow-forming eruption per century was established for the last millennium, ranking Tungurahua amongst the most active volcanoes of the Northern Andes (Le Pennec et al., 2008). More recent eruptive products, such as pyroclastic flows, tephra deposits and lavas display andesitic compositions (58–59 wt% SiO₂; Samaniego et al., 2011) and contain plagioclase (5–15 vol.%), clinopyroxene (2–4 vol.%), orthopyroxene (2–4 vol.%), and magnetite, with trace olivine. This is similar to compositions reported by Samaniego et al. (2011) for the 2006 juvenile blocks from the pyroclastic flow deposits also analyzed in this study, which are dark, vesicular, porphyritic (~10–20 vol.% phenocrysts) andesites (57.6–58.9 wt.% SiO₂) composed of similar mineral assemblage.

## 4. Methods and analysis

### 4.1 Noble gases in Fluid Inclusions

Although our study does not offer petrographic evidence of FI in olivine and pyroxene phenocrysts, it is generally assumed that these phases often contain primary and secondary FI that are trapped during crystal growth in the magma. The element and isotope compositions of He, Ne, and Ar in olivine- and orthopyroxene-hosted fluid inclusions (FIs) were measured at the noble gas laboratory facilities at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Palermo. Phenocrysts (0.25 to 0.50 mm fractions)
were separated from lavas and scoriae layers from Nevado del Ruiz, Galeras, El Reventador, Cotopaxi and Tungurahua using sodium polytungstate (SPT) heavy liquid. The individual crystals without impurities were then carefully handpicked under a binocular microscope and cleaned in multi-stage ultra-sonic baths (e.g., Di Piazza et al., 2015; Rizzo et al., 2015, 2018). For analysis, the samples were accurately weighed and loaded into a stainless-steel crusher for noble gas extraction. The gases were consequently released by in-vacuo single-step crushing of minerals at about 200 bar applied by a hydraulic press, which minimizes the contribution of in-situproduced He, such as cosmogenic ³He and radiogenic ⁴He possibly trapped in the crystal lattices (e.g., Scarsi, 2000). The Total Gas Content (TGC) was first quantified during noble-gas extraction at the time of crushing by measuring the total gas pressure (CO₂+N₂+O₂+noble gases) and subtracting the residual pressure oses after removing CO₂ using a “cold finger” immersed in liquid N₂ at –196°C. Residual gases were then cleaned under getters in an ultra-high-vacuum (10⁻⁹–10⁻¹⁰ mbar) purification line, and all species in the gas mixture, except noble gases, were removed. A “cold finger” with active charcoal immersed in liquid N₂ then removed Ar, while He and Ne were separated by using a cold head cooled at 10K and then moved at 40 and 80K in order to release He and Ne, respectively.

Helium (³He and ⁴He) and Ne (²⁰Ne, ²¹Ne, and ²²Ne) isotopes were measured separately by two different split-flight-tube mass spectrometers (Helix SFT-Thermo). The ³He/⁴He ratios are expressed in units of R/R<sub>A</sub> (where R<sub>A</sub> is the ³He/⁴He of air; 1.39 × 10<sup>-6</sup>). The analytical uncertainty of He-isotope ratio measurements (1σ) was <4% (except for the pyroxene phenocrysts from Cotopaxi whose uncertainty was 13.5%), whereas in Ne-isotope ratios (1σ) was <1.7% and <4.6% for ²⁰Ne/²²Ne and ²¹Ne/²²Ne, respectively. The reported values of both Ne-isotope ratios are corrected for isobaric interferences at m/z values of 20 (⁴⁰Ar²⁺) and 22 (⁴⁴CO₂²⁺; Rizzo et al., 2018). Argon isotopes (³⁶Ar, ³⁸Ar, and ⁴⁰Ar) were analyzed by a multicollector mass spectrometer (GVI Argus) at an analytical uncertainty of ⁴⁰Ar/³⁶Ar <0.5%. A pre-purified air standard subdivided in tanks was used for He, Ne, and Ar elemental and isotopic recalculations. The analytical reproducibility of ⁴He, ³He/⁴He, ²⁰Ne/²²Ne, ²¹Ne/²²Ne, and ⁴⁰Ar of standards were <2.4%, <2.6%, <0.4%, <0.5%, and <2.4%, respectively. These values represent the standard deviation of measurements made during >1 year of analyses for He and Ne and ~4 years for Ar, in the same source setting conditions. Typical blanks for He, Ne, and Ar were <10<sup>-15</sup>, <10<sup>-16</sup> and <10<sup>-14</sup> mol, respectively. Further details on sample preparation and analytical procedures are available in Di Piazza et al. (2015) and Rizzo et al. (2015, 2018).

## 4.2 Dry fumarolic gas sampling and Noble gas isotope analysis

Dry gas samples for the analyses of He, Ne, and Ar were collected in the flanks of the active central crater of Galeras on 14 July 2017. Fumarolic gas from two steaming vents (at temperatures of 91.3 and 87.5°C) was collected in two-way Pyrex bottles with vacuum valves at both ends. Despite the apparent weak flux and in-situ low temperatures measurements (close to boiling), the gas was channeled through a stainless-steel tube and propelled several times through the sampling circuit in order to eliminate any possible remains of atmospheric components within the sampling lines.

The concentration and isotope compositions of He, Ne and Ar in fumaroles were measured by admitting the gases into three distinct ultra-high-vacuum (10⁻⁹–10⁻¹⁰ mbar) purification lines, in which all of the species in the gas mixture, except noble gases, were removed. Prior to the analysis, He and Ne were separated from Ar by adsorbing the latter in a charcoal trap cooled by liquid nitrogen (77 K). He and Ne were then adsorbed in a cryogenic trap connected to a cold head cooled with a He compressor to ≤10 K. He was desorbed at 42 K and admitted into a GVI-Helix SFT mass spectrometer. After restoring the ultra-high vacuum in the cryogenic trap, Ne was released at 82 K and then admitted into a Thermo-Helix MC Plus
267 mass spectrometer. Ar was purified only under getters and finally admitted in a GVI-Helix MC. The
268 analytical uncertainty of He-isotope ratio measurements (1σ) was <0.9%, while that of Ne- and Ar-isotope
269 ratio was <0.1%. The same procedure was adopted for the He, Ne and Ar isotope measurements of the air
270 standards (e.g., Rizzo et al., 2016), whose reproducibility conditions are comparable to those reported for
271 FIs (see Section 4.1). Typical blanks for He, Ne, and Ar were <10<sup>-15</sup>, <10<sup>-16</sup> and <10<sup>-14</sup> mol, respectively.
272 Helium isotope ratios are reported in the form of R<sub>C</sub>/R<sub>A</sub>, where R<sub>C</sub> is the air-corrected <sup>3</sup>He/<sup>4</sup>He ratio of the
273 sample, assessed based on <sup>4</sup>He/<sup>20</sup>Ne ratios:

$$
274 \quad R_C/R_A = [(R_M/R_A)(\text{He}/\text{Ne})_M - (\text{He}/\text{Ne})_{\text{air}}]/[(\text{He}/\text{Ne})_M - (\text{He}/\text{Ne})_{\text{air}}]
$$

275 where subscripts “M” and “air” refer to measured and atmospheric theoretical values, respectively. Across
276 our dataset, R<sub>C</sub>/R<sub>A</sub> ratios are on average 2% higher than those uncorrected and 3 analysis required
277 corrections outside of quoted R<sub>C</sub>/R<sub>A</sub> errors (Tab. 1). Argon isotope ratios account for atmospheric-corrected
278 <sup>40</sup>Ar, assuming that all <sup>36</sup>Ar contained in the gas phase is of atmospheric origin:

$$
279 \quad ^{40}\text{Ar}^* = ^{40}\text{Ar}_m - [({}^{40}\text{Ar}/{}^{36}\text{Ar})_{\text{air}} \times {}^{36}\text{Ar}_m],
$$

280 where $^{40}$Ar* represents the corrected isotope value and *m* indicates the measured value (Marty and Ozima,
281 1986 and references therein). These differ by as much as two orders of magnitude in opx phenocrysts from
282 Cotopaxi (see Tab. 1).

283 5. Elemental and isotopic compositions of He, Ne, Ar and CO₂

284 5.1 Fluid inclusions in olivine and orthopyroxene phenocrysts phases

285 Noble gas abundances and isotope results obtained from single-step crushing olivine and orthopyroxene
286 phenocrysts phases from scoriae layers and lava flows from Colombia (Galeras and Nevado del Ruiz) and
287 Ecuador (Cotopaxi, El Reventador and Tungurahua) are listed in table 1. These yield R<sub>C</sub>/R<sub>A</sub> values as high
288 as 8.5 R<sub>A</sub> (measured in olivine from Nevado del Ruiz), and as low as 2.2 R<sub>A</sub> (obtained in FIs trapped within
289 orthopyroxene phenocrysts from Cotopaxi; Fig. 2). With exception of the former, all <sup>3</sup>He/<sup>4</sup>He isotope values
290 fall within the typical range found in arc-related FIs and free gases globally (Hilton et al., 2002; Sano and
291 Fischer, 2013; Mason et al., 2017). Helium abundances range from 0.12 - 3.23 ×10<sup>-13</sup> mol g<sup>-1</sup> in
292 orthopyroxene and 1.68 - 17.7 ×10<sup>-13</sup> mol g<sup>-1</sup> in olivine (Fig. 3A). Despite the contrast in gas contents,
293 mineral pairs show indistinguishable R<sub>C</sub>/R<sub>A</sub> ratios (Tab. 1), the exception being the two mineral pairs from
294 Cotopaxi lavas which also yield distinct <sup>3</sup>He/<sup>4</sup>He ratios (opx<oliv.; Fig. 3B). Olivine phenocrysts from
295 Galeras and Nevado del Ruiz lavas yield He concentrations between 0.24 and 1.19 (×10<sup>-13</sup> mol g<sup>-1</sup>).
296 <sup>40</sup>Ar/<sup>36</sup>Ar isotope ratios range from 297.9 to 471.7 (avg. of 328.3 across all samples), supporting a prevalent
297 atmospheric derivation (<sup>40</sup>Ar/<sup>36</sup>Ar in air = 295.5) and confirming the <sup>40</sup>Ar/<sup>36</sup>Ar ratio range observed in the
298 fumarolic gases from Galeras central crater (297.0 and 302.1; Fig. 2).

299 Our results imply Ar isotope ratios well below those characteristic of the upper mantle (⁴⁰Ar/³⁶Ar ~ 40,000;
300 Fischer et al., 2005). Nonetheless, these fall within the typical range of subduction-related volcanism
301 (Hilton et al., 2002; Sano and Fischer, 2013), even in opx from Ecuadorian samples which consistently
302 show lower ⁴⁰Ar/³⁶Ar than those of cogenetic olivine. Atmospheric contamination is also reflected in the
303 ⁴He/²⁰Ne ratios here reported, that vary from 2.2 in orthopyroxenes from Cotopaxi (also the lowest ³He/⁴He
304 obtained analytically) to 522.3 measured in Olivine phenocrysts from El Reventador (Fig. 2; atmospheric
305 ⁴He/²⁰Ne = 0.318; mantle air-free gases are generally characterized by values ≥1000; e.g., Rizzo et al.,
306
307

2018). Olivine phenocrysts also yield systematically higher ⁴He/²⁰Ne ratios than their cogenetic orthopyroxene pairs (Tab. 1).

308
309
310
311
312
313
314
315

Concentrations of CO₂ obtained in olivine fluid inclusions from Nevado del Ruiz (0.16 × 10⁻⁹ mol g⁻¹) and Galeras (0.62 and 0.31×10⁻⁹ mol g⁻¹) were in the range of CO₂ contents measured in orthopyroxene phenocrysts from Ecuadorian volcanoes (only as high as 8.63×10⁻⁹ mol g⁻¹ in opx from Reventador) and considerably lower than CO₂ concentrations measured across their olivine separates (up to 69.4×10⁻⁹ mol g⁻¹ in Reventador samples; Tab. 1). Estimated CO₂/³He ratios span from 6.13 (in olivines from Reventador) to 0.28×10⁹ (measured in orthopyroxene phenocrysts from Tungurahua; Tab. 1). The carbon isotope characterization of NVZ fluids was not possible due to the gas-poor nature of the inclusions, in which carbon was not sufficiently abundant to allow further analysis after the noble gases had been extracted.

316

## 5.2. Isotope geochemistry of fumarolic gases

317
318
319
320
321
322
323

Sampling details and analytical data from fumarolic discharges measured at the central crater of Galeras are provided in table 2. The high R<sub>C</sub>/R<sub>A</sub> values (8.3 and 8.2 R<sub>A</sub>, and ⁴He/²⁰Ne of 7.3 and 29.6, respectively) are in agreement with values reported by Sano and Williams (1996) and Sano et al. (1997) for nearby fumarolic discharges (Fig. 2). Argon isotope values also show very limited variability between the two near sites, with ⁴⁰Ar/³⁶Ar of 297.9 ± 0.1 and 302.1 ± 0.2, respectively. Figure 2 shows the new isotope geochemistry data from fumarolic gases and FIs integrated with existing literature data for all 5 volcanoes studied (Ecuador and Colombia).

324

## 6. Discussion

325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341

In order to assess local and regional isotope variations along the Northern Volcanic Zone it is crucial to account for the various processes that have the potential to mask the geochemical characteristics of the deep mantle source underlying the northernmost segment of the Andean Volcanic Arc. In volcanic gases, close-to-MORB or within-MORB ³He/⁴He ratios are commonly measured along volcanic front regions where direct input of magma occurs (e.g. Sano and Wakita 1987; Sano and Wakita 1988a; Giggenbach et al., 1993; Hulston et al., 2001; Umeda et al., 2007; Di Piazza et al., 2015; Robidoux et al., 2017; Battaglia et al., 2018; Rizzo et al., 2019). Tectonically active regions such as the Andes provide a wide range of sampling media for noble gases, especially through active volcanism (Hilton et al., 2002; Aguilera et al., 2012; Benavente et al., 2016; Lopez et al., 2018). Surface discharges of magma degassing at depth can vary largely in nature and are typically found in the vicinity of active craters (as high-temperature fumarolic gas), and/or in peripheral areas as geothermal fields and low-temperature bubbling springs. Such variability had some studies reporting a wide range of ³He/⁴He isotope signatures within individual volcanic systems, such as Sano et al. (1984), following their study of Mt. Ontake in Japan, and Williams and Sano (1987) at Nevado del Ruiz, in Colombia. These studies typically reveal decreasing ³He/⁴He ratios with increasing distance from volcanic craters, indicating that despite effectively carrying magmatic volatiles to the atmosphere, volcanic steam escaping through fractures/soil around peripheral areas is increasingly contaminated by crustal fluids (in comparison to high-temperature, summit discharges).

