Petrographic features of Late Cretaceous biotite granites in the Kurtoğlu region (Elazığ/Turkey)

Abstract

The study area is located in a local area around Kurtoğlu village of Elazığ province, located within the Southeast Anatolian Orogenic Belt. The studied biotite granites belong to the Elazig Magmatic Complex. The Elazığ Magmatic Complex is grouped into volcanic, sub-volcanic and plutonic rocks and mafic and felsic. Felsic rocks belonging to the Elazığ Magmatic Complex are represented by granite, granodiorite, tonalite, quartz monzonite, monzodiorite, and mafic rocks are represented by diorite, quartz diorite and gabbros. The biotite granites are porphyric biotite minerals with an average size of one cm. Petrographically, they are composed of K-feldspar, plagioclase, quartz, biotite and opaque minerals. K-feldspars have low birefringence colours, grey tones, and earthy colours in single nicol. Plagioclases; anhedral, euhedral and mostly subhedral crystals. They typically indicate albite, albite+karlsbad and polysynthetic twinning. In some samples, sericitization and carbonation are observed mostly in the middle parts of the plagioclase resulting from alteration.  Biotites; It is generally in the form of subhedral platy-prismatic, rod-like crystals. Pleochroism is seen in brown tones in single nicol. It has high birefringence colours and indicates vivid interference colours in yellowish, blue and green, especially brown tones in double nicol.  Porphyritic texture in which phenocryst and smaller crystals are generally observed in granites.