Constraints on the Age of Metasediments from the Western Part (Ortaköy, Aksaray) of the Central Anatolian Crystalline Complex, Turkey

Abstract

The Central Anatolian Crystalline Complex (CACC) is the largest metamorphic domain, a ~300 × 200 km triangular region, exposed in Turkey. The basement is composed mainly of migmatites, paragneisses, alternations of marble and paragneiss, and a thick metacarbonate sequence. The sequence in the area starts with graphite-bearing paragneiss with interlayers of marble, and metabasics (Tamadağ Formation), and continues with marble containing paragneiss, and rare metabasics (Bozçaldağ Formation). The basement is overlain by Cretaceous ophiolites, which are cut by voluminous Late Cretaceous–Palaeocene granitoids. Neogene formations complete the rock sequence in the area. The first certain macrofossil, Heliolitinae (Heliolitidae fam.) Paeckelmannophora sp., has been discovered in the marble of the Tamadağ Formation. Also found are Acritarchs Leiosphaeridia sp. and Lophosphaeriduim sp. together with possible graptolite fragments (questionably of Retiolites sp.) in the marble residue obtained by treatment with acetic acid. Paeckelmannophora sp. and fragments of Retiolites sp. have been found, pointing to a Silurian–Devonian age. The Bozdağ Formation, overlying conformably the Tamadağ Formation, could hence be late Palaeozoic in age. Based on the age of the metasediments and the geochemistry of the amphibolites in the Nigde Massif, it has been suggested that the CACC could have undergone Hercynian metamorphism, whose effects may have been destroyed by intensive polyphase Alpine metamorphism. The Tamadağ Formation may be correlated with the Silurian–lower Carboniferous Bozdağ Formation of the Konya Complex (Afyon–Bolkardağ Zone), 200 km WSW of the study area.KeywordsAcritarchPalaeozoicMassifAksarayTurkey