# New insights from plumbing system below composite mafic volcanoes: Post-glacial volatile contents and magmatic fluids from Villarrica magmas

Philippe Robidoux, Yves Moussallam, Estelle F. Rose-Koga, Andrea Luca

Rizzo, Guillaume Georgeais, Joao Lages, Gilles Lévresse, Simona Ferrando, Alessandro Aiuppa

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Philippe Robidoux, Yves Moussallam, Estelle F. Rose-Koga, Andrea Luca Rizzo, Guillaume Georgeais, et al. New insights from plumbing system below composite mafic volcanoes: Post-glacial volatile contents and magmatic fluids from Villarrica magmas. Lithos, 2024, pp.107786. 10.1016/j.lithos.2024.107786. insu-04690511

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New insights from plumbing system below composite mafic volcanoes: Post-glacial volatile contents and magmatic fluids from Villarrica magmas

Philippe Robidoux, Yves Moussallam, Estelle F. Rose-Koga, Andrea Luca Rizzo, Guillaume Georgeais, Joao Lages, Gilles Lévresse, Simona Ferrando, Alessandro Aiuppa

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PII: S0024-4937(24)00299-8

DOI: https://doi.org/10.1016/j.lithos.2024.107786

Reference: LITHOS 107786

To appear in: *LITHOS*

Received date: 5 February 2024

Revised date: 26 August 2024

Accepted date: 30 August 2024

Please cite this article as: P. Robidoux, Y. Moussallam, E.F. Rose-Koga, et al., New insights from plumbing system below composite mafic volcanoes: Post-glacial volatile contents and magmatic fluids from Villarrica magmas, *LITHOS* (2024), https://doi.org/10.1016/j.lithos.2024.107786

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
**New insights from plumbing system below composite mafic volcanoes: post-glacial volatile contents and magmatic fluids from Villarrica magmas »**

**Author names and affiliations:** Philippe Robidoux<sup>a</sup>, Yves Moussallam<sup>b,c</sup>, Estelle F. Rose-Koga<sup>d</sup>, Andrea Luca Rizzo<sup>e,f</sup>, Guillaume Georgeais<sup>b</sup>, Joao Lages<sup>g,h</sup>, Gilles Lévresse<sup>i</sup>, Simona Ferrando<sup>j,k</sup>, Alessandro Aiuppa<sup>g,h</sup>

**Corresponding author.**

Dr. Philippe Robidoux

Department of Geology, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, 8370450, Santiago, Chile

E-mail address: robidouxphilippe@gmail.com

<footnote><sup>a</sup>Department of Geology, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 8370450 Santiago, Chile</footnote>

<footnote><sup>b</sup>Lamont-Doherty Earth Observatory, Columbia University, New York, USA</footnote>

<footnote><sup>c</sup>American Museum of Natural History, Department of Earth and Planetary Sciences, NY 10024, New York, USA</footnote>

<footnote><sup>d</sup>Institut des Sciences de la Terre d'Orléans (ISTO), CNRS UMR 7327, Université d'Orléans, BRGM, 1A rue de la Férollerie, 45071 Orléans, Cedex 2, France</footnote>

<footnote><sup>e</sup>Dipartimento di Scienze dell'Ambiente e della Terra, Università degli Studi di Milano-Bicocca, Piazza della Scienza 4, 20126 Milano, Italy</footnote>

<footnote><sup>f</sup>Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Milano, Via Alfonso Corti 12, 20133 Milano, Italy</footnote>

<footnote><sup>g</sup>Dipartimento DiSTeM, Università degli Studi di Palermo, Palermo, Italy</footnote>

<footnote><sup>h</sup>Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo, Via Ugo La Malfa 153, 90146, Palermo, Italy</footnote>

<footnote><sup>i</sup>Centro de Geociencias, UNAM Campus Juriquilla Blvd. Juriquilla 3001, Querétaro 76230, Mexico</footnote>

<footnote><sup>j</sup>Department of Earth Sciences, University of Torino, Via Valperga Caluso 35,10125, Torino, Italy</footnote>

<footnote><sup>k</sup>Consiglio Nazionale delle Ricerche - Istituto di Geoscienze e Georisorse (CNR-IGG), Sezione di Torino, via Valperga Caluso 35, 10125 Torino, Italy</footnote>
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**Abstract**

Villarrica volcano, in the southern Andes, is a composite mafic volcano whose persistent open-vent activity is punctuated by frequent Strombolian/Hawaiian eruptions and, more rarely, by more energetic (sub-Plinian) events. Here, we investigate the volatile composition of the parental melts that sustain this activity, and the conditions of pre-eruptive magma storage, by characterizing the composition of olivine-hosted melt and fluid inclusions. We concentrate on inclusions entrapped in minerals from pyroclastic materials erupted from both Villarrica summit and from its flank Minor Eruptive Centers (MECs) post the 14.5-13.5 kyr caldera collapse event that formed the Licán ignimbrite. Our micro-FTIR and SIMS measurements indicate that the Pucón eruption records the highest volatile contents, with 6.0 wt.% H₂O, >1500 ppm CO₂, 1330 ppm S, 1556 ppm Cl, and 2055 ppm F. These volatile contents imply a volatile-saturated magma originating from a depth of 14.4 to 17 km below Villarrica. Results for other flank eruptions highlight a similarly deep (17–21 km depth) source for basaltic CO₂-rich mafic magmas erupted at regional MECs (Los Nevados, Caburgua). Melt inclusion results also reveal that deep rising mafic magma batches, when temporarily stored at 1–5 km depth, produce the more differentiated and degassed magma batches that sustain the decadal-old persistent effusive-explosive eruptive activity at Villarrica. Helium isotope ratios (³He/⁴He; Rc/Ra when corrected for atmosphere) measured in bulk noble gases from olivines (Fo₇₅–₈₈) indicate that the parental magmatic fluid signature (Rc/Ra = 6.7–7.6; CO₂/³He = 4.7–7.5E+⁰⁸) is only recorded during central paroxysmal subplinian eruption, and that this primitive gas signal is diluted in lateral MECs (Rc/Ra<6.5; CO₂/³He = 1.4x10+⁹–3.1x10+¹⁰).

**Keywords**

Composite volcano, Mafic magma, Melt inclusion, Noble gas, Eruptive Paroxysm
# 1. Introduction

Villarrica, located at 39°24'S and 71°55'W (Fig. 1a), is one of the few composite volcanoes worldwide hosting an active lava lake (e.g., Witter et al., 2004; Moussallam et al., 2016, 2023). The volcano, one of the most active of the Southern Andes Volcanic Zone (SVZ) that formed as a consequence of the subduction of the 12–20 My-old Nazca plate beneath the South American plate (Jarrard, 1986; Stern, 2004), typically produces Strombolian/Hawaiian volcanic activity at its central (summit) vent. However, geological evidence also exists for more energetic Vulcanian to sub-Plinian eruptions (Silva et al., 2010; Costantini et al., 2011; Lohmar et al., 2012) and for mafic ignimbrite-forming eruptions (Moreno and Clavero, 2006), as observed elsewhere as a consequence of fast ascent, decompressional degassing, and fragmentation of basaltic magma (Moitra et al., 2018; Stix, 2007; Heinrich et al., 2020). Postglacial volcano stratigraphy also indicates frequent outbursts of voluminous lava flows accompanied by small explosive eruptions, resulting in the formation of spreading clusters of minor eruptive centers (MECs) (Moreno and Clavero, 2006). Examples of these volcanic centers are Caburgua-Huelemolle Small Eruptive Centers (CHSEC), located in the southern sector of lake Caburgua, a few kilometers northeast of the Villarrica stratovolcano, and the small eruptive centers on Villarrica flank itself (McGee et al., 2017). As seen at other mafic volcanoes worldwide (Smith and Németh, 2017; Robidoux et al., 2020), MECs can allow characterizing magma transport from the volcanic edifice towards its peripheries.

Stratigraphic mapping at Villarrica over the last few decades has led to an improved model of the eruptive sequence (Moreno and Clavero 2006) as monitoring and risk management programs (Muñoz et al., 2024). However, understanding how magma origin, evolve and eruptive properties control the switch between such different activity styles at Villarrica (Moreno and Clavero, 2006) requires a thorough examination of pre-eruptive magma conditions since volatiles are especially key factors in controlling eruptive style and explosivity at basaltic volcanoes (Cashman et al. 2017). The study of melt inclusions (MIs; e.g., Wallace et al., 2021) hosted in mafic phenocrysts from volcanic rocks is especially suitable for investigating pre-eruptive conditions. Hence, our attempt here is to characterize the magmatic plumbing system that sustains the variety of eruption styles at Villarrica by studying the pre-eruptive volatile contents in the source parental magmas of both central and peripheral volcanic centers. Our aim, in particular, is to determine whether magmas erupted at the post-glacial regional edifices (MECs), and at the flank volcanic centers that formed within the current 2 km-wide caldera (Villarrica Unit 3, <~ 3.7 Kyr AP; Moreno and Clavero, 2006), share the same characteristics (same volatile content) as those erupted at the volcano summit. We complement this analysis of Villarrica pre-eruptive magma conditions (from melt inclusion major volatile contents) with the determination of volatile chemistry and isotope compositions (noble gases) in fluid inclusions (FIs), in the attempt to characterize the magmatic fluid source.
## 2. Tectonic context and post glacial magmatic volatile background

Villarrica is part of the oblique Villarrica-Quetrupillán-Lanín chain in front of the Southern Volcanic Zone (SVZ). It is bounded by the Juan Fernandez Ridge at its northern edge (~33°S) and the Chile Rise to the south (~46°S) (Fig. 1 a). Volcanism in the Andes is the result of the subduction of the Nazca (10–60 My old) and Antarctic oceanic plates (<12–24 My old) beneath the South American continental plate (Stern, 2004), which is moving obliquely (20–30°) to the NE at a rate of 7–9 cm/yr (DeMets, 2001). The basement beneath the Pleistocene-to-Holocene SVZ stratovolcanoes consists of continental crust which is ~ 35–60 km in thickness, above a shallowly dipping (< 25°) Benioff zone (Tassara and Echaurren, 2012). Where the mantle wedge is less well developed (~ 50 km thick), the overlying crust is much younger, with Paleozoic pre-Andean basement and Mesozoic-Cenozoic igneous rocks (Stern, 2004). Within the tectonic context, Villarrica has undergone eruptions of magma evolving at shallow crustal depths, sourced from > 45 km depth in the MOHO-lithospheric mantle (Tassara and Echaurren, 2012; Hickey-Vargas et al., 2016).

Villarrica volcano is close to densely populated urban and tourist areas, and has persistent degassing (e.g., Moussallam et al., 2016; Liu et al., 2019) and frequent effusive and explosive activity (Costantini et al., 2011). Petrological studies and the interpretation of seismic and geodetic data indicate a wide range of pre-eruptive magma storage conditions, in the range of 1.5–8 km in depth (Lohmar et al. 2012; Delgado et al., 2017; Lehr et al., 2022), considering volatile saturation conditions farther below ~12 km depth (Cortés et al., 2024). Pressures conditions determined with crystallization geothermobarometric methods delivered 0.9–3.5 kb values using augite-melt pair (Cortés et al., 2024) and may reach > 7 kb with olivine-augite pair models to represent post-1971 actual crater conditions (Boschetty et al., 2022) (8.1±1.7 kb; Morgado et al., 2015). According to mineral-liquid geothermobarometry, the last Strombolian paroxysm, characterized by lava fountaining, may have been sourced from magma stored at conditions of 0.2–3.5 kb pressure range and a temperature around ~1140 °C (Romero et al., 2022, Moussallam et al., 2023). Farther beyond Villarrica flank and regional MEC such as CHSEC, between 10.8 and 11.4 1.7 kb were measured in Caburgua according to olivine-augite phenocrysts (Morgado et al., 2015). Since Caburgua have been classified between 8,6 and 6, Kyr AP according to stratigraphic relationship with Villarrica Unit 2 (Moreno and Clavero, 2006), Caburgua cone could exceed the age of Pucón Ignimbrite, but younger than Licán Ignimbrite.

Three major evolutionary steps define the construction and collapse of Villarrica stratovolcano, with respect to past deglaciation ages (Moreno and Clavero, 2006; Watt et al., 2013). The occurrence of major VEI events has been identified from volcano stratigraphy and ¹⁴C geochronology, from the oldest identified intra-glacial Pyroclastic Deposit of 40–14 ky to several post-glacial to Holocene events (Moreno and Clavero, 2006). The history
associated with the development of the stratovolcano is divided into Villarrica units 1, 2, and 3. We focus here on Unit 3 of Villarrica because it represents the series of volcanic layers that cover the current structure of Caldera 2 (Fig. 1b; Moreno and Clavero, 2006), which formed after the 14.5–13.5 ky BP ($^{14}$C date) Licán ignimbrite and reached a minimum depth of 1.5 km (6.8 kb) and marked the end of a major volcanic cycle at Villarrica (Lohmar et al., 2012).

At central crater, so far 5 eruptive events, Pucón Ignimbrite, Chaimilla (Pioli et al., 2015), 1971, 1984 and 2015 have been studied to quantify S and Cl contents in MIs by electron microprobe. These studies report maximum contents of 1230 ppm S and 963 ppm Cl (Pioli et al., 2015; Cortés et al., 2024; Mason et al., 2024). In sequences from Chaimilla fallout, the 1971 to 2000s tephra series, H₂O and CO₂ were determined by Fourier Transform Infrared Microspectrometry (FTIR) technique used and the following maximums values were determined; 2.7 wt.% and 500 ppm, respectively (Pioli et al., 2015; Cortés et al., 2024). Elsewhere on NE Villarrica flanks, in the Los Nevados sector (Gr. 2), the H₂O and CO₂ contents have reached values up to 3.0 wt.% and 1586 ppm, respectively (Robidoux et al., 2021).

