Chaldoran area in NW of Iran has Mesozoic oceanic crust basement. The studied rocks of this region can be divided into three groups: ophiolitic gabbros and pillow lavas, ophiolitic volcanoclastics and Eocene lava flows. Ophiolitic mafic rocks show continental volcanic arc natures and Eocene lava flow shows OIB-like nature. During the Mesozoic,the Chaldoran region was situated in the active continental margin of the Iranian plate due to Neotetyhan subduction beneath the SSZ (Sanandaj-Sirjan Zone). As the Neo-Tethyan subduction regime changed, a rift in the Chaldoranareagenerated, which caused a continental back arc basin during the Upper Cretaceous. Along with spreading basin in the oceanic ridge, in the surface of new formed oceanic crust, some oceanic island were active and formed volcanoclastic rocks in the Chaldoran Oceanic crust. They were result of ascending continental arc nature plumes that formed in the sub-oceanic crust and up on Neo-Tethys subducted slab in the mantle wedge. After of finishing of spreading this basin in early time of Paleocene, sedimentation followed up to the Middle Eocene. In the Upper Eocene, alkaline and OIB-like volcanism was active in the Chaldoranareadue to breaking off the Neo-Tethyan subducted slab in the sub-oceanic crust of Chaldoran area and developed an asthenosphric window.