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Zircon typology and chemistry of the granitoids from central anatolia, Turkey

Köksal, Serhat
This thesis investigates the morphological, chemical and growth characteristics of zircon mineral in relation with the granitoid petrology. Physical and chemical variations recorded within zircon crystals during evolution of the Central Anatolian Granitoids are discussed. The thesis focuses on twelve granitoid samples from the Ekecikdag, Agaçören and Terlemez regions from western part of central Anatolia. These granitoids are differentiated into S- and H-type granitoids on the basis of field, petrographical and whole-rock geochemical aspects. In granitoids concerned, zircon is associated with biotite, allanite and plagioclase, and zircon populations mainly comprise P- and S-type zircon crystals, with rare G-, L- and J-types. Typology method combined with cathodoluminescence imaging revealed that S- and H-type granitoids show intrusive aluminous autochthonous and hybrid character, respectively. Zircons generally have euhedral to subhedral cores exhibiting zoning, although sometimes faint, but inherent and embayed cores also exist. Large scale, first order, and/or small-scale second order oscillatory zoning and effects of late stage recrystallization are observed within zircon crystals. Multi-corrosion zones within zircons are characterized by sharp changes in crystal forms with decreased Zr and Si, and increased U, Th and REE+Y contents, beside infrequent increase in Hf, Sc, Ta, Ti, Ca, Al and Fe elements. These zones are interpreted to be formed by transient heating of the resident felsic magma due to mafic melt contribution, at the time of mixing/mingling processes of the H-type granitoids, and then zircons re-grow in magma source reflecting a mafic character. Corrosion stages within zircons of S-type granitoids, on the other hand, were probably formed by mantle-derived melts producing heat for resorption of zircons without direct contribution.