Petrographical, geochemical and petrological features the of eocene volcanic rocks in the Gümüşdamla-Erikdibi (Bayburt) and surrounding region

Eocene volcanic rocks in the Gümüşdamla-Erikdibi (Bayburt) 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, and the origin and the evolution of the magma that forms the rocks were tried to determined. Study area is in the south of the Eastern Pontides. The main units consist of Late Cretaceous Ardıç Volcanites, Eocene Sırataşlar Formation, Eocene Yazyurdu Formation, Eocene Taşlıburun Diorite that cut this unit and Quaternary alluviums. Eocene volcanic rocks in the study area are consist of basalt, basaltic andesite and andesite in composition. Main minerals consist of plagioclase, alkali feldspar, pyroxene, amphibole, biotite and opaque minerals. Plagioclases of the Eocene volcanic rocks in the Gümüşdamla-Erikdibi (Bayburt) and surrounding area are in the composition of An39-86, and are consist of bitownite, labrador and andesine. Besides, pyroxenes are clino-pyroxene in composition (Wo40-48En39-46Fs9-19), and differ from diopside to augite. Studied volcanic rocks have low to high potassium (K) values and show calc-alkaline and partly tholeitic character. These 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 are concave in shape and enrich medium level (La/LuN=9.04-16.34). This case indicates that the rocks forming the volcanics are derived from similar sources. Crystallization temperatures calculated from plagioclase are between 928 to 1126 °C and water content are between 0.12 and 0.97 %. Crystallization temperatures calculated from clino-pyroxene minerals are between 921 and 1077 °C and the pressure values are between 0.24 and 3.62 kbar. In the light of these data, the parental magma(s) of the studied volcanics rocks were derived from an enriched lithospheric mantle source previously enriched by subduction related fluids and it reached the final composition with the effect of fractional crystallization and minor amount of magma mixing and crustal contamination.