342
343
344
345
346

On the other hand, primary noble gas compositions in fluid inclusions may be affected by post-eruption ⁴He in-growth and diffusion-controlled isotope fractionation. These processes are discussed in detail in supplementary material S1. However, predominantly MORB-like ³He/⁴He isotope ratios obtained in this study suggest that diffusive fractionation plays a minor role in our dataset. Differences in the chemistry of FIs obtained in orthopyroxene and olivine, in part expected due to the lower effective closure temperature
and pressure of pyroxenes (that continue to exchange helium with the magma after olivine had been closed),
are also not observed systematically (Fig. 3; see also supplementary material S1).

## 6.1. Atmospheric contamination

Due to their high concentration in the atmosphere, light noble gases such as Ar are more susceptible to atmospheric contamination. In subduction-related volcanism, Ar-isotope ratios are systematically low and close to theoretical values in the atmosphere (Hilton et al., 2002; Martelli et al., 2014; Di Piazza et al., 2015; Rizzo et al., 2015, 2016, 2019; Robidoux et al., 2017; Battaglia et al., 2018). This is even more pronounced when compared to those from intra-plate or ridge environments (e.g., Burnard et al., 1997; Moreira et al., 1998; Ballentine et al., 2005; Boudoire et al., 2018; Rizzo et al., 2018). Figure 2A confronts our new results to those reported in the literature for high- and low-temperature free gases and shows that variable extents of air contamination affected nearly all the ³He/⁴He ratios reported. Similarly, ⁴⁰Ar/³⁶Ar values (Fig. 2B) are well below the theoretical MORB-like mantle ratio (⁴⁰Ar/³⁶Ar ~30,000 to 40,000; Burnard et al., 1997; Moreira et al., 1998) or typical mantle-derived samples (e.g., Kaneoka, 1983; Ozima and Podosek, 1983; Allègre et al., 1987; Rizzo et al., 2018). As many authors have suggested over the years (e.g., Gurenko et al., 2006; Di Piazza et al., 2015; Rizzo et al., 2018)), the trend observed may indicate mantle contamination at depth from atmospheric Ar derived from dehydration of the subducting oceanic crust. However, a minimum contribution associated with crystals exposure to the atmosphere cannot be ruled out (see also supplementary material S2 for atmospheric components in the Neon isotope systematics).

## 6.2. Inferences on local and regional ³He/⁴He isotope signatures

The overprint of noble gas mantle signatures, especially helium, has always appeared quite significant in the northernmost region of the Andean Volcanic Arc. Negative correlations between ³He/⁴He and distance from active volcanic craters are common (Sano et al., 1984; Williams and Sano, 1987; Sano and Wakita 1992; Sano, et al., 1994; van Soest et al., 1998; Sano and Nakajima, 2008), as degassing of fresh, uncontaminated magma supplies helium that disperses through continental lithologies in which radiogenic ⁴He is abundant (see Sano et al., 1990 and Sano et al., 2012 for details on hydrodynamic dispersion models of helium at active volcanic systems such as Nevado del Ruiz). Previous global compilations of helium isotope data (e.g. Hilton et al., 2002; Sano and Fischer, 2013; Oppenheimer et al., 2014; Mason et al., 2017) reported ³He/⁴He averages of 3.2 ± 1.0 R<sub>A</sub> and 5.7 ± 2.4 R<sub>A</sub> (<< MORB-range of 8 ± 1 R<sub>A</sub>) for Ecuador and Colombia, respectively (e.g., Hilton et al., 2002). These may in large reflect significant extents of mixing between mantle-derived and radiogenic helium produced in the crust. For instance, an extensive study by Inguaggiato et al. (2010) that reported on the geochemical signature of 56 thermal and cold waters sites, as well as 32 dissolved gases and 27 bubbling springs, collected north-south along the Ecuadorian arc, obtained a wide range of helium isotope results, from 0.1 and 7.1 R<sub>A</sub>.

As a result, deep mantle noble gas isotope signatures can be overprinted, especially in regions characterized by older, flatter dipping slabs such as in the south of Ecuador (Barazangi and Isacks, 1979; Gutscher et al., 1999). Actively degassing volcanoes, especially those with accessible high-temperature fumarolic fields such as Galeras, Cumbal, Cerro Machin and Purace, were successfully sampled in the past (Sano and Williams, 1987; Sano et al., 1990; Sturchio et al., 1993; Sano and Williams, 1996; Sano et al., 1997; Lewicki et al., 2000), with maximum ³He/⁴He isotope ratios reported of 8.8, 7.9, 6.8 and 7.1 R<sub>A</sub>, respectively. However, for large portions of the arc, helium isotope signatures remained uncharacterized.
Here we provided the first helium isotope constrains on the mantle sources feeding the volcanic systems of Cotopaxi, Tungurahua and El Reventador, for which only peripheral gas data were reported in the past (Inguaggiato et al. 2010). While limited site-to-site variability is observed in Ecuador (when considering the new estimated values for El Reventador, Cotopaxi and Tungurahua; Tab. 3), a manifest disparity arises from the comparison between He isotope compositions obtained for Ecuadorian volcanoes and those of Colombia with significantly higher $ ^{3}\text{He}/^{4}\text{He} $ ratios (Fig. 4). In the following sections, we attempt at identifying the causal mechanisms driving the isotopic differences between the two arc regions.

### *Subduction-related controls on the noble gas chemistry of NVZ fluids*

We initially explore a possible link between noble gas compositions and processes occurring within the slab. In other volcanic arcs, such as the Central America Volcanic Arc (CAVA), pronounced along-arc variations in volcanic rock Ba/La ratios, for example within the Nicaraguan segment (Carr, 1984; Protti et al., 1995), coincide with changes in the dipping of the subducting slab, whereby the steepest dip sections induce intensive metasomatism and melting of a smaller volume of mantle (Carr et al., 1990). As a result, melts generated in this region are heavily imprinted with the signature of the subducted slab (e.g., high Ba/La). It is also suggested that local anomalous OIB-like signatures in the CAVA volcanic front are derived from the interaction of the mantle wedge with the Cocos aseismic ridge, the Galapagos Hostpot track, subducting beneath the arc (Benjamin et al., 2007, Hoernle et al., 2008, Wegner et al., 2010; Gazel et al., 2010;). Abratis and Wörner (2001) proposed that a “slab window” in the subducting Cocos Plate (Johnston and Thorkelson, 1997) allows a Galapagos-modified asthenosphere to flow into the Central American subduction system, which may culminate in the high $ ^{3}\text{He}/^{4}\text{He} $ ratios (as high as 8.9 $R_A$ in Guatemala; Battaglia et al., 2019) previously reported along CAVA (see also Shaw et al., 2003; Tassi et al., 2004; Shaw et al., 2006; Di Piazza et al., 2015; Rizzo et al., 2016; Robidoux et al., 2017; Battaglia et al., 2018).

Similarly, Bryant et al. (2006) reported relatively primitive isotopic signatures (e.g., Pb and Nd) for Ecuadorian lavas. These isotope compositions, as reported, appear largely independent on their major elements and on the age or composition of the crust through which they were erupted. Moreover, they partially overlap the range of Galapagos Plume basalts (Bryant et al., 2006). Ancellin et al. (2017, 2019) described similar evidence for the interaction between melts from the subducting Carnegie Ridge (Galapagos Plume track) and the mantle wedge in the northern Andean volcanic zone in Ecuador. A further role of the slab in the region may manifest in a northward increasing input of C-rich fluids from slab sediment decarbonation (Marín-Cerón et al., 2010), which may well explain the higher $CO_2/S_T$ ratios found in volcanic gases from Galeras and Nevado del Ruiz volcanoes (Aiuppa et al., 2017 and 2019; Lages et al., 2019; Fig. 4), as well as the higher Ba/La averages in Colombian rocks (e.g., Nevado del Ruiz up to ~62) relative to the Ecuadorian volcanoes here studied (Fig. 4). Fluid-mobile (e.g., B, Pb, Sr and Li) and -immobile (e.g., Nb and La) element ratios have also been used to distinguish between dehydration (low temperature) or melting (high temperature) processes of the basaltic oceanic crust and their relative contribution to the nature of the slab components identified along the NVZ (e.g., Marín-Cerón et al., 2010; Samaniego et al., 2010; Narvaez et al., 2018). Interestingly, whether due to changes in the slab component (e.g., Marín-Cerón et al., 2010; Ancellin et al., 2017; Narvaez et al., 2018) or to increasing average depths of arc magma evolution within the overriding plate crust (as argued by Chiaradia et al., 2020 due to effect of the subduction of the Carnegie aseismic ridge), magma chemistry seems to vary significantly along the NVZ.
If gas and rock chemistry data (Fig. 4) point to increasing fractions of slab fluids toward the north, our results, on the other hand, do not echo that same along-segment variability. Slab sediment fluids and melts are effective U and Th carriers (e.g., Kelley et al., 2005), so the injection of a slab component should contribute significant amounts of radiogenic ⁴He into the overriding mantle wedge, thus lowering its ³He/⁴He ratio. If the addition of slab sediment was the primary driver of along-arc noble gas isotope variations, then lower ³He/⁴He ratios should in principle be observed in Colombia. In contrast, our results imply an Ecuador average of ~7.2 R<sub>A</sub> (Cotopaxi, Tungurahua and Reventador maximum ³He/⁴He values of 7.0, 7.0 and 7.4 R<sub>A</sub>, respectively; maximum R<sub>C</sub>/R<sub>A</sub> ratios obtained for each volcano are taken into account as their primitive/magmatic “end-member”), whereas FIs from Nevado del Ruiz (~8.5 R<sub>A</sub>) and fumarolic gases from Galeras (8.8 R<sub>A</sub>, from Sano et al., 1997; and 8.3 R<sub>A</sub> from this study) all show significantly higher R<sub>C</sub>/R<sub>A</sub> ratios (>1 R<sub>A</sub> unit; Tab. 1).

In summary, although changes in subduction-related parameters (e.g., slab angle and slab descent rate; see Syracuse and Abers, 2006) and in slab thermal regime (due to the presence of the subducted Carnegie ridge; Syracuse et al., 2010; Yepes et al. 2016; Narvaez et al., 2018) appear key to generating the chemical/isotopic (Sr, Nd, Pb) diversity of NVZ magmas, they do not seem to be the main drivers of helium isotopic variations in magmatic fluids registered here. More broadly, the ≤8.5 R<sub>A</sub> ratios observed here indicate a negligible contribution of hot-spot-related fluids (measured up to ~18 R<sub>A</sub> in the Galapagos; see Goff et al., 2000), and indicate that a variable extent of crustal fluid-addition to primary (mantle-derived) melts may be the governing process as to explain the He isotope difference between Ecuador and Colombia.

## 6.3. Crustal assimilation of radiogenic ⁴He

As previously discussed, ³He/⁴He values recorded in orthopyroxenes from Cotopaxi (<< 8 R<sub>A</sub>) seem to be linked to processes of isotope fractionation and extensive helium loss. However, apart from this sample, all ³He/⁴He ratios in phenocrysts and fumarolic gases reported (Tab. 1 and 2) are significantly higher than orthopyroxenes from Cotopaxi, with most samples lying approximately within MORB range (8 ± 1 R<sub>A</sub>). The notable exceptions here are the olivine phenocrysts from Galeras A and B, both yielding slightly lower-than MORB R<sub>C</sub>/R<sub>A</sub> ratios. This is even more emphasized by the discrepancy between the R<sub>A</sub> values reported in olivine inclusions and those of fumarolic gases sampled at the central crater in July 2017 (8.3 ± 0.1 and 8.2 ± 0.1 R<sub>A</sub>; see Tab. 2 and Fig. 4) and reported by Sano et al. (1997) between 1988-1993 (as high as 8.8 ± 0.6 R<sub>A</sub>). Another important observation from our newly reported dataset is that averaged ³He/⁴He isotope values for Ecuador and Colombia, calculated by considering the highest measured ³He/⁴He (R<sub>C</sub>/R<sub>A</sub>) ratio for each volcano (from fluid inclusions or free gases), differ by 1.5 R<sub>A</sub> units (Ecuador ~7.2 R<sub>A</sub>; Colombia ~8.5 R<sub>A</sub>).

Compositional and isotope variations recorded in magmatic fluids can be explained through multiple contributions that, in addition to the mantle and the subducted slab, include fluids derived from the continental crust (e.g., Garrison et al., 2011; Nauret et al., 2018). Interestingly, models of crustal thickness for the continental Andes (e.g., Assumpção et al., 2013) reveal significant along-arc variations. Bryant et al. (2006) reported a very thick crust (≥50 km) underlying the currently active volcanic arc in Ecuador (e.g., Moho depths of ~53 km under Cotopaxi volcano; Bishop et al., 2017; see Vaca et al., 2019 for more detail information). In Colombia gravity data showed the thickness of the crust for this region to be between 30-40 km (e.g., Mooney et al., 1998; Ojeda and Havskov, 2001). Schaefer (1995) found a thin crust (<35 km) and/or an anomalous dense crust around the Nevado del Ruiz (Fig. 5A).
According to most authors, NVZ magmas appear to be contaminated to a greater extent in the lower crust (Garrison et al., 2011; Bryant et al., 2006; Ancellin et al., 2017; Nauret et al., 2018). Nonetheless, previous works (Barragan et al., 1998; Bourdon et al., 2003; Bryant et al., 2006; Samaniego et al., 2005; Chiaradia et al., 2011; Hidalgo et al., 2012; Ancellin et al., 2017, 2019; Nauret et al., 2018) also estimated the amount of upper crustal contamination in Ecuadorian magmas (using different tools such as trace elements and Sr-Nd-O isotopes) to be 7 to 14 vol % in the Western Cordillera and 6 to 13 vol % in the Eastern Cordillera. In fact, partial or bulk assimilation of crustal lithologies by basaltic-andesite magmas is an intuitively reasonable and thermodynamically possible explanation for the chemistry of these magmas (e.g., Kerr et al., 1995), especially those extruding in arc regions characterized by exceptionally thick continental crust, such as the Ecuadorian arc (≥50 km) and southernmost regions of Colombia (45-50 km; Feininger and Seguin, 1983; Prévot et al., 1996; Guillier et al., 2001). The link between crustal thickness and magma composition (Leeman, 1983; Plank and Langmuir, 1988) may be the driver for the formation of more evolved eruptive products, as those seen throughout the Northern Volcanic Zone. Some of these rocks were investigated by James and Murcia (1984) for Galeras and Nevado del Ruiz (Colombia), that found isotopic evidence for significant ¹⁸O-rich crustal components in the petrogenesis of these eruptive products, mostly related to processes happening during magmatic ascent. The lack of basalts in this part of the arc also suggests assimilation and/or magma mixing process of crustal materials by mantle-derived arc-magmas (Marín-Cerón et al., 2010).

