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Home , Aguilera (volcano), Antuco (volcano), Copahue, Explosive eruption, Fumarole, Fumarole mineral

SEGUNDO BOLETÍN VOLCANOLÓGICO CHILENO 2020

Miembros Dra. Inés Rodríguez Araneda–Universidad Católica de Dr. (c) Jorge Romero Moyano–University of Manchester Sr. Franco Vera Rivadeneira–Servicio Nacional de Geología y Minería Sr. Nicolás Luengo Vásquez–Universidad de Concepción Dr. (c) Gabriel Orozco Lanfranco–Universidad de Concepción Srta. Verónica Valdés Velásquez–Universidad Andrés Bello

INTRODUCCIÓN

El grupo Volcanología está conformado por geólogas y geólogos, quienes están desarrollando trabajos de investigación en algunos de los volcanes activos en nuestro país. Mediante esta iniciativa, sin fines de lucro, se busca acercar a la comunidad nacional a través de la divulgación de contenidos científicos sobre volcanes, con el fin de incrementar el conocimiento de la sociedad sobre este tipo de fenómenos geodinámicos. Entre nuestros objetivos está la creación de una red de colaboradores especialistas en volcanes a nivel nacional, entre los cuales exista un flujo constante de información académica vanguardista, que permita mantener a la ciudadanía informada sobre los últimos avances en volcanología.

El objetivo de este boletín es difundir y entregar a la comunidad, de todos los ámbitos, los trabajos científicos de investigadores chilenos y extranjeros, en lo que compete a las geociencias en el área de la volcanología en Chile.

Solicitamos a los investigadores nacionales e internacionales que se encuentran trabajando en volcanes chilenos y que publican sus resultados en revistas indexadas durante 2020, comunicarse con nosotros para considerarlos en la próxima edición de este boletín. Así mismo, invitamos a estudiantes de pregrado a enviar información equivalente respectiva a sus tesis o memorias de pregrado que se encuentren aprobadas.

Contacto:

[email protected]

Numerical wave propagation study of the unusual response of Nevados de Chillán to two aftershocks of the 2010 MW= 8.8 Maule . Cristian Faríasac*, Boris Galvánb a Departamento de Geología y Obras Civiles, Facultad de Ingeniería, Universidad Católica de Temuco, Temuco, Chile b The Centre for Hydrogeology and Geothermics, University of Neuchatel, Neuchatel, Switzerland c GeoKimün, Centro de Investigación en evaluación de riesgos y mitigación de procesos geológicos

Abstract In 2012, two large aftershocks of the MW = 8.8 Maule, Chile earthquake occurred near the Central Chilean coast. Both events, with magnitudes MW = 6.1 and MW = 7.1 were located about 200 km away from the volcanic/hydrothermal Nevados de Chillán (NdC) complex.

The system responded with a significant increase in seismicity to the MW = 6.1 event, and with a reduction in seismicity following the latter, larger MW = 7.1 earthquake. To understand the physical changes induced by both at the NdC, we set up a numerical wave propagation study. Our results show that these observations likely result from dynamic changes at the NdC complex during the passage of the seismic waves. In the case of the MW = 6.1 aftershock, the extensive stress transfer was large enough to induce changes at the hydrothermal system, which could have later led to an increase in fluid- driven seismicity. In the case of the MW = 7.1 earthquake, the oblique arrival of seismic waves to the main of the NdC due to the MW = 7.1 earthquake induced slight compressions at the reservoir and created openings in the main fault, promoting fluid migration, which can explain the reduction in seismicity beneath the main craters of the volcano. Results also show that the geometry of an underlying fault system can influence the volumetric response, suggesting that the role of local structures in earthquake- volcano interactions influence the behavior of triggered systems and should therefore not be disregarded.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2019.106735

Upper crustal differentiation processes and their role in 238U-230Th disequilibria at the San Pedro-Linzor volcanic chain (Central )

Benigno Godoya, Lucy McGeeb1, Osvaldo González-Maurelcd, Inés Rodrígueze, Petrus le Rouxd, Diego Morataa, Andrew Menziesf a Centro de Excelencia en Geotermia de los Andes (CEGA) y Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile b Department of and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia c Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avda. Angamos, 0610, , Chile d Department of Geological Sciences, University of Cape Town, Rondebosch, 7700, South Africa e Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Rudecindo Ortega, 02950, Chile f Bruker Nano GmbH, Am Studio 2D, Berlin 12489, Germany

Abstract U-series data are combined with major and trace element constraints to construct a detailed view of the magmatic system feeding the San Pedro-Linzor volcanic chain, aiding the understanding of how stratovolcanoes in extremely thick arc evolve. from the San Pedro-Linzor volcanic chain (Central Andes) have (238U/230Th) ranging 238 from 1.015 to 1.072, with U excess even in the less evolved (~57 wt% SiO2) analyzed lavas. Contrary to well-established trends between fluid mobile elements and 238U excess, 238 230 ( U/ Th)0 shows no systematic correlation with ratios indicative of fluid-driven melting (e.g. Ba/Hf and K/La). Moreover, the inverse correlation between (238U/232Th) with the amount of slab-derived fluid and the oxidation state of the mantle below Central Andes, which decreases eastwards, suggests that the main control of the 238U excess is not 238 232 230 232 associated with hydration of the mantle wedge. Changes in ( U/ Th) and ( Th/ Th)0 87 86 are observed with variations in SiO2 and CaO + Al2O3 contents, and Sr/ Sr and Dy/Dy* ratios of the lavas. These changes correspond to increasing (238U/232Th) with decreasing

Dy/Dy* and CaO + Al2O3 ratios, which is attributed to changes in crystallization of mineralogical phases within magmatic chambers during differentiation. Also, 230Th in- growth is produced during stagnation within magmatic chambers located below the San 230 232 Pedro-Linzor volcanic chain. Finally, a positive correlation between ( Th/ Th)0 and 87Sr/86Sr indicates an important role of crustal contamination, and of new inputs during evolution of the volcanic chain with time. Our observations suggest that better constraints of all magmatic processes are needed to fully understand the U-series disequilibria recognized for the different volcanic structures developed within - related tectonic environments.