### 3. Methodology

#### 3.1 Global Strategy

The method proposed here to investigate pre-eruptive conditions is based on the study of MIs hosted in mafic phenocrysts from volcanic rocks. The idea behind this approach is to characterize the chemistry of the magmatic fluids associated with eruptive products coming from a deeper source in the volcano-magmatic plumbing system of the whole Villarrica complex. Specifically, to study the "magmatic volatile" content at saturated conditions, this study relies on the MIs which represent, at a given pressure and temperature, trapped silicate melt, with in some cases, magmatic fluids produced and exsolved during igneous processes. Those fluids are assumed to be the source of volatile elements (H₂O, CO₂, S, Cl, F; e.g. Wallace et al., 2021) and for this reason, the term "magmatic fluids" here refers to the exsolved gases that moves through magmatic conduits to the surface.

It is possible to trace the origin of the magmatic fluids by measuring the specific noble gas isotopic $^{3}$He/$^{4}$He ratio of fluid inclusions (FIs) in olivine phenocrysts, at the time of eruption (e.g. Hilton et al., 2002). For example, previous authors showed that $^{3}$He/$^{4}$He measurements in olivine-hosted FIs from the 2015 Villarica eruption have an isotopic signature as high as 6.7 Ra (Lages et al., 2021b). This is still lower than the typical homogeneous Andean signature in the mantle along the South American Arc of 8–9 Ra (Lages et al., 2021a,b). Even though, uncertainties exist on local cause behind variation on isotopic helium variations at this volcano (Lages et al., 2021a). To explore further on this issue, we investigate $^{3}$He/$^{4}$He variations in olivine-hosted FIs from magma batches generated
within the post-glacial eruptive period at Villarrica. This latter implies sampling additional regional MECs and several pyroclastic deposits pertaining to central crater explosive paroxysm that were supplied by mafic magmas.

## 3.2 Petrologic Approach

The major eruptive events have been studied through a series of n = 15 volcanic rock units sampled from Villarrica and the MECs (Table 1). The most well-documented explosive mafic eruptions at Villarrica were selected because they were produced chronologically after the Licán ignimbrite, so that we can focus on the postglacial context of the actual Villarrica edifice. The list of samples and analytical methods is given in Tables 1 and 2, with full details of the methodology given in Appendix A “Supplementary Material Methodology Review” as result tables in Appendix B (Tables A.1 to A.10).

To obtain preserved volcanic rock products, volcanic deposits known from literature were systematically sampled between 2017 and 2022 on Villarrica flanks (Fig. 1b), targeting juvenile pyroclasts representing rapid cooling rates to best preserve original magmatic fluids and volatile compositions from melt as fluid inclusions (MIs and FIs) (Lloyd et al., 2013; Wallace et al., 2021). Total grain size distributions (TGSDs) of entire fall deposits are examined to confirm the fragmentation processes associated with sampled outcrop pyroclast deposits known from the literature in order for name assignation of pyroclastic flow deposits, surge and fallout deposits (details in Appendix A). Olivine-hosted MIs are carefully exposed by polishing single crystals (see details of analytical methods in Appendix A; e.g. Rose-Koga et al., 2021). Special attention was given to the diversity of naturally quenched and preserved MI textural groups (Roedder, 1984) and textural statistics on MI typologies (Robidoux et al., 2018). Quantitative parameters related to post-entrapment crystallization (PEC) are reported in Table 3 and Appendix B and the PEC correction procedure is detailed in Appendix A.

### 3.2.1 Bulk rock chemistry of sampled volcanic pyroclasts

Bulk rock chemistry was carried out to compare with literature compositional ranges of magmas. n = 26 bulk rock samples are analysed by inductively coupled (IC) plasma mass spectrometry (PMS) as plasma-optical emission spectroscopy (POES). The methods determine the major, trace and rare earth element compositions of the collected samples (Table 2, A.1, A.2). Powders are prepared at the Universidad Mayor, Escuela de Geología (Santiago, Chile) using a sample pulveriser and sent to a private laboratory for analysis (ActLabs, Canada). The standards, duplicates and blanks accuracy are detailed in Appendix C for the following analysis: major/trace elements fusion ICPOES/ICPMS, fluorine titration for FeO content and H₂O content by gravimetry.
### 3.2.2 Electron microprobe analysis (EMPA)

To provide the chemistry of the major elements from pre-eruptive magmatic processes, the selected MIs were measured with n = 163 electron microprobe analysis (EMPA) in mineral samples as for the glass inclusions they host (Table 2, A.1). The surfaces were probed with an electron microprobe analyser (EMPA), model JXA-8200 (JEOL), equipped with five wavelength dispersive X-ray spectrometers and one energy dispersive X-ray spectrometer analyser, at the HPHT (high pressure/high temperature) laboratory of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Rome (see technical conditions in Robidoux et al., 2021).

### 3.2.3 Volatile element contents of glass inclusions

Volatile element contents (H₂O, CO₂, Cl, F, S) in glassy MIs, embayments and matrix glasses were determined using a Cameca IMS 1280 ion microprobe at the CRPG-CNRS-Nancy. The smallest range of MIs sizes (2-100 µm) was selected for SIMS (Table A.3), and a total of n = 57 MIs were measured to allow double calibration of CO₂ and H₂O, on the smallest MIs measured by microFTIR (here using abbreviation FTIR for consistency) (Table 1, Table A.1, A.5-A.7); a total of n = 37 inclusion duplicates were obtained by both SIMS and FTIR to fit for correlation tests (Table A.7), while n = 167 MIs FTIR analyses were performed on the total set of inclusions.

SIMS concentrations were determined using calibration curves (Fig. A.1). Maximum errors, based on reproducibility over 10 cycles of analyses, were less than 15% for CO₂, 3% for Cl, 4% for S, and 5% for H₂O and F. The FTIR technique, in comparison, determines the content of water and carbon species according to the Beer-Lambert law, following the same procedure for data treatment as Robidoux et al. (2021). The parameters of the volatile element content calculations are described in detail in Appendix A.

### 3.2.4 Correction for CO₂ contents and solubility models

Due to the need to account for the shrinkage bubble for the CO₂ content estimation (e.g. Rasmussen et al., 2020), the Raman microspectrometer was used for the measurement of CO₂ in 25 bubbles (diameter 2 to 20 µm) of 25 unexposed MIs. The instrument is the Horiba Jobin Yvon high-resolution HR800 LABRAM of the Interdepartmental Center ‘G. Scansetti’ (Dipartimento di Scienze della Terra, University of Torino). The excitation source was a 532 nm green laser, with power at the emission source of 100 mW (e.g. Robidoux et al., 2017,
2018). The analyses were performed with a confocal setup, with the resulting spot size, calibration and spectral treatment (e.g. Frezzotti et al., 2012), being the same procedure as in Robidoux et al. (2018). The CO₂ bubble contents have been calculated starting from the Fermi diad split. The CO₂ µRaman spectrum is characterized by two intensity peaks at ~1285 and ~1380 cm⁻¹, defined as Fermi diad peaks; in melt and fluid inclusions, the Fermi diad split is proportional to the fluid density inside the bubble (Esposito et al., 2011; Frezzotti et al., 2012; Remigi et al., 2021). The chosen densimeter is able to accommodate a large range of Fermi diad space (102,65 – 105,47 cm⁻¹) that fit the polynomial equation from the previous authors and the used instrumental setting (Robidoux et al., 2018). The MIs not corrected for CO₂ content (no shrinkage bubbles) are used in solubility model from Iacono-Marziano et al. (2012) to calculate isobars, degassing curves and calculate saturation depths. The selected MIs corrected for CO₂ contents (µRaman or alternative model Mimic from Rasmussen et al., 2020) are treated with the same criteria. The degassing curve models are proposed as second alternative to minimum saturation pressure conditions.

### 3.2.5 Bulk analysis of isotopic noble gases

To explore the source and spatial distribution of magmatic fluids and volatiles, eleven isotopic analyses of He-Ne-Ar were carried out in fluid inclusions (FIs) trapped in olivine crystals from the Villarica volcanic system at the laboratory of INGV, Sezione di Palermo (Italy). These measurements were combined with three other samples previously studied by Lages et al. (2021b), which are part of the same suite of samples. Those FIs occur within pyroclasts of mafic composition for each investigated eruptive event, and the whole-rock composition was also analyzed (Table 2, Table A.2). Approximately 0.1–1.2 g of unaltered crystals were hand-picked for noble gas analysis. After cleaning in an ultrasonic bath under nitric acid, acetone and deionised water, the crystals were loaded into a single-stage crusher and then baked under pumping to achieve ultra-high vacuum conditions. After crushing, the gas mixture released from the opening of the fluid inclusions was purified in a preparation system capable of separating noble gases from the main components, and then further separating helium from neon from argon (see Rizzo et al., 2018, 2022, Lages et al., 2021a, 2021b for further details).

Two distinct split-flight-tube mass spectrometers (Helix SFT-Thermo) were used to measure the isotopes of helium (³He and⁴He) and ²⁰Ne, independently. The ³He/⁴He ratios are stated in Rc/Ra units, where Ra represents the ³He/⁴He of atmospheric air, which is 1.39 × 10⁻⁶. The analytical error for the ²⁰Ne (1σ) was <0.8%. The He-isotope ratio measurements had an uncertainty (1σ) of less than 6%. According to Rizzo et al. (2018), the ²⁰Ne has been corrected for isobaric interferences at m/z values of 20 (⁴⁰Ar²⁺). A multicollector mass spectrometer (GVI Argus) was used to measure the stable argon isotopes (³⁶Ar, ³⁸Ar, and ⁴⁰Ar) with an analytical uncertainty of ⁴⁰Ar/³⁶Ar < 0.2%. For the elemental and isotopic recalculations of He, Ne, and Ar, a pre-purified air standard separated into tanks was utilized. The standards for ⁴He, ³He/⁴He, ²⁰Ne and ⁴⁰Ar had analytical reproducibilities of less than 2.4%, 2.6%, 2.5% and 2.4%, respectively, over a period of >1 year for He and Ne and ~4
years for Ar. For He, Ne, and Ar, the typical blanks were at least two orders of magnitude lower than samples and standard signals. Additional information regarding sample preparation and analytical techniques can be found in Rizzo et al. (2018, 2022) and Lages et al. (2021a, 2021b).

Helium isotopic ratios are expressed as Rc/Ra, where Rc is the air-corrected ³He/⁴He ratio of the sample, determined using the ⁴He/²⁰Ne ratios. The Rc/Ra value is equal to:

[(R<sub>m</sub>/R<sub>a</sub>)(He/Ne)<sub>m</sub> – (He/Ne)<sub>air</sub>]/[(He/Ne)<sub>m</sub> – (He/Ne)<sub>air</sub>], where "m" and "air" denote air and measured values, respectively.

Because the argon concentration in the atmosphere is much higher than in magmatic fluid inclusions, it was necessary to make a correction, which assumes that all of the ³⁶Ar in the gas phase is atmospheric in origin. Thus, in the samples with ⁴⁰Ar/³⁶Ar>300, the ⁴⁰Ar concentration can be corrected as follows:

⁴⁰Ar* = ⁴⁰Arm – [(⁴⁰Ar/³⁶Ar)air × ³⁶Arm], where m is the measured value and ⁴⁰Ar* is the corrected isotope value.

# 4. Results

## 4.1 Pyroclastic deposit classification and fragment size distribution

Sample collection and preparation for the study of volatiles in glassy inclusions and olivine separation for bulk isotopic noble gas analyses were carried out to select material below lapilli size granulometry (e.g. Lloyd et al., 2013). Both the pyroclasts of this size and the olivine mineral inclusions will have cooled rapidly, providing ideal trapping conditions for the inclusion in the host mineral and avoiding significant loss of H₂O due to H⁺ diffusion (Gaetani et al., 2012). The study covers all the pyroclastic deposits in both the monogenetic center, MECs and the adjacent Villarrica stratovolcano. At each site, ~5,000 grams of sample were sieved in the laboratory to retrieve the granulometric parameter and compare it with datasets in the literature from Silva et al. (2010)(Appendix A).

The full description of the samples is resumed by 3 undergraduate theses at Universidad Mayor and summarized in Table 1, where key statistical parameters for the distribution are the median Mdφ (50), then the graphical standard deviation σ (φ). The comparison with datasets from Silva et al. (2010) classification fields confirm volcanostratigraphy assignations (details in Appendix A). To compare the different volcanic deposits, the median weight was calculated for grain size distribution in pyroclastic flow deposits, surge, and fallout deposits (Table 1, and Appendix A). The Pucón Ignimbrite data represents the initial fall deposit (TVP10E; Md = -1.547; σ = 1.449) and matches the onset of the “Pb” eruptive phase of the Pucón Ignimbrite (Moreno & Clavero, 2006), preceding the ignimbrite pyroclastic flow sequence (P1, P2; Silva, 2010, and references therein). The
extreme end member for well-sorted and small fragments is associated with the Chaimilla and Caburgua fallout deposits (TVP06 series; Md = -0.97 to 1.1; σ = -2.1 to -1.41). Los Nevados, Chaillupén and the March 2015 Villarrica volcanic episode all fall below -2 and -6 Mdφ (50), due to the sampling collection of single lapilli- to bomb-sized fragments.

