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Volume 9, Issue 2 (10-2010)
Abstract
Intrusions between Arak and Borujerd in northern Sanandaj Sirjan zone are present different field and lithology. Three different groups: (a) the Astaneh intrusion, (b) the Borujerd complex, and (c), Tavandasht-Gosheh intrusions can be identified. First attempt to date these intrusions began with K-Ar method and obtained ages were about 60Ma based on studies on Alvand in Hamadan. Further Rb-Sr dating, published older ages and revealed two phases 60Ma and -120Ma for Borujerd complex and 100Ma for Astaneh intrusion. Following dating based on zircon, established the age of 170Ma for all unites. In order to cover gaps in data, we have undertaken MS U-Pb zircon geochronological studies for selected granitoids. Results confirm the presence of granitoids with 170Ma in Astaneh and Borujerd complex. But, for first time, the young age of 34.8Ma initiated for Tavandasht intrusions. It could be concluded that emplacements of plutons in this part of Sanandaj Sirjan began in Mid Jurassic (Bathonian stage) and last phase was on Late Eocene (Priabonian stage). However, based on the presence of field and geochemical differences between intrusions, more study needs to find the interval phases. Emplacement of these intrusions are related to calk alkaline subduction of Arabian plate with Central Iran plate, and obtained data, could assist on timing of offered tectonomagmatic models.
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.
