Late Quaternary Tephrostratigraphy of South-Central Chile (~ 38 – 40 °S)

Wednesday, 17 December 2014
Karen Fontijn1, Harriet Louise Rawson1, Maarten E Van Daele2, Jasper Moernaut3, Ana M Abarzúa3, David M Pyle1, Tamsin A Mather1, Marc A O De Batist2, Hugo Moreno-Roa4 and José Antonio Naranjo5, (1)University of Oxford, Department of Earth Sciences, Oxford, United Kingdom, (2)Ghent University, Renard Centre of Marine Geology, Ghent, Belgium, (3)Universidad Austral de Chile, Escuela de Geología, Instituto de Ciencias Ambientales & Evolutivas, Valdivia, Chile, (4)SERNAGEOMIN, Observatorio Volcanológico de los Andes del Sur, Temuco, Chile, (5)SERNAGEOMIN, Geología Regional, Santiago, Chile
The volcanoes of the Siete Lagos region (“Lake District”) in South-Central Chile form part of the Southern Volcanic Zone of the Andes and include some of the most active volcanoes in South America, i.e. Villarrica and Llaima. The Late Quaternary (~ last 15 ka) regional tephrostratigraphic record for this region is however still poorly developed. We combine detailed stratigraphic logging of terrestrial sections in the vicinity of Llaima, Sollipulli, Villarrica, Quetrupillan, Mocho-Choshuenco and Puyehue-Cordón Caulle volcanoes with petrological, whole-rock and glass geochemical data, and 14C dating on charcoal entrained in volcanic deposits, and correlate the on-land sequences with tephra layers in existing 14C-dated lacustrine records of Laguna Las Ranas and Lagos Villarrica, Calafquén and Riñihue. The combined record includes previously described major eruptions, e.g. Llaima Pumice (Llaima) and Alpehue Pumice (Sollipulli), which help to constrain the relative timing of events. These correlations suggest that several widespread volcanic units are several hundreds to thousands of years older than previously thought. The record also includes newly described pumice-producing events, e.g. for the poorly studied Quetrupillan volcano, and provides new insights into the post-glacial eruptive frequency in the Southern Volcanic Zone. The newly updated stratigraphy with high-quality geochemical data also contributes to the regional tephrochronological framework which helps to significantly improve age models for lacustrine palaeoseismological and palaeoenvironmental archives.