Structural and thermal history of poly-orogenic basement : U-Pb geochronology of granitoid rocks in the southern Menderes Massif, Western Turkey

Ion microprobe U-Pb dating of granitoid rocks from key structural outcrops of the Menderes Massif in western Turkey provides an important constraint to the thermal and deformational history of a structurally complex metamorphic belt within the Alpine chain. Crystallization ages of two granite protoliths, derived from the weighted means of rim ages and the ages of homogeneous prismatic zircon grains, are 541 +/- 14 Ma and 566 +/- 9 Ma, whereas the cores of zoned pyramidal and short-prismatic zircon grains range from Palaeoproterozoic to Neoproterozoic in age. These ages indicate that amphibolite- to gramilite-facies metamorphic rocks in much of the Menderes Massif were deformed, metamorphosed and intruded during the Pan-African Orogeny, and neither crystallized nor remelted during an Alpine event. Structural and metamorphic evidence for Alpine convergence in Pan-African basement rocks is limited to greenschist-facies top-to-the-south shear zones, which occur on a regional scale across a number of tectonic units.