Evolution of northern branch of neotethys between Ankara and Tuzgölü (Geotectonic evolution and stratigraphy of Haymana and Tuzgölü basins)

The study area is located in the south of Ankara province, and is bounded by Temelli and Haymana towns in the west, Kulu town and Tuzgölü (Salt Lake) in the south, and Kızılırmak river and Bala town in the east, covering an area of approximately 4050 km2. In the study area, there are Sakarya and Kırşehir continents, the collision zone of the northern branch of Neotethyan ocean and its units and structures in between. As a result of the detailed studies of the area's stratigraphy, the presence of two stratigraphic associations with two different basements were determined at the northwest and southeast of a belt in which is composed of basic and ultrabasic rocks and basic volcanics belonging to Samsam group running across approximately middle of the study area. The association in the northwest of the Samsam ophiolitic belt constitutes a basement belonging to the Sakarya continent and overlying Liassic - Middle Eocene sediments. The association in the southeast, on the other hand, consists of the Kırşehir metamorphic basement and overlying Upper Cretaceus - Middle to Upper Eocene. Upper Eocene - Pliocene continental deposits overlie both associations and the ophiolitic belt. The northern branch of the Neotethyan ocean which had been opening between the Sakarya continent in the north-nortwest and the Kırşehir continent in the south-southeast since Liassic, was found to be closing since Upper Cretaceous, and as a result, the development of sedimentary units, ophiolitic melange and volcanic arc was observed. Later, Samsam high where two different sedimentary environments developed in the northwest and southeast (Haymana and Tuzgölü basins, respectively), was formed in as a result of uplift due to collision-induced melange and arc volcanism. Moreover, the Haymana basin was internally broken up by reverse faults and thrusts as a result of increasing compression due to approach and collision of two continents in the Middle-Upper Eocene period. During this period the deformation has not started in the Tuzgölü envirous yet, and the effect of deformation in the north was limited in this area to copious amount of clastic material input and shallowing of the sedimentary stack. Due to theXX continuation of collision in the Upper Eocene period, the sedimentary association of the Haymana basin together with the Samsam ophiolitic association were thrusted over the sedimentary association of the Tuzgölü basin. During Upper Eocene-Middle Miocene period, while uplift and rapid erosion around Haymana were being observed, the continuation of presence of closed continental sedimentary environments whose connection to open sea was cut, was determined. In the Upper Miocene - Pliocene period, by the erosion of Haymana environs finally, the region became a peneplain and the general presence of widespread lacustrine (continental) environment in the area was determined. As a conclusion, the presence of three different basements above which sedimentary units developed, were recognized, and it was determined that their present positions were resulted from a chain of structural events, and that they came together along large tectonic zones. Key Words : Haymana - Tuzgölü Basins, Northern Branch of Neotethys, Tectono-stratigraphy, Tectonic, Geotectonic evolution