Geologic reconnaissance of Lautaro Volcano, Chilean Patagonia

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. Reconocimiento geológico del volcán Lautaro, Patagonia chilena. El volcán Lautaro es el más próximo alPunto Triple de la dorsal de Chile en la Zona Volcánica Austral de los Andes. El edificio volcánico de 3.607 m s.n.m. se destaca como el punto más alto en la parte noroeste del plateau del Campo de Hielo Patagónico Sur. El basamento del volcán está compuesto por metapelitas de bajo grado metamórfico que están atravesadas por cuerpos tabulares constituidos por granitos de hornblenda-biotita. El volcán está casi completamente cubierto por hielo y el estudio se

Elevation and Mass Changes of the Southern Patagonia Icefield Derived from TanDEM-X and SRTM Data

“…This agrees with the interpretation by de Angelis stating that his class B glaciers have long and narrow tongues that are nourished by a large high elevation accumulation area [17]. It may hence be speculated that continuous positive surface mass balances together with the particular glacier geometry may be responsible for the observed dh/dt pattern of Pío XI rather than surging or geothermal activity in the accumulation area (e.g., reported by [60]). …”