Glasgeochemie und Datierung mittelpleistozäner (130–770 ka) Pyroklastika der Ägäis: Ein Ansatz zur Verbesserung der Tephrostratigraphie des östlichen Mittelmeerraums
Mineralogie, Petrologie und Geochemie
Zusammenfassung der Projektergebnisse
Unearthing the potential of tephrochronology for correlation and dating of disparate paleoclimate archives depends critically on the availability of robust glass geochemical signatures and wellconstrained age estimates for volcanic sources of distal tephra. The proximal tephrostratigraphy of the Aegean Arc, a key building block for the Eastern Mediterranean tephrostratigraphic framework, has remained poorly constrained, which is particularly true for the Middle Pleistocene (c. 130–770 ka). On this basis, a reference glass geochemical dataset underpinned by zircon double dating (ZDD) eruption ages was generated for the Aegean Arc focusing on Middle Pleistocene explosive eruptions of the Aegina–Poros–Methana, Milos, and Kos–Nisyros–Yali volcanic fields. The dataset contains 1792 single-shard major-element analyses and 778 trace-element analyses on 62 samples from these volcanic fields. In total, 18 samples representing 11 key eruptions were dated by ZDD. There is significant geochemical variation between and within individual volcanic fields in the Aegean Arc. The western Aegean Arc is characterized by overall less evolved tephra compositions. Rhyolitic to dacitic tephras from Methana have similar glass geochemistry but can be distinguished based on subtle variations in major- and trace-element abundances. They are geochemically distinct from more K-rich rhyolitic to dacitic-andesitic pyroclastics from Aegina. In the central Aegean Arc, all tephra deposits on Milos and Kimolos are high-Si rhyolitic. The youngest Trachilas and Fyriplaka complexes and most of the older pyroclastic deposits from both islands are compositionally distinctive and can be separated using major- and trace-element data. In the eastern Aegean Arc, the high-Si rhyolitic Kefalos Tuff and Kos Plateau Tuff on Kos have overlapping major-element compositions but different trace-element fingerprints. They can be clearly distinguished from high-Si rhyolitic and trachydacitic tephras from Nisyros. On Methana, the pumice lapilli deposits that have so far been assigned to the Early Pleistocene yielded Middle Pleistocene ZDD ages. They appear to represent three closely-timed eruptions at 363±41 ka, 320±19 ka, and 294±9.2 ka. On Milos, the Fyriplaka complex was emplaced at 44.7±1.6 ka and the Trachilas complex at 268±18 ka based on ZDD. The former date is consistent with the age estimate of c. 37 ka for the distal Fyriplaka tephra layer. The previously undated pyroclastic sequence underlying Fyriplaka revealed a ZDD eruption age of 331±28 ka. Pumice lapilli deposits near the Catacombs representing another previously unknown eruption were dated at 1510±110 ka. Two ZDD eruption ages of 2660±160 ka and 2860±250 ka were obtained for the Profitis Illias pumice breccias, allowing pinpointing the hitherto poorly constrained onset of volcanism on Milos. On Kos, the Kefalos Tuff yielded a ZDD age of 511±18 ka, which is younger and more precise than the previous age estimates. Our results demonstrate consistently younger ZDD eruption ages compared to the K-Ar or 40Ar/39Ar ages on the same tephra units. The comparison of the revised Aegean Arc proximal tephrostratigraphy for the Middle Pleistocene with Eastern Mediterranean distal tephra records revealed that although many yet uncorrelated tephra layers at Tenaghi Philippon, Lake Ohrid, and ODP Site 964 have age estimates that overlap with those of Methana and Milos tephra deposits, their compositions rule out an origin from the Aegean Arc. At ODP Site 967, a rhyolitic tephra at c. 410 ka has a Milos geochemical fingerprint but the source eruption remains elusive. Nevertheless, the distinctive geochemistry and robust radiometric ages of the investigated proximal tephra units including four newly identified Middle Pleistocene eruptions from Methana and Milos make them valuable new markers for the Eastern Mediterranean tephra lattice.
Projektbezogene Publikationen (Auswahl)
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Advancing Middle Pleistocene tephrostratigraphy of the Eastern Mediterranean region: Insight from terrestrial and marine cryptotephra records. GFZ Potsdam, 16.11.2021 (Invited Talk)
Vakhrameeva, P.
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Cryptotephra records as chronicles of explosive volcanism in the Eastern Mediterranean region: Deciphering the sources of unknown tephra layers. ETH Zurich, 01.12.2021 (Invited Talk)
Vakhrameeva, P.
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Refining the Middle Pleistocene (130–770 ka) tephrostratigraphy of the Eastern Mediterranean region based on glass geochemical characterization and dating of Aegean Arc tephra deposits. XXI INQUA Congress, 13–20 July 2023.
Vakhrameeva, P., Bachmann, O., Schmitt, A.K., Xydous, S., Sturm, A., Koutsodendris, A., Popa, R., Portnyagin, M. & Pross, J.
