Akademik Veri Yönetim Sistemi
INTERNATIONAL GEOLOGY REVIEW, cilt.58, sa.10, ss.1234-1252, 2016 (SCI-Expanded)
The lower Miocene (similar to 22-19Ma) volcanic units in the NE-SW-trending Tuncbilek-Domanic basin, located in the northeastern-most part of the Neogene successions in western Anatolia, are composed of (1) high-K, calc-alkaline dacitic to rhyolitic volcanic rocks of the Oklukda volcanics; (2) calc-alkaline low-MgO (evolved) basalts; and (3) high-MgO mildly alkaline basalts of the Karakoy volcanics. Sr isotopic ratios of the volcanic units increase from high-MgO (similar to 0.7055-0.7057) to low-MgO basaltic rocks (similar to 0.7066-0.7072) and then to dacitic-rhyolitic rocks (0.7081-0.7086). Geochemical features of the volcanic rocks reveal that the calc-alkaline evolved basalts were formed by mixing of basic and acidic magmas.Geochemical studies in the last decade show that the Miocene mafic volcanic rocks in western Anatolia are mainly composed of high-MgO shoshonitic-ultrapotassic rocks (SHO-UK), of which mantle sources were variably, but also intensely metasomatized with crustally derived materials during collisional processes in the region. However, geochemical comparison of the high-MgO basalts of the Karakoy volcanics with the SHO-UK rocks in this region reveal that that the former has too low Sr-87/Sr-86((i)) and high Nd-143/Nd-144((i)) ratios, with lower LILE and LREE abundances, which are firstly described here. These features are interpreted to be derived from more slightly enriched lithospheric mantle sources than that of the SHO-UK. Accepting the SHO-UK rocks in the region were derived from mantle sources that had been metasomatized by northward subduction of crustal slices during Alpine collisional processes, it is proposed that the imbrication and direct subduction of crustal slices were not reached to, and were limited in the mantle domains beneath the basin. The dacites of the Oklukda volcanics might be formed either by high-degree melting of the same sources with the SHO-UK, or by melting of the lower crustal mafic sources as previously proposed, and then evolved into the rhyolites via fractional crystallization with limited crustal contribution.