Despite the recognition of crustal processes as key drivers of magma evolution in the NVZ, it is assumed that they do not overprint slab and mantle signatures in Ecuador and have overall little effect on Sr-Nd-O isotope systematics and trace elements of magmas erupted in the region (e.g., Barragan et al., 1998; Hidalgo et al., 2012; Ancellin et al., 2017). Our isotope systematics, on the other hand, confirm that shallow (crustal) noble gas imprint is significant in the area, and key to explaining the helium isotope signature differences between Ecuador and Colombia. The extent of fluid contamination by radiogenic crustal components can vary substantially depending on a wide range of geochemical and geophysical parameters. We propose that fluids trapped in olivine from Ecuadorian volcanoes, yielding lower limit-MORB range ³He/⁴He isotope signatures (avg. 7.2 R<sub>A</sub>), may reflect crustal assimilation of deep magmatic fluids, slowly ascending to shallower sub-reservoir levels, especially along the main volcanic arc where crustal thickness is reported to be ≥50 km. Furthermore, basement below Cotopaxi, Tungurahua and Reventador correspond to mature lithologies, which might enhance the role of crustal contamination and hence reduce the ³He/⁴He ratios of magmatic fluids. Given the high U and Th contents of lower and upper crust materials (0.2 and 1.2 ppm, to 2.7 and 10.5 ppm, respectively; Rudnick and Fountain, 1995; Rudnick and Gao, 2003, 2014; see also Hacker et al., 2011), we argue that noble gas isotope compositions, especially helium, in the NVZ may well be impacted by (and be suitable tracers of) shallow crustal assimilation processes, either related to stationary magma bodies (magma aging) and/or interaction of fluids with crustal rocks. We therefore suggest that crustal processes play a crucial role in controlling to lower the ³He/⁴He isotope compositions (at the lower MORB range) in Ecuadorian samples, at least in comparison to the higher R<sub>C</sub>/R<sub>A</sub> values seen in phenocrysts from Nevado del Ruiz and measured in fumarolic gases at Galeras.

If contamination of pristine noble gas compositions is essentially occurring in the crust, as our data seem to support, it is therefore plausible to suggest a homogenous noble gas signature to the mantle source beneath the NVZ. Perhaps, an inefficient slab transport of light noble gases (He, Ne, Ar) in sub-arc regions, due to early (in the trench) devolatilization of these gases, may lead to a relatively homogeneous, MORB-type mantle wedge. Previous studies have relied heavily on ¹³C/¹²C and CO₂/³He to constrain mixing of
marine limestones and organic sediments with upper mantle fluids (e.g., Marty and Jambon, 1987; Sano and Marty, 1995; and references therein). Although we were unable to estimate the δ¹³C of individual samples (due to the CO₂-poor nature of FIs analyzed), our study reports on the first CO₂ concentrations in FIs from arc volcanism. From these, we find CO₂/³He ratios in the Ecuadorian samples that suggest early exsolution of CO₂ from the magma, and subsequent entrapment of CO₂-depleted fluids by crystals forming at shallow depths with variable extents of crustal contamination (Fig. 5B). Notably, CO₂/³He measured in FIs of Galeras reflect greater outgassing than those of surface fumaroles with ³He/⁴He ratios in the range of Nevado del Ruiz FIs results. Else, we suggest that the slight increase in CO₂/³He ratios in olivines from El Reventador, Cotopaxi and Tungurahua (as high as 6.1 ×10⁹ in olivine phenocrysts from El Reventador lavas) may reflect higher degrees of crustal outgassing. This is consistent with the lower Ecuadorian ³He/⁴He "end-member" that point to assimilation of radiogenic ⁴He from the surrounding crust during magma storage in the thicker continental crust.

## 7. Concluding remarks

Processes of magmatic fluids ascent and consequent interactions with continental crust make volcanic arcs a challenging geodynamic setting when it comes to characterizing the pristine noble gas composition of upper mantle fluids feeding volatiles, including noble gases, to shallower magmatic reservoirs. In regions of thick crust, like the Andes, such task becomes increasingly difficult, with rare petrogenetic examples of uncontaminated mantle products rising to the Earth's surface. Depending on the isotopic system used, the amount of the crustal imprint is different, the challenge being to resemble all the different (and intrinsically incomplete) perspectives into a more complete view of the evolutionary stages of arc magmas and their inherited isotopic signatures.

New noble gas data reported here for FIs hosted in olivine and orthopyroxene phenocrysts from 5 of the most active volcanoes in the Northern Volcanic Zone, and updated fumarolic isotope compositions for Galeras, have allowed us to characterize the noble gas signatures of deep fluids along the northernmost segment of the Andean Volcanic Belt, with the following important conclusions:

1. New He isotope data reported for the Ecuadorian arc, and first helium isotope characterization of eruptive products from Reventador, Cotopaxi and Tungurahua (for which only peripheral, low-temperature data had yet been reported) revealed significantly higher helium isotope signatures (Avg. R<sub>C</sub>/R<sub>A</sub> ~7.2) than those previously reported in literature (max. 6.8 and 5.1 R<sub>A</sub> for Cotopaxi and Tungurahua, respectively; Inguaggiato et al., 2010).

2. The highest ³He/⁴He ratio measured in rocks and gases for each individual volcanic system (7.0–8.5 R<sub>A</sub>) are consistent with the typical MORB-range expected for arc volcanism (8 ± 1 R<sub>A</sub>). Excluding Galeras, for which in previous studies R<sub>C</sub>/R<sub>A</sub> values reached up to ~8.8 R<sub>A</sub>, all values obtained in this study represent the highest R<sub>C</sub>/R<sub>A</sub> values reported to date on these volcanic systems.

3. A significant discrepancy arises when averaging the highest ³He/⁴He from individual volcanic centers from the two arc segments, with an estimated average of ~7.2 R<sub>A</sub> for Ecuador and ~8.5 R<sub>A</sub> for Colombia. Although the reported constrains fall within the expected MORB range, we argue that a systematic difference exists between the two NVZ regions.

4. Whole rock chemistry (e.g., Ba/La, La/Yb) from lavas and other eruptive products show significant N-S variation in trace element signatures that can either be explained by changes in the slab component or
555 variations in the average depth of evolution of arc magmas within the NVZ crust. However, noble gas
556 isotope systematics, especially ³He/⁴He ratios, show little intra-segment variability within both Ecuador and
557 Colombia.

558 5. Instead, while comparing the two arc segments (between Colombia and Ecuador), a positive correlation
559 is observed between thickness of the overlying of continental crust and helium isotope signature, suggesting
560 that noble gas compositions are likely controlled by shallower addition of crustal (radiogenic) ⁴He whether
561 as gas percolates through the host rock, or by assimilation of U-Th-rich crustal lithologies as magma
562 reservoirs interact with the host rock. The first CO₂ concentration measurements in FIs from Andean
563 volcanoes, integrated with noble gases, support this interpretation.

564 6. We therefore suggest a rather homogeneous, MORB-like helium isotopic signature to the mantle
565 underlying the active volcanism along the arc segments of Colombia and Ecuador (Northern Volcanic
566 Zone).

567 In summary, this study brings significant contribution to our knowledge of noble gas circulation and crustal
568 assimilation processes happening at arc segments of exceptionally thick continental crust. Our results
569 underline the sensitivity of He in identifying and assessing crustal contamination processes at volcanic arc
570 settings. We also demonstrate the importance of using FIs to constrain ³He/⁴He mantle/magma signatures,
571 the message from surface gases being more subtle and difficult to interpret. In order to better constrain
572 volatile source/behavior at arcs and understand the possible role of slab geometry along the Northern
573 Volcanic Zone, future studies must concentrate on establishing a much more systematic approach to
574 sampling of noble gases and expanding current datasets.

575 **Declaration of competing interest**

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

578

579 **Acknowledgements**

580 This research was conducted as part of Joao Lages Ph.D. research which was financially supported by the
581 Università degli Studi di Palermo. The Ecuador portion of this investigation was conducted as part of the
582 “Trail by Fire” project (P.I. Moussallam, Y.). We would like to acknowledge all the staff members from
583 the Instituto Geofísico — Escuela Politécnica Nacional, (Quito, Ecuador) for their incredible logistical and
584 technical support throughout our field campaign (February 2017). Special thanks to Dr. Benjamin Bernard
585 for his assistance and scientific advice, and for providing the rock samples from Reventador analyzed in
586 this study. We would also like to thank the Servicio Geológico Colombiano, the volcanological
587 observatories of Pasto and Manizales, and their staff, for their crucial assistance with fieldwork in Galeras
588 and Nevado del Ruiz. INGV-Palermo provided the analytical facilities and we would also like to thank their
589 staff members Mariano Tantillo and Mariagrazia Misseri for their support in sample preparation and noble
590 gases analysis of FIs. The fieldwork portion of this work was funded by the DECADE initiative, from Deep
591 Carbon Observatory - Alfred P. Sloan Foundation and by the Royal Geographical Society (with the Institute
592 of British Geographers) with the Land Rover Bursary. A.A. and A.L.R. also received funding from the
593 MIUR (under grant PRIN2017 - 2017LMNLAW).
594 References

595 Abratis, M., Wörner, G., 2001. Ridge collision, slab-window formation, and the flux of Pacific asthenosphere into the Caribbean realm. Geology 29, 127–130. https://doi.org/10.1130/0091-7613(2001)029<0127:RCSWFA>2.0.CO;2

598 Aguilera, E., Almeida, E., Balseca, W., Barberi, F., Innocenti, F., Coltelli, M., Pasquare, G., 1988. El Reventador: an active volcano in the sub-andean zone of Ecuador. Rendiconti della Societa Italiana di Mineralogia e Petrologia 43, 853–875.

601 Aguilera, F., Tassi, F., Darrah, T., Moune, S., Vaselli, O., 2012. Geochemical model of a magmatic–hydrothermal system at the Lastarria volcano, northern Chile. Bulletin of volcanology 74(1), 119–134. https://doi.org/10.1007/s00445-011-0489-5

604 Aiuppa, A., Fischer, T.P., Plank, T., Bani, P., 2019. CO₂ flux emissions from the Earth’s most actively degassing volcanoes, 2005–2015. Sci. Rep. 9, 2005–2015. https://doi.org/10.1038/s41598-019-41901-y

607 Aiuppa, A., Fischer, T.P., Plank, T., Robidoux, P., Di Napoli, R., 2017. Along-arc, inter-arc and arc-to-arc variations in volcanic gas CO₂/Sₜ ratios reveal dual source of carbon in arc volcanism. Earth-Science Rev. 168, 24–47. https://doi.org/10.1016/j.earscirev.2017.03.005

610 Allègre, C.J., Staudacher, T., Sarda, P., 1987. Rare gas systematics: formation of the atmosphere, evolution and structure of the Earth’s mantle. Earth Planet. Sci. Lett. 81, 127–150. https://doi.org/10.1016/0012-821X(87)90151-8

613 Ancellin, M-A., Samaniego, P., Vlastelic, I., Nauret, F., Gannoun, A., Hidalgo, S., 2017. Across-arc versus along-arc Sr-Nd-Pb isotope variations in the Ecuadorian volcanic arc. Geochemistry Geophysics, Geosystems, 1–26. https://doi.org/10.1002/2016GC006679.Received

616 Ancellin, M-A., Vlastélic, I., Samaniego, P., Nauret, F., Gannoun, A., Hidalgo, S., 2019. Up to 1% Pb isotope disequilibrium between minerals hosted in dacites from the Guagua Pichincha volcano, Ecuador: Implication for tracing the source and crustal history of continental arc magmas. Chem. Geol. 525, 177–189. https://doi.org/10.1016/j.chemgeo.2019.07.016

620 Annen, C., Blundy, J.D., Sparks, R.S.J., 2006. The genesis of intermediate and silicic magmas in deep crustal hot zones. J. Petrol. 47, 505–539. https://doi.org/10.1093/petrology/egi084

622 Assumpção, M., Feng, M., Tassara, A., Julià, J., 2013. Models of crustal thickness for South America from seismic refraction, receiver functions and surface wave tomography. Tectonophysics 609, 82–96. https://doi.org/10.1016/j.tecto.2012.11.014

625 Ballentine, C.J., Burgess, R., Marty, B., 2002. Tracing fluid origin, transport and interaction in the crust. Rev. Mineral. Geochemistry 47, 539–614. https://doi.org/10.2138/rmg.2002.47.13

627 Ballentine, C.J., Marty, B., Lollar, B.S., Cassidy, M., 2005. Neon isotopes constrain convection and volatile origin in the Earth’s mantle. Nature 433, 33–38. https://doi.org/10.1038/nature03182
629 Barazangi, M., Isacks, B.L., 1979. Subduction of the Nazca plate beneath Peru: evidence from spatial distribution of earthquakes. Geophys. J. R. Astron. Soc. 57, 537–555. https://doi.org/10.1111/j.1365-246X.1979.tb06778.x

632 Barragan, R., Geist, D., Hall, M., Larson, P., Kurz, M., 1998. Subduction controls on the compositions of lavas from the Ecuadorian Andes. Earth Planet. Sci. Lett. 154, 153–166. https://doi.org/10.1016/s0012-821x(97)00141-6

635 Battaglia, A., Bitetto, M., Aiuppa, A., Rizzo, A.L., Chigna, G., Watson, I.M., D'Aleo, R., Juárez Cacao, F.J., de Moor, M.J., 2018. The magmatic gas signature of Pacaya Volcano, with implications for the volcanic CO₂ flux from Guatemala. Geochemistry, Geophys. Geosystems 19, 667–692. https://doi.org/10.1002/2017GC007238

639 Benavente, O., Tassi, F., Reich, M., Aguilera, F., Capecchiacci, F., Gutiérrez, F., Vaselli, O., Rizzo, A., 2016. Chemical and isotopic features of cold and thermal fluids discharged in the Southern Volcanic Zone between 32.5 S and 36 S: Insights into the physical and chemical processes controlling fluid geochemistry in geothermal systems of Central Chile. Chemical geology, 420, 97–113. https://doi.org/10.1016/j.chemgeo.2015.11.010

644 Benjamin, E.R., Plank, T., Wade, J.A., Kelley, K.A., Haun, E.H., Alvarado, G.E., 2007. High water contents in basaltic magmas from Irazu Volcano, Costa Rica. J. of Volcanol. And Geotherm. Res. 168, 68-92. https://doi.org/10.1016/j.jvolgeores.2007.08.008

647 Bijwaard, H., Spakman, W., Engdahl, E.R., 1998. Closing the gap between regional and global travel time tomography. J. Geophys. Res. Solid Earth 103, 30,055–30,078. https://doi.org/10.1029/98jb02467

649 Bishop, J.W., Lees, J.M., Ruiz, M.C., 2017. Receiver function stacks: initial steps for seismic imaging of Cotopaxi volcano, Ecuador. In AGU Fall meeting, Abstract 31.

