Mineral Chemistry and thermobarometry of biotite in Youseflo pluton,NW Iran

The Youseflo pluton, a part of Ahar - Arasbaran magmatic belt, is located in south east of Ahar city in north east of East Azarbayejan province of Iran. The pluton is mainly composed of quartz monzonite, granodiorite and granite, however, the major investigated rock is granodioritic in composition. Quartz, Plagioclase, biotite, amphibole, K-feldspar, chlorite, zircon, sphene, apatite and opaque minerals are the minerals of these rocks. Biotites, as a significant ferromagnesian mineral in Youseflo pluton, are Mg- rich, Cl-poor where all are primary types. Considering Fe/(Fe+Mg) (from 0.36 to 0.43) and Al IV (average 2.32 apfu), minerals are classified as biotite between Annite- siderophyllit endmembers. The study of mineral chemistry of biotites demonstrates that the calculated pressure based on total Al content in biotites varies from 0.19 to 0.89 kb which is indicative of a shallow emplacement depth. Crystallization temperature of biotites based on Ti content and Ti/Fe+2 ratio suggests an average temperature of 735 oC.