Provenance and tectonometamorphic evolution of the Uppermost Unit (External Hellenides, Cete).

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The Island of Crete is situated in a fore-arc position above northward-directed active subduction of the African plate underneath the Aegean. A similar active plate-margin setting was repeatedly given since Precambrian times, as is documented by at least two sutures in the Cretan nappe stack. The Alpine Pindos suture separates the unmetamorphic Pindos Unit from the Uppermost Unit, the latter consisting of different nappes (Arvi, Vatos, Miamou, Spili, Preveli, Asteroussia), which differ considerably in age, type and grade of metamorphism. While an affiliation of the Uppermost Unit to the Internal Hellenides is beyond dispute, a Pelagonian provenance, as assumed by most workers, is not in line with (1) Middle Jurassic ophiolites in the Spili nappe, (2) Upper Jurassic blueschists in the Preveli nappe, and (3) Campanian arc-type granitoids in the Asteroussia nappe. Such rocks are lacking in the Pelagonian Zone, but are common in the Vardar, Serbomacedonian and Rhodope domains. To verify such a provenance and to reveal how the rocks of the Uppermost Unit succeeded to end up in Crete and Gavdos, are the main goals of present proposal. Our hypothesis can be tested by comparing the nappes of the Uppermost Unit with possible provenance domains concerning protolith age, age of metamorphism, cooling history and tectonometamorphic evolution. At present, however, the age and evolution of most nappes of the Uppermost Unit are still poorly constrained. For this reason the following investigations will be carried out on rocks of the Uppermost Unit exposed on Crete and Gavdos: (1) Microscopic, EBSD, µCT and microprope analyses of rocks of the Vatos and Spili groups focusing on the deformation microfabrics, finite and incremental strain, and crystallization-deformation relation to constrain the tectonometamorphic evolution and kinematics during nappe emplacement. (2) U-Pb dating (small-scale isochrones) of fluid-derived minerals (calcite, prehnite, epidote), which formed synkinematically in veins, strain fringes and shear zones to date the age of deformation. (3) U-Pb dating of metamorphic aragonite to constrain the age of HP-LT metamorphism. (4) U-Pb dating of zircons and titanite to constrain the age of protolith and metamorphism of the Preveli blueschists. (5) U-Pb dating of detrital zircons to determine the maximum age and provenance of metasediments of the Asteroussia, Vatos and Preveli nappes. The new results will be of interest for all workers dealing with the Alpine geodynamic evolution of the eastern Mediterranean. They will help to reveal the provenance area and the tectonometamorphic evolution of the Uppermost Unit, both of which are essential for post-Triassic map-view restorations of the eastern Mediterranean region.