New insights from 40 Ar/ 39 Ar laserprobe dating of white mica fabrics from the Pelion Massif, Pelagonian Zone, Internal Hellenides, Greece: implications for the timing of metamorphic episodes and tectonic events in the Aegean region

Abstract

Abstract 40 Ar/ 39 Ar laserprobe dating of mylonites fabrics from the Pelion Massif in the Pelagonian Zone of mainland Greece has characterized its Mid-Late Alpine deformation history. Following high pressure (HP) metamorphism, ductile deformation occurred under greenschist-facies conditions from c. 54 Ma, and continued to affect the Pelion Massif until c. 15 Ma. The prolonged episode of ductile deformation in the Pelion Massif has resulted in the formation of an Oligocene-Early Miocene ductile domal structure. The new geochronological data obtained for the Pelion contribute to a detailed record of the Alpine kinematic history in the Pelagonian Zone and allow a discussion of P-T-t data from Aegean HP rocks to characterize the regional thermotectonic history. Comparison with the P-T-t data from the Cycladic region reinforces the point that Mid-Eocene phengite ages, commonly taken as the age of peak HP metamorphism in the Cyclades, do not always reflect the metamorphic culmination, but rather the retrograde paths of the HP rocks. It is shown that, on a regional scale, termination of HP metamorphism is a diachronous process in the Aegean region, being c. 54 Ma in the north (Pelagonian Zone) and shifting to younger ages, chiefly c. 40 Ma in the Cyclades, and c. 20 Ma on Crete, as the present-day subduction zone is approached. In contrast to the diachronous exhumation of Aegean HP assemblages, the well documented Miocene phase of ductile regional extension appears to be synchronous across the whole Aegean region and affected basement rocks until c. 15 Ma.