HR: 0800h
AN: V41B-1448    [Abstracts]
TI: Volcanic Rocks with Adakitic Affinity on the Island of Agios Efstratios, Northeastern Aegean Sea, Greece
AU: * Wohlford, T P
EM: twohlford@wesleyan.edu
AF: Wesleyan University, Dept. of Earth & Environmental Sciences 265 Church Street, Room 455, Middletown, CT 06459 United States
AB: Volcanic rocks with geochemical signature similar to adakites have been identified on the island of Agios Efstratios in the northeastern Aegean Sea, Greece. Calc-alkaline volcanism in the northeastern Aegean Sea occurred from the Oligocene through the Early Miocene when oceanic lithosphere was subducting in a zone located well to the north of the present Aegean subduction zone, south of Crete. Adakites have been previously described from the islands of Skyros and Evia in Greece, located southwest of the studied location. These three locations align with the direction of rollback of the Hellenic Subduction Zone in Greece that occurred from the Oligocene to present day. The volcanic rock samples collected from Agios Efstratios are porphyritic with phenocrysts of plagioclase, hornblende and biotite. The presence of hornblende and biotite indicate relatively high volatile concentrations, probably at least 4-5 percent H2O. The samples were analyzed for major and trace elements including the REE. The MgO contents range from 1.8 to 4.0 weight percent, the Na2O contents are all greater than 3.5 weight percent, and Al2O3 contents range from 14.0 to 16.5 weight percent. These rocks classify as trachyandesites and trachydacites, with SiO2 from 58.15 to 69.51 weight percent, and show the common enrichment in LILE and depletion in Nb and Ti of arc calc-alkaline volcanism. The heavy REE are depleted with Yb concentrations ranging from 1.1 to 1.8 ppm. High Sr concentrations (1,065-1,350 ppm) with low Y concentrations (11.3-18.9 ppm) place these samples in or near the typical adakite field in the Sr/Y vs. Y diagram, as first used by Defant and Drummond (1990). Isotope data for Sr, Nd and Pb of these samples will be presented as well (work in progress).
DE: 1037 Magma genesis and partial melting (3619)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 8400 VOLCANOLOGY
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005