Study of mineral chemistry of biotite in Zargoli granitoid, Northwest of Zahedan

Zargoli granitoid is located in the northwest of Zahedan and south-east of Iran. This granitoid is composed mainly of granodiorite. Mineral chemistry of biotite was studied in granodioite rocks with the aid of EPMA and the results of this study were compared with the mineral chemistry data of biotite in Zahedan granitoids. Total amount of aluminum in comparison to Fe / (Fe Mg) ratio in biotites of Zargoli granodiorite indicates the presence of aluminous upper crust materials (metamorphosed sediments) in magma by digestion process. Total Al amounts of biotites of Zahedan granodiorite were lower than those of Zargoli granodiorite and it is indicative that the magma of Zahedan granodiorite is less contaminated by crustal rocks. The study of mineral chemistry of biotite determines that the studied granodiorites were I-type and composed of a calc-alkaline granitic magma. This magma climbed in a subduction environment and contaminated with sedimentary rocks of the upper crust. The chemistry study of biotite determines a relatively high oxygen fugacity (10-12 to 10-13 bar) and an oxidant conditions for granodioritic magmas studied. The amount of oxygen fugacity in the Zahedan granite magma is obtained from 10-14 to 10-15 bar which in fact represents a weak oxidizing condition in the Zahedan granite magma.