Geochemical characteristics of the Cretaceous ophiolitic rocks of Ikaria island, Greece

Abstract

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.

Granitoid intrusion and high temperature metamorphism in the Asteroussia Unit, Anafi Island (Greece): Petrology and geochronology

“…Peak metamorphic temperatures of 600-650 ºC and pressures of 4-5 kbar were determined for Donoussa (Kolodner et al, 1998). On Ikaria, the HT-LP sequences include marbles, amphibolites, meta-ophiolites, and diorites (Altherr et al, 1994: Pe-Piper andPhotiades, 2006). The Asteroussia Unit sequence on Anafi, which is the focus of the current study, is built up of a series of tectonic slices comprising amphibolites, calcsilicate rocks, paragneisses, marbles, and meta-ophiolitic rocks, intruded by diorites, granites, and aplitic dikes (Reinecke et al, 1982).…”

“…70 Ma (Seidel and Okrusch, 1976;Seidel et al, 1981;Reinecke et al, 1982;Altherr et al, 1994;Langosch et al, 2000;Pe-Piper and Photiades, 2006). This age was traditionally interpreted to define cooling after the major HT-LP metamorphic event of this unit.…”

“…Estimates for the metamorphic grade of the Late Cretaceous tectonic slices on Ikaria are less definite. While Altherr et al (1994) considered this rock association to be an integral part of the Asteroussia Unit, Pe-Piper and Photiades (2006) report that the meta-ophiolite sequences record greenschist facies assemblages and that marbles are Tertiary. These authors also pointed to similarities between the Late Cretaceous rocks of Ikaria and those of Tinos, and distinguished these rock associations from the Asteroussia Unit of Donoussa, Nikoria Anafi, and Crete.…”

Map view restoration of Aegean–West Anatolian accretion and extension since the Eocene

“…The Cyclades contains multiple metamorphic domes interpreted as core complexes. The hanging wall of these detachments are typically formed by ophiolites, which, in the west, correlate to the Jurassic ophiolites that overlie the Pelagonian zone (West Vardar ophiolites in the sense of Schmid et al [2008]) and in the east to the Cretaceous age obducted ophiolites that are widespread in western Turkey (e.g., on Ikaria [ Photiades , 2002; Pe‐Piper and Photiades , 2006]). For detailed reviews of the structure of the Cycladic core complexes, we refer to Jolivet et al [2004b, 2010b], Tirel et al [2009] and Ring et al [2010].…”

New structural and U–Pb zircon data from Anafi crystalline basement (Cyclades, Greece): constraints on the evolution of a Late Cretaceous magmatic arc in the Internal Hellenides

“…This is mainly due to the scarce and limited exposures of the unit in this area and the frequent extensional reworking of the original contact between the Upper Unit and the Cycladic Blueschist Unit. Pe-Piper and Photiades (2006) and Be'eri- Shlevin et al (2009) emphasized significant differences in geochemistry, geochronology and metamorphic grade between HT-LP metamorphic rocks of the Upper Unit in the northern (Ikaria, Syros, Tinos; Fig. 1) and the southern (Anafi, Donousa, Gramvonisi, Makra, Nikouria; Fig.…”