## 4.2 Bulk rock geochemistry

The major element compositions of the bulk rock samples are presented in Table A.2. The rocks are classified within the CA and HK-CA series fields (Fig. 2a), according to Peccerillo and Taylor (1976) diagram classification as for distinguishing sodium from potassium enrichment between bulk rock and MI datasets. The Villarrica samples are heterogeneous at Pucón, ranging from basaltic to andesitic (SiO₂=52.1–61.9 wt.%, K₂O=0.52–1.47 wt.%, MgO=2.52–4.84 wt.%), homogeneous at Chaimilla (SiO₂=~53.1 wt.%, K₂O=0.57–0.61 wt.%, MgO=3.9–4.0 wt.%), and overlapping in SiO₂ concentration with the lava fountain scoria composition from 2015 (SiO₂=~53.1 wt.%, K₂O=0.77–0.86 wt.%, MgO=5.31–5.56 wt.%). The range of bulk rock compositions for MEC is restricted to basaltic andesites at Los Nevados (SiO₂=52.3–55.1 wt.%, K₂O=0.67–1.02 wt.%, MgO=4.10–4.47 wt.%) and Chaillupén (SiO₂=53.5–54.5 wt.%, K₂O=0.77–0.84 wt.%, MgO=4.84–5.07 wt.%), but strictly basaltic at Caburgua (SiO₂=50.8–51.9 wt.%, K₂O=0.67–0.75 wt.%, MgO=6.87–6.97 wt.%).

The trace element compositions of the Villarrica rocks show a slight enrichment in light rare earth elements (LREEs), compared to the moderate and heavy rare earth elements, typical of MORB (Appendix C; Hickey-Vargas et al., 2016). The rocks are slightly enriched in large-ion lithophile elements (e.g., Cs, Rb, Sr, and Ba) relative to N-MORB, but overlap with E-MORB. Most samples have low contents of the high field strength elements (HFSE) Ta, Nb, Zr, and Hf. A detailed systematic use of slab-fluid ratios is resumed in Table A.2 as calculated geochemical ratios (e.g. Robidoux et al., 2020).

## 4.3 Olivine texture, chemistry, and MI description

The olivine crystals from each eruptive event were grouped and characterized for its dominant MI textures (Table A.3). In this study, olivine hosted MI are referred to as "MI populations" when they are derived from the same layer of a volcanic deposit. The percentage variations of the MI typologies (Robidoux et al., 2018) are classified according to the "cooling rate-dependent" textural description of MI typologies of Roedder (1984). Olivine crystals with no MIs are assigned to "G1", then the MI typologies are coded, e.g. starting with homogeneous glassy MI assigned to "G2", MI with bubbles to "G3", and MI with bubbles and oxides to "G4".
The “G2” group is particularly variable in the Pucón products and reaches the highest percentages in the P2 sequence (>35%). The percentage of olivine crystals with preserved “primary MIs” (G2+G3+G4) also follows a certain order in term of the amount of olivine crystals in each volcanic deposit (considering that all the MI typologies are subject to PEC); from Pucón Ignimbrite, Chaimilla to the March 2015 eruption, the amount of olivine crystals with primary MIs (G2+G3+G4) decreases, so does the percentage of olivine crystals with vapor bubbles (G3+G4).

Olivine Mg# are listed in Table A.4. At the central eruptive vent of Villarrica, the Pucón olivine crystals are Mg-rich (Fo76-88), and those from the 2015 eruption have the lowest Fo content (Fo76), although fewer samples were analyzed, which could introduce a sampling bias. The Chaimilla olivine crystals are relatively heterogeneous in composition (Fo76-85, Fo80±3%). The MECs show slightly less Mg-rich olivine crystals compared to Villarrica (Fo73-86). Los Nevados olivine crystals are heterogeneous in composition (Fo75-85, Fo80±3%), Chaillupén has olivine crystals with high Mg# (Fo84-86, Fo84±1%), and lastly the Caburgua olivine crystals have heterogeneous Mg# (Fo73-84, Fo80±4%).

## 4.4 Major element content from glass inclusions

The inclusions shown in Figure 2 have been corrected for post-inclusion crystallisation of the corresponding phenocryst-host according to the method of Robidoux et al. (2021), following the method of Danyushevsky and Plechov, using the Petrolog 3 program (Danyushevsky, L. V., & Plechov, 2011). This data treatment considers the diffusive exchange of FeO and MgO along the walls of the inclusion and the olivine host, and then the loss of Fe from the inclusion into the olivine host. Recalculated compositions from MIs in samples are given in Table A.8 for the corresponding olivine host crystals.

The corrected MI compositions (Fig. 2; Appendix A) required in 94 samples a range of 0.6–43.5 and average 15.7% olivine to be added. The Fe-loss implied adding a range of 0.3–3.4 and average of 2.1 wt% FeOT. The total iron content assumes that Fe²⁺ = ΣFe, the best-fit FeOT/MgO regression line was used at each group of volcanic centres, ranging with modelled bulk rock iron species ratios with Fe²⁺/Fe³⁺ = 1.1–4.1.

The MIs from the Pucón series were classified as basaltic to basaltic andesites and a few andesites were observed (SiO₂ = 47.3–62.8 wt.% and K₂O=0.19–1.60 wt.%); data plot in the field from calc-alkaline (CA) to high potassium calc-alkaline (HKCA) rocks (Fig. 2). The Chaimilla series is slightly richer in K₂O (0.20–1.67 wt.%), and olivine-hosted MIs were mostly classified as basaltic andesites, whereas MIs from the 2015 eruption were basaltic- andesites, with lower K₂O contents (0.78–0.91 wt.%).
The total MIs reported by Robidoux et al. (2021), regardless of the specific eruptive center (Gr. 1, 2), were more differentiated in the Los Nevados MEC (47.6–58.0 wt.% SiO₂; 0.27–1.21 wt.% K₂O), with Chaillupén ballistics representing the most felsic MIs (57.1–59.0 wt.%; 0.93–1.35 wt.% K₂O). Caburgua represents intermediate differentiated MIs (51.1–59.3 wt.% SiO₂), but the alkaline content is highest in these samples (0.62–1.78 wt.% K₂O).

## 4.5 MI description and MI volatile concentrations

The water and carbon dioxide contents of the MIs are reported (FTIR in Table A.5, SIMS in Table A.6, reproductibility test in Table A.7). Of the 167 samples analyzed by FTIR, 37 were measured by SIMS with no loss or damage during transfer to an indium mount. The difference in water concentration between FTIR and SIMS averages 0.5% and 89 ppm for CO₂ content.

In terms of H₂O and CO₂ concentrations from the central eruptive vent of Villarrica (Table 1, Tables A.5-A.6), the Pucón Ignimbrite series records the highest H₂O-CO₂ concentrations (0.1–6.0 wt%; 9–1485 ppm, respectively), followed by the Chaimilla series (0.2–2.4 wt.%; 16–337 ppm; similar to Pioli et al., 2015) and the 2015 eruption (0.1–0.8 wt.%; 160–307 ppm). In the MECs, high values are found for the Los Nevados series (0.1–3.4 wt%; 30–1568 ppm; see also Robidoux et al., 2021), and lower values in the Chaillupén series (0.3–3.6 wt%; 29–329 ppm), and in the Caburgua series (0.6–2.8 wt%; 139–677 ppm).

The S, Cl and F concentrations at the Villarrica center (Pucón Ignimbrite, Chaimilla and 2015 eruptions) are highly variable (Appendix I) with the following ranges 103–2055 ppm, 11–1330 ppm and, 81–1556 ppm, respectively. The contents of S, Cl, F from MEC samples have the following ranges: 41–2581 ppm, 13–2356 ppm and 59–2473 ppm, respectively (Table A.8).

## 4.6 Raman-corrected CO₂ contents

Twenty-five MIs with shrinkage bubble (1.3–10.1 vol.%) were analyzed by Raman micro-spectroscopy in order to calculate their CO₂ bubble contents starting from their CO₂ density (see Methodology). In the studied shrinkage bubbles, the measured density varies between 0.004 and 0.911 g/cm³ (Table A.9). The calculated (mass / glass density x volume) total CO₂ concentrations (in glass inclusions + bubbles) range between 207–3336 ppm, using the approach described in Robidoux et al. (2018). Since no heating experiment was performed on the naturally quenched MIs of this study, the calculated CO₂ contents are compared with the contents obtained by the experimental and computational model “Mimic” of Rasmussen et al. (2020). For this reason, n = 31 shrinkage bubbles were selected from our MIs measured by EMPA and, according to the model “Mimic”, they resulted into correction on the total
CO₂ concentrations to 54–3529 ppm. These values exceed the original (uncorrected) shrinkage bubble equivalent glass inclusion CO₂ contents of 24–1413 ppm (Table A.8).

## 4.7 Noble gas isotopes in fluid inclusions

The analytical results of elemental and isotopic measurements of helium, neon and argon, together with other complementary information, are reported in Appendix K. The ⁴He and ²⁰Ne concentrations measured in FIs from olivine crystals of scoria and ash samples varied from 2.8 × 10⁻¹⁴ to 1.6 × 10⁻¹³ mol/g (Fig. 3) and from 1.7 × 10⁻¹⁵ to 1.7 × 10⁻¹⁴ mol/g, respectively. The ⁴He/²⁰Ne ratio was 3.9–42.9, compared to the atmospheric ⁴He/²⁰Ne of 0.318 from Porcelli et al. (2002). The concentrations of ⁴⁰Ar, ³⁸Ar, and ³⁶Ar ranged from 1.5 × 10⁻¹³ to 1.5 × 10⁻¹² mol/g, from 8.9 × 10⁻¹⁷ to 8.8 × 10⁻¹⁶ mol/g and from 4.9 × 10⁻¹⁶ to 5.0 × 10⁻¹⁵ mol/g, respectively. The ⁴⁰Ar/³⁶Ar ratio varied in the range 300–336, whereas the theoretical ratio in the atmospheric is ⁴⁰Ar/³⁶Ar~296 (Porcelli et al., 2002). Both ⁴⁰Ar/³⁶Ar and ⁴He/²⁰Ne indicate that all the gases released by the FIs contain an atmospheric component mixed with the magmatic one. The concentrations of ⁴⁰Ar* vary from 2.6 × 10⁻¹⁵ to 1.1 × 10⁻¹³ mol/g. The ⁴He/⁴⁰Ar* varies from 1.4 to 10.5, with the typical mantle ratio being considered to be in the range of 1–5 (Marty, 2012).

The ³He/⁴He ratios corrected for atmospheric contamination (expressed as Rc/Ra values) vary between 4.0 and 7.6 Ra (Fig. 3; Table A.10), with a bias with uncorrected ³He/⁴He ratios generally ≤0.2 Ra, except for the sample HCH-2AS that showed a bias of 0.4 Ra.

# 5. Discussion

## 5.1 Mafic magmas degas and transit from deep to shallow volatile saturation levels

At Villarrica, the Pucón Ignimbrite is the oldest and best studied postglacial eruption. It is the richest in volatile element contents, but also contains MIs the least affected by post-entrapment crystallization (PEC; Table 3). This section discusses melt inclusion volatile loss between two large sets of pre-eruptive conditions that chronologically describe Villarrica mafic magmas from the Pucón Ignimbrite (~3.7 kyr) to decadal old central crater conditions.

Before extending to discriminate degassing effects and calculating saturation pressures for the different eruptive centers (section 5.2), we first highlight the precision and accuracy of the volatile element contents produced consistent calibration curves using SIMS (Fig. A.1), and the reproducibility of FTIR vs. SIMS gave comparable results (Fig. A.2; Table A.7), although the FTIR technique is limited to larger MIs (>30 µm; Appendix A). The SIMS
divergence from 1:1 water line in figure A.2 is mainly due to the precision for smaller MIs.
The carbon dioxide 1:1 line shifts are greater when MIs contain shrinkage bubbles (Fig. A.2),
highlighting the advantages of using smaller beam diameters with the SIMS technique over
glass inclusions holding vapor bubble. To estimate minimum saturation pressures, the
volatile element contents and major element compositions of the MIs are then integrated into
the solubility model from Iacono-Marziano et al. (2012) and Witham et al. (2012) (Figs. 4,
6). Despite H₂O-CO₂ pairs being the focus of this study, the sulfur and halogen (Cl, F)
contents remained constant from the start to finish of the Pucón eruption, as well as the
subsequent paroxysmal explosions at Villarrica crater (Fig. 4; Appendix A, Table A.8).

Overall integrating observations on MI compositions and olivine hosts, Pucón
series contains the most primitive olivine crystals (with Fo content between 76,3 and 88,8 %;
Table A.4) and MIs record the highest volatile contents (Fig. 4; Table A.4-A.7). Chaimilla's
MI volatile element contents are systematically lower than those of the Pucón Ignimbrite MI
for similar major element chemistry and cogenetic parental melt differentiation (Figs. 2, 4;
Table A.8), while for the 2015 eruption, MI volatile element contents are even lower,
representing both strong pre-eruptive degassed melts, and potential post-entrapment effects
accentuated by low cooling rates of the transported magmas (Fig. 4). Considering such
compositional differences attributed to pre-eruptive conditions, we argue that pre-entrapment
degassing is not the only cause of volatile variation in our olivine-hosted MI collection. For
example, shallow melt CO₂ saturation may lead to potential gas migration into volatile CO₂-
rich bubbles at central chimney conduit and open vent conditions (Aiuppa et al., 2017), which
persists during lava lake bubbling mechanisms (Moussalam et al., 2016). The identified
shallow storage conditions may also accentuate lower magma cooling rates and melt
differentiation. Such effect is reflected by some lower trapping/ quenching MI temperatures
and differentiated MIs series (Chaillupén series; Fig. 2, 5d) revealed here with PEC treatment
(Appendix A; e.g. Giordano et al., 2008) in MI with low water contents ~<1.5 wt.% (Fig. 5;
e.g. Lloyd et al., 2013; Robidoux et al., 2021). Therefore, for some olivine the low MI-
trapping temperatures at shallow surface is expected to favor H⁺ diffusion because the low
quenching rates affect the solidification of MIs and accentuate the water glass/crystal
diffusion (Fig. 5; Table 3; e.g. Massare et al., 2002; Gaetani et al., 2012).

