Consanguineous geochemistry of the Kos Plateau and Tilos D and E Pumices, Aegean Volcanic Arc, Hellas
Zouzias, Dimitris; St. Seymour, Karen
published: Apr 1, 2008
ArtNo. ESP154018403001, Price: 29.00 €
Twenty pumice samples from the D and E ignimbrite units of Kos Plateau and Tilos Tuffs have been analyzed for major and 37 trace elements, including 14 Rare Earth elements to provide evidence for their geochemical insignia. Tilos island lies roughly 50 km from Kos and the identity of these two tuffs has been previously established in the literature on physical volcanology arguments (Allen 2001). Kos and Tilos tuff samples form a cluster of calcalkaline rhyolites transgressing the peraluminous-metaluminous boundary in ACNK-ANK space. Both pumices display well-defined partly overlapping trends, with D samples being more evolved than E, on variation diagrams for major elements, alkali earths (Ba, Rb, Sr), immobile (Zr, Y), compatible (V), highly incompatible (Pb, Th) and hygromagmatophile (Sb) trace elements.It has been suggested by Allen (2001) that the KPT has been erupted 161 Ka ago (Smith et al. 1996) ago, from a superstructure now outlined by the remains of a ∼16 km caldera which is mostly submarine. Pyroclastic density currents traveled either on land (Pe-Piper et al. 2005), or crossed open sea (Bohla 1987, Allen 2001) and deposited tuffs on Tilos, Kalymnos, on the coasts of Asian Minor and other islands in the area. The apron of this ash has traveled 300 km to the south and is thought to be equivalent with the W-3 submarine tephra layer (Federman & Carey 1980, Keller 1980, Vinci 1985).Our studies using Landsat-TM remotely sensed imagery, subaqueous distribution of hydrothermal vents and tectonic data of ring and radial faults collected on land, has indicated a caldera superstructure very similar to that proposed by Allen (2001) which "nests" smaller caldera-depressions (Kefalos, Zini, Yali, Perigusa-Pachia) or has them attached as "satellite" (Nisyros caldera) structures (St. Seymour et al. 2006). It has been proposed that these calderas represent the physical expression of interconnected magma chambers (St. Seymour 1996), satellites to a larger, active subvolcanic chamber underlying the area between Kos and Nisyros (Papadopoulos et al. 1998, Lagios et al. 2005).