Based on our observation of a 3D thermal structure in NW Iran and the surrounding areas, which has been obtained using a Vs-T conversion technique, the lithospheric mantle in Zagros Folding and Thrust Belt is very stable and rigid. Such a rigid lithosphere continues to the border of the Urmieh-Dokhtar region; but below this region, Central Iran and western Alborz, the lithosphere stability and rigidity decrease. The lateral temperature variations at a depth of 100 km indicate that the South Caspian Basin and the Kura Depression, Talesh and the Lesser Caucasus have also a rigid and stable lithosphere; Also, it seems that below Sanandaj-Sirjan Zone and parts of Urmieh Lake there are some remnants of oceanic lithosphere after the closure of Neotethys and slab brake off. The lateral temperature variations at a depth of 200 km show some indications of lithospheric delamination beneath western Alborz, parts of central Iran and the Urmieh-Dokhtar region, as well as in Eastern Anatolian Accretionary Complex and parts of NW Iran, which can explain the lack of lithospheric mantle and/or volcanic activities associated with the upper mantle in these areas.