651 Boudoire, G., Rizzo, A.L., Arienzo, I., Di Muro, A., 2020. Paroxysmal eruptions tracked by variations of helium isotopes: inferences from Piton de la Fournaise (La Réunion island). Scientific Reports, 10:9809. https://doi.org/10.1038/s41598-020-66260-x

654 Boudoire, G., Rizzo, A.L., Di Muro, A., Grassa, F., Liuzzo, M., 2018. Extensive CO₂ degassing in the upper mantle beneath oceanic basaltic volcanoes: First insights from Piton de la Fournaise volcano (La Réunion Island). Geochim. Cosmochim. Acta 235, 376–401. https://doi.org/10.1016/j.gca.2018.06.004
657 Bourdon, E., Eissen, J.P., Gutscher, M.A., Monzier, M., Hall, M.L., Cotten, J., 2003. Magmatic response to early aseismic ridge subduction: The Ecuadorian margin case (South America). Earth Planet. Sci. Lett. 205, 123–138. https://doi.org/10.1016/S0012-821X(02)01024-5

661 Bryant, J.A., Yogodzinski, G.M., Hall, M.L., Lewicki, J.L., Bailey, D.G., 2006. Geochemical constraints on the origin of volcanic rocks from the Andean Northern volcanic zone, Ecuador. J. Petrol. 47, 1147–1175. https://doi.org/10.1093/petrology/egl006
664 Burnard, P., 2004. Diffusive fractionation of noble gases and helium isotopes during mantle melting. Earth
665 and Planetary Science Letters 220, 287–295. https://doi.org/10.1016/S0012-821X(04)00060-3

666 Burnard, P., 2013. The noble gases as geochemical tracers, The Noble Gases as Geochemical Tracers.
667 https://doi.org/10.1007/978-3-642-28836-4

668 Burnard, P., Graham, D., Turner, G., 1997. Vesicle-specific noble gas analyses of “popping rock”: Implications for primordial noble gases in earth. Science, 276, 568–571.
669
670 https://doi.org/10.1126/science.276.5312.568

671 Calvache, M.L., 1990. Geology and volcanology of the recent evolution of Galeras volcano, Colombia. M. S Thesis, Louisiana State University.

673 Calvache V., M.L., Williams, S.N., 1997a. Emplacement and petrological evolution of the andesitic dome
674 of Galeras volcano, 1990-1992. J. Volcanol. Geotherm. Res. 77, 57–69.
675 https://doi.org/10.1016/S0377-0273(96)00086-8

676 Calvache V., M.L., Williams, S.N., 1997b. Geochemistry and petrology of the Galeras Volcanic Complex,
677 Colombia. J. Volcanol. Geotherm. Res. 77, 21–38. https://doi.org/10.1016/S0377-0273(96)00084-4

678 Capasso, G., Carapezza, M.L., Federico, C., Inguaggiato, S., Rizzo, A., 2005. Geochemical monitoring of
679 the 2002-2003 eruption at Stromboli volcano (Italy): Precursory changes in the carbon and helium
680 isotopic composition of fumarole gases and thermal waters. Bull. Volcanol. 68, 118–134.
681 https://doi.org/10.1007/s00445-005-0427-5

682 Caracausi, A., Italiano, F., Paonita, A., Rizzo, A., Nuccio, P.M., 2003. Evidence of deep magma degassing
683 and ascent by geochemistry of peripheral gas emissions at Mount Etna (Italy): Assessment of the
684 magmatic reservoir pressure. J. Geophys. Res. Solid Earth 108, 1–15.
685 https://doi.org/10.1029/2002jb002095

686 Carr, M.J., Feigenson, M.D., Bennett, E.A., 1990. Incompatible element and isotopic evidence for tectonic
687 control of source mixing and melt extraction along the Central American arc. Contrib. to Mineral.
688 Petrol. 105, 369–380. https://doi.org/10.1007/BF00286825

689 Carr, M.J., 1984. Symmetrical and segmented variation of physical and geochemical characteristics of the
690 central american volcanic front. J. Volcanol. Geotherm. Res. 20, 231–252.
691 https://doi.org/10.1016/0377-0273(84)90041-6

692 Carr, M.J., Saginor, I., Alvarado, G.E., Bolge, L.L., Lindsay, F.N., Milidakis, K., Turrin, B.D., Feigenson,
693 M.D., Swisher, C.C., 2007. Element fluxes from the volcanic front of Nicaragua and Costa Rica.
694 Geochemistry, Geophys. Geosystems 8. https://doi.org/10.1029/2006GC001396

695 Chiaradia, M., Müntener, O., Beate, B., 2011. Enriched basaltic andesites from mid-crustal fractional
696 crystallization, recharge and assimilation (Pilavo Volcano, Western Cordillera of Ecuador). J. Petrol.
697 (6), 1107–1141. https://doi.org/10.1093/petrology/egr020.
698 Chiaradia, M., Müntener, O., Beate, B., 2020. Effects of aseismic ridge subduction on the geochemistry of
699 frontal arc magmas. Earth Planet. Sci. Lett. 531, 115984. https://doi.org/10.1016/j.epsl.2019.115984

700 Craig, H., Lupton, J.E., 1976. Primordial neon, helium, and hydrogen in oceanic basalts. Earth Planet. Sci.
701 Lett. 31, 369-385. https://doi.org/10.1016/0012-821X(76)90118-7

702 Di Piazza, A., Rizzo, A.L., Barberi, F., Carapezza, M.L., De Astis, G., Romano, C., Sortino, F., 2015.
703 Geochemistry of the mantle source and magma feeding system beneath Turrialba volcano, Costa Rica.
704 Lithos 232, 319-335. https://doi.org/10.1016/j.lithos.2015.07.012

705 Farley, K.A., Neroda, E., 1998. Noble gases in the Earth's mantle. Annu. Rev. Earth Planet. Sci. 26, 189-
706 218. https://doi.org/10.1146/annurev.earth.26.1.189.

707 Feigenson, M.D., Carr, M.J., 1986. Positively correlated Nd and Sr isotope ratios of lavas from the Central
708 American volcanic front. Geology 14, 79-92. https://doi.org/10.1130/0091-
709 7613(1986)14<79:PCNASI>2.0.CO;2

710 Feigenson, M.D., Carr, M.J., Maharaj, S.V., Juliano, S., Bolge, L.L., 2004. Lead isotope composition of
711 Central American volcanoes: Influence of the Galapagos plume. Geochemistry, Geophys. Geosystems
712 5. https://doi.org/10.1029/2003GC000621

713 Feininger, T., Seguin, M.K., 1983. Simple Bouguer gravity anomaly field and the inferred crustal structure
714 of continental Ecuador. Geology 11, 40-44. https://doi.org/10.1130/0091-
715 7613(1983)11<40:SBGAFA>2.0.CO;2

716 Fischer, T.P., Takahata, N., Sano, Y., Sumino, H., Hilton, D.R., 2005. Nitrogen isotopes of the mantle:
717 Insights from mineral separates. Geophys. Res. Lett. 32, L11305.
718 https://doi.org/10.1029/2005GL022792

719 Fukao, Y., Widiyantoro, S., Obayashi, M., 2001. Stagnant slabs in the upper and lower mantle transition
720 region. Rev. Geophys. 39, 291-323. https://doi.org/10.1029/1999RG000068

721 Garrison, J.M., Davidson, J.P., Hall, M., Mothes, P., 2011. Geochemistry and petrology of the most recent
722 deposits from Cotopaxi Volcano, Northern Volcanic Zone, Ecuador. J. Petrol. 52, 1641-1678.
723 https://doi.org/10.1093/petrology/egr023

724 Gautheron, C., Moreira, M., 2002. Helium signature of the subcontinental lithospheric mantle. Earth
725 Planet. Sci. Lett. 199, 39-47. https://doi.org/10.1016/S0012-821X(02)00563-0

726 Gazel, E., Hoernle, K., Carr, M.J., Herzberg, C., Saginor, I., Bogaard, P. Van Den, Hauff, F., Feigenson,
727 M., Swisher, C., 2011. Plume-subduction interaction in southern Central America: Mantle upwelling
728 and slab melting. Lithos 121, 117-134. https://doi.org/10.1016/j.lithos.2010.10.008

729 Giggenbach, W.F., Sano, Y., Wakita, H., 1993. Isotopic composition of helium, and CO₂ and CH₄ contents
730 in gases produced along the New Zealand part of a convergent plate boundary. Geochim. Cosmochim.
731 Acta 57, 3427-3455. https://doi.org/10.1016/0016-7037(93)90549-C
732 Goff, F., McMurtry, G.M., Counce, D., Simac, J.A., Roldán-Manzo, A.R., Hilton, D.R., 2000. Contrasting hydrothermal activity at Sierra Negra and Alcedo volcanoes, Galapagos Archipelago, Ecuador. Bull. 734 Volcanol. 62, 34–52. https://doi.org/10.1007/s004450050289

735 Graham, D.W., 2002. Noble gas isotope geochemistry of mid-ocean ridge and ocean island basalts: Characterization of mantle source reservoirs. Rev. Mineral. Geochemistry 47, 247–317. 737 https://doi.org/10.2138/rmg.2002.47.8

738 Graham, D.W., Hanan, B.B., Hémond, C., Blichert-Toft, J., Albarède, F., 2014. Helium isotopic textures in Earth's upper mantle. Geochemistry, Geophys. Geosystems 15, 2048–2074. 740 https://doi.org/10.1002/2014GC005264

741 Grove, T.L., Elkins-Tanton, L.T., Parman, S.W., Chatterjee, N., Müntener, O., Gaetani, G.A., 2003. Fractional crystallization and mantle-melting controls on calc-alkaline differentiation trends. Contrib. to Mineral. Petrol. 145, 515–533. https://doi.org/10.1007/s00410-003-0448-z

744 Guillier. B., Chatelain, J.L., Jaillard, E., Yepes, H., Poupinet, G., Fels, J. F., 2001. Seismological evidence on the geometry of the orogenic system in central-northern Ecuador (South America). Geophys. Res. Lett. 28, 3749-3752. https://doi.org/10.1029/2001GL013257

747 Gurenko, A. A., Hoernle, K. A., Hauff, F., Schmincke, H. U., Han, D., Miura, Y. N., and Kaneoka, I., 2006. Major, trace element and Nd-Sr-Pb-O-He-Ar isotope signatures of shield stage lavas from the central and western Canary Islands: insights into mantle and crustal processes. Chem. Geol. 233, 75–112. 750 https://doi.org/10.1016/j.chemgeo.2006.02.016

751 Gutscher, M.A., Malavieille, J., Lallemand, S., Collot, J.Y., 1999. Tectonic segmentation of the North Andean margin: Impact of the Carnegie Ridge collision. Earth Planet. Sci. Lett. 168, 255–270. 753 https://doi.org/10.1016/S0012-821X(99)00060-6

754 Hacker, B.R., Kelemen, P.B., Behn, M.D., 2011. Differentiation of the continental crust by relamination. Earth Planet. Sci. Lett. 307, 501–516. https://doi.org/10.1016/j.epsl.2011.05.024

756 Hall, M.L., Samaniego, P., Le Pennec, J.L., Johnson, J.B., 2008. Ecuadorian Andes volcanism: A review of Late Pliocene to present activity. J. Volcanol. Geotherm. Res. 176, 1–6. 758 https://doi.org/10.1016/j.jvolgeores.2008.06.012

759 Hall, M.L, Mothes, P., 2008. The rhyolitic-andesitic eruptive history of Cotopaxi volcano, Ecuador. Bull. 760 Volcanol. 70, 675–702. https://doi.org/10.1007/s00445-007-0161-2

761 Hall, M.L., Robin, C., Beate, B., Mothes, P., Monzier, M., 1999. Tungurahua Volcano, Ecuador: Structure, eruptive history and hazards. J. Volcanol. Geotherm. Res. 91, 1–21. https://doi.org/10.1016/S0377-0273(99)00047-5

764 Hart, S.R., 1984. He diffusion in olivine. Earth Planet. Sci. Lett. 70, 297–302. https://doi.org/10.1016/0012-821X(84)90014-1

766 Harrison, D., Barry, T., and Turner, G., 2004. Possible diffusive fractionation of helium isotopes in olivine and clinopyroxene phenocrysts. Eur. J. Mineral., 16, 213-220. https://doi.org/10.1127/0935-1221/2004/0016-0213
769 Hauri, E., 2002. SIMS analysis of volatiles in silicate glasses, 2: Isotopes and abundances in Hawaiian melt inclusions. Chem. Geol. 183, 115–141. https://doi.org/10.1016/S0009-2541(01)00374-6

771 Heier, K.S., Adams, J.A.S., 1965. Concentration of radioactive elements in deep crustal material. Geochimica et Cosmochimica Acta, 29, pp. 53-61. https://doi.org/10.1016/0016-7037(65)90078-5

773 Hickey, R.L., Frey, F.A., Gerlach, D.C., Lopez-Escobar, L., 1986. Multiple sources for basaltic arc rocks from the southern volcanic zone of the Andes (34°–41°S): Trace element and isotopic evidence for contributions from subducted oceanic crust, mantle, and continental crust. J. Geophys. Res. 91, 5963. https://doi.org/10.1029/jb091ib06p05963

777 Hidalgo, S., Battaglia, J., Arellano, S., Sierra, D., Bernard, B., Parra, R., Kelly, P., Dinger, F., Barrington, C., Samaniego, P., 2018. Evolution of the 2015 Cotopaxi eruption revealed by combined geochemical and seismic observations. Geochemistry, Geophysics, Geosystems, 19, 2087–2108. https://doi.org/10.1029/2018GC007514

781 Hidalgo, S., Gerbe, M.C., Martin, H., Samaniego, P., Bourdon, E., 2012. Role of crustal and slab components in the Northern Volcanic Zone of the Andes (Ecuador) constrained by Sr-Nd-O isotopes. Lithos 132–133, 180–192. https://doi.org/10.1016/j.lithos.2011.11.019

784 Hildreth, W., Moorbath, S., 1988. Crustal contributions to arc magmatism in the Andes of Central Chile. Contrib. to Mineral. Petrol. 98, 455–489. https://doi.org/10.1007/BF00372365

