EMPLACEMENT CHARACTERISTICS OF THE GNEISSIC GRANITES IN THE MENDERES MASSIF (WESTERN ANATOLIA) AND THEIR IMPLICATIONS ON THE TECTONIC EVOLUTION OF THE MASSIF: NEW FIELD OBSERVATIONS AND RADIOGENIC AGE DETERMINATIONS

Understanding the ages and emplacement mechanism of the gneissic granites cropping out in large areas of the Menderes Massif has a critical importance in its tectonic evolution. Based on some radiogenic age data, the gneissic granites and the surrounding high-grade micaschists have been advocated to be the Precambrian "Core Succession" that was undergone high-grade metamorphism during the Pan-African Orogenesis. The micascists and marbles of Palaeozoic-Mesozoic age have been defined as the "Cover Succession" unconformably overlying the core assemblages. It has also been indicated that during the Alpine Orogenesis and by the Main Menderes Metamorphism the core and cover successions were metamorphosed together in relatively lower grade conditions. Although the Menderes succession underlies a large region in the western Anatolia and display uncovered outcrops, in nowhere structural evidences of the unconformity between Pan-African core and the Palaezoic-Mesozoic cover series has been reported. It is very difficult to expect the Alpine Orogeny to erase the older Pan-African structures to a point of undefinable state. In this study, we have new mapped and examined the boundary relations between the so-called Pre-Cambrian core and Palaeozoic-Mesozoic country succession around Dibek Mountain, Çine-Yataðan and Ýncirliova Dam site. In Dibek Mountain gneissic granites were emplaced, as migmatitic fronts, into the marble lenses-bearing micaschists parallel to their foliation planes. Along the Çine-Yataðan road, migmatitic syn-tectonic granitic fronts injected into and engulfed the Palaeozoic black marble, black chert and micaschist alternation. In this region, the Palaeozoic units pass upward into the Triassic metadetritals with mafic volcanic intervals and they in turn grade into the Mesozoic platform-type marble succession. In this location the granites intrude into the Palaezoic and Mesozoic series which were paleontologically dated in some other areas of the masif. Similarly around the Ýncirliova Dam site the augen gneisse-migmatitic granite complex intruded into a complete stratigraphic section from Palaeozoic to Triassic and the Mesozic marble succession. New field data indicate that the high-temperature-type Barrowien Main Menderes Metamorphism caused a rejuvenation in the crust and granites with large migmatitic fronts emplaced syntectonically into the entire section of the masif from thick metadetrital units below and the Palaeozoic-Mesozoic cower series above. Precambrian and Alpine zircon ages determined from the gneissic granites could be explained by the rejuvenation and migmatism during the Main Menderes Metamorphism.