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Geological Magazine; July 2006; v. 143; no. 4; p. 417-429; DOI: 10.1017/S0016756806002081
© 2006 Cambridge University Press (CUP)
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Geochemical characteristics of the Cretaceous ophiolitic rocks of Ikaria island, Greece

GEORGIA PE-PIPER*,* and ADONIS PHOTIADES{dagger}

* Department of Geology, Saint Mary’s University, Halifax, Nova Scotia, B3H 3C3, Canada
{dagger} Department of General Geology and Geological Mapping, Institute of Geology and Mineral Exploration (IGME), 70 Messoghion Street, GR 115 27 Athens, Greece

* Author for correspondence: gpiper{at}smu.ca.

Scattered occurrences of ophiolitic rocks are widespread in the Cyclades islands of Greece and are important for understanding the later Mesozoic ocean spreading and collisional history of the region, which has been obscured by Cenozoic nappe stacking, metamorphism, plutonism and extension. Ophiolitic rocks in the Upper Tectonic Unit of Ikaria are preserved in a mélange underlying Triassic limestones in the Kefala Unit and in a coarse-grained conglomerate at Faros directly overlying the mid-crustal detachment fault. The geochemistry of these rocks has been determined, their mineralogy investigated by electron microprobe, and K–Ar radiometric dating was carried out. Sole rocks are amphibolite of alkaline basalt protolith. Most ophiolitic samples from Ikaria consist of hornblende gabbro with MORB geochemistry that underwent sea-floor hydration, deformation and metamorphism. The large variation in degree of deformation, grade of metamorphism, and radiometric ages suggest syn-spreading extensional deformation at a slow-spreading ridge. The ophiolitic mélange on Ikaria, because it is unaffected by younger metamorphism, provides clear evidence for Late Cretaceous ocean-crust formation in the Cyclades region.

Key Words: ophiolite • mélange • conglomerate • Cyclades • Cretaceous






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