Abstract <p>The Paleogene back-arc basin tectonic evolution of NW Iran is closely related to the tectonic activities in the Lesser Caucasus and neighboring region. During this period, the region experienced significant tectonic, magmatic and metamorphic activities, including the formation of ortho-amphibolites. Amphibolites from NW Iran are located between three main suture zones: (i) the Sevan-Akera suture zone in Armenia, (ii) the Bitlis-Zagros suture zone in Türkiye, and (iii) the Zagros suture zone in Iran. They are spatially associated with various magmatic intrusions of the Shahjahan batholith. These amphibolites have an igneous protolith, primarily consisting of plagioclase and hornblende as the main mineral phases, along with rutile and opaque minerals as accessory phases. Based on whole rock, major, and trace element geochemistry, the protolith of the amphibolites formed from a sub-alkaline basalt to andesite basalt magma with tholeiitic affinity. This magma originated from high partial melting (more than 10%) of a mantle source with a spinel lherzolite to spinel-garnet lherzolite composition. The rocks lack negative Ti, Nb, and Ta anomalies in the spider diagrams normalized to NMORB and chondrite and are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) such as Rb, Sr, U, Th, and Cs, rather than heavy rare earth elements (HREE) and high field strength elements (HFSE). These geochemical features indicate a sialic back-arc basin tectonic setting. Amphibole in these rocks is metamorphic and edenitic, while plagioclase is andesine. The <i>P‒T</i> estimation of metamorphism indicates <i>T</i> = ~697‒778°C and <i>P = ~</i>3.5‒5.5 kbar, correlating with low-pressure‒high-temperature (LP‒HT) metamorphic facies, suggesting their formation at shallow crustal depths. The studied amphibolites formed due to the closure of the back-arc basin during the Paleocene‒Eocene.</p>