Nature of Beypazari Granitoid: Geology and geochemistry, Northwest Anatolia, Turkey

Abstract

Beypazari Granitoid represents one of the widest exposure bodies within the Sakarya continent. It has several exposure bodies at Beypazari, Oymaagac, Tahir, Kirbasi and Yalnizcam of Eskisehir city. Although Beypazari Granitoid has several independence outcrops, the field geology and the aeromagnetic anomaly reveal that they are a unique body at the lower part of the crust. Field observations, mineralogical and petrographical investigations reveal that Beypazari Granitoid is composed of five different units these are monzonite, quartz monzonite, granodiorite, granite and alkali feldspar granite. Alkali feldspar granite cuts all the other subunits in the form of aplitic dyke. All the other subunits have gradual contact with the each other. Excluding alkali feldspar granite mafic enclaves are observed within the other 4 subunits as angular and elliptical in shape and changing from mm up to 20 cm in size. These enclaves can be divided genetically into three different types according to the field observation, textural features and mineralogical compositions. The first type has igneous texture, sharp contact with host rock, rimmed by fine crystalline mafic minerals and represents the abundant enclave type within the monzonite, quartz monzonite, granodiorite and granite as elliptical to sub-angular in shape. These enclaves mostly have subophitic texture in the composition of diorite, quartz diorite and monzodiorite. Ocellar quartz, acicular apatite, poiclitic feldspars and blade shaped biotite are the most characteristic features of the first type of these enclaves, which may represent the magma mixing/mingling enclaves in origin. The second type of these enclaves has a cumulate texture and is representing a segregation of early crystallization processes of mafic minerals. The second type of these enclaves is the product of the early crystallization of magmatic differentiation and is forming the magma segregation enclave types. The third type of the enclaves have metamorphic texture with clear metamorphic lineation, sharp contact with host rock and mostly observed at the northwest part of Kirbasi and Tahir region in the form of xenolithic enclaves. They have angular to sub-angular in shape. These types of the enclaves have hornfels in composition at the contact with the host rock as a product of contact metamorphism and amphibolites in composition at the core as a product of high temperature and middle pressure metamorphism. The textural features and mineral composition of the third type of the enclaves may indicate a fragment of metapelitic rocks, which caught by the granitoid magma in the form of xenolithic enclaves. Whole rock geochemistry reveals that Beypazari granitoids are subalkaline and calcalkaline in nature. They are enriched in Light-REE and LIL with respect to High-REE and HFS elements. Tectonic discrimination diagrams of Beypazari granitoid suggest a product of plate convergence and probably belong to Volcanic Arc Granitoid (VAG). The field observations, mineralogy, petrography with the whole geochemical data reveal that the Beypazari Granitoid magmas are derived from a subduction-modified magma and metasomatized mantle source with considerable crustal contribution.