786 Hilton, D.R., Hammerschmidt, K., Teufel, S., Friedrichsen, H., 1993a. Helium isotope characteristics of Andean geothermal fluids and lavas. Earth Planet. Sci. Lett. 120, 265–282. https://doi.org/10.1016/0012-821X(93)90244-4

789 Hilton, D.R., Fischer, T. P., Marty, B., 2002. Noble Gases and Volatile Recycling at Subduction Zones. Rev. in Mineralogy and Geochemistry 47 (1), 319–370. https://doi.org/10.2138/rmg.2002.47.9

791 Hoernle, K., Werner, R., Morgan, J.P., Garbe-Schonberg, D., Bryce, J., Mrazek, J., 2000. Existence of complex spatial zonation in the Galapagos plume for at least 14 m.y. Geology 28, 435-438. https://doi.org/10.1130/0091-7613(2000)28<435:EOCSZI>2.0.CO;2

794 Huang, Y., Chubakov, V., Mantovani, F., Rudnick, R.L., McDonough, W.F., 2013. A reference Earth model for the heat-producing elements and associated geoneutrino flux. Geochem. Geophys. Geosyst. 14, 2003–29. https://doi.org/10.1002/ggge.20129

797 Hulston, J.R., Hilton, D.R., Kaplan, I.R., 2001. Helium and carbon isotope systematics of natural gases from Taranaki Basin, New Zealand. Appl. Geochemistry 16, 419–436. https://doi.org/10.1016/S0883-2927(00)00045-7

800 Inguaggiato, S., Hidalgo, S., Beate, B., Bourquin, J., 2010. Geochemical and isotopic characterization of volcanic and geothermal fluids discharged from the Ecuadorian volcanic arc. Geofluids 10, 525–541. https://doi.org/10.1111/j.1468-8123.2010.00315.x

803 Inguaggiato, S., Londoño, J.M., Chacón, Z., Liotta, M., Gil, E., Alzate, D., 2017. The hydrothermal system of Cerro Machín volcano (Colombia): New magmatic signals observed during 2011–2013. Chem. Geol. 469, 60–68. https://doi.org/10.1016/j.chemgeo.2016.12.020
806 Jackson, C.R.M., Parman, S.W., Kelley, S.P., Cooper, R.F., 2013. Noble gas transport into the mantle facilitated by high solubility in amphibole. Nat. Geosci. 6, 562–565. https://doi.org/10.1038/ngeo1851

807
808 James, D.E., Murcia, L.A., 1984. Crustal contamination in northern Andean volcanics. J. Geol. Soc. London. 141, 823–830. https://doi.org/10.1144/gsjgs.141.5.0823

810 Jarrard, R.D., 1986. Relations among subduction parameters. Rev. Geophys. 24, 217–284.
811 https://doi.org/10.1029/RG024i002p00217

812 Johnston, S.T., Thorkelson, D.J., 1997. Cocos–Nazca slab window beneath Central America. Earth and Planetary Science Letters 146, 465–474. https://doi.org/10.1016/S0012-821X(96)00242-7

814 Jean-Baptiste, P., Allard, P., Fourré, E., Bani, P., Calabrese, S., Aiuppa, A., Gauthier, P.J., Parello, F., Pelletier, B., Garaebiti, E., 2016. Spatial distribution of helium isotopes in volcanic gases and thermal waters along the Vanuatu (New Hebrides) volcanic arc. J. Volcanol. Geotherm. Res. 322, 20–29.
815
816
817 https://doi.org/10.1016/j.jvolgeores.2015.09.026

818 Kaneoka, I., 1983. Noble gas constrains on the layered structure of the mantle. Nature 302, 698–700.
819 https://doi.org/10.1038/302698a0

820 Kelemen, P.B., Hanghøj, K., Greene, A.R., 2014. One view of the geochemistry of subduction-related magmatic arcs, with an emphasis on primitive andesite and lower crust. The Crust, Treatise on Geochemistry, edited by H. D. Holland and K. K. Turekian, 69–701, Elsevier-Pergamon, Oxford, U.

823 Kelley, K.A., Plank, T., Farr, L., Ludden, J., Staudigel, H., 2005. Subduction cycling of U, Th, and Pb. Earth Planet. Sci. Lett. 234, 369–383. https://doi.org/10.1016/j.epsl.2005.03.005

825 Kendrick, E., Bevis, M., Smalley, R., Brooks, B., Vargas, R.B., Lauría, E., Fortes, L.P.S., 2003. The Nazca–South America Euler vector and its rate of change. J. South Am. Earth Sci. 16(2), 125–131.
826
827 https://doi.org/10.1016/S0895-9811(03)00028-2

828 Kennedy, B.M., Hiyagon, H., Reynolds, J.H., 1990. Crustal neon: a striking uniformity. Earth Planet. Sci. Lett. 98, 277–286. https://doi.org/10.1016/0012-821X(90)90030-2

830 Kerr, A.C., Kempton, P.D., Thompson, R.N., 1995. Crustal assimilation during turbulent magma ascent (ATA); new isotopic evidence from the Mull Tertiary lava succession, N. W. Scotland. Contrib. to Mineral. Petrol. 119, 142–154. https://doi.org/10.1007/BF00307277

833 Kimura, J.I., Kawabata, H., 2015. Geochemistry, Geophysics, Geosystems. Geochemistry Geophys. Geosystems 16, 267–300. https://doi.org/10.1002/2014GC005684.Key

835 Kobayashi, M., Sumino, H., Nagao, K., Ishimaru, S., Arai, S., Yoshikawa, M., Kawamoto, T., Kumagai, Y., Kobayashi, T., Burgess, R., Ballentine, C.J., 2017. Slab-derived halogens and noble gases illuminate closed system processes controlling volatile element transport into the mantle wedge. Earth Planet. Sci. Lett. 457, 106–116. https://doi.org/10.1016/j.epsl.2016.10.012

839 Kurz, M.D., Curtice, J., Fornari, D., Geist, D., Moreira, M., 2009. Primitive neon from the center of the Galápagos hotspot. Earth Planet. Sci. Lett. 286, 23–34. https://doi.org/10.1016/j.epsl.2009.06.008
841 Lages, J., Chacón, Z., Burbano, V., Meza, L., Arellano, S., Liuzzo, M., Giudice, G., Aiuppa, A., Bitetto, M., López, C., 2019. Volcanic Gas Emissions Along the Colombian Arc Segment of the Northern Volcanic Zone (CAS-NVZ): Implications for volcano monitoring and volatile budget of the Andean Volcanic Belt. *Geochemistry, Geophys. Geosystems* 20, 1–25. https://doi.org/10.1029/2019gc008573

845 Le Pennec, J.L., Jaya, D., Samaniego, P., Ramón, P., Moreno Yánez, S., Egred, J., van der Plicht, J., 2008. The AD 1300-1700 eruptive periods at Tungurahua volcano, Ecuador, revealed by historical narratives, stratigraphy and radiocarbon dating. *J. Volcanol. Geotherm. Res.* 176, 70–81. https://doi.org/10.1016/j.jvolgeores.2008.05.019

849 Lee, C.T.A., Bachmann, O., 2014. How important is the role of crystal fractionation in making intermediate magmas? *Insights from Zr and P systematics. Earth Planet. Sci. Lett.* 393, 266–274. https://doi.org/10.1016/j.epsl.2014.02.044

852 Leeman, W.P., 1983. The influence of crustal structure on compositions of subduction-related magmas. *J. Volcanol. Geotherm. Res.* 18, 561–588. https://doi.org/10.1016/0377-0273(83)90026-4

854 Lewicki, J.L., Fischer, T., Williams, S.N., 2000. Chemical and isotopic compositions of fluids at Cumbal Volcano, Colombia: Evidence for magmatic contribution. *Bull. Volcanol.* 62, 347–361. https://doi.org/10.1007/s004450000100

857 Lopez, T., Aguilera, F., Tassi, F., Maarten de Moor, J., Bobrowski, N., Aiuppa, A., Tamburello, G., Rizzo, A.L., Liuzzo, M., Viveiros, F., Cardellini, C., Silva, C., Fischer, T., Jean-Baptiste, P., Kazayaha, R., Hidalgo, S., Malowany, K., Lucic, G., Bagnato, E., Bergsson, B., Reath, K., Liotta, M., Carn, S., Chiodini, G., 2018. New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop. *Geosphere* 14, 983–1007. https://doi.org/10.1130/GES01495.1

863 Maldonado, L.F.M., Inguaggiato, S., Jaramillo, M.T., Valencia, G.G., Mazot, A., 2017. Volatiles and energy released by Puracé volcano. *Bull. Volcanol.* 79. https://doi.org/10.1007/s00445-017-1168-y

865 Marín-Cerón, M.I., Moriguti, T., Makishima, A., Nakamura, E., 2010. Slab decarbonation and CO2 recycling in the Southwestern Colombian volcanic arc. *Geochim. Cosmochim. Acta* 74, 1104–1121. https://doi.org/10.1016/j.gca.2009.10.031

868 Martelli, M., Rizzo, A.L., Renzulli, A., Ridolfi, F., Arienzo, I., Rosciglione, A., 2014. Noble-gas signature of magmas from a heterogeneous mantle wedge: The case of Stromboli volcano (Aeolian Islands, Italy). *Chem. Geol.* 368, 39–53. https://doi.org/10.1016/j.chemgeo.2014.01.003

871 Martinez, N., 1932. Las grandes erupciones del Tungurahua de los años 19 16-1918. *Publicaciones del Observatorio Astronomico de Quito. Seccion de Geofisica. Quito (Ecuador).*

873 Martínez, L.M., Valencia, L. G., Ceballos, J.A., Narváez, B.L., Pulgarín, B.A., Correa, A.M., Navarro, S.R., Murcia, H.F., Zuluaga, I., Rueda, J.B., Pardo, N., 2014. Geología y estratigrafía del Complejo Volcánico Nevado del Ruiz. *Geología de volcanes, Dirección de Geociencias básicas. Servicio Geológico Colombiano.*

877 Marty, B., 2012. The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. *Earth and Planetary Science Letters, Elsevier* 313-314, 56-66. https://doi.org/10.1016/j.epsl.2011.10.040
879 Marty, B., Jambon, A., 1987. C/³He in volatile fluxes from the solid Earth: implications for carbon geodynamics. Earth Planet. Sci. Lett. 83, 16-26. https://doi.org/10.1016/0012-821X(87)90047-1

881 Marty, B., Jambon, A., Sano, Y., 1989. Helium isotopes and CO₂ in volcanic gases of Japan. Chem. Geol. 76, 25-40. https://doi.org/10.1016/0009-2541(89)90125-3

883 Marty, B., Ozima, M., 1986. Noble gas distribution in oceanic basalt glasses. Geochimica et Cosmochimica Acta 50, 1093-1097. https://doi.org/10.1016/0016-7037(86)90390-XMason, E., Edmonds, M., Turchyn, A. V, 2017. Remobilization of crustal carbon may dominate volcanic arc emissions Science (80), 290-294. https://doi.org/10.1126/science.aan5049

887 Michelfelder, G.S., Feeley, T.C., Wilder, A.D., Klemetti, E.W., 2013. Modification of the Continental Crust by Subduction Zone Magmatism and Vice-Versa: Across-Strike Geochemical Variations of Silicic Lavas from Individual Eruptive Centers in the Andean Central Volcanic Zone. Geosciences 3, 633-667. https://doi.org/10.3390/geosciences3040633

891 Mooney, W.D., Laske, G. and Masters, T.G., 1998. CRUST 5.1: A Global Crust Model at 5 × 5 degrees. J. Geophys. Res. 103, 727-747. https://doi.org/10.1029/97JB02122

893 Montelli, R., Nolet, G., Dahlen, F.A., Masters, G., 2006. A catalogue of deep mantle plumes: new results from finite frequency tomography. Geochemistry, Geophys. Geosystems 7, Q11007. https://doi.org/10.1029/2006GC001248

896 Moreira, M., 2013. Noble gas constraints on the origin and evolution of earth's volatiles. Geochem. Perspec. 2, 229-230. https://doi.org/10.7185/geochempersp.2.2

898 Moreira, M., Blusztajn, J., Curtice, J., Hart, S., Dick, H., Kurz, M.D., 2003. He and Ne isotopes in oceanic crust: Implications for noble gas recycling in the mantle. Earth Planet. Sci. Lett. 216, 635-643. https://doi.org/10.1016/S0012-821X(03)00554-5

901 Moreira, M., Kunz, J., Allègre, C., 1998. Rare gas systematics in popping rock: Isotopic and elemental compositions in the upper mantle. Science (80) 279, 1178-1181. https://doi.org/10.1126/science.279.5354.1178

904 Mysen, B.O., Kushiro, I., Nicholls, I.A., Ringwood, A.E., 1974. A possible mantle origin for andesitic magmas: discussion of a paper by Nicholls and Ringwood. Earth Planet. Sci. Lett. 21, 221-229. https://doi.org/10.1016/0012-821X(74)90157-5

907 Narvaez, D.F., Rose-Koga, E.F., Samaniego, P., Koga, K.T., Hidalgo, S., 2018. Constraining magma sources using primitive olivine-hosted melt inclusions from Puñalica and Sangay volcanoes (Ecuador). Contrib. to Mineral. Petrol. 173, 80. https://doi.org/10.1007/s00410-018-1508-8

910 Nauret, F., Samaniego, P., Ancellin, M-A., Tournigand, P.-Y., Le Pennec, J.-L., Vlastelic, I., Gannoun, A., Hidalgo, S., Schiano, P., 2018. The genetic relationship between andesites and dacites at Tungurahua volcano, Ecuador. J. Volcanol. Geotherm. Res. 349, 283-297. https://doi.org/10.1016/j.jvolgeores.2017.11.012

914 Nicholls, I.A., Ringwood, A.E., 1972. Production of silica-saturated tholeiitic magmas in island arcs. Earth Planet. Sci. Lett. 17, 243-246. https://doi.org/10.1016/0012-821X(72)90282-8
916 Nocquet, J.M., Villegas-Lanza, J.C., Chlieh, M., Mothes, P.A., Rolandone, F., Jarrin, P., Cisneros, D.,
917 Alvarado, A., Audin, L., Bondoux, F., Martin, X., Font, Y., Régnier, M., Vallée, M., Tran, T., Beauval,
918 C., Maguiña Mendoza, J.M., Martinez, W., Tavera, H., Yepes, H., 2014. Motion of continental slivers
919 and creeping subduction in the northern Andes. Nat. Geosci. 7, 287–291.
920 https://doi.org/10.1038/ngeo2099

921 Notsu, K., Nakai, S., Igarashi, G., Ishibashi, J., Mori, T., Suzuki, M., Wakita, H., 2001. Spatial distribution
922 and temporal variation of 3He/4He in hot spring gas released from Unzen volcanic area, Japan. J.
923 Volcanol. Geotherm. Res. 111, 89–98. https://doi.org/10.1016/S0377-0273(01)00221-9

