Petrographical, geochemical and petrological study of eocene volcanic rocks in the bahçeci̇k (Torul/Gümüşhane) and its surrounding region

Eocene volcanic rocks in the Bahçecik (Torul/Gümüşhane) and its surrounding area is the subject of this thesis. Within this scope, petrographical, geochemical and petrological characteristics of volcanic rocks from the study area were investigated, by using data and facts acquired, the origin and the evolution of the rocks were tried to determined. Study area is in the North Zone of the Eastern Pontides, main units consist of Late Cretaceous Kızılkaya Formation and Çağlayan Formation, Late Cretaceous Kastel Granodiorite that cut these two units, Eocene Alibaba Formation and Quaternary alluviums. Studied Eocene volcanic rocks are in composition of basaltic trachyandesite, trachyandesite, basaltic andesite, andesite, trachydacite and dacite. Main minerals consist of plagioclase, hornblende, augite, quartz, biotite and opaque minerals. Plagioclases in the Eocene Bahçecik volcanic rocks are in the composition of An39-45. Magnesium numbers (Mg/(Mg+Fe2+) belonging to hornblends change between 0.85 and 1.00. Fe(T)/Fe(T)+Mg values of the pyroxenes are between 0.19 and 0.26. Besides, pyroxenes have Wo44-46En43-44Fs10-15 compositions and they show compositions differ from diopside to augite. Eocene volcanic rocks in the Bahçecik (Torul) and its surroundings have medium to high K values and show calc-alkaline characteristics. Volcanic rocks are enriched in light rare earth elements (LREE) and depleted in high field strength elements (HFSE). The chondrite-normalized light rare earth elements (REE) distributions show low to medium enrichment level and are concave in shape (La/Lu=9.04-16.34). This case indicates that the volcanic rocks have similar sources. Moreover, during the formation of the volcanic rocks mainly fractional crystallization and minor crustal contamination ± magma mixing took place. All of these evidences support the conclusion that the parental magma of the studied volcanic rocks probably derived from an enriched lithospheric mantle, previously metasomatized by fluids. Keywords: Bahçecik, Eastern Pontides, Eosen volcanic rocks, Geochemistry, Petrology, Petrography, Torul.