Taking into account the temporal variation of volatile contents through mafic
magmatic events at Villarrica, we observe a transition in the pre-eruptive minimum saturation
pressure conditions at Villarrica during paroxysmal inner crater eruptions (Fig. 5a). As a
result, major subdivisions in the Pucón sequence of "Pb" and "P1 to P3" (Silva et al., 2010)
represent individually different equilibrium pressure ranges, suggesting a polybaric system
that may have transported several masses of ascending magmas. The minimum saturation
pressure values were higher during climax of the sub Plinian activity, 4.6±1.6 down to
0.020±0.006 kb while the opening of the eruptive sequence (Pb) represents decompression
of volatiles for minimum saturation pressures from 2.15±0.47 to 0.68±0.26 kb (violent
strombolian; Table A.8). These pressures are thus traduced in lithostatic depths, resulting among these subsequent batches of Pucón magmas to 2.5–7.9±0.63 km (1SD). When the first magma batch reached the surface as the "Pb" opening sequence, it consisted of hot, volatile-element saturated melts (1070–1140 °C). This phase has been described as evolving from a strombolian to a more explosive sub Plinian eruptive style (Moreno and Clavero, 2006), and our new dataset shows that it was relatively water-rich (<3.6 wt%; starting composition “Pucón” in Fig. 4a, c) and CO₂-rich (1485 ppm corresponding lithostatic depths of 16.6±5.9 km, 1SD) (Figs. 4, 5). This study shows that the last Pucón event (P3) finally recorded ~>1200 ppm CO₂ and a maximum water content of 6.0 wt.% (starting composition “Pucón: water-rich”; Fig. 4a, c), which is higher than the previous 4.65 wt.% water content estimated with the thermobarometric model by Boschetty et al. (2022) (Figs. 4, 5, 6).

The subsequent explosive events to the present day at Villarrica Central Crater may also represent the potential for magma transport between deeper and shallower parts of the volcano's plumbing system, according to our assessment of pre-eruptive conditions. The Chaimilla fall deposit 3,180±40 yr B.P. (Costantini et al., 2011) is a key explosive eruptive event that occurred when the crater formed after the collapse of the edifice following the eruption of the Pucón Ignimbrite (e.g. "C3" in Moreno and Clavero, 2006). On account of the very thin stratigraphic separation between the Pucón and the Chaimilla subsequent deposit (this study; Pioli et al., 2015), our new MI dataset demonstrate that the Chaimilla mafic magma represents a degassed, cooler (<1018–1134 °C; Fig. 5d) endmember of the Pucón Ignimbrite (ibid. for S; Cl, F contents; Table A.8); it records lower pressure ranges (0.4–0.9 kb corresponding to the volatile-rich type 2 magma defined by Pioli et al., (2015) (Fo₈₁-₈₅ at 1.2 kb). The subsequent Chaimilla event, although similar in composition, is a shallow (1.7–3.2 km) degassed residual melt, produced in similar conditions to the current feeder system (Fig. 2, 4, 5, 6).

The present-days conditions of mafic magma below Villarrica central crater are still reflecting two ranges of storage depths settings for magma evolutions according to our new MIs dataset. The 2015s low contents of the water-CO₂ pair recorded in this study (0.84 wt.% and 307 ppm, respectively) are consistent with the 2015 volatile contents recorded in the MIs of Cortés et al. (2024) (1.45 wt.% and 468 ppm, respectively), implying that the mafic magmas produced during the last decade at central Villarrica crater are strongly degassed at shallow depths. These volatile element contents are used as starting conditions in our proposed solubility model (Fig. 6) and demonstrate volatile saturation of low-water contents reaches minimum stalling lithostatic depth of 1.7 km. Even our estimated depth results are 3.1 ±0.6 km for CO₂-corrected MIs (±8.3kb) (Fig. 5a), which is still below ≤5.3 km crystallization equilibrium during the 2015 Strombolian paroxysm (ca. 1110 °C) (Romero et al., 2022). Given those solubility model results representing magmas that persist below the present-day central crater (Figs. 4, 5, 6), this investigation does not discard that the volatiles reach saturation conditions >14.2–16.6 km, which could then support the existence of a
deeper reservoir until present-days (Cortés et al., 2024). The magma still crystallizes olivine at a depth of 19–35 km (Morgado et al., 2015), for this reason, deeper portion of the plumbing systems could persist and launch new magma batches (Edmonds et al., 2022). This range of saturation depths partially matches the ~8–20 km zone of low resistivity detected by magnetotelluric analysis which could be related to a region that favor melt transport below Villarrica (Pavez et al., 2023).

## 5.2 Deep reservoir inferred from CO₂-rich mafic magmas and volatile saturation at Villarrica and MECs

The eruptions monitored at Villarrica over the last decades still record lower minimum solubility pressures for volatile elements (< 5 km), but these conditions are largely reported for lateral volcanic centers according to the comparative data set of our solubility model. Only post-glacial paroxysms such as Pucón Ignimbrite have been able to deliver evidence of a deep zone (> 17 km) for subsequent mafic magma recharges, but such characteristics are even met at lateral MECs.

Systematically, the explosive strombolian to violent strombolian eruptions of Chaimilla and subsequent crater explosions after 1971 (Cortés et al., 2024) did not record the deepest saturation levels despite assuming to represent continuous volatile-rich recharge (>12 km; Edmonds et al., 2022). To support this new observation, we present new MI saturation pressure dataset from all MECs and Villarrica paroxysmal eruptive events are fed by magma coming from similar maximum depth estimates (from volatile saturation; ~17–21 km). Basaltic andesites with similar pre-eruptive P-T compositional evolution are thus sourced from similar ranges of depths in small as for larger volcanic edifices (Figs. 5, 6) (e.g. Cascades, Mordensky and Wallace, 2018). Nevertheless, nearby as beyond Villarrica flanks, melt-volatile element chemistry transported as magmatic fluids may reflect a distinct compositional evolution during deep transport beyond the 45 km local cortical thickness (Tassara and Echaurren, 2012). Therefore, before evaluating such causes of heterogeneities in magmatic fluids (section 5.3-5.4), this section shows that pre-eruptive conditions derived from our MI study support consistent deeper regional starting pressures for volatile saturation since the post-Lican Ignimbrite (13.5 ky) Villarrica volcanic event.

At Villarrica central crater, the entrapment pressure of MIs records the same order of lithostatic depth (≤ 21.3 km), somewhat deeper than the 12.7 km vertical extension of the transcrustal system of Cortés et al. (2024) post-1971 eruptive events. This new depth from MI estimate is now closer to the 22.8–29.2±6.1 km bracket of Morgado et al. (2015) at central Villarrica since the 1971 eruption (Fig. 6). This is consistent even with the case of distant Caburgua (~25 km NE Villarrica), the new MIs here are also below the range of 39.0–41.2 ±6.1 km depths recorded by the same authors for Caburgua (CHSEC). Based on our new
CO₂ density-µRaman corrections and derived saturation pressures (3.7–4.8 kb; Fig. 5a), we argue that the regional monogenetic cone of Caburgua has equivalent depth pressure from volatile element saturations down to ~13.5–17.3 km, despite ascending through a lithological basement far from the main stratovolcano.

Under these circumstances, a consistent deep magmatic storage or transport zone exist also at a distance from Villarrica even at several MECs (CO₂-rich MIs and µRaman MIs corrected collections). This unique storage level can be identified among the complexity of typical trans-crystalline mush systems (TCMS) but provide even more extended information on lithostatic depths according to our sampling of lateral MECs (e.g., Llaima; DeMaisonneuve et al. 2012; Ruth et al., 2017; Cashman et al., 2017). Within the primary structure of Villarrica Caldera 1, there are also explosive flank volcanic activity, such as the Los Nevados cones (<2600 yr B.P.), which also trapped relatively deep magmatic batches (9.2 km; Robidoux et al., 2021) compared to present-day crater conditions (maximum 5 km at Villarrica; this study and Cortés et al., 2024) (Fig. 6). The new MI-CO₂ content correction at Los Nevados now gives minimum equivalent depth pressure values to saturate volatiles down to 14.2–21.3 km. In comparison, the Chaillupén MEC cones, a few hundred meters south of the central crater of Villarrica, record saturated volatiles below <1.9 kb, (Avg. °T= 1169±8°C)(Fig. 5a), resulting in a lithostatic depth of < 0.3–6.8 km for melts erupting on the southern flanks of Villarrica; such values may still represent deeper sources if MIs are not affected by shallow olivine-MI diffusive H⁺ processes.

## 5.3 Magmatic fluid evidence for atmospheric and crustal-derived components

The magmatic volatiles transported at Villarrica and MECs in this study reflect a common atmospheric component and probably also other South American volcanoes, according to the magmatic fluid tracer ³He/⁴He used in this study. The new dataset here provides evidence that the magmatic fluid isotopic noble gas signature is either recycled into the mantle wedge from the subducting slab and/or acquired during magma ponding within the continental crust. To investigate the role of the subducting slab and continental crust on the composition of the degassed magmatic fluids at Villarrica, ³He/⁴He measured in FIs from the same MI olivine batches can be used as a useful tracer, coupled with petrological and geodynamic evidence (Fig. 7; Table A.10).

In support of the use of noble gas isotopes as magmatic fluid tracers, Hilton et al. (2002) reported in a global review of arc volcanism that: i) the highest ³He/⁴He ratios measured in arc volcanism are in the MORB range (i.e. 8 ± 1Ra; Graham, 2002); ii) in many arc segments (including central and northern Chile, Peru and Ecuador) the highest ³He/⁴He ratio is below the MORB range (i.e. below 7 Ra); iii) the mean ³He/⁴He ratio of all arc segments is 5.4 ± 1.9 Ra. Volatiles transported as magmatic fluids are thus of great
importance since they are cycled between the atmosphere and the Earth's interior at subduction zones (Zellmer et al., 2015). In this geodynamic setting, slab dehydration at depths of several kilometers can differentially influence the composition of magmatic fluids generated in the overlying wedge. Subduction-related fluids are known to contain higher proportions of atmospheric components than intraplate and mid-oceanic ridge environments (Burnard et al., 1997). According to Hilton et al. (2002) and Sano and Fischer (2013), noble gases found in arc magmatic/hydrothermal fluids and trapped as fluid inclusions (FIs) in minerals are important indicators of the relative contributions of the subducted slab, crust and mantle to the fluids emitted by arc volcanoes. A recent compilation of light noble gases in the South American arc revealed that the average $^{40}$Ar/$^{36}$Ar signature of all gas-rocks samples is ~339 (Lages et al., 2021b), which is well below that of MORB (~44,000; Moreira et al., 1998) and close to the atmospheric signature (~296; Porcelli et al., 2002). In rocks from Villarica (our samples and ones from Lages et al., 2021b), the observed $^{40}$Ar/$^{36}$Ar ratios in FI range from 300 to 336, supporting the low isotopic signature already found along the South American Arc. Similar inferences can be made from the $^{4}$He/$^{20}$Ne range (3.9–50.8), which is not far from the atmospheric ratio (0.318) and well below typical mantle values ($^{4}$He/$^{20}$Ne>1,000).

Recent studies in the Central and South American Volcanic Arcs have provided new measurements of helium isotopes in FIs hosted in olivine and pyroxene crystals, clarifying the reasons of $^{3}$He/$^{4}$He variability in those arc volcanoes (Lages et al., 2021a, 2021b; Rizzo et al., 2022 and references therein). The main findings are that: i) the mantle $^{3}$He/$^{4}$He signature of the Central and South American Volcanic Arcs is within the MORB range, with the highest values measured in Guatemala (9 Ra, Pacaya volcano) and Colombia (8.8 Ra, Galeras volcano; Fig. 3b); ii) $^{3}$He/$^{4}$He values below the MORB range are indicative of variable crustal contamination, often with an inverse relationship between Rc/Ra values and crustal thickness (this feature is mainly observed in the South American Volcanic Arc; Lages et al., 2021a, 2021b; Barry et al., 2022); iii) there is a progressive decrease in mantle wedge $^{3}$He/$^{4}$He values, with $^{3}$He/$^{4}$He values still within the MORB range, coupled with variations in some key trace element ratios (i.e. Ba/La, Th/La, U/Th), resulting from a higher presence of subducted slab sediment fluids (rich in U and Th, from which radiogenic He is produced). This has been observed particularly in the Central American Volcanic Arc and the SVZ (Lages et al., 2021a, 2021b; Rizzo et al., 2022 and references therein).

## 5.4 Olivine FIs record primitive magmatic fluid during Villarrica subplinian climax

The present study completes the Villarrica volcanic complex understanding of the magmatic fluid signature by confirming that $^{4}$He contamination is stronger in flank MECs according to systematic variations in FIs $^{3}$He/$^{4}$He. Interestingly, according to MI as bulk rock composition, the systematic FIs $^{4}$He contamination is stronger in differentiated-cortically
contaminated MECs as Villarrica typical shallow degassed reservoir but is least contaminated in Pucón paroxysm (Fig. 7b, 8b). As to evaluate variation in magmas that are transporting the volatile phases, the bulk rock sample composition of this study does not indicate yet clear systematic correlation with slab fluid markers within the Caldera 1 complex and beyond its boundary (Figs. 7).

