The bimodal Piranshahr massif is composed of coeval but geochemically unrelated mafic (40.7 ± 0.2 Ma zircon U–Pb sensitive high-resolution ion microprobe (SHRIMP) age) and A-type felsic rocks (41 ± 0.5 Ma Rb–Sr and 41.3 ± 0.8 Ma zircon U–Pb SHRIMP age). The mafic rocks consist of two geochemical types of gabbros that derived from different magmas. The more abundant gabbros are moderately alkaline, have ratios of large ion lithophile elements to REE and high field strength elements to REE similar to those of intraplate mantle magmas, 87 Sr/ 86 Sr 41 Ma ≈ 0.7036 and ε(Nd) 41 Ma ≈ +7.2. The less abundant gabbros have calc-alkaline affinities, 87 Sr/ 86 Sr 41 Ma ≈ 0.7043 and ε(Nd) 41 Ma ≈ +4.78. Felsic rocks are metaluminous A2-type annite–fayalite–hedenbergite, hypersolvus, leucocratic, coarse-grained agpaitic syenites, pulaskites and granites, with 87 Sr/ 86 Sr 41 Ma ≈ 0.7048 and ε(Nd) 41 Ma ≈ +3.6–4.5. Syenites, pulaskites and granites are genetically related. Pulaskites probably represent alkali-enriched water-rich residual melts from which an F-rich vapour phase was later separated. Granites were probably generated during open-system processes, in which F-rich hydrous alkaline fluids released from the syenites acted upon pre-existing felsic rocks. The c . 41 Ma age of the post-collisional Piranshahr massif indicates that the related collision probably occurred at 50–60 Ma (i.e. Late Palaeocene or Early Eocene), thus resolving a much debated question.

The granitic unit is a component of the Naqadeh plutonic complex, NW of Sanandaj-Sirjan Zone (NW Iran). This unit is composed of high-K calc-alkaline, slightly peraluminous (ASI=1.12-1.17) evolved monzogranites. These monzogranites have 41.85±0.81 Ma (zircon U-Pb sensitive, high-resolution ion microprobe (SHRIMP) age) with two inherited zircon ages of 98.5±1.7 and 586.6± 13.1 Ma, respectively. The only enclave type consists of quartz-amphibolite enclaves indicating residual parental rocks. Chemical and isotopic ( 87 Sr/ 86 Sr 40Ma =0.708638; εNd 40Ma =−4.26) characteristics of monzogranites suggest that they could be derived by partial melting of crustal mafic rocks followed by some assimilation of metasedimentary rocks. With regards to inherited zircon age and quartz-amphibolite composition of Naqadeh granite, the old mafic rocks of this complex (Naqadeh dioritic rocks with 100 Ma) can be considered as parental rocks, and their partial melting under high water content, and assimilation of produced melt by metasedimentary rocks, would lead to the generation of a Naqadeh granitic unit.

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