Abstract
Lautaro is the volcano closest to the Chile Triple Junction in the Andean Austral Volcanic Zone. The volcanic edifice of 3,607 m a.s.l. stands out on the north-western part of the plateau of the South Patagonian Ice Field. The volcano basement is composed of low-grade meta-pelites that are cut by tabular intrusive bodies of hornblende-biotite granite. The volcano is almost completely covered by ice and the study was performed on volcanic detritus present in terminal moraines of the Lautaro Glacier and the tephra on the surface of the O'Higgins Glacier. The terminal moraines of Lautaro Glacier contain fragments of light grey dacite rich in plagioclase and hornblende phenocrysts. Some dacite blocks show prismatic jointing, suggesting an origin of hot emplacement and subsequent rapid cooling, possibly resulted from collapse of a steep lava front. Some samples have glassy groundmass and rhyolite-like flow texture, with presence of mafic inclusions and bread crust bomb texture. The surface of the O'Higgins Glacier is covered by lapilli-size pumice fallout deposit. There are many dirt cones covered by volcanic ash composed of pumice fragments, volcanic glass, quartz, plagioclase, biotite, hornblende, and orthopyroxene. The ash and pumice are similar in chemical composition, both indicating an adakitic signature. At least three layers of fallout deposits have been recognised in parts of the surface of the glacier, which may correspond to the latest known eruptions.
Highlights
Lautaro volcano (Volcán Lautaro) is located at 49°01’S, 73°33’W, in southern Chilean Patagonia (Fig. 1)
Volcanoes located to the south of the Chile Triple Junction (CTJ) are characterised by adakitic composition and are grouped in the Andean Austral Volcanic Zone (AVZ; Stern and Kilian, 1996; Stern, 2004)
Lautaro volcano is located at the northern end of the AVZ, being the closest eruptive centre to the CTJ (Fig. 1)
Summary
Lautaro volcano (Volcán Lautaro) is located at 49°01’S, 73°33’W, in southern Chilean Patagonia (Fig. 1). Volcanoes located to the south of the CTJ are characterised by adakitic composition and are grouped in the Andean Austral Volcanic Zone (AVZ; Stern and Kilian, 1996; Stern, 2004). Three northern volcanoes of this volcanic zone, Lautaro, Viedma, and Aguilera, are called northern AVZ and show adakitic signatures with strong crustal overprint (Stern and Killian, 1996). Lautaro volcano is located at the northern end of the AVZ, being the closest eruptive centre to the CTJ (Fig. 1). 1. Locality map of Lautaro volcano, Chilean Patagonia: AVZ, Austral Volcanic Zone; SVZ, South Volcanic Zone; CTJ, Chile Triple Junction. Anma the Lautaro Glacier (1:50,000 topographic map ‘Portezuelo Santa Bárbara’, IGM 5-04-11-0007-00 of the Instituto Geográfico Militar, Chile), on the western side of the South Patagonian Ice Field, and from the surface deposits of the O’Higgins. This work complements that of Orihashi et al (2004)
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