Original paper

Petrology of major granitic plutons of the northwestern part of the Sanandaj-Sirjan Metamorphic Belt, Zagros Orogen, Iran: with emphasis on A-type granitoids from the SE Saqqez area

Sepahi, Ali Asghar; Athari, Seyed Fakhraddin


Various types of granitic rocks occur in several plutonic complexes in the Sanandaj-Sirjan Metamorphic Belt (SSMB), Zagros Orogen, Iran including I-type, M-type, S-type and H-type granitoids. A-type granites are less abundant; their outcrops are seen in some localities such as Muteh, Almogholagh and Saqqez in the northwest of the SSMB. Radiometric dating has resulted in upper Jurassic to Tertiary ages for major plutonic bodies, especially for granitic rocks of the SSMB. These bodies indicate a magmatic suite generated in a continental arc setting followed by collisional and post-collisional magmatism. In the Saqqez area, there are two contrasting granitoid complexes (G1 and G2). G1 granitoids are peralkaline whereas G2 granitoids are subalkaline (calc-alkaline) and metaluminous. G1 granitoids are ferroan alkali and ferroan alkali-calcic but G2 granitoids are magnesian and calcic. G1 granitoids show agpaitic trends on Harker diagrams. They contain high concentrations of alkalis, Zr, Rb, Nb, Y, Ce, Th, high FeO/MgO ratios and low concentrations of Mg, Ca and Sr. According to tectonic discrimination diagrams, G1 granitoids plot into the field of within plate granites and G2 granitoids into the field of granitic rocks of volcanic arc setting. Considering petrographic and geochemical characteristics it seems likely that G1 granitoids are of A-type whereas G2 granitoids have similar properties to I-type granites. G1 granitoids of SE Saqqez resemble the A2 subtype of A-type granites, which are generated in a postorogenic/post-collisional setting.


a-type granitecalc-alkalinegranitoidi-type graniteiranmetaluminousperalkalines-type granitesanandaj-sirjan metamorphic beltsaqqez