U-PB AND AR-40 AR-39 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 vergen t thrusting and continental subduction within the Alpine collisional o rogen but has subsequently been greatly extended on a northeast-southw est 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-Oli gocene 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 str uctural systems. The earliest of these, the ''Symvolon shear zone'', a ppears to represent a midcrustal, coaxial rupture of the Falakron marb le series, a carbonate platform >5000 m thick that was subducted north eastward 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 inci pient mylonitization of the Symvolon or ''Kavala'' granodiorite within the Symvolon shear zone at similar to 21-22 Ma. Following its emplace ment, the Symvolon body resided at temperatures between 300 degrees C and 500 degrees C for 5-7 m.y., during which coaxial deformation may h ave continued within a widening Symvolon rupture. The Strymon Valley d etachment, a regionally southwest dipping low-angle normal fault succe eded the Symvolon shear zone in middle Miocene time. Southwestward dis placement of the Serbo-Macedonian gneiss complex by as much as 80 km i n the hanging wall of this detachment facilitated the unroofing of the Rhodope metamorphic core complex, including the Falakron marble serie s and several Tertiary plutons, in its footwall. Biotite and K-feldspa r 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 cor e complex below 150 degrees C-300 degrees C during its southwestward-p rogressive exhumation in the footwall of the Strymon Valley detachment .