Timing of tectonic events in the Menderes Massif, Western Turkey - Implications for tectonic evolution and evidence for Pan-African basement in Turkey

The Menderes Massif forms the western of the two large metamorphic culminations within the Turkish Alpide orogen. It has three major lithologic units, with a gneissic “core” at the base and a “schist” and a “marble” envelope overlying it successively, although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the Massif. We present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the Massif to constrain the timing of major tectonic events that shaped the Massif since the late Proterozoic (Pt3). In the southern part of the Massif (sensu stricto) three episodes of deformation and metamorphism are distinguished, whereas in its northern part there are four. The first episode occurred at −500 ± 10 Ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis. In the central part of the Massif, the 470 ± 9 Ma-old now highly deformed tonalitic and granitic intrusions mark the end of this episode. On a Cambrian reconstruction of continents around the eastern Mediterranean, the Menderes Massif forms the southern end of the Pan-African orogenic collage of northeastern Africa and Arabia. The area of earliest Palaeozoic deformation in the Menderes may connect with the northwest African orogenic collage along the strike via the Bozburun and Saricicek diabases, arkoses, and schists in the center of the Karacahisar dome interpreted herein as fragments of a Pan-African suture. The earliest Palaeozoic deformations to affect the rocks were probably related to the last Pan-African collisions and associated postcollisional convergence. The southern part of the Massif was undeformed from early Ordovician to the early (? later) Eocene, whereas the northern part was deformed, metamorphosed and intruded possibly during the late Triassic, related to the closure of the Karakaya marginal basin of Palaeo-Tethys. The next major event affecting the whole of the Massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts, and only greenschist grade in the outermost envelope. This metamorphism, here called the “main Menderes metamorphism” (MMM), is biostratigraphically constrained between early Eocene and early Oligocene time. Rb/Sr isotopic data show a spread of ages between 60 Ma and 25 Ma, with the greatest number of determinations around 35 ± 5 Ma. This number is in excellent agreement with the stratigraphic evidence and shows that MMM took place during latest Eocene time or at the transition from Eocene to Oligocene time. Along the northern border of the Massif, deformation and metamorphism had already taken place during the late Cretaceous in a high pressure/low temperature (HP/LT) metamorphic belt (northernmost part of Menderes Massif sensu lato), which was then covered by Palaeocene molasse. The evolution of the HP/LT belt was probably related to the obduction of the Bozkir ophiolites from the Izmir-Ankara branch of the Neo-Tethys ocean and preceded terminal collision in the evolution of the Massif. The MMM was a product of the latest Palaeocene collision across Neo-Tethys and the consequent internal imbrication of the Menderes-Taurus block that resulted in the burial of the Menderes Massif area beneath the Lycian nappe complex. A low grade metamorphic event dated at 10 to 5 Ma is interpreted to be related to the extensional deformation in the Aegean and western Turkey, which has been dated stratigraphically to have begun during the Tortonian(11.5 Ma).