The Rahjerd intrusive pluton, located southwest of Qom, constitutes a part of the Urmia-Dokhtar magmatic belt. This pluton comprises gabbro, gabbro-diorite and diorite, predominantly characterized by a granular texture. The primary mineral assemblages consist of plagioclase, pyroxene, and amphibole. The amphiboles are identified as magnesio-hornblende and the pyroxenes as diopside.
The studied intrusive rocks exhibit a subalkaline (calc-alkaline) nature, characterized by significant enrichment in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) relative to heavy rare earth elements (HREEs) and high field strength elements (HFSE). This enrichment pattern is a diagnostic feature of volcanic arc magmatism in continental margin subduction zones, reflecting the mobilization of slab-derived fluids into the magma. Tectonic setting diagrams confirm that these rocks are situated within an active continental margin volcanic arc. Geochemical evidence suggests that the magmas were generated from a mantle- crust source. This is supported by positive anomalies in incompatible elements (U, La, Th, Ba, Rb, and K), a negative Eu anomaly accompanied by a relatively flat HREE pattern, and depleted Ti and P concentrations. Collectively, these geochemical signatures indicate the significant involvement of middle-to-lower crustal melts during magma formation. Consequently, a hybrid origin involving both mantle and crustal components is proposed for the formation of this intrusive pluton.