Geochemical and Isotopic Constraints on Petrogenesis of the Beypazari Granitoid, NW Ankara, Western Central Anatolia, Turkey

The Upper Cretaceous Beypazari granitoid of the western Ankara, Turkey, is composed of two different units, on the basis of petrography and geochemical composition; these are granodiorite and diorite. The granitoid is subalkaline, belonging to the high-K calc-alkaline I-type granite series, which have relatively low initial Sr-87/Sr-86 ratios (0.7053-0.7070). All these characteristics, combined with major, trace element geochemical data as well as mineralogical and textural evidence, reveal that the Beypazari granitoid formed in a volcanic arc setting and was derived from a subduction-modified and metasomatized mantle-sourced magma, with its crustal and mantle components contaminated by interaction with the upper crust. The rocks have epsilon Nd-(75Ma) values ranging from -5.5 to -2.0. These characteristics also indicate that a crustal component played a very important role in their petrogenesis