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

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.