924 Ojeda, A., Havskov, J., 2001. Crustal structure and local seismicity in Colombia. J. Seismol. 5, 575–593.
925 https://doi.org/10.1023/A:1012053206408

926 Oppenheimer, C., Fischer, T.P., Scaillet, B., 2014. Volcanic Degassing: Process and Impact, 2nd ed,
927 Treatise on Geochemistry: Second Edition. Elsevier Ltd. https://doi.org/10.1016/B978-0-08-095975-7.
928 7.00304-1

929 Ozima, M., Igarashi, G., 2000. The primordial noble gases in the Earth: A key constraint on Earth evolution
930 models. Earth Planet. Sci. Lett. 176, 219–232. https://doi.org/10.1016/S0012-821X(00)00005-4

931 Ozima, M., Podosek, F.A. 1983. Noble Gas Geochemistry, 367. Cambridge, London, New York, New
932 Rochelle, Melbourne, Sydney: Cambridge University Press.
933 https://doi.org/10.1017/S0016756800029587

934 Ozima, M., Podosek, F.A. 2009. Noble Gases in the Earth. Noble Gas Geochemistry 217–252.
935 https://doi.org/10.1017/cbo9780511545986.009

936 Panter, K.S., Kyle, P.R., Smellie, J.L., 1997. Petrogenesis of a phonolite-trachyte succession at Mount
937 Sidley, Marie Byrd Land, Antarctica. J. Petrol. 38, 1225–1253.
938 https://doi.org/10.1093/petroj/38.9.1225

939 Paonita, A., Caracausi, A., Iacono-Marziano, G., Martelli, M., Rizzo, A., 2012. Geochemical evidence for
940 mixing between fluids exsolved at different depths in the magmatic system of Mt Etna (Italy).
941 Geochim. Cosmochim. Acta 84, 380–394. https://doi.org/10.1016/j.gca.2012.01.028

942 Paonita, A., Caracausi, A., Martelli, M., Rizzo, A.L., 2016. Temporal variations of helium isotopes in
943 volcanic gases quantify pre-eruptive refill and pressurization in magma reservoirs: The Mount Etna
944 case. Geology 44, 499–502. https://doi.org/10.1130/G37807.1

945 Pennington, W.D., 1981.Subduction of the Eastern Panama Basin and Seismotectonics of Northwestern
946 South America. J. Geophys. Res. 86, 10753-10770. https://doi.org/10.1029/JB086iB11p10753

947 Plank, T., Langmuir, C.H., 1988. The chemical composition of subducting sediment and its consequences
948 for the crust and mantle. Chemical Geology 145, 325–394.
949 https://doi.org/10.1594/PANGAEA.706145

950 Pistolesi, M., Rosi, M., Cion, R., Cashman, K. V., Rossotti, A., Aguilera, E., 2011. Physical volcanology
951 of the post-twelfth-century activity at Cotopaxi volcano, Ecuador: Behavior of an andesitic central
952 volcano. Bull. Geol. Soc. Am. 123, 1193–1215. https://doi.org/10.1130/B30301.1
953 Porcelli, D., Wasserburg, G.J., 1995a. Mass transfer of helium, neon, argon, and xenon through a steady-
954 state upper mantle. Geochim. Cosmochim. Acta 59, 4921-4937. https://doi.org/10.1016/0016-
955 7037(95)00336-3

956 Porcelli, D., Woolum, D., Cassen, P., 2001. Deep earth rare gases: Initial inventories, capture from the solar
957 nebula, and losses during moon formation. Earth Planet. Sci. Lett. 193, 237-251.
958 https://doi.org/10.1016/S0012-821X(01)00493-9

959 Prévot, R., Chatelain, J.-L., Guillier, B., Yepes, H., 1996. Tomographie des Andes Équatoriennes: évidence
d'une continuité des Andes Centrales. Comptes Rendus l'Académie des Sci. Paris 323, 833-840.

961 Protti, M., Giiendel, F., Mcnally, K., 1995. Correlation between the age of the subducting Cocos plate and
962 the geometry of the Wadati-Benioff zone under Nicaragua and Costa Rica. Geol. Soc. of America.
963 https://doi.org/10.1130/SPE295-p309

964 Rama, S.N.I., Hart, S.R., Roedder, E., 1965. Excess radiogenic argon in fluid inclusions. J. Geophys. Res.
965 70, 509-511. https://doi.org/10.1029/JZ070i002p00509

966 Reubi, O., Blundy, J., 2009. A dearth of intermediate melts at subduction zone volcanoes and the
967 petrogenesis of arc andesites. Nature 461, 1269-1273. https://doi.org/10.1038/nature08510

968 Ridolfi, F., Puerini, M., Renzulli, A., Menna, M., Toulkeridis, T., 2008. The magmatic feeding system of
969 El Reventador volcano (Sub-Andean zone, Ecuador) constrained by texture, mineralogy and
970 thermobarometry of the 2002 erupted products. J. Volcanol. Geotherm. Res. 176, 94-106.
971 https://doi.org/10.1016/j.jvolgeores.2008.03.003

972 Rizzo A.L., Caracausi, A., Favara, R., Martelli, M., Nuccio, P.M., Paonita, A., Rosciglione, A., Paternoster,
973 M., 2006. New insights into magma dynamics during last two eruptions of Mount Etna as inferred by
974 geochemical monitoring from 2002 to 2005. Geochem. Geophys. Geosyst. 7, Q06008.
975 https://doi.org/10.1029/2005GC001175

976 Rizzo, A.L., Grassa, F., Inguaggiato, S., Liotta, M., Longo, M., Madonia, P., Brusca, L., Capasso, G.,
977 Morici, S., Rouwet, D., Vita, F., 2009. Geochemical evaluation of observed changes in volcanic
978 activity during the 2007 eruption at Stromboli (Italy). J. Volcanol. Geot. Res. 182, 246-254.
979 https://doi.org/10.1016/j.jvolgeores.2008.08.004

980 Rizzo, A.L., Federico, C., Inguaggiato, S., Sollami, A., Tantillo, M., Vita, F., Bellomo, S., Longo, M.,
981 Grassa, F., Liuzzo, M., 2015a. The 2014 effusive eruption at Stromboli volcano (Italy): Inferences
982 from soil CO2 flux and 3He/4He ratio in thermal waters. Geophys. Res. Lett., 42(7), 2235-2243.
983 https://doi.org/10.1002/2014GL062955

984 Rizzo, A.L., Barberi, F., Carapezza, M.L., Di Piazza, A., Francalanci, L., Sortino, F., D'Alessandro, W.,
985 2015b. New mafic magma refilling a quiescent volcano: Evidence from He-Ne-Ar isotopes during
986 the 2011-2012 unrest at Santorini, Greece. Geochem. Geophys. Geosyst., 16, 798-814.
987 https://doi.org/10.1002/2014GC005653.

988 Rizzo, A.L., Caracausi, A., Chavagnac, V., Nomikou, P., Polymenakou, P.N., Mandalakis, M., Kotoulas,
989 G., Magoulas, A., Castillo, A., Lampridou, D., Marusczak, N., Sonke, J.E., 2019. Geochemistry of
990 CO2-Rich Gases Venting from Submarine Volcanism: the case of Kolumbo (Hellenic Volcanic Arc,
991 Greece). Front. Earth Sci. 7, 60. https://doi.org/10.3389/feart.2019.00060
992 Rizzo, A.L., Di Piazza, A., de Moor, J.M., Alvarado, G.E., Avard, G., Carapezza, M.L., Mora, M.M., 2016. Eruptive activity at Turrialba volcano (Costa Rica): Inferences from ³He/⁴He in fumarole gases and chemistry of the products ejected during 2014 and 2015. *Geochem. Geophys. Geosyst.*, 17, 4478–4494. https://doi.org/10.1002/2016GC006525.

996 Rizzo, A.L., Pelorosso, B., Coltorti, M., Ntaflos, T., Bonadiman, C., Matusiak-Małek, M., Italiano, F., Bergonzoni, G., 2018. Geochemistry of noble gases and CO₂ in fluid inclusions from lithospheric mantle beneath Wilcza Góra (Lower Silesia, Southwest Poland). *Frontiers in Earth Sciences* 6, 215. https://doi.org/10.3389/feart.2018.00215.

1000 Robidoux, P., Aiuppa, A., Rotolo, S.G., Rizzo, A.L., Hauri, E.H., Frezzotti, M.L., 2017. Volatile contents of mafic-to-intermediate magmas at San Cristóbal volcano in Nicaragua. *Lithos* 272–273, 147–163. https://doi.org/10.1016/j.lithos.2016.12.002

1003 Rudnick, R.L., Gao, S., 2013. Composition of the Continental Crust, 2nd ed, Treatise on Geochemistry: Second Edition. Elsevier Ltd. https://doi.org/10.1016/B978-0-08-095975-7.00301-6

1005 Rudnick, R.L., 1995. Nature and composition of the continental crust: a lower crustal perspective. *Phys. Earth Planet. Inter.* 145, 267–309. https://doi.org/10.1029/95RG01302

1007 Samaniego, P., Eissen, J.P., Le Pennec, J.L., Robin, C., Hall, M.L., Mothes, P., Chavrit, D., Cotten, J., 2008. Pre-eruptive physical conditions of El Reventador volcano (Ecuador) inferred from the petrology of the 2002 and 2004-05 eruptions. *J. Volcanol. Geotherm. Res.* 176, 82–93. https://doi.org/10.1016/j.jvolgeores.2008.03.004

1011 Samaniego, P., Le Pennec, J.L., Robin, C., Hidalgo, S., 2011. Petrological analysis of the pre-eruptive magmatic process prior to the 2006 explosive eruptions at Tungurahua volcano (Ecuador). *J. Volcanol. Geotherm. Res.* 199, 69–84. https://doi.org/10.1016/j.jvolgeores.2010.10.010

1014 Samaniego, P., Martin, H., Monzier, M., Robin, C., Fornari, M., Eissen, J.P., Cotten, J., 2005. Temporal evolution of magmatism in the Northern Volcanic Zone of the Andes: The geology and petrology of Cayambe volcanic complex (Ecuador). *J. Petrol.* 46, 2225–2252. https://doi.org/10.1093/petrology/egi053

1018 Samaniego, P., Robin, C., Chazot, G., Bourdon, E., Cotten, J., 2010. Evolving metasomatic agent in the Northern Andean subduction zone, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador). *Contrib. to Mineral. Petrol.* 160, 239–260. https://doi.org/10.1007/s00410-009-0475-5

1022 Sano, Y., Fischer, T.P., 2013. The analysis and interpretation of noble gases in modern hydrothermal systems. In: Burnard P. (eds) *The Noble Gases as Geochemical Tracers. Advances in Isotope Geochemistry*. Springer, Berlin, Heidelberg

1025 Sano, Y., Gamo, T., Williams, S.N., 1997. Secular variations of helium and carbon isotopes at Galeras volcano, Colombia. *J. Volcanol. Geotherm. Res.* 77, 255–265. https://doi.org/10.1016/S0377-0273(96)00098-4

1028 Sano, Y., Hirabayashi, J.I., Oba, T., Gamo, T., 1994. Carbon and helium isotopic ratios at Kusatsu-Shirane Volcano, Japan. *Appl. Geochemistry* 9, 371–377. https://doi.org/10.1016/0883-2927(94)90059-0
1030 Sano, Y., Kagoshima, T., Takahata, N., Nishio, Y., Roulleau, E., Pinti, D.L., Fischer, T.P., 2015. Ten-year helium anomaly prior to the 2014 Mt Ontake eruption. Sci. Rep. 5, 1–7.
1031 https://doi.org/10.1038/srep13069
1032 https://doi.org/10.1038/srep13069

1033 Sano, Y., Marty, B., 1995. Origin of carbon in fumarolic gas from island arcs. Chem. Geol. 119, 265-274.
1034 https://doi.org/10.1016/0009-2541(94)00097-R

1035 Sano, Y., Nakajima, J., 2008. Geographical distribution of ³He/⁴He ratios and seismic tomography in Japan. Geochem. J. 42, 51–60. https://doi.org/10.2343/geochemj.42.51

1037 Sano, Y., Nakamura, Y., Wakita, H., Urabe, A., Tominaga, T., 1984. Helium-3 Emission Related to Volcanic Activity Science 224,150-151. https://doi.org/10.1126/science.224.4645.150

1039 Sano, Y., Takahata, N., Seno, T., 2006. Geographical distribution of ³He/⁴He ratios in the Chugoku District, Southwestern Japan. Pure Appl. Geophys. 163, 745–757. https://doi.org/10.1007/s00024-006-0035-0

1041 Sano, Y., Wakita, H., 1985a. Geographical distribution of ³He/⁴He ratios in Japan: implications for arc tectonics and incipient magmatism. J. Geophys. Res. 90, 8729–8741.
1042 https://doi.org/10.1029/JB090iB10p08729
1043 https://doi.org/10.1029/JB090iB10p08729

1044 Sang, Y., Wakita, H., 1987. Helium isotopes and heat flow on the ocean floor. Chem. Geol. Isot. Geosci. Sect. 66, 217–226. https://doi.org/10.1016/0168-9622(87)90043-1

1046 Sang, Y., Wakita, H., 1988a. Helium isotope ratio and heat discharge rate in the Hokkaido Island, Northeast Japan. Geochem. J. 22, 293-303. https://doi.org/10.2343/geochemj.22.293

1048 Sano, Y., Wakita, H., Williams, S.N., 1990. Helium-isotope systematics at Nevado del Ruiz volcano, Colombia: implications for the volcanic hydrothermal system. J. Volcanol. Geotherm. Res. 42, 41–52. https://doi.org/10.1016/0377-0273(90)90068-Q

1051 Sano, Y., Williams, S.N., 1996. Fluxes of mantle and subducted carbon along convergent plate boundaries. Geophys. Res. Lett. 23, 2749-2752. https://doi.org/10.1029/96GL02260

1053 Sarda, P., Staudacher, T., Allègre, C.J., 1988. Neon isotopes in submarine basalts. Earth Planet. Sci. Lett. 91, 73–88. https://doi.org/10.1016/0012-821X(88)90152-5

1055 Scarsi, P., 2000. Fractional extraction of helium by crushing of olivine and clinopyroxene phenocrysts: Effects on the ³He/⁴He measured ratio. Geochimica et Cosmochimica Acta, 64, 3751–3762. https://doi.org/10.1016/S0016-7037(00)00419-1

1058 Schaefer, S.J., 1995. Nevado del Ruiz Volcano, Colombia: Magmatic System and Evolution, PhD. Thesis, Arizona State University. 147 pp.

