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Geochemical insights into pre- and post-flank collapse at Antuco Volcano, Southern Volcanic Zone, Chile

Francisca Mallea-Lillo1 , Lucy McGee1, Jorge Romero2, Eduardo Morgado3, Carl Spandler1

  • Affiliations:  1Department of Earth Sciences, School of Physics, Chemistry and Earth Sciences, University of Adelaide, SA 5005, Australia; 2 Instituto de Ciencias de la Ingeniería, Universidad de O'Higgins, Libertador Bernardo O\'Higgins 611, Rancagua, Chile; 3 Escuela de Geología, Universidad Mayor, Manuel Montt 318, Providencia, Chile 

  • Presentation type: Poster

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

  • Poster Board Number: 46

  • Programme No: 1.7.33

  • Theme 1 > Session 7

Abstract

The volcanic products from Antuco volcano are amongst the most isotopically primitive in the Chilean Southern Volcanic Zone. A significant collapse of the western flank occurred 7.1 ka BP removing ~6.4 km3 of volcanic material, emphasising its hazard potential. We study the chemical compositions and pre-eruptive conditions of pre- and post-collapse products to compare the magmatic source of these two volcanic stages, alongside with the Los Pangues small eruptive centres in the west flank of Antuco volcano (1845 AD). These volcanic products are characterised by their primitive composition, abundant resorbed plagioclase and well-preserved olivine with large melt inclusions, which we interpret as a mafic magma intrusion into the crystal mush of Antuco volcano, driving Hawaiian activity and spatter cone formation. Pre- and post-collapse basalts and basaltic andesites comprise plagioclase and olivine phenocrysts, with rare pyroxenes and inclusions of Cr-spinels in olivine cores. Andesites from both volcanic stages are characterised by the presence of abundant crystal clots of plagioclase, ortho and clinopyroxene, titanomagnetites and rare ilmenite and apatite. Preliminary pre-eruptive conditions show temperature ranges between 1020 and 1120 °C for both pre- and post-collapse units, pressure ranges up to 4 kbar for the post-collapse volcanic products, and oxygen fugacity of ΔNNO-1.3 using one of the pre-collapse samples. Understanding the characteristics of the magmatic source as well the magmatic processes which occur during the ascent path and crustal storage in a volcano which has had a significant flank collapse gives important insights into the causes of this event, aiding future hazard scenarios.