INTRUSION AGE OF PAN-AFRICAN AUGEN GNEISSES IN THE SOUTHERN MENDERES MASSIF AND THE AGE OF COOLING AFTER ALPINE DUCTILE EXTENSIONAL DEFORMATION

Pb-Pb single zircon ages of 546.2 +/- 1.2 Ma demonstrate that the auge n gneisses in the southern Menderes Massif were generated from Pan-Afr ican intrusions. During the Alpine orogenic evolution of the Menderes Massif these granites were metamorphosed and transformed into augen gn eiss in an extensional top-to-the-south shear zone, located between au gen gneisses and overlying schists. Quartz fabrics suggest a pronounce d static recrystallization that post-dates the ductile deformation in the shear zone. Ar-Ar muscovite ages of 43-37 Ma from augen gneisses a nd schists suggest that ductile deformation and aa subsequent cooling occurred in the Eocene. These results contradict previous models that (1) interpret the extensional shear zone as late Oligocene in age and (2) regard the augen gneisses as syntectonic with respect to ductile e xtensional deformation.