Corresponding author: [email protected] https://doi.org/10.1016/j.jsames.2020.102672

Living near volcanoes: Scoping the gaps between the local community and volcanic experts in southern Chile

Andrés Marína,⁎, Francisca Vergara-Pintoa, Francisco Pradob, Cristian Faríasb a Centro de Estudios del Desarrollo Regional y Políticas Públicas CEDER, Universidad de Los Lagos, Chile b Departamento Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Chile

Abstract Human societies have always inhabited volcanic zones, but only recently scientists and decision-makers have turned the attention to volcanic risk prevention and reduction. Despite a growing consensus about the importance of engaging with nearby populations, in practice there is little dialogue with them regarding volcanic threats and opportunities. We study the experiences, impacts and concerns of an indigenous community, inhabiting in-between two major volcanic systems (Carrán Los Venados and Puyehue-Cordón Caulle), regarding past and recent eruptions. Results show a longstanding cultural and economic interrelationship between people and volcanoes, representing both benefits and barriers to development; existing local/traditional knowledge is necessary but not sufficient to meet people’s needs for adequate understanding and forecasting; despite community interest on volcanic science and risk reduction, important communication and trust gaps with experts persist. Our findings suggest the importance for scientists to establish collaborative and participatory relationships with local communities and decision-makers, with the goal of not only reducing negative volcanic impacts and uncertainty, but also taking advantage of the potential of volcanic environments to boost local sustainable livelihoods.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2020.106903

Pyroclastic deposits and eruptive heterogeneity of Volcán (37°A; Southern Andes) during the Mid to Late (<7.2 Ka)

Jorge E. Romeroa, Victoria Ramíreza, Mohammad Ayaz Alama, Jorge Bustillosb, Alicia Guevarac, Roberto Urrutiad, Alessandro Piselloe, Daniele Morgavie, Evelyn Criolloc a Departamento de Geología, Facultad de Ingeniería, Universidad de Atacama, Avenida Copayapu 485, Copiapó, Chile b Carrera de Ingeniería en Geología, Facultad de Ingeniería en Geología, Minas, Petróleos y Ambiental, Universidad Central de Ecuador, Quito, Ecuador c Departamento de Metalurgia Extractiva Escuela Politécnica Nacional, Quito, Ecuador d Centro de Ciencias Ambientales (EULA), Universidad de Concepción, Concepción, Chile e Department of Physics and Geology, University of Perugia, Piazza dell’ Università, 06123 Perugia,

Abstract Volcán Antuco (37°24′ S, 71°22′W; 2979 m asl) is the 13th ranked high threat volcano in Chile with 27 recorded historical eruptions, mostly (~96%) with volcanic explosivity indices (VEI) of ~1–2. An older eruptive record has been reconstructed from sections exposed on the western flank and is intimately related to a well-documented catastrophic at ~7.2 cal ka BP. However, very little is known about Antuco's post-collapse eruptive history in other sectors, especially on the eastern flanks where prevalent westerly winds favor optimal eastward transport and deposition. Our study reveals a more complete record of activity that has already been indicated from previous work with at least 23 tephra-forming eruptions, most of them within the last c. 7.2 ka, including 4 events that have generated pyroclastic density currents that have widely inundated the lower eastern flanks. Tephra from these eruptive events are typically composed of , free crystals and lithics, with occasional . The composition of juvenile fragments varies between and (50.2–62.2 wt% SiO2) and show of , and . Our results show that most of the eruptions of Antuco (c. 79%) are Strombolian to violent Strombolian. These eruptions have an estimated longer repose times (c. 200 year) and are likely higher in magnitude than those registered during historical times. This study also shows that the composition, style and magnitude may change from one eruptive episode to the next. This eruptive variability seems in complete accord with recent findings from other centers in the Southern Volcanic Zone exhibiting similar temporal eruptive diversity and ultimately, has significant implications with respect to hazard assessment.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2019.106759

The interaction between active crustal faults and : A case study of the Liquiñe-Ofqui Fault Zone and volcano, Southern Andes, using

Daniel Díazab, Felipe Zúñigaa, Angelo Castrucciobc a Departamento de Geofísica, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile b Centro de Excelencia en Geotermia de Los Andes, Plaza Ercilla 803, Santiago, Chile c Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile

Abstract The relationship between subduction in convergent margins, crustal structures and magmatism is crucial to understand processes such as the type and frequency of volcanic activity in these areas. Although it is well known that the release of fluids by the subducting slab is the main cause of the arc volcanism in areas like the Central and Southern Andes, details such as the timing and pathways of ascent and storage are still not well understood. A key factor that needs to be better studied in the Southern Volcanic Zone of the Andes of Chile is the role of large tectonic features in fluid transport and magma ascent processes, such as the Liquiñe-Ofqui Fault Zone, a N-S strike-slip crustal structure parallel to the main . In this study, we focus on Osorno volcano, a composed mainly by products of basaltic to basaltic- composition with minor and with historical Hawaiian-Strombolian eruptions. Through the measurement of magnetotellurics and the use of 3-D modeling tools and petrologic constraints, two magmatic reservoirs have been inferred, which suggest a complex magmatic system with reservoirs of different depths and compositions. The shallowest magmatic reservoir (4–8 km) has a dacitic composition, while the deepest one (7–15 km), has an andesitic composition instead. The shallow reservoir is located 2 km to the E of the volcano and the deepest one is located 10 km to the E. Considering that the Liquiñe-Ofqui Fault Zone is located 20 km to the E of the volcano, we suggest that eruptions of Osorno volcano are associated with the ascent of deep crustal basaltic magma enhanced by this master fault, re-activating the inferred reservoirs and the volcano.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2020.106806

Fabrics, , and flow thorough a large-volume : Pampa De Oxaya, Chile

E.S. Platzman1, R.S.J. Sparks2, F.J. Cooper2

1 Department of Earth Sciences, University of Southern California,3651 Trousdale Parkway, Los Angeles, CA 9008, USA 2 School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK

