Petrographical, geochemical and petrological investigation of the Cakirbag (Bayburt) granitoid

In this study, mineralogical-petrographical characteristics, mineral chemistry and whole-rock geochemical characteristics of Çakırbağ Granitoid in the Çakırbağ (Bayburt) area were determined, and the origin and evolution of plutonic rocks were investigated. The studied area located on the southern zone in the eastern Pontide. The basement is represented by Eocene aged andesite, basalt and pyroclastics. This unit are cut by the Eocene Çakırbağ Granitoid and, are overlie uncorformably by Quaternary alluvium. The Çakırbağ Granitoid is elipse shaped, and settled approximately in an area of 9 km2. It consists of monzonite and quartz monzonite, and shows disequilibrium textures showing magma mixing. The granitoid rocks are fine to medium grained, and composed of plagioclase, orthoclase, quartz, pyroxene, hornblende, biotite, apatite, zircon and opaque minerals. Plagioclases in the Çakırbağ Granitoid rocks are in the composition of An47-21. K-feldspar are in the composition of Or78-65. Magnesium numbers belonging to biotites change between 0.6 and 0.7. Pyroxenes are diopsite and augite in composition, and magnesium numbers are between 0.73 and 0.76. The Çakırbağ granitoid is generally I-type, high-K and shoshonitic characters, and has high SiO2 (56-63 wt.%) contents. The samples have metalüminous character and enriched in large ion lithophile elements. Chondrite normalized REE patterns are concave shaped (LaN/YbN=8.96-11.26), and show negative Eu-anomalies (EuN/Eu*=0.50-0.76). Major and trace element variations indicate significant role of plagioclase, hornblende and Fe-Ti oxide fractionation during the evolution of the granitoidic rocks. All these features indicate that the Çakırbağ Granitoid were produced by the partial melting of lithospheric mantle, with minor contribution from the crustal rocks.