By reviewing closely, the local³He/⁴He variations and bulk rock composition, we present new helium isotopic data in FIs that mostly reflect the measurements presented by Lages et al. (2021b), except for one sample from Pucón that has a value of 7.6 Ra. This value is almost 1 Ra unit higher than the average values for Villarrica volcano, suggesting that the continental crust effectively plays a role in lowering the ³He/⁴He values of pristine mantle fluids. A helium isotopic signature of 7.6 Ra is still lower than that expected for mantle values. However, in the light of the slab sediment fluid contribution suggested by Plank (2005) for this region of the SVZ and the relation between Rc/Ra and Th/La ratios of Lages et al. (2021b) (Fig. 7ab), we argue that the ³He/⁴He signature below Villarrica is confirmed to be within the MORB range and that the cortical contamination plays an important role in lowering the original mantle ³He/⁴He. Close examination of the literature dataset with our bulk rock samples (Fig. 7; Table A.2) shows the regional Th/La trend typical of other volcanic centers in the SVZ (Hickey-Vargas et al., 2016; McGee et al., 2017), but it is difficult to observe coupling with the ³He/⁴He signature at the scale of the Villarrica volcanic complex. It is still not possible to observe this correlation beyond the most distant regional volcanic center, Caburgua, unless larger amounts of FI-hosted olivines are encountered to extend the topic (Appendix A). At a distance from the subducting trench, Caburgua is the only regional MEC that deviates from the slab fluid signature data cluster (Fig. 8; Table A.2), implying that it is significantly modified with respect to asthenospheric slab fluid melting. Chemical tracers of magmatic fluids require systematic studies of regional MECs and stratovolcanoes in the same region (e.g., . More work is also required regionally to investigate the variation in radiogenic ⁴He (bulk mol/g content) in olivine FIs (Lages et al., 2021b and references therein) or fumaroles (Tardani et al., 2017; Barry et al., 2022 and references therein) for the most well-studied polygenetic Villarrica basaltic andesites produced since the postglacial period.

The most interesting observation at the Villarrica polygenetic complex is from the variation of ³He/⁴He between successions of different scales of explosive eruptions between central and peripheral craters. The presence of ⁴He contamination at most differentiated products and the ³He/⁴He values being the highest in olivine-FIs from the most primitive batch of magma at Pucón Ignimbrite (highest post glacial VEI; Table 1). Regardless of the primitive nature of the olivine (olivine Fo% or MI Mg# show no correlation with our Rc/Ra ratios; Figs. 3, 8), we suggest that the magmatic ³He/⁴He signature decreases with crustal ponding and contamination, when wall rock interaction is more likely to decrease cooling rates of large-scale magma reservoirs. This latter conclusion is already supported
petrologically by major element MI trends (Fig. 2), bulk-rock trace element tracers and noble
gas isotopes (Figs. 3, 8), but could depend on cooling rates and potential magma chamber
timescales (e.g. U-Th-He isotopic systematic; Kuritani et al., 2007; McGee et al., 2017). In
addition, figure 8 details peripheral plumbing system contamination effect as a potential
source of recycled ⁴He increase, which also occurs for bulk rock compositions indicating
crustal interaction, such as Sr/Y ratios (> 20), and K₂O (wt%) content (Fig. 8cd). This
correlation is still not systematic for the Th/La ratio (Fig. 7a), used as an indicator of slab
sediment fluid contribution (Plank, 2005). When examining chronological evolution of
geochemical markers, this geochemical anomaly is only found for the Pucón recharge event
(Th/La >0.2) during the post-glacial period of Villarrica and is absent from the Chaimilla-
derived magma and other MEC eruptions (Fig. 8ab; Th/La < 0.2). Thus, ⁴He contamination
is weaker during Plinian events with high VEI explosive paroxysms, and the slab fluid
signature is only detected for the parental magma fluids that represent volatile-rich element
contents (Pucón). Our olivine FI dataset records the lowest ⁴He content (g/mol) during the
climax eruptive phase (Fig. 8). Taken together, such geochemical parameters (olivine MI as
Fis compositional trends) thus indicate that less peripheral contamination is expected in
basaltic andesites from the parental magma (Pucón) that feed the main explosive paroxysms
of Villarrica.

**5. Conclusions**

For the first time a joint comparison has been made based on melt volatiles, major and noble
gases for a polygenetic volcanic system, that of Villarrica in the southern Andes. This study
includes new detailed data on volatile saturation depths, with improved analyses for P-T and
compositional pre-eruptive magma conditions based on new geobarometry calculations, and
a solubility model that uses novel µRaman dataset to predict the original CO2 contents in MIs
with shrinkage bubbles. The temporal/spatial portrait of pre-eruptive conditions as magmatic
fluid compositional variations were explored within this research providing of the following
conclusions:

I) The Villarrica stratovolcano forms a polygenetic system in which the magmatic volatile content decreases from the Pucón event (3.7 ky) until the last decade at central crater: According to the new rich MI dataset collected during most of the documented explosive mafic eruptions at Villarrica, a significant decrease in volatile content is observed. Since the current 2 km wide caldera formation (postglacial, see Villarrica Unit 3, <~ 3.7 Kyr AP; Moreno and Clavero, 2006), close evaluation of the major oxide composition/volatile content of the MI (EMPA, SIMS, FTIR) provides clear evidence that the parental mafic magma of the Pucón eruption may have produced a derived degassed magma that fed the Chaimilla event (<~ 2.6 Kyr AP (Pioli et al., 2015). The current central
crater setting (post-1970s) may favor degassing/differentiation of melt pockets at shallow depths ~<5 km, while the lava lake persistently coalesces CO₂-rich bubbles in the central conduit (Witter et al., 2004; Moussalam et al., 2016; Aiuppa et al., 2017).

II) **Lateral, regional, such as Villarrica volcanic vents confirm evidence of both shallow volatile-poor and deep CO₂-rich magmatic reservoirs:** The solubility models presented in this study confirm that the lithostatic depth ranges for melt inclusion entrapments are within the range of documented crystallized mafic mineral phases from the literature (Morgado et al., 2015; Boschetty et al., 2022; Cortés et al., 2024), but two depth zones are clearly identified at central as well as peripheral MECs (e.g. Mordensky and Wallace, 2018). These key depth zones at Villarrica may represent features similar to polygenetic volcanic systems in other volcanic arcs (Rasmussen et al., 2022), distinguishing eruption depths controlled by high CO₂ saturation in deep Villarrica reservoirs (~17–21 km) from those controlled by water loss in shallow reservoirs (<1.7–4.4 km). The pre-eruptive conditions of mafic magmas evolve similarly at the present central crater, as well as laterally at nearby postglacial MECs characterized by degassing/differentiation of trapped melts in olivine phenocrysts (Chaillupén, Los Nevados).

III) **The Pucón Ignimbrite during its climax phase represents the postglacial parental magmatic fluids from the Composite volcanic system:** Beyond the petrogenetic causes associated with eruptive paroxysms with relatively high Rc/Ra in a single volcanic complex (Piton de la Fournaise in Boudoire et al, 2020), this study identifies the temporal evolution of magmatic differentiation/cortical contamination processes using bulk rock as melt inclusion compositions: e.g., fluid radiogenic ⁴He (g/mol) is accentuated during magma-crustal interactions, a feature consistently observed in volcanic arcs (Lages et al., 2021a,b). The Pucón Ignimbrite contains the highest volatile content of melt inclusions and high CO₂/³He ratio of fluid inclusions in olivines, where the cortical contamination effect is much weaker. The ³He/⁴He signature attributed by our olivine collection is lower at MECs and smaller for low-VEI eruptions (2015) (<6.7 Ra), while it reaches ~7.6 Ra during the peak of the high-VEI explosive paroxysm at Villarrica (Pucón Ignimbrite climax) (closer to a mantle signature of 8-9 Ra expected along the South American arc; Lages et al., 2021).

## Acknowledgements

This work is part of ANID, Fondecyt Iniciacion No 11190846 project of Philippe Robidoux (2019–2022). We are grateful to Dra Manuela Nazzari and Dir. Piergiorgio Scarlato for providing access to electron microprobe EMPA at Istituto Nazionale di Geofisica e Vulcanologia Sezione di Roma 1, HP-HT Lab. of Experimental Volcanology and Geophysics. The measurements were also supported by Elisabetta Del Bello and Alessio Pontiselli (INGV-Roma) through participation at the TransNational Access (TNA) in the framework of the EXCITE (Horizon 2020) research infrastructure. Special thanks are for Mariano
Tantillo and Mariagrazia Misseri from INGV-Palermo, who helped in mineral preparation and noble gases isotope analysis. Special thanks are also addressed to Dra. We address special acknowledgements for Universidad Mayor, Escuela de Geología Bsc. students Gloria Díaz, Aaron Sancho, Daniela Pasten and Prof. Clavero for active participation in the 2017–2022 field trips. ER-K, YM and PR deeply thank Nordine Bouden and Johan Villeneuve for their flawless support with the SIMS measurements and for the access to the Nancy preparation lab.

# CAPTIONS

## Table Captions:

**Table 1 – Volcanic deposit characteristics.** Sieved and non-sieved volcanic deposits are given geographical coordinates for outcrop location and additional material description. The granulometry is in Phi (φ) size. Fragment size and typology distribution (% per 100 randomly selected clasts) are classified strictly on Fisher (1966) classification in addition to the full spectrum of clastic material typology, classified according to White & Houghton (2006).

**Table 2 – Volcanic event references for analysis**

**Table 3 – Parameters of post entrapment crystallization effects**

## Figure Captions

**Figure 1 – Location of study area.** a) Map of the subduction zone, including arc segments from the Central Volcanic Zone (CVZ). White lines are inferred tectonic plate boundaries and arrow indicates direction of subduction. Colored dots are sampled spring sites with Rc values marked using quartile color code. All eruptive centers listed in the Smithsonian Global Volcanism Program's Holocene Volcano List (small black triangles). From north to south, oceanic plate segments with fracture zone abbreviations ending in “FZ” are linked to Juan Fernandez Ridge; Mocha FZ, Valdivia FZ, Chiloe FZ, and Chile Rise FZ. b) Stratigraphic extent of Villarrica Pucón Ignimbrite for Units P1, P2 and initial
Base Surge Deposit “Pb” (Moreno and Clavero, 2006) as delimited by Silva et al. (2010). The Caldera 1,2 and 3 boundaries (Moreno and Clavero, 2006) are marked, as well as extent of for Chaillupén and Los Nevados Groups (modified from same source; Robidoux et al., 2021), with Caburgua MECs restricted to Caburgua cone #1 sector for lava and pyroclastic deposits (modified from Moreno and Clavero, 2006; Morgado et al., 2015). The Chaimilla fallout deposit (Costantini et al., 2011) and Pucón (Silva et al., 2010) are shown with maximum covered areas from isopach ellipsoid.

**Figure 2 – Major element compositions.** The post entrapment-corrected MIs (colored circles) with their major element contents as a function of SiO₂ wt.% (see corrected dataset in Appendix I). The bulk rock analyses are shown by colored squares for each series. Dashed arrows indicate the approximate trend for groundmass crystallization of plagioclase (Pgl In) ± clinopyroxene (Px In). The trapped melts (MIs) evolve via a parental melt differentiation path (red arrow) or post-entrapment crystallization effects (PEC) (orange arrow). The post-entrapment crystallization effects are interpreted in Table 3. The bulk rock composition of the 1971 Villarrica eruption is represented by grey dots and Caburgua-Huellemolle by a dark grey box (Hickey-Vargas et al., 2002; Morgado et al., 2015). a) K₂O vs SiO₂ classification for the volcanic series, b) CaO wt.%, c) Al₂O₃ wt.% where plagioclase (Pgl-In) is interpreted as residual melt plagioclase crystallization occurring before/during MI entrapment, d) Na₂O wt.% where the dark arrow represents the general tendency toward cogenetic differentiation in all our MI collection, e) MgO wt.%, f) FeOₜ wt.%.

**Figure 3 – The FI helium dataset.** ³He/⁴He (Rc/Ra) ratio vs He concentration (mol/g) collected from analytical data of bulk fluid inclusions (FIs) hosted in olivine (Table A.10). Data from Rizzo et al. (2022) and Lages et al. (2021ab) represent the literature FI data, while our dataset of FIs in olivine crystals is represented by colored symbols (see legend in Figure 2). Samples 2015_B* (Villarrica 2015), HCH2A1* and HCH2A4C* (Chaillupén) are from Lages et al. (2021b) (Appendix K). Data are grouped as combined segments from Central American Volcanic Arc (CAVA; green/black colored symbols) and South American Volcanic Arc (South American VZ; yellow symbols). b) ³He/⁴He (R/Rᴀ) vs He/Ne data (⁴He/²⁰Ne) in FIs and free gases. Binary mixing (air-magmatic endmember) curves are from Lages et al. (2020, 2021) and calculated using maximum Rᴄ/Rᴀ values for each segment; grey delimits the MORB range (8±1 Rᴀ). The free gas results are classified according to Lages et al. (2021); Free gases of temperature > 100 °C; Free gases 50–100°C; Free gases < 50 °C.

