Geochemistry and Geochronology of Quaternary Calderas in North and Central Sumatra (Indonesia)
Abstract
During the Quaternary, 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 characterising the mineralogy, geochemistry, crystallinity and age of the proximal deposits of five large ignimbrites from north and central Sumatra (Singkut, Maninjau, Hopong and Kerinci-Lempur tuffs). Our research indicates that between ~500 and 30 ka the region experienced multiple cataclysmic eruptions that culminated with caldera collapses. These calderas vary in diameter between ~5 and 30 km, and the erupted volumes, although not very well constrained, are on the order of hundreds of km3. 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 is rhyolitic, indicating that crystallinity controls the bulk-rock compositions more than melt composition. The geochemical signatures (in particular the 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 reconstruct the frequency of caldera-forming eruptions on Sumatra and the geochemical variations of erupted magmas along 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.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V51H0140F
- Keywords:
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- 1115 Radioisotope geochronology;
- GEOCHRONOLOGY;
- 3625 Petrography;
- microstructures;
- and textures;
- MINERALOGY AND PETROLOGY;
- 3642 Intrusive structures and rocks;
- MINERALOGY AND PETROLOGY;
- 8032 Rheology: general;
- STRUCTURAL GEOLOGY