U-Pb single zircon ages and geochemistry of metagranitoid rocks in the Cycladic Blueschists (Evia Island): Implications for the Triassic tectonic setting of Greece

U-Pb zircon geochronology, geochemical and microstructural analyses were carried out to a metagranitoid suite exposed in the Blueschist unit of the Attic-Cycladic zone on Evia Island. Concordant zircons from three metagranitoid samples yielded ID-TIMS U-Pb single grain ages of 234 +/- 12 Ma, 232 +/- 1 Ma and 214 +/- 0.7 Ma, which are interpreted to constrain the intrusion of the igneous protolith in Late Triassic times. These age data in combination with previously published Early-Middle Triassic protolith ages of (meta-)igneous rocks from other Greek islands support magmatic activity in the Cycladic area throughout the Triassic. Major and trace element whole rock analyses reveal that the granitic protolith of the Evia metagranitoid suite is of A-type affinity implying Triassic magmatism in an extensional setting along the northern Gondwanan margin rather than back-arc extension above a subduction zone. Subsequent Alpine subduction and related high-pressure metamorphism led to pervasive non-coaxial fabrics of the Evia metagranitoid, which indicate top-to-the-E(SE) shearing. This Alpine deformation took place under ductile (viscous) conditions at temperatures close to 450-500 degrees C and differential stresses of 65 + 15/-10 MPa. (C) 2012 Elsevier B.V. All rights reserved.