Abstract The Oxaya Formation, exposed along the western Andean slope in northern Chile, represents one of the largest ignimbrite provinces on earth. In this study, magnetic fabric data were acquired from a ~ 1-km-long core drilled vertically through a single cooling unit of the Oxaya Formation the ca.22 Ma Cardones ignimbrite. Samples for magnetic analysis were obtained every 20 m from the fine-grained of the core. Detailed measurements of the variation in bulk magnetic properties, including natural remanent magnetization (NRM), susceptibility, and anisotropy of magnetic susceptibility (AMS), were used to monitor changes in magnetic mineralogy as well as changes in the strength and orientation of the magnetic fabric throughout the flow. AMS ellipsoid orientation and shape reflect rapid deposition from a concentrated granular fluidized flow and constrain both the location of the source for this catastrophic eruption and processes of transport and deposition in this large-volume ignimbrite. After utilizing the magnetic remanence to correct for rotation about the core axis, well-grouped and imbricated petrofabric orientations reveal a well-defined SW (247°) transport direction down a proto-Western Andean slope indicating syn- or post- flow and confirming the deformed caldera as the likely source of the eruption. Systematic variations in fabric shape (T) and intensity (P) with depth reveal a predominately oblate fabric toward the top and base of the flow and predominately prolate fabrics in the center. These vertical changes in fabric reveal that this massive, apparently homogeneous, deposit has a systematic layering. This layering reflects depth-dependent temperature variations, temporal changes in the flow boundary zone during deposition and post-depositional processes.

Corresponding author: [email protected] https://doi.org/10.1007/s00445-019-1345-2

Statistical separation of tectonic and inflation-driven components of deformation on silicic reservoirs, Laguna del Maule , Chile

N. Garibaldia, B. Tikoffa, D. Petersonb, J. R. Davisc, K. Keranenb

a Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA b Cornell University, Ithaca, NY, USA c Carleton College, Northfield, MN, USA

Abstract The reconstruction of the structural history of inflating silicic systems is challenging because their faulting record encompasses tectonic and inflation-driven deformation, and separating the two can rarely be accomplished. Here, we present and utilize a statistical methodology to differentiate tectonic from inflation-driven deformation in the Laguna del Maule (LdM), a post-glacial rhyolitic volcanic field (Southern Volcanic Zone, Chile, latitude 36° S). LdM is cut by the Troncoso fault, a major normal fault that strikes NE and dips to the NW. The Troncoso hanging wall contains abundant, young (< 23 ka) NE-striking normal faults, whereas the footwall is largely unfaulted, with few NNW-striking faults. Activity within the shallow (<8 km) LdM reservoir has caused two inflation events, both centered in different areas of the footwall: 1) a geodetic-based (InSAR) inflation, acting since 2007; and 2) a shoreline-based inflation, evidenced by warping of a 9.4 ka high-stand shoreline. To separate tectonic and inflation-driven faults in the Troncoso hanging wall, we perform a statistical analysis of fault orientation to compare them to the elongation direction predicted by tectonics. The orientation of normal faults is consistent with NW-SE tectonic elongation recorded outside the inflating area. To evaluate if either inflation event has reactivated these tectonic faults, we perform a statistical analysis of orientation-and- heave (horizontal offset on a fault): we calculate the maximum elongation direction (the accumulated horizontal offset) and compare it to elongation predicted by tectonics, shoreline-based inflation and geodetic-based inflation. The maximum elongation direction is sub-parallel to elongation predicted by shoreline-based inflation and is statistically different from tectonic elongation. We interpret a first stage of tectonic extension (>19– 9.4 ka) where normal faults are developed on the Troncoso hanging wall. During shoreline-based inflation (<9.4 ka), faults on the hanging wall are reactivated, suppressing uplift; the largely unfaulted footwall uplifts instead. The differential uplift is accommodated by slip on the Troncoso fault. The current, geodetic based uplift, nucleates few faults with large offsets, and potentially reactivates the Troncoso fault. From the structural history, we suggest that the structural architecture is associated with surface volcanism: deformation of the Troncoso hanging wall appears to facilitate repeated, small volume, post-glacial rhyodacitic and andesitic eruptions, whereas the largely unfaulted Troncoso footwall seems to favor accumulation and eruption during the late Holocene.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2019.106744

Geochemistry of gas and discharge from the magmatic-hydrothermal system of volcano, northern Chile

Manuel Inostroza1,2, Franco Tassi3,4, Felipe Aguilera2,5,6, José Pablo Sepúlveda3, Francesco Capecchiacci7, Stefania Venturi3,4, Giorgio Capasso8

1 Programa de Doctorado en Ciencias, mención Geología, Universidad Católica del Norte, Avenida Angamos, 0610 Antofagasta, Chile 2 Núcleo de Investigación en Riesgo Volcánico - Ckelar Volcanes, Universidad Católica del Norte, Avenida Angamos 0610 Antofagasta, Chile 3 Dipartimento di Scienze della Terra, Università di Firenze, via G. la Pira 4, Florence, Italy 4 CNR-IGG Institute of Geosciences and Earth Resources, via G. la Pira 4, Florence, Italy 5 Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos, 0610 Antofagasta, Chile 6 Centro de Investigación para la Gestión Integrada del Riesgo de Desastres (CIGIDEN), Avenida Vicuña Mackenna 4860 Macul, Santiago, Chile 7 Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli, Osservatorio Vesiviano, via Diocleziano, 328 Naples, Italy 8 Istituto Nazionale di Geofisica e Vulcanologia – sezione di Palermo, via U. La Malfa, 153 Palermo, Italy

Abstract This work presents the first chemical and isotopic (δ13C-CO2, δ13C-CH4, 3He, 4He, 20Ne, 40Ar, 36Ar, δ18O, and δD) data for fluid discharges from Guallatiri volcano, a remote and massive stratovolcano, which is considered as the second most active volcano of the Central Volcanic Zone (CVZ) in northern Chile. Fumarolic gases had outlet temperatures of between 80.2 and 265 °C, and showed a significant magmatic fluid contribution marked by the occurrence of SO2, HCl, and HF that are partially scrubbed by a hydrothermal . The isotope ratios (< 3.2) were relatively low compared to those of other active volcanoes in CVZ, possibly due to contamination of the magmatic source by 4He-rich crust and/or crustal fluid addition to the hydrothermal reservoir. Geothermometry in the H2O- CO2-CO-H2-CH4 system suggests equilibrium temperatures of up to 320 °C attained in a vapor phase at conditions intermediate between those typical of hydrothermal and magmatic environments. Thermal springs located 12 km northwest of the volcano’s summit had outlet temperatures of up to 50.1 °C, neutral to slightly basic pH, and a sodium bicarbonate composition, typical of distal fluid discharges in volcanic systems. Cold springs at the base of the volcanic edifice, showing a composition, were likely produced by interaction of shallow meteoric water with CO2- andH2S-rich gases. A geochemical conceptual model was constructed to graphically represent these results, which can be used as an indication for future geochemical monitoring and volcanic hazard assessment.

