Consanguineous Geochemistry of the Kos Plateau and Tilos D and E Pumices, Aegean Volcanic Arc, Hellas

Consanguineous geochemistry of the Kos Plateau 231

N. Jb. Miner. Abh. 2008, Vol. 184/3, p. 231–241, Stuttgart, March 2008, published online 2008 © by E. Schweizerbart’sche Verlagsbuchhandlung 2008

Consanguineous geochemistry of the Kos Plateau and Tilos D and E Pumices, Aegean Volcanic Arc, Hellas

Dimitris Zouzias and Karen St. Seymour

With 7 ﬁ gures and 2 tables

Abstract: 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-deﬁ ned 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).

Key words: Aegean Arc, Kos, Tilos Pumices, consanguineous geochemistry, major, trace, REE.

Introduction that crossed the open sea according to Stadlbauer et al. (1988) and Allen & Cas (2001). However, Pe-Piper et This paper documents the geochemical insignia of the al. (2005) argued for an “on-land” transport and deposi- Kos Plateau Tuff and the Tilos Pumices. Allen (1998), tion of the KPT to the adjacent areas. Allen & Cas (1998a, b), Allen et al. (1999) and Al- Complementary to physical volcanology arguments the len & McPhie (2000) have presented arguments based consanguineous relationship of the KPT and Tilos pum- on volcanic stratigraphy and physical volcanology for the ices presented here is based on major and trace, including lateral equivalence of the two tuffs. The volcanic stratig- Rare Earth, element data obtained from the two tuffs. A raphy and sedimentology of the KPT have been brieﬂ y sequel paper will present the geochemical ‘evidence’ for discussed also by other workers (Keller 1969, 1971, the coeval relationship of three most extensive occurrenc- Bohla 1987, Dalabakis 1986, 1988, Stadlbauer et es of Kos Plateau Tuff D and E ignimbrite units based on al. 1986, and Keller et al. 1990). The deposition of the chronostratigraphically controlled major, trace and REE KPT on Tilos, Kalymnos and other islets, as well as, on data for melt and mineral compositions (Zouzias & St. the shores of the Asian Minor opposite to Kos (Alikar- Seymour, in prep.). nassos), was the result of transport of pyroclastic ﬂ ows