**Figure 4 – Volatile contents from melt inclusions at Villarrica.** The solubility model is used for PEC-treated MIs only, applying the Iacono-Marziano et al. (2012) model to calculate isobars and degassing curves. a) CO₂ vs H₂O concentrations in melt inclusions from Villarrica. b) CO₂ vs H₂O concentrations in melt inclusions from MECs, c) Raman-corrected degassing paths (closed system degassing). The µRaman density represents all MIs treated with the method described in Robidoux et al. (2018) (Table A.8-A.9). The Mimic model is applied to all MIs measured by EMPA with vapor bubbles and allows to obtain the CO₂ content as output CO₂vbg (Rasmussen et al., 2020), which is the result of the calculated reconstruction of the total MI volume and CO₂ content using the vapor growth model of the same authors.
**Figure 5 – Post entrapment crystallization saturation pressure and temperature conditions: chronological order.** a) Saturation pressure (kb) of Villarrica center (red) and MECs (blue) for minimum saturation pressures. The µRaman CO₂-corrected MIs represent pressures with open circle symbols; the vertical black arrow points connect non-corrected to CO₂-corrected contents (Table A.8). b) H₂O wt% content from MIs is represented by vertical bars for Villarrica center (red) and MECs (blue). H⁺ diffusion is interpreted for increasing effect (upward arrow) or decreasing effect (downward arrow). c) Inman's (1952) Md grain size parameter indicate increased negative values for larger pyroclast size. Explosive fragmentation is inferred to cause an increased production of large clast sizes at the sampled outcrop (upward arrow), while clast cooling rate decreases (downward arrow) as clast size increases. d) Temperature (°C), of Villarrica center (red) and MECs (blue). The thin vertical bars are minimum to maximum recorded PEC MIs for this study. The colored boxes represent minimum and maximum temperatures (°C) using the Tg output obtained from the Mimic model (Rasmussen et al. 2020), which is the glass transition temperature (Giordano et al., 2008). The “MI quenching rate” variation (interpreted) decreases systematically along the same series of olivine crystals (downward arrow). The left vertical axis is used for trapping MI temperatures while right vertical axis is used for quenching MI temperatures.

**Figure 6 – Villarrica depth cross section for solubility model.** West to east Villarrica profile for magma crystallization conditions (lithostatic pressure gradient is 0.27 km/kb). Vertical scale X2 applies to framework below >2.0 km in depth and vertical scale X1 applies to framework between summit (2847 m.) and 2.0 km in depth. Horizontal distances are not to scale. Minimum saturation depths (km) are shown with an abbreviation code for each eruptive event based on the literature (Moreno and Clavero, 2006); same color code as for Figure 2, except for literature Chaimilla black letters abbreviated to "Ch*" are crystallization depths of ascending magmas from Pioli et al. (2015). The boxes with colored borders are minimum and maximum saturation pressures (Bar) recorded by MI solubility models and thin vertical bars are minimum and maximum ranges for µRaman CO₂ corrections applied in the present study. Arrow intervals stand for vertical interval depths in black characters for Magma reservoir* (Lohmar et al. 2012; Delgado et al., 2017), Paroxysm source* (2015) (Romero et al., 2022). Villarrica olivine* (19–35 km) and CHSEC olivine (32–44 km) are from Morgado et al. (2015) and represent assumed olivine crystallization depths calculated using pyroxene-olivine geothermobarometry. Background volcanism is modified from Moreno and Clavero (2006). The Rc/Ra dataset is from this study, except for the Villarrica paroxysm source and the duplicate Chaillupén sample (Lages et al., 2021b).

**Figure 7 – ³He/⁴He for FIs corrected for atmospheric contamination (Rc/Ra) vs magmatic fluid tracers.** a) Mean Th/La in subducting sediment columns (Plank, 2014) and volcanic arc trenches (bulk composition added in this paper for CVZ and Lages et al., 2021b; database filtered for < 58 wt% SiO₂). CAVA bulk composition from Rizzo et al., 2022. The same symbols are used as in previous figures for MIs, with the Pucón Ignimbrite series Pb considered as the parental magmatic fluid and/or melt for the rest of the dataset produced in this study. b) The ³He/⁴He FIs corrected for atmospheric contamination (Rc/Ra) vs. CO₂/³He systematics for South American fluids calculated as mol/g from mass
spectrometry; the crust-mantle binary mixing line (in blue) assumes an Ra of 7.9 (avg. SVZ taken from Lages et al., 2021b). All lines and “X” symbols are fumarole data taken from Lages et al. (2021ab) and CAVA data from Rizzo et al. (2022).

**Figure 8** – **The influence of geochemical parameters on trapping conditions of ³He/⁴He FIs: chronological order.** The bulk rock collection is from the following authors: Hickey-Vargas, 1989; Lohmar et al. 2012; Costantini et al., 2011; Pioli et al., 2015; Morgado et al., 2015; Hickey-Vargas et al., 2016; McGee et al., 2017). a) Th/La slab sediment ratio used to test possible slab control on the ³He/⁴He signature of the mantle wedge along the Andes and Villarrica, b) ⁴He content (g/mol) from this study, c) Sr/Y to detect peripheral contamination, from our bulk rock collection and the literature d) K₂O wt.% content from PEC melt inclusions, with minimum and maximum interval bars. The median value is arbitrary, representing the range of minimum and maximum K₂O wt.% contents in the dataset by eruptive event. The bulk rock K₂O wt.% contents are from this study and the literature.

**Supplementary Material**

**(File)**

**Appendix A – Supplementary Material Methodology Review.**

**(Tables)**

**Appendix B**

**Table A.1: Full inclusion reference analysis.**

**Table A.2: Bulk-rock analysis of Villarrica samples.**

Major element analysis based on ICPMS. LOI values were corrected for oxygen uptake in the conversion of FeO to Fe₂O₃T (wt.%) in the furnace. Ratios for each eruptive event were reported as FeO/Fe₂O₃. Trace elements and REE were analyzed by inductively coupled plasma mass spectrometry. Trace element ratios are calculated directly from the values in the table (weight ppm ratio) with no normalization to the standards in the literature.

**Table A.3: Olivine populations statistics.**

Classification of olivine series described for the presence of the following MI typologies (Robidoux et al., 2018): G1 (no inclusions), G2 glassy inclusions, G3 glassy inclusions+vapor bubble, G4 glassy inclusions+vapor bubble+spinel, G5 crystallized MI, GR MI associated with boundary (reentrant or hourglass). Inclusion morphologies and dimensions are given in microns.

**Table A.4: Electron microprobe analyses of original Villarrica and MEC olivine chemistry.**

**Table A.5: H₂O-CO₂ contents from FTIR.**
a) H₂O (as OH⁻) at 3,550 cm⁻¹ peak, b) CO₂ content as CO₃²⁻ double peak (1,435-1,515 cm⁻¹).

**Table A.6: Volatile contents from SIMS.**

**Table A.7: FTIR and SIMS reproducibility.**

The selected FTIR H₂O - CO₂ contents are compared to H₂O SIMS contents with error bars according to respective error sources. The wt. % error for [H₂O] with FTIR assumes the sum of the following errors: (1) median absorbance (Abs.) graphical error between closest cm⁻¹ records on IR spectrum to the left and right of the central peak position 3,550 cm⁻¹, (2) thickness deviation from the wafer (µm), (3) difference between replicate analysis "a" and "b". The STD error on eruption series from the density (g/cm³) and absorption coefficients (mol⁻¹ cm⁻¹) is only considered if EMPA results are not available. The wt. % error for [H₂O] with SIMS uses the %STD error from "¹⁶O - ¹H" calibration curves. The wt. % error for [CO₃²⁻] using FTIR (ppm units) uses the same parameters as for [H₂O] (in wt.%), but graphical error depends on the double peak 1,435 – 1,515 cm⁻¹. The wt. % error for [CO₂] using SIMS (ppm units) uses the %STD error from "¹²C" calibration curves.

**Table A.8: Major element and volatile chemistry of Villarrica PEC glass inclusions.**

Olivine compositions are given in Fo%, and geothermobarometer results for solubility models are calculated according to Iacono-Marziano et al. (2012). Conditions for Rasmussen method and Raman corrected volatile contents are given for saturation pressure models.

**Table A.9: Raman CO₂ density and spectrum identification in shrinkage bubbles.**

**Table A.10: Noble gas isotopes.**

**Supplementary Material (Figures)**

**Figure A.1: Calibration of SIMS parameters for volatiles species.**

The set of standards with known volatile contents are given for a) ¹²C⁻, b) ¹³C⁻, c) ¹⁶OH⁻, d) ¹⁹F⁻, e) ³²S⁻, f) ³⁵Cl⁻. A Cs⁺ primary beam with a current of 1 nA and an electron gun is used to compensate for charge build-up at the sample surface. A 3-minute pre-sputter with a 30 × 30 µm square raster was applied, then analyses were performed on the 15 to 20 µm spot in the centre of the raster-cleaned area by a mechanical aperture placed at the secondary ion image plane. The resolving mass of ≈7000 (with the contrast aperture at 400 µm, the energy aperture at 40 eV, the entrance slit at 52 µm and the exit slit at 173 µm) meant that complete discrimination of mass interferences was achieved (³⁴S¹H from ³⁵Cl, ¹⁷O from ¹⁶O¹H, ²⁹Si¹H from ³⁰Si and ³¹P¹H from ³²S). We collected signals for ¹²C (8 seconds), ¹⁷O (3 seconds), ¹⁶O¹H (6 seconds), ¹⁸O (3 seconds), ¹⁹F (4 seconds), ²⁷Al (3 seconds), ³⁰Si (3 seconds), ³²S (4 seconds) and ³⁵Cl (6 seconds; counting times in brackets), with 2 seconds waiting time after each switch of the magnet. This cycle was repeated 10 times for each analysis. One measurement lasted 12 min per spot.
**Figure A.2: FTIR and SIMS reproductibility.**

Volatile contents of MIs at Villarrica with H₂O concentrations in MIs from Villarrica. The FTIR H₂O–CO₂ content is compared with the H₂O–CO₂ SIMS content with error bars. The MI samples containing shrinkage bubbles are represented by a circle with a black border. a) Comparison of the H₂O content is shown with error bars from Appendix C. The legend shows the four groups of quartiles used with grey-toned circles and each one represents the following categories in µm³ unit volume (Vo) Q₁ (3,4E-09 – 8,0E-08); Q₂ (8,0E-08 – 2,5E-07); Q₃ (2,5E-07 – 5,4E-07); Q₄ (5,4E-07b – 1,2E-05). b) Comparison of the CO₂ content is shown with error bars. Each eruption is color coded according to the legend.

**References**

1. Aiuppa, A., Bitetto, M., Francofonte, V., Velasquez, G., Parra, C.B., Giudice, G., Liuzzo, M., Moretti, R., Moussallam, Y., Peters, N. and Tamburello, G., (2017). A CO2-gas precursor to the March 2015 Villarrica volcano eruption. Geochemistry, Geophysics, Geosystems, 18(6), 2120-2132.

2. Barry, P. H., De Moor, J. M., Chiodi, A., Aguilera, F., Hudak, M. R., Bekaert, D. V., ... & Giovannelli, D. (2022). The helium and carbon isotope characteristics of the Andean Convergent Margin. Frontiers in Earth Science, 10, 897267.

3. Battaglia, A., Bitetto, M., Aiuppa, A., Rizzo, A. L., Chigna, G., Watson, I. M., ... & de Moor, M. J. (2018). The Magmatic gas Signature of Pacaya Volcano, with implications for the volcanic CO2 flux from Guatemala. Geochemistry, Geophysics, Geosystems, 19(3), 667-692.

4. Boschetty, F.O., Ferguson, D.J., Cortés, J.A., Morgado, E., Ebmeier, S.K., Morgan, D.J., Romero, J.E. and Silva Parejas, C., (2022). Insights into magma storage beneath a frequently erupting arc volcano (Villarrica, Chile) from unsupervised machine learning analysis of mineral compositions. Geochemistry, Geophysics, Geosystems, 23(4), e2022GC010333.

5. 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(1), 9809.

6. Brahm, R., Parada, M. A., Morgado, E., Contreras, C., & McGee, L. E. (2018). Origin of Holocene trachyte lavas of the Quetrupillán volcanic complex, Chile: Examples of residual melts in a rejuvenated crystalline mush reservoir. Journal of Volcanology and Geothermal Research, 357, 163-176.

7. Burnard, P., Graham, D., & Turner, G. (1997). Vesicle-specific noble gas analyses of "popping rock": implications for primordial noble gases in Earth. Science, 276(5312), 568-571.

8. Cashman, K. V., Sparks, R. S. J., & Blundy, J. D. (2017). Vertically extensive and unstable magmatic systems: a unified view of igneous processes. Science, 355(6331), eaag3055.

9. Cortés, J. A., Gertisser, R., & Calder, E. S. (2024). Magma recharge in persistently active basaltic-andesite systems and its geohazards implications: the case of Villarrica volcano, Chile. International Journal of Earth Sciences, 1-19.

10. Costantini, L., Pioli, L., Bonadonna, C., Clavero, J., & Longchamp, C. (2011). A late
Holocene explosive mafic eruption of Villarrica volcano, Southern Andes: The Chaimilla deposit. *Journal of Volcanology and Geothermal Research*, 200(3-4), 143-158.

11. Danyushevsky, L. V., & Plechov, P. (2011). Petrolog3: Integrated software for modeling crystallization processes. *Geochemistry, Geophysics, Geosystems*, 12(7).

12. Delgado, F., Pritchard, M. E., Ebmeier, S., González, P., & Lara, L. (2017). Recent unrest (2002–2015) imaged by space geodesy at the highest risk Chilean volcanoes: Villarrica, Llaima, and Calbuco (Southern Andes). *Journal of Volcanology and Geothermal Research*, 344, 270-288.

13. De Maisonneuve, C. B., Dungan, M. A., Bachmann, O., & Burgisser, A. (2012). Insights into shallow magma storage and crystallization at Volcán Llaima (Andean southern volcanic zone, Chile). *Journal of Volcanology and Geothermal Research*, 211, 76-91.

14. DeMets, C. (2001). A new estimate for present-day Cocos-Caribbean plate motion: Implications for slip along the Central American volcanic arc. *Geophysical research letters*, 28(21), 4043-4046. https://doi.org/10.1029/2001GL013518

15. Edmonds, M., Liu, E. J., & Cashman, K. V. (2022). Open-vent volcanoes fuelled by depth-integrated magma degassing. *Bulletin of Volcanology*, 84(3), 28.

