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

The protoliths of mylonitized augen gneisses exposed in the southern s ector of the Menderes Massif (West Turkey) are calc-alkaline, peralumi nous, S-type, late- to post-tectonic tourmaline- and garnet-bearing, t wo-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 themsel ves cut by an extensive network of tourmaline-rich dykes. Chemical, mi neralogical, isotopic and field relations suggest that the granitic pr otolith crystallized from a boron-rich, water-saturated melt, derived from partial melting of metagreywacke in the lower crust during peak B arrovian-type metamorphism. The protolith was probably emplaced during lateorogenic extensional collapse of the thickened crust in west Turk ey during late Oligocene time.