First evidence of high-pressure metamorphism in the "Cover Series" of the southern Menderes Massif. Tectonic and metamorphic implications for the evolution of SW Turkey

The Menderes Massif occupies a large part of western Turkey. It is tectonically overlain by nappes of the Izmir-Ankara Suture Zone (including the Bomova Flysch Zone) on its northern flank, the Afyon Zone on its eastern border, and the Lycian Nappes on its southern flank. The discovery of magnesiocarpholite-kyanite assemblages in the Mesozoic 'cover' sequence of the southern Menderes Massif leads to the very first consideration that a major high-pressure (HP) metamorphic event affected the massif during its Alpine evolution. Estimations of minimum pressure-temperature conditions about 10-12 kbar and 440 degreesC suggest a minimum burial of 30 km for the metasedimentary rocks of the Menderes Massif, similar to that for the Eocene Dilek Blueschists, which belong to the Cycladic complex. This finding of high-pressure rocks within the Menderes 'cover' series, as well as the recent description of low-grade high-pressure parageneses in the basal thrust sheets of the overlying Lycian nappe complex, has strong implications for the tectono-metamorphic evolution of these units. The characteristics of this high-pressure metamorphism and the deformation features observed in the southern Menderes Massif allow consideration of a fast burial during Alpine subduction and nappe stacking. Three high-pressure units were piled up during the Eocene collision of the Sakarya continent and the Tauride-Menderes block. The lowermost unit consists of the imbricated 'core' and 'cover' of the Menderes Massif. The intermediate unit is the Cycladic Blueschist complex (Dilek and Samos regions) and the uppermost unit is made of the Lycian Nappes. The retrogression of high-pressure parageneses from the Menderes Massif follows an isothermal decompression path and the associated deformation is characterized by a severe stretching oriented N-S to NE-SW during the high-pressure event and its exhumation. We propose a tectono-metamorphic model in three main stages: (1) the southward translation of the high-pressure Lycian Nappes and the burial of the Menderes (and Cycladic) metasediments to a depth of at least 30 kin to allow their Eocene high-pressure metamorphism; (2) a northward continuum of deformation responsible for top-to-the-north fabrics associated with the Main Menderes Metamorphism peak (Paleocene-Eocene) and its progressive cooling (Late Eocene), north-verging folding, thrusting, imbrication of 'core' and 'cover' series, and N-S to NE-SW intense stretching associated with the Menderes high-pressure metamorphism and its exhumation. These top-to-the-north to top-to-the-northeast movements are probably related to the northward backthrusting of the Lycian Nappes, reactivating the contact between the Menderes Massif and the Lycian Nappes as a top-to-the-NE shear zone that allowed exhumation of the Lycian high-pressure rocks; (3) Oligo-Miocene N-S extension during which the final exhumation of the metamorphic rocks along kilometre-scale low-angle detachments occurred. (C) 2003 Elsevier B.V. All rights reserved