16. Esposito, R., Bodnar, R.J., Danyushevsky, L.V., De Vivo, B., Fedele, L., Hunter, J., Lima, A. and Shimizu, N., (2011). Volatile evolution of magma associated with the Solchiaro eruption in the Phlegrean Volcanic District (Italy). *Journal of Petrology*, 52(12), 2431-2460.

17. Ferrando, S., Petrelli, M., &amp; Frezzotti, M. L. (2019). Gradual and selective trace-element enrichment in slab-released fluids at sub-arc depths. *Scientific Reports*, 9(1), 16393.

18. Frezzotti, M. L., Tecce, F., & Casagli, A. (2012). Raman spectroscopy for fluid inclusion analysis. *Journal of Geochemical Exploration, 112*, 1-20.

19. Gaetani, G. A., O'Leary, J. A., Shimizu, N., Bucholz, C. E., & Newville, M. (2012). Rapid reequilibration of H2O and oxygen fugacity in olivine-hosted melt inclusions. *Geology*, 40(10), 915-918.

20. Giordano, D., Russell, J. K., & Dingwell, D. B. (2008). Viscosity of magmatic liquids: a model. *Earth and Planetary Science Letters*, 271(1-4), 123-134.

21. Graham, D. W. (2002). Noble gas isotope geochemistry of mid-ocean ridge and ocean island basalts: Characterization of mantle source reservoirs. *Reviews in mineralogy and geochemistry*, 47(1), 247-317.
https://doi.org/10.2138/rmg.2002.47.8

22. Heinrich, M., Cronin, S. J., Torres-Orozco, R., Colombier, M., Scheu, B., & Pardo, N. (2020). Micro-porous pyroclasts reflecting multi-vent basaltic-andesite Plinian eruptions at Mt. Tongariro, New Zealand. *Journal of Volcanology and Geothermal Research*, 401, 1069-1086.

23. Hickey-Vargas, R., Sun, M., & Holbik, S. (2016). Geochemistry of basalts from small eruptive centers near Villarrica stratovolcano, Chile: evidence for lithospheric mantle components in continental arc magmas. *Geochimica et Cosmochimica Acta*, 185, 358-382.

24. Hickey-Vargas, R., Roa, H. M., Escobar, L. L., & Frey, F. A. (1989). Geochemical variations in Andean basaltic and silicic lavas from the Villarrica-Lanin volcanic chain (39.5 S): an evaluation of source heterogeneity, fractional crystallization and
crustal assimilation. Contributions to Mineralogy and Petrology, 103, 361-386.

25. Hilton, D. R., Fischer, T. P., & Marty, B. (2002). Noble gases and volatile recycling at subduction zones. Reviews in mineralogy and geochemistry, 47(1), 319-370.

26. Iacono-Marziano, G., Morizet, Y., Le Trong, E., & Gaillard, F. (2012). New experimental data and semi-empirical parameterization of H₂O–CO₂ solubility in mafic melts. Geochimica et Cosmochimica Acta, 97, 1-23.

27. Jarrard, R. D. (1986). Relations among subduction parameters. Reviews of Geophysics, 24(2), 217-284.

28. Kuritani, T., Yokoyama, T., & Nakamura, E. (2007). Rates of thermal and chemical evolution of magmas in a cooling magma chamber: A chronological and theoretical study on basaltic and andesitic lavas from Rishiri Volcano, Japan. Journal of Petrology, 48(7), 1295-1319.

29. Lages, J., Rizzo, A. L., Aiuppa, A., Robidoux, P., Aguilar Contreras, R., Apaza Choquehuayta, F. E., & Masías Alvarez, P. J. (2021a). Crustal controls on light noble gas isotope variability along the Andean Volcanic Arc. uri: issn: 2410339X. https://doi.org/10.1016/j.chemgeo.2020.119966

30. Lages, J., Rizzo, A.L., Aiuppa, A., Samaniego, P., Le Pennec, J.L., Ceballos, J.A., Narvaez, P.A., Moussallam, Y., Bani, P., Schipper, C.I. and Hidalgo, S., (2021b). Noble gas magmatic signature of the Andean Northern Volcanic Zone from fluid inclusions in minerals. Chemical Geology, 559, 119966. https://doi.org/10.1016/j.chemgeo.2020.119966

31. Liu, E.J., Wood, K., Mason, E., Edmonds, M., Aiuppa, A., Giudice, G., Bitetto, M., Francofonte, V., Burrow, S., Richardson, T. and Watson, M., (2019). Dynamics of outgassing and plume transport revealed by proximal unmanned aerial system (UAS) measurements at Volcán Villarrica, Chile. Geochemistry, Geophysics, Geosystems, 20(2), 730-750.

32. Lloyd, A. S., Plank, T., Ruprecht, P., Hauri, E. H., & Rose, W. (2013). Volatile loss from melt inclusions in pyroclasts of differing sizes. Contributions to Mineralogy and Petrology, 165, 129-153.

33. Lohmar, S., Parada, M., Gutiérrez, F., Robin, C., & Gerbe, M. C. (2012). Mineralogical and numerical approaches to establish the pre-eruptive conditions of the mafic Licán Ignimbrite, Villarrica Volcano (Chilean Southern Andes). Journal of Volcanology and Geothermal Research, 235, 55-69.

34. Marty, B. (2012). The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters, 313, 56-66.

35. Mason, E. M., Edmonds, M., Hammond, S., Ilyinskaya, E., Jenner, F., Kunz, B., ... & Velasquez, G. (2024). Chalcophile element degassing at an active continental arc volcano. Geochimica et Cosmochimica Acta, 367, 72-86.

36. Massare, D., Métrich, N., & Clocchiatti, R. (2002). High-temperature experiments on silicate melt inclusions in olivine at 1 atm: inference on temperatures of homogenization and H₂O concentrations. Chemical Geology, 183(1-4), 87-98.

37. McGee, L.E., Brahm, R., Rowe, M.C., Handley, H.K., Morgado, E., Lara, L.E., Turner, M.B., Vinet, N., Parada, M.Á. and Valdivia, P., (2017). A geochemical approach to distinguishing competing tectono-magmatic processes preserved in small eruptive centres. Contributions to Mineralogy and Petrology, 172, 1-26.

38. Moitra, P., Gonnermann, H. M., Houghton, B. F., & Tiwary, C. S. (2018). Fragmentation and Plinian eruption of crystallizing basaltic magma. *Earth and
*Planetary Science Letters*, **500**, 97-104.

39. Mordensky, S. P., & Wallace, P. J. (2018). Magma storage below Cascades shield volcanoes as inferred from melt inclusion data: A comparison of long-lived and short-lived magma plumbing systems. *Journal of Volcanology and Geothermal Research*, **368**, 1-12.

40. Moreira, M. A., & Kurz, M. D. (2013). Noble gases as tracers of mantle processes and magmatic degassing. The noble gases as geochemical tracers, 371-391.

41. Moreno, H., & Clavero, J. R. (2006). Geología del volcán Villarrica: Regiones de la Araucanía y de Los Lagos. Servicio Nacional de Geología y Minería, Subdirección Nacional de Geología.

42. Morgado, E., Parada, M. A., Contreras, C., Castruccio, A., Gutiérrez, F., & McGee, L. E. (2015). Contrasting records from mantle to surface of Holocene lavas of two nearby arc volcanic complexes: Caburgua-Huelemolle Small Eruptive Centers and Villarrica Volcano, Southern Chile. *Journal of Volcanology and Geothermal Research*, **306**, 1-16.

43. Moussallam, Y., Lee, H.J., Ding, S., DeLessio, M., Everard, J.L., Spittle, E., Lu, G., Baur, J., Glazer, E., Peccia, A. and Zaman, M., (2023). Temperature of the Villarrica lava lake from 1963 to 2015 constrained by phase-equilibrium and a new glass geothermometer for Basaltic Andesites. *Journal of Petrology*, **64**(2), egad003.

44. Moussallam, Y., Bani, P., Curtis, A., Barnie, T., Moussallam, M., Peters, N., Schipper, C.I., Aiuppa, A., Giudice, G., Amigo, Á. and Velasquez, G., (2016). Sustaining persistent lava lakes: Observations from high-resolution gas measurements at Villarrica volcano, Chile. *Earth and Planetary Science Letters*, **454**, 237-247.

45. Moussallam, Y., Towbin, W. H., Plank, T., Bureau, H., Khodja, H., Guan, Y., ... & Rose-Koga, E. F. (2024). ND70 Series Basaltic Glass Reference Materials for Volatile Element (H2O, CO2, S, Cl, F) Measurement and the C Ionisation Efficiency Suppression Effect of Water in Silicate Glasses in SIMS. *Geostandards and Geoanalytical Research*.

46. Muñoz, F. A., Peña-Cortés, F., Inostroza-Matus, C., & Callejas, R. C. (2024). El riesgo en torno al volcán Villarrica en Chile: Exposición, peligrosidad e instrumentos de gestión del riesgo en Coñaripe, Licán Ray, Pucón y Villarrica. *Revista de Estudios Latinoamericanos sobre Reducción del Riesgo de Desastres REDER*, **8**(1), 115-130.

47. Pavez, M., Brasse, H., Kapinos, G., Díaz, D., Lara, L. E., & Schill, E. (2023). Magma storage and transfer in the Villarrica volcanic chain, South Chile: MT insights into volcano-tectonic interactions. *Journal of Volcanology and Geothermal Research*, **439**, 1078-1052.

48. Plank, T. (2005). Constraints from thorium/lanthanum on sediment recycling at subduction zones and the evolution of the continents. *Journal of Petrology*, **46**(5), 921-944.

49. Plank, T. (2014). The chemical composition of subducting sediments. Elsevier.

50. Pioli, L., Scalisi, L., Costantini, L., Di Muro, A., Bonadonna, C., & Clavero, J. (2015). Explosive style, magma degassing and evolution in the Chaimilla eruption, Villarrica volcano, Southern Andes. *Bulletin of Volcanology*, **77**, 1-14.

51. Porcelli, D., Ballentine, C.J. and Wieler, R. (2002). An introduction to noble gas geochemistry and cosmochemistry. *Rev. Min. Geoch.* **47**: 1-18.

52. Putirka, K. D. (2008). Thermometers and barometers for volcanic systems. *Reviews*
in mineralogy and geochemistry, 69(1), 61-120.

53. Rasmussen, D. J., Plank, T. A., Wallace, P. J., Newcombe, M. E., & Lowenstern, J. B. (2020). Vapor-bubble growth in olivine-hosted melt inclusions. American Mineralogist, 105(12), 1898-1919.

54. Rasmussen, D. J., Plank, T. A., Roman, D. C., & Zimmer, M. M. (2022). Magmatic water content controls the pre-eruptive depth of arc magmas. Science, 375(6585), 1169-1172.

55. Remigi, S., T. Mancini, S. Ferrando, M.-L. Frezzotti (2021). Interlaboratory Application of Raman CO 2 Densimeter Equations: Experimental Procedure and Statistical Analysis Using Bootstrapped Confidence Intervals. Applied Spectroscopy, 75(7), 867-881.

56. Rizzo, A. L., Robidoux, P., Aiuppa, A., & Di Piazza, A. (2022). 3He/4He Signature of Magmatic Fluids from Telica (Nicaragua) and Baru (Panama) Volcanoes, Central American Volcanic Arc. Applied Sciences, 12(9), 4241.

57. Rizzo, A.L., Pelorosso, B., Coltorti, M., Ntaflos, T., Bonadiman, C., Matusiak-Małek, M., Italiano, F. and 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 Science, 6, 215

58. 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, 147-163.

59. Robidoux, P., Frezzotti, M. L., Hauri, E. H., & Aiuppa, A. (2018). Shrinkage bubbles: the C-O-H-S magmatic fluid system at San Cristóbal volcano. Journal of Petrology, 59(11), 2093-2122.

60. Robidoux, P., Roberge, J., & Adams, C. (2020). Spatial visualization of geochemical data: application to the Chichinauzin volcanic field, Mexico. In Updates in Volcanology-Transdisciplinary Nature of Volcano Science. IntechOpen.

61. Robidoux, P., Pastén, D., Levresse, G., Diaz, G., & Paredes, D. (2021). Volatile content implications of increasing explosivity of the strombolian eruptive style along the fracture opening on the NE Villarrica Flank: Minor eruptive centers in the Los Nevados Group 2. Geosciences, 11(8), 309.

62. Rose-Koga, E.F., Bouvier, A.S., Gaetani, G.A., Wallace, P.J., Allison, C.M., Andrys, J.A., De La Torre, C.A., Barth, A., Bodnar, R.J., Gartner, A.B. and Butters, D. (2021). Silicate melt inclusions in the new millennium: a review of recommended practices for preparation, analysis, and data presentation. Chemical Geology, 570, 120145.

63. Roedder, E. (1984). Volume 12: fluid inclusions. Reviews in mineralogy, 12, 644.

64. Romero, J.E., Morgado, E., Pisello, A., Boschetty, F., Petrelli, M., Cáceres, F., Alam, M.A., Polacci, M., Palma, J.L., Arzilli, F. and Vera, F. (2022). Pre-eruptive Conditions of the 3 March 2015 Lava Fountain of Villarrica Volcano (Southern Andes). Bulletin of Volcanology, 85(1), 2.

65. Ruth, D. C., Cottrell, E., Cortes, J. A., Kelley, K. A., & Calder, E. S. (2016). From passive degassing to violent Strombolian eruption: the case of the 2008 eruption of Llaima volcano, Chile. Journal of Petrology, 57(9), 1833-1864.

