| Summary: | <p>The Cycladic Islands in the Aegean region, southern Greece, has been indisputably under lithospheric extension throughout the last 10 Myrs but there remains a limited understanding of the regional tectono-metamorphic evolution prior to extension. In this thesis, new structural mapping, petrography, thermobarometry, phase equilibria modelling, U–Th–Pb and Lu–Hf garnet geochronology is presented from the islands of Tinos, Naxos and Delos and reveal the Cyclades have experienced a complete cycle of mountain building. The Tsiknias Ophiolite on Tinos formed at 161.9 ± 1.3 Ma and is underlaid by a metamorphic sole which displays a highly condensed and inverted temperature gradient, with partial melting directly below the ophiolite contact at P–T conditions of 8.5 kbar, 850°C. The timing of metamorphism is constrained as 74.0 ± 3.3 Ma from leucosomes and 66.6 ± 2.0 Ma from garnets in the underlying meta-sediments, and is interpreted to represent the initiation of a NE-dipping subduction zone that remained active for ~ 20 Myrs associated with the closure of the Vardar Ocean to the NE. The arrival of the leading edge of the Cycladic continental margin caused high-pressure metamorphism (22–26 kbar, 500–570°C at 46.4 ± 3.4 Ma on Tinos and 14.5 kbar, 470°C at 49–46 Ma on Naxos. Crustal thickening resulted in regional metamorphism and climaxed with kyanite-grade conditions (10 kbar, 670–730°C) at 18.5–16 Ma followed by sillmanite-grade anatexis (5–6 kbar, 690–730°C) at 15.5–14 Ma on Naxos. The transition from overall crustal shortening/thickening to extension is constrained to 15 Ma in the Naxos migmatite dome. I and S–type granites intruded contemporaneously between 14.6–12.2 Ma, suggesting a regional-scale partial melting event affected the deepest levels of the Cyclades, possibly associated with the onset of extension and exhumation.</p>
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