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

E Namnabat, M Ghorbani, SH Tabatabaei
Volume 29 Issue 115 Pages 87-96 Publisher GEOSCIENCES
Description: The Youseflo pluton, a part of Ahar-Arasbaran magmatic belt, is located in south east of Ahar city, north-east of East Azarbaiejan Province of Iran. The constituents of this pluton are mainly quartz monzonite, granodiorite and granite, nevertheless, the major studied rock is granodiorite. The pluton mineralogically includes quartz, plagioclase, biotite, amphibole, K-feldspar, chlorite, zircon, sphene, apatite and opaque minerals. Biotites, as a significant ferromagnesian mineral in Youseflo pluton, are Mg-rich, Cl-poor all of which are primary type. Considering Fe/(Fe+ Mg)(from 0. 37 to 0. 43) and Al IV (average 2. 32 apfu), minerals are classified as biotite between Annite-siderophyllit endmembers. The study of biotites’ mineral chemistry indicates 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 depth emplacement. Crystallization temperature of biotites based on Ti content and Ti/Fe+ 2 ratio suggests an average temperature of 749 oC. According to MgO, Al2O3, FeO in biotites, magmatic series of the host rocks display calc-alkaline orogenic nature. The study of biotites shows fairly high oxygen fugacities (ranged from10-10 to 10-12 bars) and oxidizing conditions. Consequently, the Youseflo pluton is classified as the magnetite series granitoids. The Yousflo pluton is an I-type granite, originated from a mixed mantle-crust source.

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