Corresponding author: [email protected] https://doi.org/10.1007/s00445-020-01396-2

Deposition of metals and metalloids in the fumarolic fields of Guallatiri and volcanoes, northern Chile

Manuel Inostrozaab, Felipe Aguilerabcd, Andrew Menziese, Susana Layanaab, Cristóbal Gonzálezab, Gabriel Uretaabd, José Sepúlvedabc, Samuel Schellere, Stephan Böehme, María Barrazaf, Roald Taglee, Max Patzschkee a Programa de Doctorado en Ciencias Mención Geología, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta 1270709, Chile b Núcleo de Investigación en Riesgo Volcánico - Ckelar Volcanes, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta 1270709, Chile c Departamento de Ciencias Geológicas, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta 1270709, Chile d Centro Nacional de Investigación para la Gestión Integrada de Desastres (CIGIDEN), Av. Vicuña Mackenna 4860, Macul, Santiago 7820436, Chile e Bruker Nano GmbH, Am Studio 2D, Berlin 12489, Germany f Maini, Unidad de Equipamiento Científico, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta 1270709, Chile

Abstract A detailed study on the mineralogy and chemistry of fumarolic deposits with a focus on metals and metalloids is presented. Two active volcanoes in northern Chile, Guallatiri and Lastarria, are characterised by vigorous and persistent fumarolic activity and the formation of zoned fumarolic deposits. Twelve were identified in the studied deposits by X-ray diffraction: , barite, , rhomboclase, orpiment, , , cristobalite, , , , and native sulphur. Chemical analyses revealed the presence of 30 chemical elements, including metals and metalloids such as As, Hg, Pb, Sb, Te, and Tl. Backscattered-electron imaging revealed four types of rock textures in the fumarolic deposits: i) massive and poorly vesiculated, ii) highly vesiculated, iii) clastic-like, and iv) flow-like. Micro-chemical analyses showed the presence of cinnabar nataliyamalikite and unidentified assemblages of As S, Te S, Pb S, Hg S, Tl I, and Tl-I-Pb compositions. Based on colour, outlet gas temperature, mineralogy, and chemistry, four distinct zones of fumarolic deposits are identified. (1) Grey zone: sulphide and silicate dominant with minor native elements, high concentrations of Pb and As, and a clastic-like texture (gas outlet temperature > 265 °C). (2) Red zone: sulphide and silicate dominant with minor and native elements, small As, Pb, Tl, I, and Te minerals, and predominance of a flow-like texture (200–280 °C). (3) Yellow-orange zone: dominated by native sulphur and minor borates and sulphur with small As-, Sb-, Hg-, and I-containing minerals, massive and vesiculated texture (80–200 °C). (4) Yellow-white zone: formed by native sulphur, minor borates and As-rich zones, usually displaying a vesiculated texture (<100 °C).

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2020.106803

Seismic interferometry applied to regional and teleseismic events recorded at Planchón-Peteroa Volcanic Complex, -Chile

José Augusto Casasa, Gabriela Alejandra Badib, Luis Francoc, Deyan Draganovd a Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, CONICET, Argentina b Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina c Observatorio Volcanológico de los Andes del Sur (OVDAS-SERNAGEOMIN), Chile d Department of Geoscience and Engineering, Delft University of Technology, the Netherlands

Abstract

The Planchón-Peteroa Volcanic Complex (PPVC) is located in the Central Andes, Argentina- Chile. Even though this active volcanic system is considered one of the most dangerous volcanoes in the region, with more than twenty modest (VEI < 4) Holocene eruptions, knowledge of its subsurface structures, internal processes, dynamics, and their relation, is still limited.

Seismic interferometry (SI) is a high-resolution technique based on analyses of the interference of the propagation seismic energy at one or many stations. SI can be used to characterize the subsurface properties of a target area. In particular, previous SI studies performed in the area of the PPVC describe specific ranges of depth; therefore, more information is required for a thorough description of the subsurface features in the area and for a better understanding of the PPVC dynamics.

We apply SI based on autocorrelations of selected regional and teleseismic events to image the subsurface structures below stations located in Argentina and Chile during 2012. The selection of the events is performed according to their location, magnitude, angle of incidence of P-wave seismic energy, and signal-to-noise ratio in the records. For each station, we extract time windows and we process them using two ranges of frequency, which are sensitive to different depth ranges.

This work describes depths and zones previously not analyzed in the area using SI methods. The results not only complement the available geological, geochemical, and geophysical information, but present new information for depths between 10 and ~750 km depth, increasing the general knowledge of the subsurface features in the PPVC. Finally, we also propose a model for the subsurface down to the Moho, which indicates the crustal structure and the likely distribution of magma bodies in depth.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2020.106805

Processes culminating in the 2015 phreatic explosion at volcano, Chile, evidenced by multiparametric data

Ayleen Gaete1, Thomas R. Walter1, Stefan Bredemeyer1,2, Martin Zimmer1, Christian Kujawa1, Luis Franco Marin3, Juan San Martin4, and Claudia Bucarey Parra3

1GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany 2GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany 3Observatorio Volcanológico de Los Andes del Sur (OVDAS), Servicio Nacional de Geología y Minería (SERNAGEOMIN), Temuco, Chile 4Physics Science Department, Universidad de la Frontera, Casilla 54-D, Temuco, Chile

Abstract

Small steam-driven volcanic explosions are common at volcanoes worldwide but are rarely documented or monitored; therefore, these events still put residents and tourists at risk every year. Steam-driven explosions also occur frequently (once every 2–5 years on average) at Lascar volcano, Chile, where they are often spontaneous and lack any identifiable precursor activity. Here, for the first time at Lascar, we describe the processes culminating in such a sudden volcanic explosion that occurred on 30 October 2015, which was thoroughly monitored by cameras, a seismic network, and gas and temperature sensors.

