The Eruptive Chronology of the Ampato-Sabancaya Volcanic
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Journal of Volcanology and Geothermal Research 323 (2016) 110–128 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores The eruptive chronology of the Ampato–Sabancaya volcanic complex (Southern Peru) Pablo Samaniego a,⁎,MarcoRiverab, Jersy Mariño b, Hervé Guillou c,CélineLiorzoud, Swann Zerathe e, Rosmery Delgado b, Patricio Valderrama a,b,VincentScaoc a Laboratoire Magmas et Volcans, Université Blaise Pascal - CNRS - IRD, 6 Avenue Blaise Pascal, TSA 60026 - CS 60026, 63178 Aubière, France b Observatorio Vulcanológico del INGEMMET, Dirección de Geología Ambiental y Riesgo Geológico, Urb. Magisterial B-16, Umacollo, Arequipa, Peru c Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91198 Gif-sur-Yvette, France d Laboratoire Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, Rue Dumont d'Urville, 29280 Plouzané, France e Institut des Sciences de la Terre, Université Grenoble Alpes – CNRS - IRD, 1381 rue de la piscine, 38400 Saint Martin d'Hères, France article info abstract Article history: We have reconstructed the eruptive chronology of the Ampato–Sabancaya volcanic complex (Southern Peru) on Received 14 January 2016 the basis of extensive fieldwork, and a large dataset of geochronological (40K–40Ar, 14Cand3He) and geochemical Received in revised form 1 April 2016 (major and trace element) data. This volcanic complex is composed of two successive edifices that have experi- Accepted 29 April 2016 enced discontinuous volcanic activity from Middle Pleistocene to Holocene times. The Ampato compound Available online 07 May 2016 volcano consists of a basal edifice constructed over at least two cone-building stages dated at 450–400 ka and – fi fi Keywords: 230 200 ka. After a period of quiescence, the Ampato Upper edi ce was constructed rstly during an effusive – – Ampato stage (80 70 ka), and then by the formation of three successive peaks: the Northern, Southern (40 20 ka) and Sabancaya Central cones (20–10 ka). The Southern peak, which is the biggest, experienced large explosive phases, resulting Central Andes in deposits such as the Corinta plinian fallout. During the Holocene, eruptive activity migrated to the NE and con- Eruptive chronology structed the mostly effusive Sabancaya edifice. This cone comprised many andesitic and dacitic blocky lava flows Eruptive rates and a young terminal cone, mostly composed of pyroclastic material. Most samples from the Ampato–Sabancaya Volcanic hazards define a broad high-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagio- clase, amphibole, biotite, ortho- and clino-pyroxene, and Fe–Ti oxides. A secondary trend also exists, correspond- ing to rare dacitic explosive eruptions (i.e. Corinta fallout and flow deposits). Both magmatic trends are derived by fractional crystallisation involving an amphibole-rich cumulate with variable amounts of upper crustal assimilation. A marked change in the overall eruptive rate has been identified between Ampato (~0.1 km3/ka) and Sabancaya (0.6–1.7 km3/ka). This abrupt change demonstrates that eruptive rates have not been homogeneous throughout the volcano's history. Based on tephrochronologic studies, the Late Holocene Sabancaya activity is characterised by strong vulcanian events, although its erupted volume remained low and only produced a local impact through ash fallout. We have identified at least 6 eruptions during the last 4–5 ka, including the historical AD 1750–1784 and 1987–1998 events. On the basis of this recurrent low-to-moderate explosive activity, Sabancaya must be considered active and a potentially threatening volcano. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Zone (CVZ) results from the subduction of the oceanic Nazca plate below the South American continental lithosphere. As a result, the Reconstructing the eruptive chronology of active volcanic systems volcanic front includes at least twelve volcanic centres of Pleistocene represents a key step for any hazard assessment initiative. However, age (Fig. 1a) of which seven have experienced historical eruptive the recent eruptions of Chaitén (2008, Major and Lara, 2013)and activity (i.e. since the arrival of the Spanish conquistadors in the 16th Reventador volcanoes (2002, Hall et al., 2004) showed that the eruptive century). These volcanoes include El Misti (Thouret et al., 2001; chronology of many active volcanic complexes remains poorly known. Harpel et al., 2011), which threatens the city of Arequipa, the active vol- In the Andean cordillera, the Peruvian segment of the Central Volcanic canoes of Ubinas (Thouret et al., 2005; Rivera et al., 2014)and Sabancaya (Gerbe and Thouret, 2004), and Huaynaputina volcano (Thouret et al., 1999; Adams et al., 2001), which has had the biggest ⁎ Corresponding author. historical eruption in the Andes. However, little is still known about E-mail address: [email protected] (P. Samaniego). the eruptive chronology of some of these volcanic centres, such as the http://dx.doi.org/10.1016/j.jvolgeores.2016.04.038 0377-0273/© 2016 Elsevier B.V. All rights reserved. 