STRATIGRAPHY AND NEW AGE FINDINGS IN THE VOLCANIC ROCKS AROUND, ÇUBUK (ANKARA)-TURKEY

In the region, Triassic rocks which are concerned as Karakaya komplex of Sakarya Continent, Upper Cretaceous Dereköy Ophiolitic melange and Karadag formation consisting flysch type deposits of Ýzmir-Ankara-Erzincan zone and Tertiary volcanic and sedimentary cover rocks take place.The relation of the rocks of both groups is tectonic and the rocks belonging to Sakarya Continent overthrusted the rocks of Ýzmir-Ankara-Erzincan Zone. The main subject of the study is the Tertiary volcanic rocks which are unconformable/cutting the rocks of both groups. The oldest volcanic rocks of the Çubuk area are Paleocene-Early Eocene Sarýkoz volcanite consisting dacite and graniteporphyry. The radiometric age taken from Sarýkoz volcanite by K/Ar method gives the value of 56.4 ± 2.4 Ma which corresponds to late Paleocene-Early Eocene. Sarýkoz volcanite is overlain by Middle Eocene Kurtsivrisi, Sele, Ömercik, Susuz and Yukarýemirler volcanites respectively. Kurtsivrisi volcanite consisting of andesite, trackyandesite and dacite overlies Sarýkoz volcanite unconformably. The radiometric age taken from Kurtsivrisi volcanite by K/Ar method gives the value of 44.5 ± 1.7 Ma. which corresponds to Middle Eocene (Lutetian). Andesitic Sele volcanite cuts Sarýkoz and Kurtsivrisi volcanite. The radiometric age taken from Sele volcanite by K/Ar method gives 44.8 ± 1.7 and 44.3 ± 1.9 Ma which corresponds to Middle Eocene (Lutetian). Ömercik volcanite consisting basaltic lava and pyroclastic overlies Sele volcanite and is cut by Susuz volcanite consisting rhyolites and dacites. The radiometric age taken from Susuz volcanite by K/Ar method gives 43.1 ± Ma corresponding to Middle Eocene (Lutetian). Therefore, Ömercik volcanite which was active between Sele and Susuz volcanite is Middle Eocene in age. The last Eocene volcanism in the region is the basaltic Yukarýemirler volcanite which cuts Susuz volcanite and flows on it. The radiometric age taken from Yukarýemirler volcanite by K/Ar method gives 43.1 ± 1.7 Ma corresponding to Middle Eocene.The volcanites of the region are alcaline and calcalcaline in character. They have different compositions and characteristics indicating bimodal volcanism. The volcanic activity in the Çubuk region ends with Early Miocene Aydos basalt. The age taken from Aydos basalt by K/Ar methods gives 18.4 ± 0.7 Ma corresponding to Early Miocene.