Ecuadorian Andes volcanism: A review of Late Pliocene to present activity
Introduction
The abundance and diversity of Ecuadorian volcanism that includes Quaternary calc-alkaline, alkalic, and adakitic magmatism were highlighted recently at the International Association of Volcanology and Chemistry of the Earth's Interior's (IAVCEI) Cities on Volcanoes IV meeting held in Quito, Ecuador, in January 2006. At this conference a special workshop was convened to propose that a collection of articles focusing upon Ecuadorian volcanoes be published in a special theme volume. Herein, geologists, volcanologists, petrologists, and geophysicists have contributed 18 papers related to past, recent, and on-going volcanic activity in the Ecuadorian Andes. This collection of papers deals with Ecuador's four volcanic rows and specifically 11 volcanic centers, many of which have not been described previously. The articles in this special issue are organized according to five sub-disciplines: (1) geological and volcanological studies (9 papers); (2) petrology and geochemistry (3 papers); (3) remote gas-sensing studies (3 papers); and (4) geophysical investigations (3 papers).
This Special Issue on Ecuadorian Volcanism represents an important resource for scientists studying continental arc volcanism via a spectrum of multidisciplinary approaches as well as those interested in the development of specific volcanoes. This collection of papers will contribute to a better understanding of the volcanism in this relatively unknown segment of the Andean Cordillera. Our short overview provides background information and context for the volcanic arc's physiographic and tectonic setting, the unusual distribution of the volcanoes, and their diversity. Galápagos volcanism is not considered in this Special Issue.
Section snippets
Physiographic setting
Continental Ecuador can be divided into three physiographic provinces: the Andes, the Oriente, and the coastal zone. The Ecuadorian Andes represent a 650 km-long, 150 km-wide segment of the great Andean mountain chain, which in northern Ecuador consists of two parallel mountain ranges, the Western or Cordillera Occidental and the Eastern or Cordillera Real. These two cordilleras have average elevations of 3500–4000 m above sea level, upon which are built most of the volcanoes whose summits
Tectonic setting
Major plate reorganization of the old Farallón Plate in Late Oligocene times (∼ 28 Ma) gave birth to the Cocos and Nazca Plates (Lonsdale and Klitgord, 1978, Lonsdale, 2005) and led to the onset of subduction of the Nazca Plate beneath the South American continental plate estimated to have begun some 2–9 Ma ago (Gutscher et al., 1999, Witt et al., 2006). Three tectonically distinct ocean-floor domains characterize the Nazca Plate west of Colombia and Ecuador (Fig. 1). Between latitudes 7° N and
Volcanism in continental Ecuador
Ecuador is a small Andean country with an impressive volcanic arc hosting many active and potentially active volcanoes. Four of these volcanoes have erupted repeatedly since 1999, and dozens more have been identified as being potentially active. Volcanic studies in Ecuador go back several centuries, beginning with Ch. La Condamine and H. Bouguer in 1736 and continuing with A. von Humboldt in 1803, W. Reiss and A. Stübel in the 1870's, T. Wolf in the 1870's, E. Whymper in 1880, N. Martinez in
Geochemical characteristics of the magmatism
Calc-alkaline, alkalic, and adakitic volcanic rocks have been reported in the Ecuadorian arc (Monzier et al., 1997, Barragán et al., 1998, Bourdon et al., 2003, Bryant et al., 2006). In addition, large edifices, such as those of Cayambe (Samaniego et al., 2002, Samaniego et al., 2005), Pichincha (Bourdon et al., 2002a), Mojanda–Fuya Fuya (Robin et al., 1997), and Iliniza (Hidalgo et al., 2007) illustrate an evolution from an early calc-alkaline magmatism to that of a later, adakitic one.
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Present eruptive activity and volcano monitoring
Following the eruptions at Colombia's Nevado del Ruiz in 1985 and Galeras in 1988, Ecuador's recent volcanism began at Guagua Pichincha and Tungurahua in October 1999, after many months of precursory activity that included increased seismicity and SO2 emission. Energetic seismicity under Cotopaxi in November 2001 warned of its possible reactivation (Molina et al., 2008-this issue), but this activity slowly dissipated in subsequent months. In November 2002 Reventador volcano, in repose since
Acknowledgements
The authors wish to especially thank Tom Simkin and Bob Tilling for their review and constructive criticism of the submitted manuscript.
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