GEOCHEMISTRY AND TECTONIC SIGNIFICANCE OF AUGEN GNEISSES FROM THE SOUTHERN MENDERES MASSIF (WEST TURKEY)

The protoliths of mylonitized augen gneisses exposed in the southern sector of the Menderes Massif (West Turkey) are calc-alkaline, peraluminous, S-type, late- to post-tectonic tourmaline- and garnet-bearing, two-mica leucogranites. They cut and post-date the fabrics of the 'main Menderes metamorphism' which took place between the early Eocene and early Oligocene and intrude metamorphic basement rocks comprising the so-called 'Palaeozoic schist envelope' of the massif. They are themselves cut by an extensive network of tourmaline-rich dykes. Chemical, mineralogical, isotopic and field relations suggest that the granitic protolith crystallized from a boron-rich, water-saturated melt, derived from partial melting of metagreywacke in the lower crust during peak Barrovian-type metamorphism. The protolith was probably emplaced during lateorogenic extensional collapse of the thickened crust in west Turkey during late Oligocene time.