Petrographical, geochemical and petrological investigation of the Arslandede (Bayburt) granitoid and their mafic magmatic enclaves

In this study, mineralogical-petrographical composition and their mafik magmatik enclaves and whole-rock geochemical characteristics of Arslandede Granitoid in the Arslandede (Bayburt) area were determined, and the evolution and origin 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 and pyroclastics. This unit are cut by the Eocene Arslandede Granitoid and are overlie uncorformably by Quaternary alluvium. The granitoid rocks are fine to medium grained, and composed of plagioclase, ortoclase, quartz, hornblende, biotite, clinopyroxene, apatite, zircon and opaque minerals. The Arslandede Granitoid surfaces are elipse shaped, and settled approximately in an area of 24 km2. It consists of monzogabbro, monzodiorite, monzonite, quartz monzonite ve granite in composition. The Arslandede Granitoid shows disequilibrium textures showing magma mixing. Mafic microgranular enclaves (MMEs) are observed in the Arslandede Granitoid. Although enclaves are finer granular and darker coloured than their host rocks, they aslo show similar mineralogic, petrographic and geochemical properties. MMEs are composed of diorite and monzodiorite, and are observed in the monzonite and monzogranite composed host rocks. The Arslandede granitoid is generally I-type, high-K to shoshonitic characters, and has high SiO2(% 49.49-71.21) contents. The rocks have metalüminous characters and enriched in large ion lithofile elements. Chondrite normalized REE patterns are concave shaped (LaN/YbN=7.11-11.57), and show negative Eu-anomalies (EuN/Eu*=0.37-0.91). Major and trace element variations indicate significant role of plagioclase, hornblende and Fe-Ti oxide fractionation during the evolution of rocks. The compositions of the MMEs change from medium to strong metaluminous (A/CNK=0.75-0.90) and they have lower A/CNK and SiO2 (53.93-58.83 wt.%) and higher Na2O/K2O (1.42-2.27) ratios than the host rocks. When SiO2 values are compared with major oxide and trace element contents, MMEs show a correlation with their hosts. Rocks are enriched in LILE, LREE and HREE, and depleted in HFSE (Nb, Ti) and show a concordant trend with MMEs. Considering all of the similarities between host rocks and MMEs, MMEs are accepted as magma mixing (mixing/magma mingling) products that are small bodies of the similarly aged mafic magma and solidify in the host rock. The calculated values of apatite and zirconcrystallization temperatures, the plutons and MMEs in them are nearly the same value, and range between 671 to 836 °C in the host rocks and 647 to 836 °C in MMEs. Petrographical and geochemical features indicate that the Arslandede Granitoid were produced by the partial melting of lithospheric mantle, with minor contribution from the crustal rocks.