66. Sano, Y., & Fischer, T. P. (2013). The analysis and interpretation of noble gases in modern hydrothermal systems. The noble gases as geochemical tracers, 249-317.

67. Silva Parejas, C., Druitt, T. H., Robin, C., Moreno, H., & Naranjo, J. A. (2010). The Holocene Pucón eruption of Volcán Villarrica, Chile: deposit architecture and
eruption chronology. Bulletin of volcanology, 72, 677-692.

68. Smith, I. E. M., & Németh, K. (2017). Source to surface model of monogenetic volcanism: a critical review. Geological Society, London, Special Publications, 446(1), 1-28.

69. Stern, C. R. (2004). Active Andean volcanism: its geologic and tectonic setting. Revista geológica de Chile, 31(2), 161-206. Revista Geológica de Chile, Vol. 31, No. 2, p http://dx.doi.org/10.4067/S0716-02082004000200001

70. Stimac, J., Goff, F., & Goff, C. J. (2015). Intrusion-related geothermal systems. In The encyclopedia of volcanoes (pp. 799-822). Academic Press.

71. Stix, J. (2007). Stability and instability of quiescently active volcanoes: The case of Masaya, Nicaragua. Geology, 35(6), 535-538.

72. Tardani, D., Reich, M., Roulleau, E., Takahata, N., Sano, Y., Pérez-Flores, P., ... & Arancibia, G. (2016). Exploring the structural controls on helium, nitrogen and carbon isotope signatures in hydrothermal fluids along an intra-arc fault system. Geochimica et Cosmochimica Acta, 184, 193-211.

73. Tassara, A., & Echaurren, A. (2012). Anatomy of the Andean subduction zone: three-dimensional density model upgraded and compared against global-scale models. Geophysical Journal International, 189(1), 161-168.

74. Wallace, P. J., Plank, T., Bodnar, R. J., Gaetani, G. A., & Shea, T. (2021). Olivine-hosted melt inclusions: a microscopic perspective on a complex magmatic world. Annual Review of Earth and Planetary Sciences, 49, 465-494.

75. Watt, S. F., Pyle, D. M., & Mather, T. A. (2013). The volcanic response to deglaciation: Evidence from glaciated arcs and a reassessment of global eruption records. Earth-Science Reviews, 122, 77-102.

76. Witham, F., Blundy, J., Kohn, S. C., Lesne, P., Dixon, J., Churakov, S. V., & Botcharnikov, R. (2012). SolEx: A model for mixed COHSCI-volatile solubilities and exsolved gas compositions in basalt. Computers & Geosciences, 45, 87-97.

77. Witter, J. B., Kress, V. C., Delmelle, P., & Stix, J. (2004). Volatile degassing, petrology, and magma dynamics of the Villarrica Lava Lake, Southern Chile. Journal of volcanology and geothermal research, 134(4), 303-337.

78. Zellmer, G. F., Edmonds, M., & Straub, S. M. (2015). Volatiles in subduction zone magmatism. Geological Society, London, Special Publications, 410(1), 1-17.
<table><thead><tr><th>Eruptive event</th><th>Sample</th><th>Deposit</th><th>Unit Association</th><th>Primary volcanic clast size: Fisher (1966)</th><th>Volcanic clast components: White y Houghton (2006)</th><th>Grabenal Std. (σφ)</th><th>Sorption</th><th>Inamana (1952) Parameter (Mdp): Grainsize</th></tr></thead><tbody><tr><td rowspan="4">Pucón Ignimbrite<sup>7</sup></td><td>TVP10E</td><td>Fall deposit Piroclastic flow deposit rich in juvenile Piroclastic flow deposit rich in lithic Piroclastic flow deposit rich in lithic</td><td>Villarrica: Pucon Pb</td><td>Toba Lapilli</td><td>Lithic Toba</td><td>1.45</td><td>-</td><td>1.55</td></tr><tr><td>TVP03<sup>1</sup></td><td></td><td>Villarrica: Pucon P1</td><td>Toba Lapilli</td><td>Vitric Toba</td><td>2.68</td><td>-</td><td>0.72</td></tr><tr><td>TVPI5AB</td><td></td><td>Villarrica: Pucon P2-P3</td><td>Toba Lapilli</td><td>Lithic Toba</td><td>2.19</td><td>-</td><td>0.43</td></tr><tr><td>TVPI5C</td><td></td><td>Villarrica: Pucon P2-P3</td><td>Toba Lapilli</td><td>Lithic Toba Lithic</td><td>1.35</td><td>-</td><td>1.52</td></tr><tr><td rowspan="3">Chaimila fallout<sup>8</sup></td><td>TVP06B</td><td>Fallout deposit</td><td>Villarrica: Chaimilla Lower Sequence (18% lithics= A+B)</td><td>Toba Lapilli Breccia</td><td>Toba with 18% lithics Lithic</td><td>1.1</td><td>-</td><td>1.41</td></tr><tr><td>TVP06C</td><td>Fallout deposit</td><td>Villarrica: Chaimilla Lower Sequence (18% lithics= A+B)</td><td>Toba Lapilli Breccia Toba</td><td>Toba with 18% lithics Lithic</td><td>1.1</td><td>-</td><td>1.40</td></tr><tr><td>TVP06D</td><td>Fallout deposit</td><td>Villarrica: Chaimilla Lower Sequence (B-C)<sup>6</sup></td><td>Toba Lapilli Breccia</td><td>Lithic Toba</td><td>0.97</td><td>-</td><td>2.10</td></tr><tr><td>March 2015 Paroxysm<sup>9</sup></td><td>Villa_p2015+m2015; 2015_B<sup>2</sup></td><td>Piroclast - Scoriaceous bomb</td><td>Villarrica: March, 2015</td><td>Breccia lapilli</td><td>Vitric Toba</td><td>-</td><td>-</td><td>6.00</td></tr><tr><td>Los Nevados MEC</td><td>HLN1 A3D<sup>3,4</sup></td><td>Piroclast - Scoriaceous bomb</td><td>Los Nevados Gr. 1</td><td>Lapilli breccia</td><td>Vitric Toba</td><td>3.30</td><td>-</td><td>3.78</td></tr></tbody></table>
<table><tr><td>Pucón ignimbrite (P1)</td><td>4</td><td>1</td><td>1</td><td>1</td><td>1</td><td>2</td><td>2</td><td>4</td><td>5</td><td>1</td></tr><tr><td>Pucón ignimbrite (P2)</td><td>3</td><td>2</td><td>1</td><td>1</td><td>1</td><td>2</td><td>1</td><td>1</td><td>0</td><td>3</td></tr><tr><td>Pucón ignimbrite (P3)</td><td>2</td><td>3</td><td>1</td><td>0</td><td>2</td><td>3</td><td>0</td><td>1</td><td>8</td><td>5</td></tr><tr><td>Chaimilla (A+B) Opening</td><td>2</td><td>1</td><td>1</td><td>1</td><td>6</td><td>3</td><td>5</td><td>6</td><td>0</td><td>1</td></tr><tr><td>Chaimilla (B+C)</td><td>1</td><td>1</td><td>2</td><td>2</td><td>3</td><td>1</td><td>1</td><td>1</td><td>0</td><td>4</td></tr><tr><td>Villarrica: March, 2015</td><td>2</td><td>2</td><td>1</td><td>1</td><td>2</td><td>7</td><td>1</td><td>2</td><td>0</td><td>1</td></tr><tr><td>Los Nevados Gr.1</td><td>3</td><td>3</td><td>1</td><td>1</td><td>6</td><td>2</td><td>3</td><td>6</td><td>1</td><td>0</td></tr><tr><td>Los Nevados Gr.2</td><td>3</td><td>3</td><td>2</td><td>1</td><td>2</td><td>-</td><td>6</td><td>4</td><td>8</td><td>1</td></tr><tr><td>Chaillupén Gr.2</td><td>2</td><td>3</td><td>4</td><td>2</td><td>1</td><td>1</td><td>0</td><td>1</td><td>2</td><td>0</td></tr><tr><td>Caburgua</td><td>10</td><td>5</td><td>1</td><td>0</td><td>1</td><td>2</td><td>3</td><td>1</td><td>8</td><td>2</td></tr></table>

*Lages, J., Rizzo, A. L., Aiuppa, A., Robidoux, P., Aguilar Contreras, R., Apaza Choquehuayta, F. E., & Masías Alvarez, P. J. (2021). Crustal controls on light noble gas isotope variability along the Andean Volcanic Arc. Geochemical Perspectives Letters, uri: issn: 2410339X.

<table><caption>Table 3: Review of melt inclusion compositional dataset</caption><thead><tr><th>A. Chemistry Parameter</th><th>A. Changing attribut<br>e</th><th>B. Complementary observations</th><th>B. Changing attribut<br>e</th></tr></thead><tbody><tr><td>KD desviation (avg.)</td><td></td><td>(Mdφ) (Grain Size)</td><td></td></tr><tr><td>Los Nevados (0.078)</td><td rowspan="6">Increase Mg-Fe<br>diffusion</td><td>Chaimilla (-2.1)</td><td rowspan="6">Increase clast size</td></tr><tr><td>Pucon (0.080)</td><td>Caburgua (-1.1)</td></tr><tr><td>Chaimilla (0.091)</td><td>&lt; Pucón Ignimbrite (0.72)</td></tr><tr><td>Caburgua (0.093)</td><td>Los Nevados (-7.0 to - 3.8)</td></tr><tr><td>2015 (0.141)</td><td>Chaillupén (-7.0)</td></tr><tr><td>Chaillupén (0.172)</td><td>2015 (-6.0)</td></tr></tbody></table>
<table><thead><tr><th>Water contents (wt.%)<br>(Md)</th></tr></thead><tbody><tr><td>Pucon Ignimbrite (6.0)</td></tr><tr><td>Caburgua (3.6)</td></tr><tr><td>Los Nevados (3.3)</td></tr><tr><td>Chaillupen (2.8)</td></tr><tr><td>Chaimilla (2.4)</td></tr><tr><td>2015 (0.84)</td></tr></tbody></table>

Increase H⁺ diffusion

<table><thead><tr><th>Trapping MI - Glass transition (°C) °T<br>(range+STD)</th></tr></thead><tbody><tr><td>Pucón Ignimbrite Te(1135 SD 16) -<br>Tg(580 SD 30)</td></tr><tr><td>Chaimilla Te(1134 SD 48) - Tg (534 SD<br>43)</td></tr><tr><td>Los Nevados Te(1128 SD 19) Tg(653 SD<br>82)</td></tr><tr><td>Caburgua Te(1127 SD 14) - Tg(560 SD<br>140)</td></tr><tr><td>2015 Te(1076 SD 10) - Tg (614)</td></tr><tr><td>Chaillupén Te(1069 SD 8) - Tg (673 SD<br>43)</td></tr></tbody></table>

Decrease cooling °T

<table><thead><tr><th>The CO₂ content<br>(g/mol)/crystal batch<br>(range)</th></tr></thead><tbody><tr><td>Pucón Ignimbrite (3.1–4.6<br>·10⁻¹⁰)</td></tr><tr><td>Chaillupén (3.0–7.0 ·10⁻¹⁰)</td></tr><tr><td>Chaimilla (1.8–4.0 ·10⁻¹⁰)</td></tr><tr><td>2015 (?; Lages et al., 2021)</td></tr><tr><td>Caburgua (n.d.)</td></tr><tr><td>Los Nevados (2.92 ·10⁻¹⁰)</td></tr></tbody></table>

Decrease mass of CO₂<br>(bubble+crystal lattices)

<table><thead><tr><th>% Total Primary MI + bubble (range)</th></tr></thead><tbody><tr><td>Pucón Ignimbrite (13–81%)</td></tr><tr><td>Chaillupén (13.8–43.4%)</td></tr><tr><td>Chaimilla (21.7–24.4%)</td></tr><tr><td>2015 (15.5%)</td></tr><tr><td>Caburgua (14.8%)</td></tr><tr><td>Los Nevados (11.0–14.0%)</td></tr></tbody></table>

Decrease amount of vapor<br>bubble

<table><thead><tr><th>Maximum CO₂ contents<br>(max. + STD)</th></tr></thead><tbody><tr><td>Pucon Ignimbrite (1485 SD<br>274)</td></tr><tr><td>Chaillupen (863 SD 145)</td></tr><tr><td>Caburgua (607 SD 325)</td></tr><tr><td>Los Nevados (583 SD 176)</td></tr><tr><td>Chaimilla (409 SD 108)</td></tr><tr><td>2015 (307 SD 48)</td></tr></tbody></table>

Decrease dissolved CO₂

<table><thead><tr><th>Maximum %Forsterite contents (max. +<br>STD)</th></tr></thead><tbody><tr><td>Pucón Ignimbrite (87 SD 4)</td></tr><tr><td>Chaillupén (84 SD 0.3)</td></tr><tr><td>Chaimilla (83 SD 0.4)</td></tr><tr><td>Los Nevados (82 SD 3.5)</td></tr><tr><td>Caburgua (80.9 SD 3.4)</td></tr><tr><td>2015 (76)</td></tr></tbody></table>

Melt differentiation increase
**Declaration of interests**

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

[ ] The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Highlights

* Pucón Ignimbrite represent Villarrica postglacial primitive mafic magma.

* Polygenetic eruptive vents source >17 km depth CO2-rich volatile melts.

* Villarrica and lateral vent degas mafic magma at < 5km storage depths.

* Shallow atmospheric and mixed crustal ⁴He in volcanic arc fluids.

* Sublplinian paroxysm preserve MORB-like ³He/⁴He fluid ratios.
<figure><img src="image_4.png" /><figcaption>Figure 1</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Figure 2</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Figure 3</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Figure 4</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure 5</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Figure 6</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Figure 7</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Figure 8</figcaption></figure>