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Pre-eruptive conditions of the 800 BP Plinian Eruption of Quilotoa volcano (Ecuador)

Nicole Vizuete 1, Pablo Samaniego1, Etienne Médard1, Diego F. Narváez2, Silvana Hidalgo3, Jean-Luc Devidal1, Federica Schiavi1

  • Affiliations: 1Laboratoire Magmas et Volcans, Université Clermont Auvergne-CNRS-IRD, Clermont-Ferrand, France; 2Departamento de Geología, Escuela Politécnica Nacional, Ladron de Guevara E11-253, Quito, Ecuador; 3Instituto Geofísico, Escuela Politécnica Nacional, Ladron de Guevara E11-253, Quito, Ecuador

  • Presentation type: Poster

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

  • Poster Board Number: 37

  • Programme No: 1.7.24

  • Theme 1 > Session 7

Abstract

Highly explosive dacitic eruptions often follow prolonged periods of volcanic quiescence and multiple succession of recharges and reheating steps. Understanding these pre-eruptive "priming" steps is critical for understanding processes in the volcanic plumbing system. The 800 BP Plinian eruption (VEI=6) of Quilotoa volcano, in Ecuador, caused significant devastation due to pyroclastic density currents and severe regional impacts due to ash fallouts. Despite this, the petrological characteristics of its products remain insufficiently studied. This research uses petrology to reconstruct pre-eruptive conditions, to investigate potential triggers for the eruption, and to understand magma evolution prior to eruption. Three juvenile clast types ---white pumice, gray pumice, and dense clasts--- are identified within deposits from the tephra fallout and pyroclastic flow deposits. Whole-rocks are homogeneous medium-K calc-alkaline dacites (65--66 wt.% SiO2), with rhyolitic groundmass glass compositions (70-79 wt.% SiO2). The mineral assemblage includes plagioclase (An30-54), amphibole (Mg# 59--78), biotite, Fe-Ti oxides (magnetite and ilmenite), and quartz, with minor orthopyroxene and apatite. Disequilibrium textures in plagioclase, such as sieve and patchy textures, and reverse zoning patterns, indicate shifts in pressure, temperature, and magma composition. Pre-eruptive conditions are preliminary estimated at 754 ± 40 °C, 433 ± 86 MPa (15 ± 3 km), with water contents (melt inclusions) of at least 6-8 wt.% (probably close to saturation conditions). We show that multiple successive magmatic recharges may constitute the main trigger mechanism for the eruptive activity, evidenced by disequilibrium textures and compositional variations (e.g. higher An, MgO, FeO in plagioclase rims).