Schindlbeck, J. C. (2015) Explosive volcanism at the Pacific Ring of Fire: Emplacement and Provenance of marine tephras- Central America and Nankai Trough. (PhD/ Doctoral thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 154 pp.

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Abstract

This thesis is a cumulative work based on four independent manuscripts. All studies use tephrostratigraphy and geochemistry as tools for identifying the emplacement processes and/or provenance of marine tephra layers. The study areas are located at the Pacific Ring of Fire and used drill core samples from ODP and IODP Legs. Papers 1 and 2 (Schindlbeck et al., 2013 and Kutterolf et al., 2014) deal with tuffaceous sandstones, which were recovered during IODP Expedition 322 in the Nankai Trough. These packages are part of the Late Miocene middle Shikoku Basin Facies. Geochemical homogeneity and density-graded structures (pumice enrichment at the top, lithic enrichment at the bottom) support the emplacement by large volume, high-energy turbidity currents, which are each the product of a major volcanic eruption. Major and trace element, and isotope compositions of glass shards indicate a Japanese mainland source. Therefore we propose the collision zone of Paleo-Honshu and the Izu-Bonin-arc as possible source region, which implies ~350 km transport distance from the source to Site 322. Manuscripts 3 and 4 (Schindlbeck et al., submitted and Schindlbeck et al., in preparation) study ODP and IODP cores offshore the southern part of the Central American Volcanic Arc (CAVA). Six sites offshore Costa Rica recovered a well-preserved tephrostratigraphy from the Miocene to the Pleistocene. The subduction-related volcanism at the CAVA is known for highly explosive Plinian eruptions. These eruptions generate eruption columns, which rise up to 40 km into the stratosphere. When reaching their level of neutral buoyancy, they spread laterally with the prevailing wind and generate widely dispersed ash deposits covering areas up to >106 km2. f an ash cloud travels over oceans, the ash is deposited as Imarine ash layers, which are best preserved, since the marine environment is relatively non-erosive. The marine tephra inventory is therefore a very good archive for highly explosive Plinian eruptions. ODP and IODP cores recovered a well-preserved stratigraphy of Plinian eruptions derived from the CAVA from Miocene to Pleistocene, but also an extensive record of mainly Miocene tephra layers originated at the Galápagos hotspot. These layers from Plinian eruptions from the Galápagos are particularly interesting, since such abundant Plinian eruptions from this oceanisland setting were not described before, and the onland tephra record on the Galápagos islands is limited to Quaternary deposits. To conclude, the manuscripts presented in this study emphasize the advantage of marine tephrostratigraphy as a useful tool in volcanology. The well-preserved marine tephra layers (1) complement onland volcanic records, (2) expose previously undiscovered volcanic activity (e.g., Galápagos), (3) provide insights and comprehension of geological processes and (4) help to understand the reasons of variability of volcanic activity in time.

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