Arc-type magmatism in middle part of the Sanandaj-Sirjan Zone (western Iran) and geochemical characteristics of the granitoids of this area

Granitoids of Aligoodarz, Dehno, Boroujerd and Alvand are located in the middle part of the Sanandaj-Sirjan Zone (SSZ), western Iran and intruded the regional metamorphic rocks. Granite, granodiorite and tonalite are the most abundant rock types. Comparison of chemical composition of Aligoodarz granitoids with those from other areas indicates that they are co-genetic and have petrogenetic relations. All of them show continuous trends on Harker variation diagrams and have similar chondrite-normalized multi elements patterns. Fractionation of biotite, amphibole, feldspar and Fe-Ti oxides had important effect on magma evolution and generation of different magma types. In contrast to other rock types, tonalites show relatively different chemical behavior. They have abundant amphibole and are similar to cumulative rocks. The granitoids in this study are similar to I-type granitoids generated in continental arcs. They have relatively the same age and are the result of intense magmatic activity during Middle Jurassic time in response to the subduction of Neotethys oceanic crust beneath Centeral Iran. Alvand granite has the slightly different composition. It is enriched in Cs, Cr, Rb, K2O and Th but depleted in Ca in comparison with other granitoids. All of these features indicate the role of sedimentary rocks in the petrogenesis of Alvand granite. Comparison of the rare earth elements abundances in SSZ granitoids with those from Andean rocks indicates magma generation at shallow crustal levels.