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

Abstract

Be'eri-Shlevin, Y., Avigad, D., and Matthews, A. 2009. Granitoid intrusion and high temperature metamorphism in the Asteroussia Unit, Anafi Island (Greece): Petrology and geochronology. Isr. J. Earth Sci. 58: 13-27.A series of amphibolite facies metamorphic rocks and granitoid intrusions is exposed on Anafi Island, Cyclades (Aegean Sea). The rock association represents a klippe of the Asteroussia Unit, a high-temperature low-pressure (HT-LP) unit of Late Cretaceous age (ca. 70 Ma), which is a prominent constituent of the allochtonous Upper Unit (UU) of the Attic-Cycladic Crystalline Belt.Garnet-biotite and hornblende-plagioclase geothermometry of metapelitic and metabasic rocks and spinel chemistry of a meta-ophiolite indicate an upper amphibolite metamorphic overprint. Multigrain zircon ID-TIMS U-Pb dating of a granitic intrusion yielded an age of 85.3 ± 2.7 Ma, indicating that felsic magmatism slightly predated or was contemporary with HT-LP metamorphism. Rb-Sr dating of biotite-plagioclase pairs from two granite samples yielded ages of 63.4 ± 0.4 Ma and 48.2 ± 0.3 Ma. The older age may relate to penetrative deformation recorded in the granites, but the younger age probably represents partial resetting of the Rb-Sr system at a later stage.Comparison between the Asteroussia Unit and other occurrences of Late Cretaceous UU on Tinos, Syros, and Andros shows that the latter followed a slightly different P-T-t path. Nevertheless, all these occurrences are considered to represent the remnants of a once-continuous and extensive nappe, in agreement with previous estimates. Age resemblance of the Asteroussia Unit with Late Cretaceous magmatic arcs in NW Turkey may indicate correlation between these two terranes, although previously-suggested formation of the Late Cretaceous UU (including the Asteroussia Unit) in association with rifting of the Apulian continent cannot be ruled out.

Upper crustal emplacement and deformation of granitoids inside the Uppermost Unit of the Cretan nappe stack: constraints from U–Pb zircon dating, microfabrics and paleostress analyses

“…Seidel et al 1982;Bonneau 1984). Most metagranitoids of the Uppermost Unit in central Crete, dated so far (Seidel et al 1982;Langosch et al 2000), show imprints of high-grade metamorphism and related viscous strain and yield Cretaceous cooling ages, which are consistent with the Pelagonian Unit to the north (e.g., Be'eri- Shlevin et al 2009). Published radiometric ages of rocks exposed in the study area are restricted to K-Ar cooling ages of hornblende and biotite obtained from the (meta)granitoids (Baranyi et al 1975;Seidel et al 1981;Langosch et al 2000), whereas their protolith age is still unknown.…”

“…1). Together with relics of Asteroussia rocks on the Cyclades, they are considered to represent remnants of a once-continuous nappe (Altherr et al 1994;Patzak et al 1994;Be'eri-Shlevin et al 2009). The Cenozoic high structural position of this nappe suggests an affinity with the Pelagonian Zone of mainland Greece (Reinecke et al 1982;Bonneau 1984).…”

“…Fragments of the Asteroussia crystalline complex are also exposed on the Cyclades, where multigrain zircon ID-TIMS U-Pb dating of a granitic intrusion, exposed on Anafi island, yielded an upper intercept age of 85.3 ± 2.7 Ma, which is interpreted as emplacement age (Be'eri-Shlevin et al 2009). …”

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

“…Crystalline rocks that underwent Late Cretaceous to Middle Palaeocene high-temperature (HT)-low-pressure (LP) metamorphism and related felsic magmatic rocks are compiled within the so-called Upper Unit (e.g. Dürr et al 1978a, b;Reinecke et al 1982;Dürr 1985;Maluski et al 1987;Altherr et al 1994;Patzak et al 1994;Be'eri-Shlevin et al 2009). The crystalline rocks of the Upper Unit display oceanic and continental affinities and rest tectonically on top of the Cycladic Blueschist Unit occupying the higher structural levels in the nappe pile of the Attic-Cycladic Complex (e.g.…”

“…Pindos Unit and Tripolitsa Unit, e.g. Dürr et al 1978a;Seidel et al 1981;Reinecke et al 1982;Bonneau 1984;Altherr et al 1994;Langosch et al 2000;Be'eri-Shlevin et al 2009). In this tectonic context, the Uppermost Unit is considered to belong to the upper plate of the Alpine subduction system in the Aegean region (Bonneau 1984).…”