Prior to the eruption, we retrospectively identified unrest manifesting as a gradual increase in the number of long-period (LP) seismic events in 2014, indicating an enhanced level of activity at the volcano. Additionally, dioxide (SO2) flux and thermal anomalies were detected before the eruption. Then, our reported a precipitation event, followed by an increase in steaming and a sudden volcanic explosion at Lascar. The multidisciplinary data exhibited short-term variations associated with the explosion, including (1) an abrupt eruption onset that was seismically identified in the 1– 10 Hz frequency band, (2) the detection of a 1.7 km high white-gray in −1 camera images, and (3) a pronounced spike in SO2 emission rates reaching 55 kg s during the main pulse of the eruption as measured by a mini-differential optical absorption spectroscopy (DOAS) scanner. Continuous dioxide (CO2) and temperature measurements conducted at a on the southern rim of the Lascar crater revealed a pronounced change in the trend of the relationship between the CO2 mixing ratio and the gas outlet temperature; we speculate that this change was associated with the prior precipitation event. An increased thermal anomaly inside the active crater as observed in Sentinel-2 images and drone overflights performed after the steam-driven explosion revealed the presence of a ∼50 m long fracture truncating the floor of the active crater, which coincides well with the location of the thermal anomaly. This study presents the chronology of events culminating in a steam-driven explosion but also demonstrates that phreatic explosions are difficult to predict, even if the volcano is thoroughly monitored; these findings emphasize why ascending to the summits of Lascar and similar volcanoes is hazardous, particularly after considerable precipitation.

Corresponding autor: [email protected] https://doi.org/10.5194/nhess-20-377-2020

Petrological and noble gas features of Lascar and Lastarria volcanoes (Chile): Inferences on plumbing systems and mantle characteristics

P.Robidouxa, A. L. Rizzob, F.AguileracdeA, A. Aiuppaf, M. Artalef, M. Liuzzob, M. Nazzarig, F. Zummof a Centro de Excelencia en Geotermia de los Andes (CEGA) y Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile b Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa, 153, Palermo, Italy c Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile d Núcleo de Investigación en Riesgo Volcanico - Ckelar Volcanes, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile e Centro de Investigación para la Gestión Integrada del Riesgo de Desastres (CIGIDEN), Vicuña Mackenna 4860, Santiago, Chile f Dipartimento DiSTeM, Università di Palermo, Via Archirafi 36, Palermo, Italy g Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma, Via di Vigna Murata, 605, Rome, Italy

Abstract

Lascar (5592 m a.s.l.) and Lastarria (5697 m a.s.l.) are Chilean active stratovolcanoes located in the Central Volcanic Zone (CVZ; 16°S to 28°S) that have developed on top of a 71 km thick continental crust. Independently of the similarities in their Plinian/Vulcanian eruptive styles, their complex magmatic feeding structures and the origins of their magmatic fluids still necessitate constraints in order to improve the reliability of geochemical monitoring. Here we investigate the petrography, bulk-rock chemistry, and mineral chemistry in products from the 1986–1993 explosive eruptive cycle at Lascar and from several Holocene eruptive sequences at Lastarria. These data are integrated with measurements of the noble gas isotopes in fluid inclusions (Fis) of minerals from the same products as well as in fumarole gases. The geochemistry of minerals and rocks shows that the studied products belong to high-K–calc-alkaline series typical of subduction-related settings, and provide evidence of differentiation, mixing, and crustal assimilation that are higher at Lastarria. The contribution of slab sediments and fluids to magma genesis in the wedge is limited, suggesting a homogeneous mantle beneath CVZ. The deepest crystallization processes occurred at variable levels of the plumbing systems according to the lithostatic equivalent depths estimated with mineral equilibrium geobarometers at Lascar (15–29 km) and Lastarria (~20–40 km). The 40Ar/36Ar and 4He/20Ne ratios in Fis and fumarole gases indicate the presence of some degree of air contamination in the fluids from both volcanoes. The 3He/4He values at Lascar (6.9–7.3 Ra) are relatively homogeneous and comparable to those of , suggesting a main zone of magma crystallization and degassing. In contrast, the 3He/4He values at Lastarria (5.31–8.01 Ra) vary over a wide range, suggesting various magma storage levels and providing evidence of crustal contamination, as indicated by the rock chemistry. We argue that mantle beneath the two volcanoes has a MORB-like signature of 3He/4He, while local crustal contamination explains the lower ratios measured at Lascar.

Corresponding author: [email protected] https://doi.org/10.1016/j.lithos.2020.105615

First Measurements of Gas Flux with a Low-Cost Smartphone Sensor-Based UV Camera on the Volcanoes of Northern Chile

Felipe Aguilera1,2,3,* , Susana Layana1,3,4 , Felipe Rojas1 , Pilar Arratia1, Thomas C. Wilkes5 , Cristóbal González1,4 , Manuel Inostroza1,4 , Andrew J.S. McGonigle5 , Tom D. Pering5 and Gabriel Ureta1,3,4

1 Núcleo de Investigación en Riesgo Volcánico—Ckelar Volcanes, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta 1270709, Chile 2 Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta 1270709, Chile 3 Centro de Investigación para la Gestión Integrada del Riesgo de Desastres (CIGIDEN), Av. Vicuña Mackenna 4860, Santiago 7810000, Chile 4 Programa de Doctorado en Ciencias mención Geología, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta 1270709, Chile 5 Department of Geography, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK

