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Title: Unravelling the structural, metamorphic and strain history of the 'Aegean Orogeny', southern Greece, with a combined structural, petrographic and geochronological approach
Author: Lamont, Thomas Neil
ISNI:       0000 0004 7966 0748
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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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.
Supervisor: Searle, Mike ; Waters, David ; Roberts, Nick Sponsor: Natural Environment Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Metamorphic Geology ; Metamorphic rocks--Maps ; Structural Geology ; Metamorphic Petrology ; Geochronology