Abstract :
Salafchegan-Khorhe volcanic rocks are exposed within Urumieh-Dokhtar magmatic belt. Different kinds of volcanic and subvolcanic rocks of calc-alkaline to alkaline character have been reported throughout this magmatic belt. Since, isotopic investigations are very useful for detection of magma petrogenesis and because no isotopic studies have been done in this area, so a geochemical and isotopic study was carried out for Salafchegan igneous rocks, Sw of Tehran, in order to constrain their petrogenesis and confirm that parental magma in this area, is similar to calc-alkaline magmas related to continental margin arc environments.The igneous rocks dominantly consist of andesite, diorite, quartz-diorite, tonalite, dacite-rhyodacite and granodiorite porphyries with calc-alkaline affinity. Harker diagram indicates that amphibole, biotite and plagioclase have played an important role during the crystallization of Salafchegan igneous rocks and proves the effect of fractional crystallization during magmatic evolution. These rocks are characterized by enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE) and depletion of HREE and HFSE and negative anomalies of Nb, Ti, Zr and P that indicated the formation of rocks in a subduction zone of active continental margin. The 87Sr/86Sr and 143Nd/144Nd isotopic ratios of the studied rocks are from 0.705201 to 0.707187 and 0.512508 to 0.512646 respectively. All of these samples are characterized by negative ?Nd values which can show the role of crustal contamination in their petrogenesis and also suggest the enrichment of the lithospheric mantle beneath this orogenic belt. The geochemical and Nd-Sr isotopic data demonstrate that fractional crystallization and assimilation have played an important role in magmatic evolution of this region.