Abstract UV cameras have been used for over a decade in order to remotely sense SO2 emission rates from active volcanoes, and to thereby enhance our understanding of processes related to active and passive degassing. Whilst SO2 column density retrievals can be more accurate/sophisticated using alternative techniques (e.g., Differential Optical Absorption Spectrometer (DOAS), Correlation Spectrometer (COSPEC)), due to their higher spectral resolutions, UVcameras provide the advantage of high time-resolution emission rates, a much greater spatial resolution, and the ability to simultaneously retrieve plume speeds. Nevertheless, the relatively high costs have limited their uptake to a limited number of research groups and volcanic observatories across the planet. One recent intervention in this regard has been the introduction of the PiCam UV camera, which has considerably lowered instrumental cost. Here we present the first data obtained with the PiCam system from seven persistently degassing volcanoes in northern Chile, demonstrating robust field operation in challenging conditions and over an extended period of time, hence adding credence to the potential of these units for more widespread dissemination to the international measurement community. Small and weak plumes, as well as strongly degassing plumes were measured at distances ranging 0.6 ±10.8 km from the sources, resulting in a wide range of SO2 emission rates, varying from 3.8 ± 1.8 to 361 ± 31.6 td-1. Our acquired data are discussed with reference to previously reported emission rates from other ground-based remotely sensed techniques at the same volcanoes, in particular considering: resolution of single plume emissions in multi-plume volcanoes, light dilution, plume geometry, seasonal effects, and the applied plume speed measurement methodology. The main internal/external factors that influence positive/negative PiCam measurements include camera shake, light dilution, and the performance of the OpenCV and control points post processing methods. A simple reprocessing method is presented in order to correct the camera shake. Finally, volcanoes were separated into two distinct groups: low and moderate SO2 emission rates systems. These groups correlate positively with their volcanological characteristics, especially with the fluid compositions from fumaroles.

Corresponding author: [email protected]

10.3390/rs12132122

Uptake of gaseous , , vanadium and into anhydrous alum, Lascar volcano fumaroles, Chile N. Sainlot a,*, I. Vlaste´lic a, S. Moune a,b, E.F. Rose-Koga a, F. Schiavi a, S. Valade a, F. c,d a Universite´ Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire et Volcans, F-63000 Clermont- Ferrand, France b Observatoire volcanologique et sismologique de la Guadeloupe, Institut de Physique du Globe, Sorbonne Paris-Cite´, CNRS UMR 7154, Universite´ Paris Diderot, Paris, France c Núcleo de Investigacio´ n en Riesgo Volca´ nico - Ckelar Volcanes, Universidad Cato´ lica del Norte, Avenida Angamos 0610, Antofagasta, Chile d Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile

Abstract Formation of secondary sulfate minerals during the reaction between volcanic gases and rocks modulates the composition and flux of gaseous emanations. We report on the sub- surface formation of anhydrous alum (MI MIII (XVIO4)2 with MI = -NH4+, Na+, K+; MIII=Al3+, Fe3+ and XVI = S6+, Mo6+) in the 330 _C fumaroles of the Lascar volcano (Chile). The alum occurs as a few millimeters thick crust that grew internally by two-way diffusion of reaction gases and diffusive influx of rock cations within the crust. The average growth rate is estimated at ca. 0.3 lm/day, based on the 19-year-long activity of the degassing fracture hosting the crust. The growth rate is controlled by the slow migration of the rock cations and decreases towards crust rim. The crust selectively concentrates Tl, V and Te (thousands of lg/g) and to a lesser extent Mo (hundreds of lg/g). The uptake of gaseous Tl, V and Mo is due to the possibility for these elements to enter the MI, MIII and XVI sites of alum, respectively. The process of Te uptake must be related to the incorporation of Tl and V with which Te tightly correlates. Extensive substitution of Tl, V and Te occurs at the surface of the crust where the supply of rock cations is the lowest. Such surface enrichment does not occur for Mo, because Mo substitutes for S, another element from the gas. These findings suggest that the surface of mature alum crust has a high adsorption capacity for those gaseous metals able to compensate for the lack of rock- derived cations. Based on the composition of gases escaping from the fracture hosting the crust, it is estimated that the partition coefficients of Tl (3.3 _ 107), V (1.1 _ 107) and Te (0.6 _ 107) between crust surface and gases are two to four orders of magnitude higher than for other volatile metals and metalloids. It follows that gases equilibrating with anhydrous alums lose between 77 and 95% of their initial Tl content, but less than 1% of Pb. Given the Tl emission rate of Lascar volcano (5 g/day), between 17 and 104 g of toxic Tl would deposit every day if all Lascar gases were to equilibrate with anhydrous alums. This study suggests that anhydrous alums significantly immobilize Tl, V and Te in the ground of quiescent volcanoes, reducing the atmospheric emissions of these three elements.

Corresponding author: [email protected] https://doi.org/10.1016/j.gca.2020.02.009

Geochemical survey of the Colpitas- volcanic-hydrothermal system, northern Chile Manuel Inostroza (1,2), Franco Tassi (3,4), José Sepúlveda (3), Francesco Capecchiacci (3), Andrea l. RIzzo (5) & FelIpe Aguilera (2,6,7) (1) Programa de Doctorado en Ciencias, mención Geología, Universidad Católica del Norte, Angamos 0610, Antofagasta, Chile. (2) Núcleo de Investigación en Riesgo Volcánico - Ckelar Volcanes, Universidad Católica del Norte, Angamos 610, Antofagasta, Chile. (3) Dipartimento di Scienze della Terra, Università di Firenze, via G. la Pira 4, Firenze, Italia. (4) CNR-IGG Institute of Geosciences and Earth Resources, via G. la Pira 4, Florence, Italy. (5) Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo, Via Ugo La Malfa 153, 90146, Palermo, Italy. (6) Departamento de Ciencias Geológicas, Universidad Católica del Norte, Angamos 610, Antofagasta, Chile. (7) Centro de Investigación para la Gestión Integrada de Riesgo de Desastres (CIGIDEN), Avenida Vicuña Mackena 4860, Macul, San- tiago, Chile.

