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New chronological and petrological constrains of the caldera-forming eruption of Cuicocha volcano (Ecuador)

Marco Almeida1, Pablo Samaniego2, Etienne Médard 2, Diego Narváez3, Federica Schiavi2, Silvana Hidalgo1

  • Affiliations: 1Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador; 2Laboratoire Magmas et Volcans, Université Clermont Auvergne, Clermont-Ferrand, France; 3Departamento de Geología, Escuela Politécnica Nacional, Quito, Ecuador

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 131

  • Programme No: 3.4.17

  • Theme 3 > Session 4

Abstract

Studying past eruptions of potentially active volcanoes gives insight into future eruptions magnitude and potential hazards. Cuicocha is a relatively young and potentially active volcanic center located in the Northern Andes of Ecuador. It is situated near densely populated areas, including Cotacachi and Quiroga (40,000 inhabitants). Previous studies described a large explosive eruption (VEI 5; 3.1 -- 2.9 ka) that destroyed an older dome complex, forming the current caldera. Our new geochronological data refine the eruptive chronology, including at least one eruption between 3890 ± 30 and 4495 ± 30 years BP (uncalibrated ages). In addition, the current Cuicocha lake fills a funnel-shaped depression (3 km diameter) associated with the large caldera-forming eruption dated between 2480 ± 30 and 2980 ± 30 years BP. The eruptive products of this eruption include large pyroclastic density currents (flow and surges), and tephra fallout deposits. The last eruptive products of this volcanic center correspond to three intra-caldera lava domes, which sealed the activity. Eruptive products display a homogeneous andesitic composition (61 -- 63 wt.% SiO2), with phenocrysts of high-alumina amphibole, plagioclase (An39-78), and magnetite. Thermo-barometry and melt inclusions study suggest that the caldera-forming eruption was fed by a magma reservoir in equilibrium at 400-600 MPa (i.e. 14-20 km depth), 830 ± 20°C and at least 4 wt.% H2O. The presence of mafic enclaves and the reverse and oscillatory zoning patterns in plagioclase phenocrysts suggest that the triggering mechanism was the recharge of deeper mafic magma into a crystal-rich reservoir.