In Taleghan, olivine basalt-basaltic andesite Dykes as part of Tertiary mamgmatic activities in central and western Alborz zone, intruded into both Karaj Formation and late Eocene-Oligocene volcanic rocks. These dykes have similar geochemical characteristic which suggest that they are originated from a common source. On the primitive mantle normalized spider diagram, the dykes are characterized by enrichment of LILEs and depletion of HFSEs. In general, these rocks show geochemical characteristics of volcanic rocks originated from partial melting of metasomatized lithospheric mantles in active continental margins. On the other hand, post collisional magmatism and anomalous thin continental crust beneath the Alborz zone confirm that extensional tectonic activities played a major role in this part of Iran. In this model, the subduction related magmas were produced by partial melting of a previously metasomatized lithospheric mantle source developed by percolation of fluid-melt released from subducted oceanic slab.