Systematic variations in the eruptive history of the Christiana-Santorini-Kolumbo volcanic field (Greece) - The IODP Expedition 398 tephra time series and its implications

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During IODP Expeditions 398 the objectives were to study the volcanic record of the central Hellenic island arc to document the links and feedbacks between volcanism/magmatism, crustal tectonics and sea level, and to investigate the processes and products of shallow submarine eruptions of silicic magma. Reconstructing the subsidence history of the southern Aegean Sea, and searching for deep life inside and outside of Santorini caldera, were additional objectives. The expedition drilled ten sites originally proposed, plus two extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from onland and others hitherto unknown, pushing back the onset of volcanism in the area into the early Pleistocene or even Pliocene. Huge events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and to open the way to unravelling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences on the basin margins served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy. Drilling inside Santorini caldera penetrated to ~120 mbsf and yielded a detailed tephra record of the history of the Kameni islands. Tephra deposits from Exp. 398 complemented by tephras found on land provide the unique opportunity to investigate and compare the history of highly explosive volcanic activity of the Christiana-Santorini-Kolumbo volcanic field in the heart of Southern Europe, including one of the most famous and most active volcanoes in our neighborhood. This project focuses therefore on the ~1200 volcanic horizons derived from highly explosive eruptions during the Pliocene and Quaternary and found in the cores. Geochemical, petrological and volcanological approaches for tephra and sediment characterization will be used to quantitatively and qualitatively decrypt their provenance and the eruption succession. Additionally, absolute age dating will improve and confirm the existing age models since robust age models are needed to study the temporal and spatial changes in eruption processes, magnitudes and frequencies of large volcanic eruptions. The herewith-established compositional data and eruptive time series will serve as base to address questions regarding recurrence rates and cyclicities, and compare them with external controlling mechanism like tectonics and sea level changes. Recovered sediments will also facilitate to investigate the temporal and quantitative characterization of the sediment composition in the basins of the Aegean Sea in relation to the volcaniclastic input and answer the question how this may be connected to the basin evolution.