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The structure of the Palaeozoic schists in the southern Menderes Massif, western Turkey: a new approach to the origin of the main Menderes Metamorphism and its relation to the Lycian Nappes

The Early Eocene to Early Oligocene tectonic history of the Menderes Massif involves a major regional Barrovian-type metamorphism (M-1, Main Menderes Metamorphism, MMM), present only in the Palaeozoic-Cenozoic metasediments (the so-called "cover" of the massif), which reached upper amphibolite facies with local anatectic melting at structurally lower levels of the cover rocks and gradually decreased southwards to greenschist facies at structurally higher levels. it is not present in the augen gneisses (the so called "core" of the massif), which are interpreted as a peraluminous granite deformed within a Tertiary extensional shear zone, and lie structurally below the metasediments. A pronounced regional (S-1) foliation and approximately N-S trending mineral lineation (L-1) associated with first-order folding (F-1) were produced during D-1 deformation coeval with the MMM. The S-1 foliation was later refolded during D-2 by approximately WNW-ESE trending F-2 folds associated with S-2 crenulation cleavage. It is now commonly believed that the MMM is the product of latest Palaeogene collision across Neo-Tethys and the consequent internal imbrication of the Menderes Massif area within a broad zone along the base of the Lycian Nappes during the Early Eocene-Early Oligocene time interval. However, the meso- and micro-structures produced during D-1 deformation, the asymmetry and change in the intensity and geometry of the F-1 folds towards the Lycian thrust front all indicate an unambiguous non-coaxial deformation and a shear sense of upper levels moving north. This shear sense is incompatible with a long-standing assumption that the Lycian Nappes were transported southwards over the massif causing its metamorphism. It is suggested here that the MMM results from burial related to the initial collision across the Neo-Tethys and Tefenni nappe emplacement, whereas associated D-1 deformation and later D-2 deformation are probably related to the northward back-thrusting of the Lycian nappes. (C) Elsevier, Paris.