EXTENSIONAL TECTONICS IN WESTERN ANATOLIA, TURKEY

Post-collisional extension in the Aegean region caused the exhumation of several Alpine metamorphic core complexes. One of these is the Menderes Massif of western Anatolia, Turkey which is located between the Izmir-Ankara Neo-Tethyan suture to the north and the Lycian Nappes to the south. The E-W trending Alasehir and Buyuk Menderes grabens divide the massif into northern, central, and southern parts. Based on our field observations, available seismic reflection profiles and geochronologic data, we suggest a testable model for the evolution of the Menderes Massif: the exhumation of the massif occurred along a N-dipping main breakaway fault, which affected the lithosphere in a similar manner to the simple shear/rolling hinge models of southern Basins and Ranges. We propose that the main breakaway fault is located on the south side of Gokova Gulf and extension may have started with a large simple shear zone at depth. Seismic reflection profiles in the Gulf of Gokova clearly show a listric normal fault and associated roll-over structure. The Oren basin is formed on the hanging wall of the main breakaway. The Yatagan and Kale-Tavas basins are extensional basins located adjacent to the main breakaway, which may have some strike-slip component as it progrades on land eastward and controls the southern margins of these basins. The presence of a large simple shear zone is also evidenced by the presence of dominant top to the north-northeast shear sense indicators in the Menderes Massif between Lycian nappes to the south and the Izmir – Ankara suture zone to the north. Available radiometric age determinations, including our limited number of monazite ages suggest that the north – northeast directed extension started in late Oligocene. Isostatic adjustment of the simple shear zone must have brought the lower plate rocks to the surface in Early Miocene when the E-W trending grabens started to take form in a bivergent rolling hinge tectonic setting.