First evienced of high-pressure metamorphism in the 'Cover Series' of the southern Menderes Massif.Tectonic and metamorjphic implications for the evolution of SW Turkey

摘要

The Menderes Massif occupies a large part of western Turkey.It is tectonically overlain by nappes of the lzmir-Ankara Suture Zone(including the Bornova Flysch Zone) on its northern flank,the Afyon Zone on its eastern border,kand the Lycian Nappes on its southern flank.The discovery of magnesiocarpholite-kyanite assemblage 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 durign its Alpine evolution.Estimations of minimum pressure-temperature conditios about 10-12 kbar and 440 deg C suggest a minimum burial of 30km for the metasedimentary rocks of the Menderes Massif,similar to that for the Eocene series,as well as the recent description of low-grade high-pressure parageneses in the basal thrust sheets of the overlying Lycian nappe complesx,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 Masif allow consideration of a fast burial during Alpine subduction and nappe stacking.Three high-pressure unit were piled up during the Eocene collision of th eSakkarya 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 mode of the Lycian Nappes.The retrogression of high-pressure p[arageneses form the Menderes Massif follows an isothermal decompression path and the associated deformation is characterized by a evere stretching oriented N-S to NE-SE during the high-pressure evet an dits exhumation.We propoe a tectono-metamorphic model inthree main stages:(1)the southward translation of th ehigh-pressure Lycian Nappes and the burial fo the menderes(and Cycladic)metasediments to a depth of at least 30km to alow their Eocene high-pressure metamorphism;(2)a northward continuum of deformation responsible for top-to-the-norht 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-SE intense stretching movements are probably related to the northward backthrusting of the Lycian nappes,reactivating the contact between the Menderes Massif and the Lycian nappes asa 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.