Interpretation of Geochemical Data of Eocene Volcanism in Eastern Sivas Province (Central Anatolia, Türkiye)

Abstract

The study area covers the eastern part of Zara district (Sivas) located in East-Central Anatolia. The units found in the region from bottom to top are characterized by the Upper Creataceous-Paleocene Refahiye Complex, the Middle-Upper Eocene Akıncılar Formation, the Karataş volcanics and Kösedağ Syenite, the Lower Miocene Onarı Formation, the Upper Miocene-Pliocene İsola volcanics, the Şerefiye volcanics, the Kadıköy Formation and the uppermost Quaternary sediments. In the frame of this study, the Karataş volcanics, which were formed as a result of the second magmatic activity of the Eocene period, are studied in detail. The Karataş volcanics are greenish black on their undisturbed clean surfaces, and some parts are brown-purple in color and have distinctive crack systems. It shows a reddish-pinkish color distribution in regions where degradation is observed intensely. The SiO2 content, which is the main criterion for determining the magma character of Karataş volcanics, is between 52.09 % and 58.45 %. MgO contents of similar importance are between 0.53 % and 2.21 %. Some of the light rare earth elements, La have 22.2-40.7 ppm, Ce 44.4-67.3 ppm, Pr 5.23-8.88 ppm, Sm 4.41-7.15 ppm, Eu 1.24-1.83 ppm; one of the heavy rare earth elements, Lu have 0.20-0.45 ppm and Yb 1.88-2.98 ppm values. The Karataş volcanics consist of basaltic-trachyandesite and trachyandesite. Evidence of liquid-crystal fractional crystallization (FC) in the phenocryst phase during the formation of the Karataş volcanics is clearly observed in the geochemical diagrams. Traces of partial melting and crustal contamination were found in geochemical studies. Following the closure of the Neo-Tethys ocean in the region, a widespread crustal thickening occurred in the region with the northward divergence of the northern branch of Neo-Tethys, and a suture zone was formed along this line. The Karataş volcanics were formed as a product of active volcanism after the collision in the region.