Original paper

Indication of pre-Alpine basement gneisses within the northern Cycladic Blueschist Unit on Syros Island, Greece

Tomaschek, Frank; Keiter, Mark; Kennedy, Allen K.; Ballhaus, Chris


The main lithological sequence on Syros Island forms part of the Blueschist Unit within the Attic-Cycladic Crystalline Complex in the Hellenides. The structurally lowermost outcrops in SW Syros expose minor occurrences of intensely deformed K- feldspar megacryst augen gneisses, considered to represent granitic protoliths. Ion microprobe U-Pb zircon geochronology yielded a range of single spot ages between ~ 331 to 299 Ma. Based on cathodoluminescence criteria, an age of 315 ± 3 Ma is interpreted to approximate the magmatic crystallization of the precursor rock. The magmatic protolith age correlates with granitoid intrusions well documented from pre-Alpine basement units of the southern Cycladic islands. The studied orthogneiss provides the first evidence that remnants of a Variscan consolidated crust are preserved within the BlueschistUnit of the northern Cyclades.