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Geochronological evolution of the potentially active Iliniza Volcano (Ecuador) based on new K-Ar ages

Abstract : The youngest volcanism of the Ecuadorian Volcanic Front (Western Cordillera) is mainly dominated by highly explosive events, including the growth and violent destruction of lava domes, and the formation of thick pyroclastic sequences. Deposits associated with such eruptive dynamics have been identified at Iliniza, a compound volcano located in the Western Cordillera with a poorly defined evolutionary history. We present the first K-Ar ages of Iliniza volcano combined with stratigraphic data, numerical reconstructions, and geochemical analyses, providing a new perspective on its evolution. Our results show that Iliniza volcano is much younger than previously proposed. The Iliniza twin-peaked shape is the result of the superposition of two andesitic to dacitic stratovolcanoes. (1) The North Iliniza (NI) edifice was constructed by two lava successions and an intermediate satellite vent, showing a short range of mainly effusive activity between 123 ± 6 and 116 ± 2 ka. (2) The South Iliniza (SI) edifice began its construction through the Lower SI stage when massive lavas dated at ~45 ka formed a basal cone. During the Upper SI stage, the uppermost part of this edifice was destroyed by the highly explosive Jatuncama phase (VEI 5) leaving a 30–40 m-thick ignimbrite sequence. The subsequent extrusion of several dacitic lava domes reconstructed the South Iliniza summit at around 35 ka. The Terminal SI stage corresponds to the emission of several andesitic lavas between 31 ± 4 and 25 ± 3 ka. The Iliniza eruptive activity extended into the Late Pleistocene and Holocene with the extrusion of the Tishigcuchi lava dome, and the emission of the Pongo lava flow dated at 6 ± 4 ka. Based on the proposed eruptive history, we suggest that a revised volcanic hazard assessment of the potentially active Iliniza volcano is required.
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Submitted on : Thursday, February 3, 2022 - 9:05:08 AM
Last modification on : Thursday, March 17, 2022 - 2:00:19 PM
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Santiago Santamaria, Xavier Quidelleur, Silvana Hidalgo, Pablo Samaniego, Jean-Luc Le Pennec, et al.. Geochronological evolution of the potentially active Iliniza Volcano (Ecuador) based on new K-Ar ages. Journal of Volcanology and Geothermal Research, Elsevier, 2022, pp.107489. ⟨10.1016/j.jvolgeores.2022.107489⟩. ⟨hal-03553857⟩



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