Abstract

This work presents chemical and isotopic (δ13C-CO2, δ13C-CH4, 3He, 4He, 20Ne, 40Ar, 36Ar, δ18O and δD) data of fluid discharges from Colpitas-Taapaca volcanic-hydrothermal system, located close to the Taapaca Volcanic Complex, with the aim to investigate the physical-chemical conditions of the fluid source and to provide a preliminary evaluation of the geothermic potential of the study area. Colpitas thermal springs (to 56 °C) and part of the cold springs (≤18°C) from this area have a Na+-Cl- composition and Total Dissolved Solids (TDS) values (from 6,059 to 19,118 mg/L). springs also show a Na +-Cl - composition, TDS values up to 7,887 mg/L, and outlet temperatures from 21 to 31 °C. Colpitas cold springs, with a Ca2+-SO42- composition and relatively low TDS values (≤1,350 mg/L), are likely produced by interaction of shallow water with uprising H2S- rich hydrothermal gases. This process is likely also controlling the chemistry of Jurase thermal springs, which have the highest outlet temperatures of the study area (up to 68 °C), a Ca2+-SO42- composition and TDS values ≤2,355 mg/L. Eventually, Las Cuevas springs have temperatures up to 36 °C, a Na+-HCO3- composition and low TDS values (≤1,067 mg/L), typical features of springs related to a shallow aquifer. The δ18O-H2O and δD-H2O values indicate that all have a dominant meteoric origin. Enrichments in 18O and D shown by Colpitas and Putre thermal waters are likely due to steam loss and water- rock interaction, masking a possible direct steam contribution from magmatic degassing. Gas emissions from Colpitas bubbling pools are dominated by CO2, with significant concentrations of CH4, H2S and H2. The Rc/Ra values (up to 2.04) of Colpitas gases indicate a significant contribution of magmatic to mantle He, whereas the high CO2/ 3He ratios, combined with d 13C-CO2 values ranging from -7.66 to -5.63 ‰ vs. PDB, imply a dominant crustal CO2 source, mostly involving . Estimated temperatures based on the composition of waters and gases from Colpitas are up to 215 °C. Higher temperatures (240 °C) are estimated for Putre thermal waters, although these waters, as well as those from Jurase and Las Cuevas, are too immature for a reliable application of geothermometric techniques. Based on the theoretical reservoir temperature and the measured Cl total output, the thermal energy released from Colpitas thermal area is estimated at up to 13.9 Mw. Such results suggest the occurrence of a promising heat source, possibly related to Taapaca volcanic complex, and encourage the development of future research based on combined geophysical and geochemical approaches, in order to provide a reliable evaluation of the geothermal potential of the whole area.

Keywords: Colpitas-Taapaca geothermal system, Fluid Geochemistry, Volcanic- hydrothermal system, Geothermal potential.

Corresponding authors e-mail: [email protected] DOI: https://doi.org/10.3301/IJG.2020.09

Combining ash analyses with to identify juvenile magma involvement and fragmentation mechanisms during the 2018/19 small eruption of Peteroa volcano (Southern Andes)

Jorge E. Romeroa,b*, Felipe Aguilerac,d,e, Francisco Delgadof, Danny Guzmáng, Alexa R. Van Eatonh, Nicolás Luengoi, Javiera Carod,e, Jorge Bustillosj, Alicia Guevarak, Sven Holbikl, Daniel Tormeym, Iver Zegarrad,e a Department of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK b Departamento de Geología, Universidad de Atacama. Av. Copayapu 485, Copiapó, Chile. c Centro para la Gestión Integrada del Riesgo de Desastres (CIGIDEN) – Universidad Católica del Norte, Antofagasta, Chile d Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile. e Núcleo de Investigación en Riesgo Volcánico-Ckelar Volcanes, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile. f Équipe de Tectonique et Mécanique de la Lithosphère, Institut de Physique du Globe de Paris, Paris, France. g Departamento de Metalurgia, Universidad de Atacama. Av. Copayapu 485, Copiapó, Chile. h U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington, USA i Departamento de Ciencias de la Tierra, Universidad de Concepción, Concepción, Chile. j Escuela de Geología, Universidad Central de Ecuador, Quito, Ecuador k Departamento de Metalurgia Extractiva, Escuela Politécnica Nacional, Quito, Ecuador l Department of Science, Valencia College, 1800 Denn John Ln, Kissimmee, FL United States. m Catalyst Environmental Solutions. 315 Montana Avenue, Suite 311, Santa Monica, California, United States.

Abstract

The Planchón Peteroa Volcanic Complex (PPVC) is located on the border of Chile and Argentina, and is one of the most active volcanic systems in the Andes. Holocene activity has included magma-water interaction with an evolving series of crater lakes, mainly sourced from Peteroa volcano. This study examines data from the 2018/19 eruption, together with the volcanic history of the PPVC, to elucidate the complex interplay between magmatic activity and summit water and . From February 2016 to mid-2019, three seismic swarms occurred in the PPVC, preceding the from September 2018 to April 2019. The activity originated from a small vent nested within the easternmost crater, the most active portion of the complex (Peteroa). The explosions interacted with a crater lake, producing ash plumes up to 2 km above the crater and building a small tephra cone. To investigate the eruption mechanisms, we performed remote sensing analysis of plume dispersal, thermal anomalies and ground deformation, and characterized the volcanic products, including grain size, componentry, morphology, internal textures, composition and mineralogy. Our results suggest that the precursory seismicity beginning in 2016 was related to the intrusion of a new magma batch that reached the surface during the 2018/19 eruption. The eruption was also preceded by thermal anomalies, geomorphic changes and increased hydrothermal activity at the surface, though without any ground deformation recognized through radar interferometry (InSAR). The eruption initially produced predominantly recycled ash (phreatic activity), then evolved to increasing proportions of juvenile magma (phreatomagmatic) by April 2019. The juvenile clasts had a trachyandesite composition (~59 wt% SiO2), with vesicular and dense scoria containing plagioclase and pyroxene. The ash surfaces show external quenching cracks and step fractures consistent with phreatomagmatic fragmentation within the active crater lake. Textural characteristics also point to a slowly ascending batch of magma that was relatively viscous by the time it interacted with water in the crater lake. Notably, these juvenile particles are distinctive from the pre-2018 products. Ash erupted from 2010/11 did not contain recognizable juvenile material, and is inferred to have been a mainly . Our findings suggest that the interplay between phreatic and phreatomagmatic eruptions fed by small magma batches intruding at shallow levels characterize much of the eruptive behavior of the PPVC during the last three decades. Multi-parametric assessment is a powerful tool to discriminate between phreatic and phreatomagmatic eruptions.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2020.106984

