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Reconstructing the geological record of caldera-forming eruptions on Sumatra (Indonesia)

Francesca Forni 1, Marcus Phua 2, Giuditta Fellin3, Jeffrey Oalmann4, Marcel Guillong3, Brian Jicha5, Kyle Bradley6, Colin Maden3, Hamdi Rifai7, Caroline Bouvet de Maisonneuve8

  • Affiliations: 1Department of Earth Sciences "A. Desio", University of Milan, Milan, Italy; 2VRock Laboratory, Department of Earth Sciences, The University of Hong Kong, Hong Kong; 3Department of Earth and Planetary Sciences, ETH Zurich, Zurich, Switzerland; 4Centre for Ore Deposits and Earth Sciences, University of Tasmania, Hobart, Australia; 5Department of Geoscience, University of Wisconsin-Madison, Madison, USA; 6Earthquake Insights, Ithaca, USA; 7Department of Physics, Universitas Negeri Padang, Padang, Indonesia; 8Earth Observatory of Singapore, Nanyang Technological University, Singapore

  • Presentation type: Poster

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

  • Poster Board Number: 270

  • Programme No: 1.3.16

  • Theme 1 > Session 3

Abstract

The island of Sumatra (Indonesia) has been the site of numerous caldera-forming eruptions that spread voluminous silicic tuffs throughout the region. Among these large eruptions, only the Toba tuffs have been studied in great detail, while others have so far received less attention. With this study, we contribute to bridging this knowledge gap by characterizing the mineralogy, geochemistry, crystallinity and age of the proximal deposits of large ignimbrites from north to south Sumatra. Our research shows that between ~7.3 Ma and ~33 ka the region experienced multiple cataclysmic eruptions that culminated with caldera collapses. The bulk-rock compositions of the pyroclastic deposits associated with these eruptions define a calc-alkaline suite ranging from andesites to high-SiO2 rhyolites. However, the matrix glass compositions of all the ignimbrites are rhyolitic, indicating that crystallinities and mineral assemblages primarily control the bulk-rock geochemistry. The geochemical signatures (particularly K2O, CaO and trace element contents), mineral assemblages (e.g, presence or absence of K-feldspars, biotite, amphibole and quartz in addition to plagioclase, pyroxenes and oxides) and mineral chemistry allow fingerprinting of the different sources. The knowledge obtained from the study of these large ignimbrites is essential to re-evaluate the frequency of caldera-forming eruptions on Sumatra and the geochemical variations of erupted magmas in the north-western sector of the Sunda volcanic arc. Furthermore, since most of the information about the volcanic activity in Indonesia comes from marine tephra layers with unknown sources, this research contributes a foundation for building a database useful to tephrostratigraphic correlations in south-east Asia.