Volume 18, Issue 47 (4-2007)
Abstract
Major cations, Fe, Mg and Al, in biotite are sensitive to magmatic processes and biotite chemistry could be used for petrogenetic investigation of granitioids. In this research composition of biotite from Boroujerd granitoids in Sanandaj-Sirjan Zone has been investigated in order to study its geochemical nature and petrogenesis. Separated biotites were analyzed by WDXRF and biotites in polished thin section were analyzed by EPMA. Samples were selected from Older granites (120 Ma) and Younger granites (60-70 Ma) after intensive petrographic examinations. Data from both techniques are in good agreement and discriminate two generation of granites clearly. Based on Mg, Mn, Fe3+, Fe2+, Ti and Al biotites in Younger granite incorporated more Mg than those in Older granites. The main differences between biotites in two generation of granites are amount of total Al and Fe/Fe+Mg ratio. Biotites in granodiorite and quartz diorite of Younger age are annite-phlogopite with 2.48-2.74 Al per formula unit, and Fe/Fe+Mg ratio of 0.375-0.600. Biotites from Older granites are annite-sidrophyllite with 2.76-3.69 and Fe/Fe+Mg ratio of 0.597-0.720. Composition of biotites indicates that two generation of granites formed under different oxygen fugacity and both are calcalkaline and shows I and S characteristics respectively.
