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 facie s with local anatectic melting at structurally lower levels of the cover ro cks and gradually decreased southwards to greenschist facies at structurall y higher levels. it is not present in the augen gneisses (the so called "co re" of the massif), which are interpreted as a peraluminous granite deforme d 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 b road 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 geome try of the F-1 folds towards the Lycian thrust front all indicate an unambi guous non-coaxial deformation and a shear sense of upper levels moving nort h. This shear sense is incompatible with a long-standing assumption that th e Lycian Nappes were transported southwards over the massif causing its met amorphism. 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.