Research Paper THEMED ISSUE: PLUTONS: Investigating the Relationship between Pluton Growth and Volcanism in the Central Andes GEOSPHERE Miocene to Holocene geological evolution of the Lazufre segment in the Andean volcanic arc GEOSPHERE; v. 15, no. 1 José A. Naranjo, Francisco Hevia, Víctor Villa, and Cristián A. Ramírez https://doi.org/10.1130/GES01352.1 Departamento de Geología Regional, Servicio Nacional de Geología y Minería, Av. Santa María #0104, Providencia, Santiago 7520405, Chile 6 figures; 2 tables ABSTRACT during the period of March 2003–May 2005, and they proposed that the great­ CORRESPONDENCE: est deformation could have a magmatic origin between 7 and 15 km deep, jose .naranjo@ sernageomin.cl The Lazufre bulging zone, in the area of the Pleistocene–Holocene Azufre, whereas a surface source related to hydrothermal fluids could have caused Cordón del Azufre, Bayo, and Lastarria volcanic complexes, has been a major only minor deformations detected during this same period. Later, for the pe­ CITATION: Naranjo, J.A., Hevia, F., Villa, V., and Ramírez, C.A., 2019, Miocene to Holocene geolog‑ focus of study over the past few decades. Since 1998, interferometric synthetic riod 2003–2006, Ruch et al. (2008, 2009) found that the deformation south of ical evolution of the Lazufre segment in the Andean aperture radar (InSar) analysis has shown structural deformation, likely a re- Lastarria volcanic complex affected an elongated area of 45 km by 55 km (1400 volcanic arc: Geosphere, v. 15, no. 1, p. 47–59, sult of an active magmatic and hydrothermal system. Our new mapping pro- km2) with a rise of up to ~3 cm/year. According to these authors, the defor­ https:// doi .org /10 .1130 /GES01352.1. vides clues about the causes and possible consequences of this deformation, mation signal could be explained by the intumescence of a magmatic body based on the reinterpretation of important structures or regional lineaments. (located ~10 km deep) that is expanding with a lateral spreading rate of up to Science Editor: Raymond M. Russo Guest Associate Editor: Rodrigo del Potro The bulge is located upon the hanging wall of the east-vergent, Pedernales- 4 km per year. For the period 2003–2008, Anderssohn et al. (2009) detected a Arizaro NE-SW–trending Middle Miocene major thrust fault. The footwall of rise of 15–16 cm and considered that the magmatic body expansion occurred Received 29 April 2016 this fault was previously affected by a major explosive activity producing the at depths between 10 and 15 km. These authors estimated a constant lateral Revision received 4 October 2018 Los Colorados caldera at ca. 9.4–9.8 Ma, the source of the homonymous 115– spreading rate of the intrusion at ~5–10 km/year. In 2010, Budach et al. (2013) Accepted 8 November 2018 185 km3 ignimbrite. Conjugated at ~30° to the Pedernales-Arizaro thrust, the conducted a magnetotelluric study at Lastarria volcanic complex area, and Published online 21 December 2018 Imilac-Salina del Fraile oblique, slightly dextral strike-slip fault constitutes a they suggested that the rise of partial melts from the asthenospheric wedge, major structure in the area, which favored the opening of transtensive spaces, which would feed a potential magmatic reservoir beneath the volcanic center, parallel to the Los Colorados caldera–Lazufre bulge alignment. Notably, since was responsible for the regional strain. In this work, we have reinterpreted the Late Pliocene, volcanism has been concentrated in the Lazufre intumes- important structures or regional lineaments, and based on new mapping, we cence, including extrusion of ~120 km3 total lava volume. The lava accumula- provide clues on the causes and possible consequences of this deformation. tion rate estimated since Late Pliocene to the present at Lazufre bulging zone Constructional volcanoes (stratovolcanoes, volcanic complexes, and lavas) area is approximately one-third of the rate estimated for the generation of the are grouped primarily on the basis of subtle differences in erosion or preserva­ Los Colorados caldera. The migration of volcanic activity from this Miocene tion degrees, supported by lithological characterization. Integrated geochrono­ caldera area to the northwestern Lazufre bulging zone could be the conse- logi cal data and the use of satellite images allowed us to recognize several quence of local strain field variations that opened tectonic space and favored Upper Miocene to Pleistocene volcano remnants, pyroclastic cones, lavas, magmatic ascent and storage. and ignimbrites based on previous works as well as new mapping (Naranjo OLD G and Cornejo, 1992; Gardeweg et al., 1993, 1994; Kraemer et al., 1999; Richards INTRODUCTION and Villeneuve, 2002; Richards et al., 2006, 2013; Schnurr et al., 2007; Seg­ giaro et al., 2007; Naranjo, 2010; Naranjo et al., 2013a, 2013b, 2016, 