180000 190000 200000 210000 74º 72ºHistorically active 70º Plio-Quaternary15º a Potentially active volcanic front SARA SARA SOLIMANA ANDAHUA c AMPATO- JULIACA COROPUNA TITICACA BOLIVIALAKE RIO COLCA SABANCAYA CHALA PUNO Madrigal 16º CHACHANI 16º Pinchollo MISTI Cabanaconde Lari UBINAS 000 AREQUIPA HUAYNAPUTINA CAMANA Maca TICSANI 8270 Y TUTUPACA MOLLENDO MOQUEGUA YUCAMANE Achoma ILO CASIRI 5-6 cm/y HUALCA Qda. Huayuray 18º HUALCA 18ºS TACNA CHILE 0 50 100 km 74º 72º 70º 000 Río Sepina 8260 Mucurca 72º Cabanaconde Chivay Trigal Río Colca lake Maca SABANCAYA Ichupamba Solarpampa Hualca Sepina Colihuiri Hualca 000 Huambo 8250 AMPATO Sabancaya Cajamarcana Ampato Collpa Río Parcomayo Sallalli Normal fault Huanca Japo Strike slip 000 Corinta Lineaments 8240 0 5 km Baylillas b 72º 16º 180000 190000 200000 210000 Fig. 1. (a) The Peruvian volcanic arc. (b) Structural context of the Ampato–Sabancaya region, including the Colca river valley. Main structures from Mering et al. (1996) and Gerbe and Thouret (2004) Sabancaya and Hualca Hualca complexes and the nearby Colca canyon. 112 P. Samaniego et al. / Journal of Volcanology and Geothermal Research 323 (2016) 110–128 Sabancaya volcano, and its neighbouring Ampato edifice. Rare historical 3. Methodology accounts mention eruptive activity that occurred in AD 1750 and 1784 (Siebert et al., 2010; Travada y Córdova, 1752; Zamácola y Jaúregui, Fieldwork was carried out during several field campaigns between 1888). More recently, Sabancaya entered a new eruptive phase in 2009 and 2012, which included geological mapping and sampling of 1988, which lasted until at least 1997 (Global Volcanism Program, most volcanic units. At high altitude (above 5000 m asl), fieldwork 1988, 1997). During this period, Sabancaya experienced low to moder- was complicated by the presence of a large icecap as well as voluminous ate explosive eruptions (VEI 1–2) that were characterised by violent glacial deposits. However, the presence of numerous deep glacial vulcanian explosions accompanied by small (up to 5–7 km height) valleys allowed sampling of almost all volcanic units, resulting in a eruption columns with a local ash fallout impact. The most significant broad sample array for petrographic and geochemical studies (Fig. 2). activity was observed between April–May 1990 and April 1991 Major and trace element whole-rock analyses were obtained from (Global Volcanism Program, 1990, 1991). Since March–April 2013, agate-crushed powders of 133 samples spanning the entire volcanic Sabancaya has shown increased fumarolic activity, accompanied by complex, at the Institut Universitaire Européen de la Mer, Université frequent seismic swarms (Global Volcanism Program, 2013; Jay et al., de Bretagne Occidentale (Brest, France), using an Inductive Coupled 2015). Plasma-Atomic Emission Spectrometer (ICP-AES) and following the Following its reactivation in 1988, several studies have been analytical procedure described by Cotten et al. (1995). These data, carried out on Sabancaya. These works include an initial geological together with petrographic descriptions, have been used to characterise reconnaissance, comprising a hazard assessment (Thouretetal., and correlate the different volcanic units. 1994), a regional tephro-chronological survey (Juvigné et al., 1998, We constrained the Pleistocene eruptive chronology via the 2008) and a petrological description of the last eruption products unspiked 40K–40Ar dating method at the Laboratoire des Sciences du (Gerbe and Thouret, 2004). Based on detailed field work and Climat et de l'Environnement (LSCE/IPSL, Gif-sur-Yvette, France). We geochronological and petrological studies, we reconstruct the obtained 10 ages covering the entire history of this volcanic complex structure and the volcanic and magmatic history of the Ampato– (Table 1). The Holocene chronology is based on 14 new radiocarbon Sabancaya volcanic complex from the Pleistocene to the present day. ages mainly obtained from peat and soil samples from several peatbogs around the volcanic complex. Most samples (8) were analysed at the Laboratoire de Mesure du Carbone 14 (LMC14, Gif-sur-Yvette, France) 2. Geological setting and an additional group (6) were analysed at the Centre for Isotope Research (CIO), Groningen University (Netherlands). Table 2 shows The Ampato–Sabancaya