Voluminous Quaternary extrusive rocks, associated with widespread volcanic activities, occur in the northwestern Iran and across the Turkish-Iranian plateau. Field and petrographic studies reveal that these volcanic rocks, consisting of basalt to trachyandesite, occur as lava flows, columnar basalts, and cinder cones in three distinct areas of northern (Bazergan-Maku-Burlan), middle (Chalderan) and southern (Tazehshahr) regions. Sr and Nd isotope compositions show that the parental magmas to these rocks originated from subduction-modified lithospheric mantle source. However, the volcanic rocks from middle and southern areas are characterized by having higher abundances of incompatible element relative to those from northern area. The formers have also higher 87Sr/86Sr and lower 143Nd/144Nd ratios relative to the latter. These geochemical features, along with the field observations and petrography, indicate that the magmas for the middle and southern areas underwent some degrees of crustal contamination in their source region.