U-PB AND 40AR/39AR GEOCHRONOLOGY OF THE SYMVOLON GRANODIORITE - IMPLICATIONS FOR THE THERMAL AND STRUCTURAL EVOLUTION OF THE RHODOPE METAMORPHIC CORE COMPLEX, NORTHEASTERN GREECE

North Aegean continental lithosphere was thickened by southwest vergent thrusting and continental subduction within the Alpine collisional orogen but has subsequently been greatly extended on a northeast-southwest axis in the back are of the Hellenic subduction zone. Crosscutting relationships with two granodiorite bodies emplaced at similar to 31-33 Ma, the Xanthi and eastern Vrondou plutons, constrain a pre-mid-Oligocene origin of Alpine convergent structures in northeastern Greece. Post-Alpine thinning of the north Aegean nappe pile began in earliest Miocene time and has been accommodated by a succession of distinct structural systems. The earliest of these, the ''Symvolon shear zone'', appears to represent a midcrustal, coaxial rupture of the Falakron marble series, a carbonate platform >5000 m thick that was subducted northeastward beneath high-grade rocks of the Rhodope metamorphic province in late Alpine time. Zircon and titanite U-Pb dates and hornblende Ar-40/Ar-39 dates obtained in this study constrain the intrusion and incipient mylonitization of the Symvolon or ''Kavala'' granodiorite within the Symvolon shear zone at similar to 21-22 Ma. Following its emplacement, the Symvolon body resided at temperatures between 300 degrees C and 500 degrees C for 5-7 m.y., during which coaxial deformation may have continued within a widening Symvolon rupture. The Strymon Valley detachment, a regionally southwest dipping low-angle normal fault succeeded the Symvolon shear zone in middle Miocene time. Southwestward displacement of the Serbo-Macedonian gneiss complex by as much as 80 km in the hanging wall of this detachment facilitated the unroofing of the Rhodope metamorphic core complex, including the Falakron marble series and several Tertiary plutons, in its footwall. Biotite and K-feldspar Ar-40/Ar-39 dates from 11.1 +/- 0.2 Ma to 15.5 +/- 0.3 Ma yielded by Symvolon granodiorite samples document the cooling of the Rhodope core complex below 150 degrees C-300 degrees C during its southwestward-progressive exhumation in the footwall of the Strymon Valley detachment.