Dynamics and physical parameters of the Lastarria debris avalanche, Central Andes

Inés Rodríguezab, Jerson Páezc, Maximillian S. van Wyk de Vriesd, Benjamin van Wyk de Vriese, Benigno Godoyf a Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Rudecindo Ortega #02950, Temuco, Chile b Centro de Investigación en Evaluación de Riesgos y Mitigación de Peligros Geológicos, Geokimϋn, Facultad de Ingeniería, Universidad Católica de Temuco, Rudecindo Ortega #02950, Temuco, Chile c Oficina Paposo #209, Villa Portada del Norte 3, Antofagasta, Chile d Department of Earth and Environmental Sciences, University of Minnesota, 116 Church Street, Minneapolis, MN 55455, United States e Clermont Auvergne, Observatoire du Physique du Globe de Clermont, Laboratoire Magmas et Volcans, UMR6524-CNRS, France f Centro de Excelencia en Geotermia de los Andes (CEGA) y Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile

Abstract

Volcanic debris avalanches are extremely destructive phenomena, with the potential to travel many kilometers from their source region, either as rockslides or as mass flows. Given that they may even be triggered at inactive volcanoes, their hazard is often underestimated. Understanding the dynamics of such mass movements is essential for evaluating and mitigating hazards. A number of case studies have been carried out around the world, but there is still a need for further studies of flow-dominated avalanches, which remain poorly constrained. These studies would have high educational value, providing striking examples to teach decision makers and at-risk populations about the hazard.

In this study, we investigate the 7500 cal. year B.P. Lastarria debris avalanche. It is a 7 km- long deposit, with exceptional preservation of both the flow structures and the collapse scar. Detailed fieldwork, morphometric mapping of over 600 surface features, and numerical modelling was carried out to constrain the avalanche's trigger and flow parameters. Numerical models and field scaling relationships are in good agreement, suggesting maximum velocities of 210 to 270 km h−1, negligible basal friction, low cohesion (50 kPa) and an intermediate friction coefficient. Structures are dominantly oriented parallel to transport direction, suggesting minimal influence from a smooth paleotopography. Lastarria provides an example of a shallow flank failure, initiated along stratigraphic planes, that allowed low strength pyroclastic strata to disaggregate rapidly and then quickly accelerate to flow as a granular material at high velocity beyond the base of the volcano. Overall, Lastarria provides excellent constraints on granular avalanche initiation and flow, which are valuable for hazard assessments and for the study of less well-preserved flow deposits elsewhere. The question of which precursory signs may warn of such a flank failure remains open, and is important to address in future studies.

Corresponding author: [email protected] https://doi.org/10.1016/j.jvolgeores.2020.106990

Reactivating and calming volcanoes: the 2015 MW 8.3 2 Illapel megathrust strike

Cristian Farías1, Daniel Basualto2;3;1

1Departamento de Geología y Obras Civiles, Universidad Católica de Temuco, Temuco, Chile. 2Departamento de Ingeniería en Obras Civiles, Facultad de Ingeniería y Ciencias, Universidad de la Frontera, Temuco, Chile. 3Escuela de Geología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.

Abstract

The 2015 MW 8.3 Illapel earthquake was followed in a timeframe of weeks to months by very different responses from Nevados de Chillán, , and volcanoes, all located more than 580 km from the rupture zone. Here we show how Nevados de Chillán and Copahue started new eruptive phases, and Villarrica entered in a period of relative calm. Using seismic, geodetic, and geochemical observations, in combination with numerical wave propagation simulations, we also show that the geometry of the fault system controlled the impact of the earthquake on each volcano. We argue that the sensitivity of a volcano towards an earthquake depends on both its critical state before the mainshock and the geometry of its fault system. This is a case where the same earthquake generates very different responses at the same time, at large distances, rendering volcanoes as very sensitive systems.

Corresponding author: [email protected] https://doi.org/10.1029/2020GL087738

Pre-Pliocene Andean Magmatism in Chile

Verónica Oliveros1, Pablo Moreno-Yaeger2 and Laura Flores1 1 Departamento Ciencias de la Tierra, Universidad de Concepción, Casilla 160-C, Concepción, Chile. 2 Departamento de Obras Civiles y Geología, Universidad Católica de Temuco, Avenida Rudencio Ortega 02950, Temuco, Chile. Present address: Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, 53706 USA

Summary Andean-type magmatism and the term ‘andesite’ are often used as the norm for the results of subduction of oceanic under a continent, and the typical rock formed. Although the Andes chain occupies the whole western margin of , the most comprehensively studied rocks occur in the present-day Chilean territory and are the focus of this paper. Andean magmatism in this region developed from the Rhaetian- Hettangian boundary (ca. 200 Ma) to the present and represents the activity of a long- lived continental magmatic arc. This paper discusses Pre- volcanic, plutonic, and volcano-sedimentary rocks related to the arc that cover most of the continental mass of Chile (between the Pacific coast and the High Andes) between the latitudes of 18° and 50°S. They comprise most of the range of sub-alkaline igneous rocks, from gabbro to monzogranite and from basalt to rhyolite, but are dominated by the tonalite- granodiorite and andesite example members. Variations in the petrographic characteristics, major and trace element composition and isotopic signature of the igneous rocks can be correlated to changes in the physical parameters of the subduction zone, such as dip angle of the subducting slab, convergence rate and angle of convergence. Early Andean magmatic products ( to Early ) are found along the Coastal Cordillera in the westernmost part of the Andes. The rock record of the subsequent stages (Late Cretaceous, Paleocene–Early , Middle Eocene–, Miocene) is progressively shifted to the east, reflecting migration of the magmatic front towards the continent. Tectonic segmentation of the convergent margin, as attested by the magmatic record, may have occurred throughout the Andean life span but it is particularly evident from the Eocene onwards, where the evolution of the northern part of the Chilean Andes (north of 27°S latitude) is very different to that of the southern segment (south of 27°S latitude).

Corresponding author: E-mail: [email protected] https://journals.lib.unb.ca/index.php/GC/article/view/28954/1882526470