Orta pontidlerin güney kısmında yüzeylenen yay ilişkili Kösdağ metavolkaniklerinin jeokimyası ve petrojenezi, Kuzey Türkiye

The Kösdağ Metavolcanics (KM) in the southern Central Pontides crops out between the Izmir-Ankara-Erzincan Suture Zone (IAESZ) in the south and the Sakarya Composite Terrane in the north. The unit is represented by a low-grade metamorphic assemblage including meta-basics, meta-intermediates, and meta felsics, interlayered with recrystallized limestone, mudstone, and chert. While the unit is bounded to the north by the North Anatolian Fault Zone (NAFZ), the Dikmen Formation stratigraphically overlie the unit in the south. Geochemically, the KM are sub-alkaline and divided into two main groups as Type 1 and Type 2, based on their relative Zr-Hf enrichment/depletion. The high Zr/Nb (3.3-85.8), low Zr/Y (0.6-6.9), and Nb/Y (0.02-0.19) ratios suggest that the KM have been derived from a depleted mantle source resembling that of N-MORBs. Positive εNd values shown by the KM, ranging from + 2.9 to + 6.5, support the dominant involvement of depleted mantle source with a minor contribution from recycled and/or subduction components. Enrichment in Th and La compared to Nb (and Ta) indicates subduction-related magmatism fort he KM. The melting models imply derivation of the KM from a spinel lherzolitic source. LA-ICP-MS U-Pb zircon ages of the KM range from 96.9 ± 1.3 Ma to 93.7 ± 1.2 Ma. Combined geological and geochemical evidence indicates an oceanic arc origin for the KM. The geodynamic model proposed in this study involves the presence of an intra oceanic subduction zone during the early Late Cretaceous within the IAE branch of the Neotethys Ocean in the Central Pontides.