1060 Schiano, P., Monzier, M., Eissen, J.P., Martin, H., Koga, K.T., 2010. Simple mixing as the major control of the evolution of volcanic suites in the Ecuadorian Andes. Contrib. to Mineral. Petrol. 160, 297–312. https://doi.org/10.1007/s00410-009-0478-2

1063 Schmidt, M.W., Jagoutz, O., 2017. The global systematics of primitive arc melts. Geochemistry, Geophys. Geosystems 18, 2817–2854. https://doi.org/10.1002/2016GC006699
1065 Shaw, A.M., Hilton, D.R., Fischer, T.P., Walker, J.A., de Leeuw, G.A.M., 2006. Helium isotope variations in mineral separates from Costa Rica and Nicaragua: Assessing crustal contributions, timescale variations and diffusion-related mechanisms. Chem. Geol. 230, 124-139.
1068 https://doi.org/10.1016/j.chemgeo.2005.12.003

1069 Shinoara, H., Fukui, K., Kazahaya, K., Saito, G., 2003. Degassing process of Miyakejima volcano: implications of gas emission rate and melt inclusion data. Dev. Volcanol. 5, 147-161.
1071 https://doi.org/10.1016/S1871-644X(03)80028-1

1072 Smye, A.J., Jackson, C.R.M., Konrad-Schmolke, M., Hesse, M.A., Parman, S.W., Shuster, D.L., Ballentine, C.J., 2017. Noble gases recycled into the mantle through cold subduction zones. Earth Planet. Sci. Lett. 471, 65-73. https://doi.org/10.1016/j.epsl.2017.04.046

1075 Sobolev, A.V., Chaussidon, M., 1996. H2O concentrations in primary melts from supra-subduction zones and mid-ocean ridges: Implications for H2O storage and recycling in the mantle. Earth Planet. Sci. Lett. 137, 45-55. https://doi.org/10.1016/0012-821x(95)00203-o

1078 Stern, C.R., 2004. Active Andean volcanism: its geologic and tectonic setting. Revista Geológica de Chile 31(2), 161-206. http://dx.doi.org/10.4067/S0716-02082004000200001

1080 Stern, R.J., 2002. Subduction zones. Rev. Geophys. 40(4), 1012. https://doi.org/10.1029/2001RG000108

1081 Stix, J., Zapata, J.A., Calvache, M.L., Cortes, G. P., Fischer, T.P., Gomez, D., Narvaez, L., Ordonez, M., Ortega, A., Torres, R., Williams, S.N., 1993. A model of degassing at Galeras Volcano, Colombia, 1988-1993. Geology 21, 963-967. https://doi.org/10.1130/0091-7613(1993)021<0963:AMODAG>2.3.CO;2

1085 Sturchio, N.C., Williams, S.N., Sano, Y., 1993. The hydrothermal system of Volcán Puracé, Colombia. Bull. Volcanol. 55, 289-296. https://doi.org/10.1007/BF00624356

1087 Syracuse E.M., Abers, G.A., 2006. Global compilation of variations in slab depth beneath arc volcanoes and implications. Geochem. Geophys. Geosyst. 7, Q05017. https://doi.org/10.1029/2005GC001045

1089 Syracuse, E.M., van Keken, P.E., Abers, G.A., Suetsugu, D., Bina, C., Inoue, T., Wiens, D., Jellinek, M., 2010. The global range of subduction zone thermal models. Phys. Earth Planet. Inter. 183, 73-90.
1091 https://doi.org/10.1016/j.pepi.2010.02.004

1092 Tassi, F., Vaselli, O., Barboza, V., Fernandez, E., Duarte, E., 2004. Fluid geochemistry and seismic activity in the period 1998-2002 at Turrialba Volcano (Costa Rica). Annals of Geophysics 47, 1501-1511. https://doi.org/10.4401/ag-3355

1095 Tatsumi, Y., 1989. Migration of fluid phases and genesis of basalt magmas in subduction zones. J. Geophys. Res. 94, 4697-4707. https://doi.org/10.1029/JB094iB04p04697

1097 Thouret, J.C., Cantagrel, J.M., Salinas, R., Murcia, A., 1990. Quaternary eruptive history of Nevado del Ruiz (Colombia). J. Volcanol. Geotherm. Res. 41, 225-251. https://doi.org/10.1016/0377-0273(90)90090-3
1100 Trenkamp, R., Kellogg, J.N., Freymueller, J.T., Mora, H.P., 2002. Wide plate margin deformation, southern
1101 Central America and northwestern South America, CASA GPS observations. J. South Am. Earth Sci.
1102 15, 157-171. https://doi.org/10.1016/S0895-9811(02)00018-4

1103 Trull, T.W., Kurz, M.D., 1993. Experimental measurements of 3He and 4He mobility in olivine and
1104 clinopyroxene at magmatic temperatures. Geochim. Cosmochim. Acta 57, 1313-1324.
1105 https://doi.org/10.1016/0016-7037(93)90068-8

1106 Trull, T.W., Kurz, M.D., 1999. Isotopic fractionation accompanying helium diffusion in basaltic glass. J.
1107 Mol. Struct. 485-486, 555-567. https://doi.org/10.1016/S0022-2860(99)00057-5

1108 Turner, S.J., Langmuir, C.H., Katz, R.F., Dungan, M.A., Escrig, S., 2016. Parental arc magma compositions
1109 dominantly controlled by mantle-wedge thermal structure. Nat. Geosci. 9, 772-776.
1110 https://doi.org/10.1038/ngeo2788

1111 Umeda, K., Asamori, K., Ninomiya, A., Kanazawa, S., Oikawa, T., 2007. Multiple lines of evidence for
1112 crustal magma storage beneath the Mesozoic crystalline Iide Mountains, northeast Japan. J. Geophys.
1113 Res. Solid Earth 112, 1-9. https://doi.org/10.1029/2006JB004590

1114 Vaca, S., Vallée, M., Nocquet, J.M., Alvarado, A., 2019. Active deformation in Ecuador enlightened by a
1115 new waveform-based catalog of earthquake focal mechanisms. J. South Am. Earth Sci. 93, 449-461.
1116 https://doi.org/10.1016/j.jsames.2019.05.017

1117 van der Hilst R.D., Widiyantoro S., Engdahl, E.R., 1997. Evidence for deep mantle circulation from global
tomography. Nature 386, 578-584. https://doi.org/10.1038/386578a0

1119 van Keken, P.E., Ballentine, C.J., 1999. Dynamical models of mantle volatile evolution and the role of
1120 phase transitions and temperature-dependent rheology. J. Geophys. Res. Solid Earth 104, 7137-7151.
1121 https://doi.org/10.1029/1999jb900003

1122 van Keken, P.E., Hauri, E.H., Ballentine, C.J., 2002. Mantle Mixing: The Generation, Preservation, and
1123 Destruction of Chemical Heterogeneity. Annu. Rev. Earth Planet. Sci. 30, 493-525.
1124 https://doi.org/10.1146/annurev.earth.30.091201.141236

1125 Vatin-Pérignon, N., Goemans, P., Oliver, R.A., Briqueu, L., Thouret, J.C., Salinas, R., Murcia, A., 1988.
1126 Magmatic evolution of the Nevado del Ruiz volcano, Central Cordillera, Colombia: Mineral chemistry
1127 and geochemistry. Géodynamique, ORSTOM 3, 163-194.

1128 Van Soest, M.C., Hilton, D.R., Kreulen, R., 1998. Tracing crustal and slab contributions to arc magmatism
1129 in the Lesser Antilles island arc using helium and carbon relationships in geothermal fluids. Geochim.
1130 Cosmochim. Acta 62, 3323-3335. https://doi.org/10.1016/S0016-7037(98)00241-5

1131 Vatin-Pérignon, N., Goemans, P., Oliver, R.A., Palacio, E.P., 1990. Evaluation of magmatic processes for
1132 the products of the Nevado del Ruiz Volcano, Colombia from geochemical and petrological data. J.
1133 Volcanol. Geotherm. Res. 41, 153-176. https://doi.org/10.1016/0377-0273(90)90087-V

1134 Wallace, P.J., 2005. Volatiles in subduction zone magmas: Concentrations and fluxes based on melt
1135 inclusion and volcanic gas data. J. Volcanol. Geotherm. Res. 140, 217-240.
1136 https://doi.org/10.1016/j.jvolgeores.2004.07.023
1137 Weber, M.B.I., Tarney, J., Kempton, P.D., Kent, R.W., 2002. Crustal make-up of the northern Andes: evidence based on deep crustal xenolith suites, Mercaderes, SW Colombia. Tectonophysics, 345, 49–82. https://doi.org/10.1016/S0040-1951(01)00206-2

1140 Wegner, W., Wörner, G., Harmon, R.S., Jicha, B.R., 2011. Magmatic history and evolution of the Central American Land Bridge in Panama since Cretaceous times. GSA Bulletin 123, 703-724. https://doi.org/10.1130/B30109.1

1143 Williams, S.N., Sano, Y., Wakita, H., 1987. Helium-3 emission from Nevado del Ruiz, Colombia. Geophys. Res. Lett. 14, 1035–1038. https://doi.org/10.1029/GL014i010p01035

1145 Yamamoto, J., Nishimura, K., Sugimoto, T., Takemura, K., Takahata, N., Sano, Y., 2009. Diffusive fractionation of noble gases in mantle with magma channels: Origin of low He/Ar in mantle-derived rocks. Earth Planet. Sci. Lett. 280, 167–174. https://doi.org/10.1016/j.epsl.2009.01.029

1148 Yepes, H., Audin, L., Alvarado, A., Beauval, C., Aguilar, J., Font, Y., Cotton, F., 2016. A new view for the geodynamics of Ecuador: implication in seismogenic source definition and seismic hazard assessment. Tectonics 35, 1249–1279. https://doi.org/10.1002/2015T C0039 41
1151 FIGURE CAPTIONS

1152 **Figure 1.** A:map showing the four volcanically active segments and volcanic gaps along the Andes (adapted from Stern, 2004). B:geological setting of the Northern Volcanic Zone (adapted from Bryant et al., 2006), showing the distribution of Quaternary volcanoes along the main magmatic arc (in light yellow); volcanoes included in this study are highlighted in red. On the upper left corner, arrows indicate the subduction direction of the Nazca and Cocos tectonic plates, overlapped on 50-meter resolution DEM map. C: Average dip angle of ~20° for Ecuadorian front arc (Yeses et al., 2016), and crustal thickness data (~50 km) is the average value proposed for the Ecuador segment (Vaca et al., 2019).

1159 **Figure 2.** A. ³He/⁴He (R/R<sub>A</sub>) vs ⁴He/²⁰Ne data from FIs and free gases (low-temperature and fumarolic gases). New data is shown in larger symbols (triangles are fumarolic gases from Galeras). Smaller triangles are fumarolic data from literature (Galeras, from Sano and Williams, 1996, and Sano et al., 1997; and Nevado del Ruiz, from Williams et al., 1987), whereas small squares represent data from low-temperature springs around Tungurahua and Cotopaxi (Inguaggiato et al., 2010). Note the ³He/⁴He avg. for Ecuador and Colombia are given as end-members for each arc segment. Blue and red curves describe a binary mixing between air (grey star) and a magma source with He-isotope compositions of 7.2 and 8.5 R<sub>A</sub>, respectively; and shaded area represents the MORB range (8±1 R<sub>A</sub>). B. ⁴He/²⁰Ne vs ⁴⁰Ar/³⁶Ar and ⁴⁰Ar/³⁶Ar vs ³He/³⁶Ar (inset) describing the general atmosphere-mantle mixing trends of the data reported for FIs and fumarolic gases.

1169 **Figure 3.** Helium characteristics of cogenetic olivine and orthopyroxene phenocrysts from Ecuador. A. He concentrates of pyroxenes are plotted against concentrations in cogenetic olivine; the 1:1 line is shown for reference in both. B. ³He/⁴He (R<sub>C</sub>/R<sub>A</sub>) ratios in orthopyroxene vs cogenetic olivine phenocrysts. Except for Cotopaxi lavas (R<sub>C</sub>/R<sub>A</sub> ratio in opx ~2.2 R<sub>A</sub>), note that ³He/⁴He ratios of olivine are indistinguishable of those obtained in cogenetic orthopyroxenes.

1174

1175 **Figure 4.** On the left: along-arc whole-rock trace element compositions of lavas from Nevado del Ruiz (Perignon et al., 1988), Galeras (Calvache and Williams, 1997a and b), Reventador (Samaniego et al., 2008), Cotopaxi (Garrison et al., 2011) and Tungurahua (Samaniego et al., 2011); shaded areas represent compositional variations between the lowest and highest value reported in literature for a given trace element ratio. At the bottom CO<sub>2</sub>/S<sub>T</sub> data is from Aiuppa et al., 2019 (in dark) and Lages et al., 2019 (in white); shaded areas represent the uncertainty associated with each volcanic gas measurement; note that CO<sub>2</sub>/S<sub>T</sub> values for Ecuador (Aiuppa et al., 2019) are predicted using regional/global relationships between the CO<sub>2</sub>/S<sub>T</sub> ratio of volcanic gases and whole-rock trace element compositions (e.g., Ba/La). On the right: geostatistical interpolation (kriging, Surfer 13 software) of along-arc ³He/⁴He for all locations reported in table 3; note that only maximum values were considered for each individual coordinate point.

1185 **Figure 5A.** Maximum R<sub>C</sub>/R<sub>A</sub> values reported in this study (in dark) and in literature (white symbols) for all five volcanoes. Data for Nevado del Ruiz is from Williams et al., 1987; Galeras is from Sano et al., 1997; Tungurahua and Cotopaxi data is from Inguaggiato et al., 2010. Note that dark yellow (Colombia) and red (Ecuador) dashed indicate R<sub>C</sub>/R<sub>A</sub> averages calculated using only the single highest value for each volcanic system. **Figure 5B.** Crustal thickness variations along the Northern Volcanic Zone from Schaefer (1995), Prévot et al. (1996), Guillier et al. (2001) and Bryant et al. (2006). Inset: CO<sub>2</sub>/³He systematics of NVZ fluids; Crust-mantle binary mixing line (in blue) assumes an R<sub>A</sub> of 8.5 (avg. Colombia).
1192 **Table 1.** Noble gas abundances and isotope ratios of mafic phenocrysts from Colombia and Ecuador

(Northern Volcanic Zone – Andean Volcanic Belt)

1193

**Table 2.** Noble gas compositions of fumarolic gases sampled at the central crater of Galeras, Colombia.

1195 **Table 3.** Helium isotope data compilation for Northern Volcanic Zone Quaternary volcanoes and hydrothermal areas.

