Petrography, mineral chemistry and crystallization conditions of cenozoic plutonic rocks located to the north of Bayburt (Eastern Pontides, Turkey)

Abstract

The Eastern Pontides comprise many intrusive bodies varying in composition, size and age from Palaeozoic to Cenozoic. Especially Cenozoic aged bodies are commonly observed in the southern part, while they are rarely exposed in the northern part of the Eastern Pontides. In this study, the petrography and mineral chemistry of the Cenozoic aged Cicekli, Somarova, Sorkunlu, Sasurluk, Aydintepe, Kemerlikdagi and Pelitli plutons located to the north of Bayburt are determined, and the crystallisation conditions of the studied bodies were estimated by means of thermobarometer calculations. The studied plutons extend mostly in NE-SW directions and are approximately ellipsoid in shape. The contacts between the plutons and surrounding rocks are sharp, and plutons commonly contain mafic microgranular enclaves (MMEs) of different sizes. Petrographic and mineral chemistry studies reveal some disequilibrium textures reflecting the magma mixing process. Based on modal mineralogy, the plutonic rocks are gabbroic diorite, diorite, tonalite, granodiorite and monzogranite in composition. The rocks have fine to medium granular, porphyric, monzonitic, poikilitic, occasionally myrmekitic and micrographic textures. The main minerals are labradorite and albite (An(68-02)), magnesiohornblende and actinolite (Mg# = 0.6-0.9), diopside and augite (Wo(44-46)), clinoenstatite (En(53-57)) and Fe-Ti oxide minerals. Crystallization temperatures calculated from amphibole, biotite, clinopyroxene, magnetite and ilmenite minerals are 405 degrees C to 1161 degrees C, pressure values are 0.1 to 2.7 kbar, and oxygen fugacity (log10 fO(2)) is -20 to -12. Estimation of water content calculated by using amphiboles is between 2.9 and 6.8%. Based on obtained data, it is suggested that the studied plutons were emplaced at shallow depths (similar to 1-8 km).