Late Miocene ultrapotassic rocks are widely exposed in the Saray Peninsula of northwestern Iran. These rocks are mainly classified as tephrite-tephritic phonolite with some trachyte and lamprophyre dikes with porphyritic textures. Ca-rich pyroxene and leucite are the main phenocrysts. Olivine and phlogopite with some sodic am- phiboles occur locally as phenocrysts. Chemically, the rocks are characterized by low contents of SiO2 (45.4–47.3 wt%), with high contents of K2O (3.4–6.6 wt%), K2O/Na2O (1.2–5.7), MgO (5.6–9.1 wt%), CaO (10.3–12.7 wt%) and Sr (826–2020 ppm) with low P2O5/Al2O3 (0.08–0.14). Chondrite normalized REE and primitive mantle-normalized patterns indicate the involvement of a LREE (La, Ce) and LILE (Cs, Ba, Pb) enriched mantle, and weak negative Ti-Nb-Ta anomalies are observed. Isotopically, the rocks show high 87Sr/86Sr ratios (0.7071–0.7084) and low εNd(t) values (–3.8 to –1.8). Their δ13C values show a variation from –13.4 ‰ to –6.5 ‰, confirming some organic carbon recycling in the subduction zone, and the absence of Ce/Ce* and Eu/Eu* negative anomalies confirm the redox system melting. The Sr– Nd isotopic values, higher contents of incom- patible elements, and lower δ13C values suggest a continental crustal material involvement for the sources of these rocks. The presence of calcite in the matrix, the inclusion of melt droplets with some calcite, and the carbonation of leucite and pyroxene grains confirm the high CO2 content during magmatic evolution and/or the late stages of reaction of CO2-fluid rocks with earlier minerals. Due to the situation of the Saray ultrapotassic rocks near the junction of the Van microplate and the NW Iran block, dragging of the Van microplate beneath NW Iran is likely to have transported some carbonate rocks and biogenetic organic carbon into the mantle and converted the primitive mantle to carbonate peridotite. A very low rate of partial melting at a pressure of less than 3 GPa around the garnet-spinel stable zone produced ultrapotassic melts. The correlation with some neighboring ultrapotassic rocks shows that this process is a dominant factor to generate the kamafugite and/or interval of kamafugite-Roman type ultrapotassic series in a collision system, without considering the role of mantle phlogopite present in the deep metasomatized mantle. This work shows why most of the ultrapotassic rocks in Iran have developed near the suture zone after the closure of Neotethys.