2018). The The central Andes volcanic arc between 25° and 26°S comprises ~220 Up­ Pleistocene–Holocene Azufre, Cordón del Azufre, Bayo, and Lastarria volcanic OPEN ACCESS per Cenozoic volcanic centers with Holocene activity at the Lastarria, Cordón complexes are the youngest volcanoes in the area and were built over the del Azufre, and Bayo volcanic complexes (Naranjo et al., 2013a), which we refer Pliocene–Pleistocene Pirámide and Atalaya­Chuta complexes along a 40 km to as the Lazufre segment of the Andean arc. The Lastarria volcanic complex NNE­SSW–trending ridge (Fig. 2; Naranjo et al., 2013a). Additionally, the area has been a major study focus over the past few decades due to the identifica­ includes two Middle Miocene NE­SW as well as NW­SE main fault systems: tion of a regional deformation producing a bulge centered near the complex Pedernales­Arizaro and Imilac­Salina del Fraile faults (Fig. 1; Naranjo et al., (Fig. 1). Between 1998 and 2000, this area suffered an intumescence attributa­ 2018). Some authors have proposed a younger age (<10 Ma) for the main This paper is published under the terms of the ble to movements of magma and hydrothermal fluids at depth (Pritchard and transversal structures (lineaments) recognized in the area (e.g., Archibarca CC‑BY‑NC license. Simons, 2002). According to Froger et al. (2007), this surface uplift persisted fault zone, Riller et al., 2001; Ramelow et al., 2006). © 2018 The Authors GEOSPHERE | Volume 15 | Number 1 Naranjo et al. | Geological evolution of the Lazufre segment Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/47/4619088/47.pdf 47 by INGEMMET user on 07 June 2019 Research Paper 0# Llullaillaco vn. Llullaillaco Arizaro Fig. 2 Pajonales Río Grande 0# Lastarria v.c. I m i l a c - S a Figure 1. Lazufre interferogram (taken 0# l Cordón del Azufre v.c. i n from Anderssohn et al., 2009) on digi- a tal elevation model image showing the d e extended intumescence attributable to l F magma movements since at least 1998. r a Late Pleistocene to Holocene volcanoes t ile l (Lazufre-Bayo volcanic complexes) are lo- u fa f a u cated within the bulged area. Main faults l r o t of the segment, Los Colorados caldera a z (LCC) and ignimbrite (LCI) with ages (see r i - A Table 1), are also indicated. Location of s Figure 2 is also specified (red dashed box). l e a n 9.8±0.5 Locations for Figure 3 sections (A, B and C) r De la Isla 9.797±0.035 8.161±0.056 e (& 9.6±0.2 are identified. d 9.419±0.042 A 9.849±0.036 e t Antofalla P 8.644±0.045 l 9.620±0.032 u Aguilar a f Las Parinas a l l a f o t Grande n A 8.31±0.12 (& B 9.01±0.03 Argentina ± Chile 8.65±0.03 0102030 8.466±0.015 (& C 9.09±0.04 Km Inferred fault ((Thrust fault LCC rim Salar Lineament Dextral oblique-slip Explosion crater LCI GEOSPHERE | Volume 15 | Number 1 Naranjo et al. | Geological evolution of the Lazufre segment Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/47/4619088/47.pdf 48 by INGEMMET user on 07 June 2019 49 Research Paper Number 1 | Figure 2. Simplified geologic map of the Lazufre bulging zone (red dashed line) and the Los Colorados caldera (LCC) and corresponding ignimbrite (LCI). Main tectonic struc- tures are also indicated (see text for details). CCE—Caletones Cori–Escorial volcanic complex; L—Lastarria volcanic complex; RG—Río Grande volcano; AG—Abra Grande volcano; G—Grande volcano; AC—Aguas Caliente volcano; Az—Azufre volcanic complex; CA—Cordón del Azufre volcanic complex; B—Bayo volcanic complex; P—Pirámide volcano; At—Atalaya volcano; C—Chuta volcano; AQH—Alto Quebrada Honda volcano. Based on ages and modified from Naranjo and Cornejo (1992), Richards and Villeneuve Volume 15 Volume (2002), Seggiaro et al. (2007), Naranjo (2010), Naranjo et al. (2013a), and Richards et al. (2013). | GEOSPHERE Naranjo et al. | Geological evolution of the Lazufre segment Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/47/4619088/47.pdf by INGEMMET user on 07 June 2019 Research Paper Using geochronological data, geological knowledge of the area of interfero­ mass (Table 1). Approximately one kilogram of sample was crushed and metric synthetic aperture radar (InSar)–detected deformation has remarkably sieved to obtain grain sizes of 100–250 µm. Minerals were separated using increased and allowed us to define in detail the geological context and the an isodynamic Frantz magnetic separator and heavy liquids, followed by temporal and structural evolution of the area (Naranjo et al., 2013a, 2013b). handpicking under binocular microscope. Samples were mounted in high-­ Thus, we are able to map important structures or regional lineaments previ­ purity Al discs (with space for 21 samples), together with sanidine crystals ously defined and interpreted by other authors (i.e., Riller et al., 2001; Reijs and of Fish Canyon standard sample (28.02 ± 0.1 Ma, Renne et al., 1998).