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The effects of hydrothermal alteration in the upper edifice of Copahue volcano (Argentina-Chile)

Matías Tramontini1, Marina Rosas-Carbajal2 , Michael Heap3,4, Pascale Besson2, Jacques Marteau5, Sebastián García6 and Fabio I. Zyserman1

  • Affiliations: 1CONICET - Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina 2Institut de Physique du Globe de Paris, CNRS, Université Paris Cité, 1 Rue Jussieu, Paris 75005, France 3Université de Strasbourg, CNRS, Institut Terre et Environnement de Strasbourg, UMR 7063, 5 rue Descartes, Strasbourg F-67084, France 4Institut Universitaire de France (IUF), Paris, France 5Institut de Physique des 2 Infinis de Lyon, UMR 5822, CNRS-IN2P3, Université de Lyon, Université Claude Bernard Lyon 1, France 6SegemAR, Observatorio Argentino de Vigilancia Volcánica, Argentina 

  • Presentation type: Poster

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

  • Poster Board Number: 41

  • Programme No: 3.8.25

  • Theme 3 > Session 8

Abstract

Copahue volcano, located at the border between Chile and Argentina, has been among the most active volcanoes in Patagonia for the last 30 years. Due to its high activity and proximity to nearby villages and tourist areas, Copahue is considered the volcano to pose the highest risk in Argentina. Copahue hosts a hyperacidic lake in its active crater, and many surface manifestations of extensive hydrothermal activity. While the geochemical composition of the lake and sources are well studied, no work has been published on the effect of this active volcano hydrothermal system on the edifice rocks. Here we study the upper edifice of Copahue volcano with muon radiography, used to infer the density structure in the east flank, and laboratory analyses of 11 rock samples that were collected from the volcano. Using a Scanning Electronic Microscope (SEM) combined with Energy Dispersive X-ray analysis (EDX), we visualize the effects of alteration and identify the minerals present. The different minerals are also further characterized by X-ray Powder Diffraction (XRPD). Furthermore, we measured density, the dry uniaxial compressive strength, and static Young's modules for all 11 blocks. The muon image reveals strong density contrasts between an edifice made of fresh andesite and notably lower bulk densities beneath the crater lake. It also maps the presence of lava flows, ash and ice in the subsurface, which correlate with satellite imagery and on-site observations. The laboratory analyses reveal a large scope of degrees of alteration and physical properties that will be discussed.