The timing of partial melting, Barrovian metamorphism and granite intrusion in the Naxos metamorphic core complex, Cyclades, Aegean Sea, Greece

Abstract

The relationship between partial melting and granite intrusion in a classic Barrovian metamorphic terrane has been assessed. Thirteen samples were dated by SHRIMP U-Pb zircon geochronology from the island of Naxos, Greece, one of the Aegean metamorphic core complexes. The effect of partial melting during peak Barrovian metamorphism on Naxos is recorded by fine (<30 μm) zircon overgrowths surrounding older cores in seven of nine samples of migmatite analyzed. The ages of these overgrowths suggest that partial melting commenced prior to 20.7 Ma. The timing of partial melting on Naxos also constrains the onset of extensional tectonism in the area to pre-20.7 Ma. The preservation of zircon overgrowth rims with distinctly different concordant ages, ranging from 20.7 to 16.8 Ma, both from different samples and from within the one handspecimen, suggests that zircon precipitation, associated with the partial melting process, was episodic over this age range on both local (cm) and regional (km) scales. Zircons from four granite intrusives were also dated and range in age from 15.4 to 11.3 Ma, with the main period of magmatic activity at ca. 12 Ma, clearly post-dating metamorphism. The sequence of partial melting, Barrovian metamorphism and magmatism in the Naxos metamorphic core complex can be related to a change from overall crustal shortening to extensional tectonism in the Aegean region, caused by post-collisional roll-back of the subducting African slab along the Hellenic trench system.