Investigation of petrographical and petrological characteristics of the Pamuktaş (Bayburt) pluton

The Eastern Pontides (NE Turkey) that formed during the Alpine-Himalayan orogeny in which geologically plays an important role in the formation of Anatolian Plate, is a significant area in term of containing different igneous rocks. Especially Carboniferous aged plutons are observed in the southern part of the eastern Pontides in larger outcrops and more commonly. This study presents new petrography and whole-rock geochemistry on granitic rocks in the Pamuktaş area of Bayburt (NE Turkey). In addition, the source region of tha magma, petrological processes and geodynamic setting prevailing in the formation of these granitic rocks are discussed. The Carboniferous aged Pamuktaş pluton, which includes an area of approximately 5 km2, represents the pre-Jurassic basement in the study area and is unconformably overlain by Early-Middle Jurassic volcanoclastic and volcanic rocks and Late Jurassic-Early Cretaceous limestones. Pamuktaş pluton mainly consists of granite/granite porphyry and aplite (microgranite), to a lesser extent granodiorite and quartz microdiorite rocks. Granitic rocks mainly consist of alkali feldspar (orthoclase), plagioclase feldspar, quartz, biotite, and amphibole (hornblende) minerals, as having euhedral and anhedral granular/microgranular textures. In some samples, larger phenocrysts form porphyritic texture. Zircon and apatite saturation temperatures were calculated between 693-844°C and 673-999°C, respectively. Granitic rocks have high SiO2 contents (65.62-75.09 wt.%) and a high K calc-alkali to shoshonitic affinities, and have been derived from an I-type source. The rocks are peralumine in character and are similar to post-collisional volcanic arc granitoids. Major and trace element trends show that the plagioclase, hornblende, apatite and Fe-Ti oxide mineral fractionations play an important role in the formation of rocks. According to the petrological properties of Pamuktaş pluton, it has been revealed that the fractional crystallization, magma mixing, and less assimilation and partial melting processes play a role in the development of granites. All obtained data suggest that the parental magma of the Carboniferous aged Pamuktaş pluton has evolved from the mixing of lithospheric mantle and middle-lower crust-derived melts as a result of partial melting and differentiated and emplaced in the continental magma chamber.