Cenozoic Extension of the Southern Menderes Massif along the Kayabuku Shear Zone, Western Anatolia Extended Terrane, Turkey

Four major low angle extensional shear zones are located in the Menderes massif of the Western Anatolia Extended Terrane in western Turkey. The shear zones are, from north to south, Simav, Alasehir, Buyuk Menderes and Kayabuku (Selimiye) shear zones. We have conducted a detailed field oriented study to determine the role of the Kayabuku (Selimiye) shear zone in the Cenozoic extensional evolution of the Menderes massif. The south-dipping Kayabuku (Selimiye) shear zone of the southern Menderes massif contains well- developed mesoscopic and microscopic shear sense indicators, and separates orthogneiss and augengneiss in its footwall from schist and marble rock units in its hanging wall. Within the shear zone, the average attitude of the foliation planes between the towns of Milas and Yatagan is measured as N86W/50°S. The shear zone shows two ductile sense of shearing; 1) top to the north and 2) top to the south which overprinted the former one. Many thin sections also show top to the south brittle shear sense indicators overprinting the ductile shear sense indicators. The trend of the ductile shear sense indicators, such as stretching lineations, range from N10E to N30E indicating that they are parallel to the shear sense indicators measured along the Simav shear zone of the northern and, Alasehir and Buyuk Menderes shear zones of the central Menderes massif. This suggests to us that the Cenozoic extension which was initiated in Oligocene by the processes of Orogenic Collapse effected the Kayabuku (Selimiye) shear zone. The hanging wall of the Kayabuku shear zone is also locally brittely deformed by a south-dipping normal fault zone, discontinuously exposed between the schist and marble units. The fault zone suggests that the hanging wall of the shear zone has been brittely deformed during the extensional exhumation of the southern Menderes massif. Our field observations and microtectonic studies suggest that the rocks within the Kayabuku (Selimiye) shear zone gained their shear sense indicators within the large Oligocene top to the north simple-shear extensional shear zone. As the extensional exhumation of the southern Menderes massif progressed, the shear zone developed top to the south ductile and brittle shear sense indicators, suggesting that the shear zone has been subjected to at least two different deformation phases.