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Lages et al. Figure 1

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Lages et al., Figure 3

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<table><caption>**Table 1**
Noble gas abundances and isotope ratios from mafic phenocrysts from Colombia and Ecuador (Northern Volcanic Zone – Andean Volcanic Belt)</caption><thead><tr><th>Volcano</th><th>Sample ID</th><th>Sample details</th><th>Rock</th><th>Min. phase</th><th>Weight (g)</th><th>[He]<br>x10<sup>-15</sup></th><th>[Ne]<br>x10<sup>-14</sup></th><th>[<sup>40</sup>Ar]<br>x10<sup>-12</sup></th><th>[<sup>36</sup>Ar]<br>x10<sup>-15</sup></th><th>[<sup>40</sup>Ar*]<br>x10<sup>-13</sup></th><th>CO<sub>2</sub><br>x10<sup>-9</sup></th><th><sup>4</sup>He/<sup>20</sup>Ne</th><th><sup>20</sup>Ne/<sup>22</sup>Ne</th><th><sup>21</sup>Ne/<sup>22</sup>Ne</th><th>He'Ar*</th><th><sup>40</sup>Ar/<sup>36</sup>Ar</th><th><sup>3</sup>He/<sup>4</sup>He<br>(R/R<sub>A</sub>)</th><th><sup>3</sup>He/<sup>4</sup>He<br>(R<sub>C</sub>/R<sub>A</sub>)</th><th>CO<sub>2</sub>/<sup>3</sup>He<br>x10<sup>9</sup></th></tr></thead><tbody><tr><td colspan="17" style="text-align: left; font-weight: bold;">Colombia</td></tr><tr><td>Nev. del Ruiz</td><td>JCH-04</td><td>Fissure lavas</td><td>BA</td><td>Oliv</td><td>0.99</td><td>0.24</td><td>0.48</td><td>1.65</td><td>5.46</td><td>0.40</td><td>0.16</td><td>5.0</td><td>10.12 ± 0.03</td><td>0.0297 ±<br>0.0005</td><td>0.60</td><td>302.8 ± 0.1</td><td>7.96</td><td>8.46 ± 0.26</td><td>0.56</td></tr><tr><td rowspan="2">Galeras</td><td>GA1</td><td>Fissure lavas</td><td>BA</td><td>Oliv</td><td>1.07</td><td>1.19</td><td>0.22</td><td>1.25</td><td>4.09</td><td>0.39</td><td>0.62</td><td>54.6</td><td>9.83 ± 0.04</td><td>0.0284 ±<br>0.0007</td><td>3.08</td><td>304.9 ± 0.1</td><td>5.70</td><td>5.73 ± 0.12</td><td>0.66</td></tr><tr><td>GA2</td><td>Fissure lavas</td><td>BA</td><td>Oliv</td><td>0.79</td><td>0.78</td><td>0.13</td><td>0.30</td><td>0.89</td><td>0.41</td><td>0.31</td><td>59.0</td><td>9.95 ± 0.08</td><td>0.0298 ±<br>0.0013</td><td>1.89</td><td>341.9 ± 0.3</td><td>6.87</td><td>6.90 ± 0.16</td><td>0.42</td></tr><tr><td colspan="17" style="text-align: left; font-weight: bold;">Ecuador</td></tr><tr><td rowspan="2">Cotopaxi</td><td rowspan="2">COT.LF.1B</td><td rowspan="2">Lava flow</td><td rowspan="2">A</td><td>Oliv</td><td>0.19</td><td>1.68</td><td>0.10</td><td>0.87</td><td>2.62</td><td>0.96</td><td>9.26</td><td>171.3</td><td>10.46 ± 0.18</td><td>-</td><td>1.75</td><td>332.2 ± 0.5</td><td>7.03</td><td>7.04 ± 0.28</td><td>5.64</td></tr><tr><td>Opx</td><td>1.12</td><td>0.12</td><td>0.53</td><td>2.19</td><td>7.35</td><td>0.18</td><td>1.14</td><td>2.2</td><td>9.90 ± 0.02</td><td>0.0287 ±<br>0.0004</td><td>0.66</td><td>297.9 ± 0.1</td><td>2.00</td><td>2.22 ± 0.30</td><td>3.19</td></tr><tr><td rowspan="2">Reventador</td><td rowspan="2">REV.BB007<br>#16</td><td rowspan="2">Lava flow</td><td rowspan="2">A</td><td>Oliv</td><td>0.33</td><td>11.70</td><td>0.22</td><td>1.97</td><td>4.17</td><td>7.34</td><td>69.4</td><td>522.3</td><td>10.15 ± 0.08</td><td>0.0376 ±<br>0.0001</td><td>1.59</td><td>471.7 ± 0.1</td><td>6.97</td><td>6.98 ± 0.08</td><td>6.13</td></tr><tr><td>Opx</td><td>0.44</td><td>3.23</td><td>1.50</td><td>6.67</td><td>21.90</td><td>1.84</td><td>8.63</td><td>21.5</td><td>9.97 ± 0.03</td><td>0.0306 ±<br>0.0001</td><td>1.75</td><td>303.9 ±<br>0.04</td><td>6.71</td><td>6.80 ± 0.13</td><td>2.83</td></tr><tr><td rowspan="2">Tungurahua</td><td rowspan="2">Tung 1100</td><td rowspan="2">Tephra<br>deposits</td><td rowspan="2">A</td><td>Oliv</td><td>0.23</td><td>17.70</td><td>3.30</td><td>8.75</td><td>26.20</td><td>10.00</td><td>31.1</td><td>53.8</td><td>9.97 ± 0.02</td><td>0.0297 ±<br>0.0002</td><td>1.77</td><td>333.8 ± 0.2</td><td>7.05</td><td>7.08 ± 0.09</td><td>1.78</td></tr><tr><td>Opx</td><td>0.89</td><td>2.55</td><td>2.88</td><td>5.88</td><td>19.60</td><td>0.87</td><td>0.70</td><td>8.9</td><td>9.98 ± 0.01</td><td>0.0294 ±<br>0.0002</td><td>2.92</td><td>300.0 ± 0.1</td><td>6.87</td><td>7.10 ± 0.12</td><td>0.28</td></tr><tr><td rowspan="2">Tung 2006</td><td rowspan="2"></td><td rowspan="2">Block<br>PDC</td><td rowspan="2">A</td><td>Oliv</td><td>0.24</td><td>14.40</td><td>1.77</td><td>6.23</td><td>19.50</td><td>4.79</td><td>60.8</td><td>81.1</td><td>10.02 ± 0.02</td><td>0.0310 ±<br>0.0003</td><td>3.00</td><td>320.0 ± 0.2</td><td>7.37</td><td>7.40 ± 0.10</td><td>4.11</td></tr><tr><td>Opx</td><td>0.87</td><td>1.40</td><td>1.35</td><td>4.33</td><td>14.30</td><td>0.97</td><td>0.84</td><td>10.4</td><td>9.97 ± 0.02</td><td>0.0293 ±<br>0.0002</td><td>1.45</td><td>302.3 ± 0.1</td><td>7.19</td><td>7.39 ± 0.11</td><td>0.58</td></tr></tbody></table>

Host rock chemical classification on the basis of SiO₂ contents: A (andesite), BA (basaltic-andesite)

Noble gas and CO₂ concentrations in mol g⁻¹

Mineral phases analyzed: Oliv (olivine), Opx (orthopyroxene)
<caption>Table 2</caption>

Noble gas compositions of fumarolic gases sampled at the central crater of Galeras, Colombia

<table><thead><tr><th>Galeras</th><th>date</th><th>Lat, Long (N, W)</th><th>Temp. (°C)</th><th>[He] ppm</th><th>CO<sub>2</sub> %</th><th><sup>40</sup>Ar* ppm</th><th><sup>4</sup>He/<sup>20</sup>Ne</th><th>He/Ar*</th><th><sup>40</sup>Ar/<sup>36</sup>Ar</th><th><sup>3</sup>He/<sup>4</sup>He <sup>a</sup> (R/R<sub>A</sub>)</th><th><sup>3</sup>He/<sup>4</sup>He <sup>b</sup> (R<sub>C</sub>/R<sub>A</sub>)</th><th>CO<sub>2</sub>/<sup>3</sup>He x10<sup>10</sup></th></tr></thead><tbody><tr><td>Central crater</td><td>14 Jul 2017</td><td>1.221, -75.360</td><td>91.3</td><td>2.18</td><td>93.41</td><td>-</td><td>7.29</td><td>-</td><td>-</td><td>8.01</td><td>8.33 ± 0.07</td><td>3.71</td></tr><tr><td>Central crater</td><td>14 Jul 2017</td><td>1.221, -75.359</td><td>87.5</td><td>1.93</td><td>96.15</td><td>1.40</td><td>29.63</td><td>1.38</td><td>302.1 ± 0.2</td><td>8.11</td><td>8.19 ± 0.07</td><td>4.38</td></tr></tbody></table>

<footnote><sup>a</sup> R/R<sub>A</sub> = <sup>3</sup>He/<sup>4</sup>He<sub>(meas.)</sub><sup>3</sup>He/<sup>4</sup>He<sub>(air)</sub> [<sup>3</sup>He/<sup>4</sup>He<sub>(air)</sub> = 1.4×10<sup>-6</sup>].</footnote>

<footnote><sup>b</sup> R<sub>C</sub>/R<sub>A</sub> is the air corrected He isotopic ratio based on the <sup>4</sup>He/<sup>20</sup>Ne ratio (Giggenbach et al., 1993).</footnote>

<footnote>Note: only <sup>40</sup>Ar/<sup>36</sup>Ar > 300 are reported in order to avoid overestimation of <sup>40</sup>Ar*</footnote>
<caption>Table 3</caption>

Helium isotope data compilation for Northern Volcanic Zone Quaternary volcanoes and hydrothermal areas.

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<table><thead><tr><th rowspan="2">Colombia</th><th rowspan="2">Latitude</th><th colspan="4">Low-T hydrothermal sources</th><th colspan="4">High-T fumarolic gases</th><th colspan="4">Fluid Inclusions (Oliv, Opx)</th></tr><tr><th>Max</th><th>Avg.</th><th>Nr. samples</th><th>Ref.</th><th>Max</th><th>Avg.</th><th>Nr. samples</th><th>Ref.</th><th>Max</th><th>Avg.</th><th>Nr. samples</th><th>Ref.</th></tr></thead><tbody><tr><td>Nevado del Ruiz</td><td>4.89</td><td>6.4</td><td>3.9±1.4</td><td>22</td><td>1,2</td><td>6.3</td><td>---</td><td>1</td><td>1</td><td>8.5</td><td>---</td><td>1</td><td>*</td></tr><tr><td>Cerro Machín</td><td>4.48</td><td>5.9</td><td>5.2±0.9</td><td>2</td><td>3</td><td>6.75</td><td>---</td><td>1</td><td>4</td><td>---</td><td>---</td><td>n/d</td><td>---</td></tr><tr><td>Purace</td><td>2.31</td><td>6.7</td><td>4.9±1.3</td><td>8</td><td>5</td><td>7.1</td><td>6.4±0.5</td><td>4</td><td>5,6</td><td>---</td><td>---</td><td>n/d</td><td>---</td></tr><tr><td>Galeras</td><td>1.22</td><td>4.6</td><td>2.0±1.3</td><td>7</td><td>7</td><td>8.8</td><td>7.7±0.9</td><td>20</td><td>4, 7, *</td><td>6.9</td><td>6.3±0.8</td><td>2</td><td>*</td></tr><tr><td>Cumbal</td><td>0.94</td><td>5.5</td><td>---</td><td>1</td><td>8</td><td>7.9</td><td>6.3±0.9</td><td>10</td><td>4, 8</td><td>---</td><td>---</td><td>n/d</td><td>---</td></tr><tr><th colspan="15">Ecuador</th></tr><tr><td>Reventador</td><td>-0.08</td><td>---</td><td>---</td><td>n/d</td><td>---</td><td>---</td><td>---</td><td>n/d</td><td>---</td><td>7.0</td><td>6.9±0.1</td><td>2</td><td>*</td></tr><tr><td>Guagua Pichincha</td><td>-0.17</td><td>3.4</td><td>---</td><td>1</td><td>9</td><td>4.1</td><td>4.1±0.2</td><td>2</td><td>p.c.</td><td>---</td><td>---</td><td>---</td><td>---</td></tr><tr><td>Cotopaxi</td><td>-0.70</td><td>6.8</td><td>---</td><td>1</td><td>9</td><td>---</td><td>---</td><td>---</td><td>---</td><td>7.0</td><td>4.6±3.4</td><td>2</td><td>*</td></tr><tr><td>Tungurahua</td><td>-1.45</td><td>2.7</td><td>4.6±0.7</td><td>2</td><td>9</td><td>---</td><td>---</td><td>---</td><td>---</td><td>7.4</td><td>7.2±0.2</td><td>4</td><td>*</td></tr><tr><td>Chimborazo</td><td>-1.47</td><td>2.1</td><td>---</td><td>1</td><td>9</td><td>---</td><td>---</td><td>---</td><td>---</td><td>---</td><td>---</td><td>---</td><td>---</td></tr><tr><th colspan="15">Other sites</th></tr><tr><td>Cuicocha</td><td>0.29</td><td>6.3</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Pululahua</td><td>0.01</td><td>3.7</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>El Pisque Balneario</td><td>0.00</td><td>4.2</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Balneario Oyacachi</td><td>-0.22</td><td>2.6</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Jamanco</td><td>-0.38</td><td>7.1</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Cachiyacu Cueva</td><td>-0.41</td><td>6.5</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Cachiyacu</td><td>-0.41</td><td>4.2</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Aguas calientes</td><td>-0.44</td><td>3.4</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Quilotoa</td><td>-0.86</td><td>2.1</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>S. Vicente</td><td>-2.23</td><td>0.1</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Jesus Maria</td><td>-2.63</td><td>0.3</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Guapan</td><td>-2.71</td><td>0.7</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>El Mozo</td><td>-3.44</td><td>0.2</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Portovelo</td><td>-3.70</td><td>0.9</td><td>---</td><td>1</td><td>9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

Max: maximum R<sub>C</sub>/R<sub>A</sub> value for a given sampling media

Avg: average of all samples for a given sampling media ± 1 σ

Ref. 1. Williams et al., 1987; 2. Sano et al., 1990; 3. Inguaggiato et al., 2016; 4. Sano and Williams, 1996; 5. Sturchio et al., 1993; 6. Maldonado et al., 2017; 7. Sano et al., 1997; 8. Lewicki et al., 2000; 9. Inguaggiato et al., 2010. *This investigation; p.c. personal communication (unpublished)
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