The Pasinler Plateau, located to the western part of the Erzurum-Kars Plateau, contains one of the best sections through the collision-related volcanic sequence in North-eastern Anatolia. Highly-evolved pyroclastic products of rhyolitic composition are intercalated with minor amount of olivine-bearing basic to intermediate lava flows on this plateau. These pyroclastic deposits consist entirely of vitrous, crystal-free, aphyric textured pyroclastic flows, falls and surges. They display a rather narrow compositional range from high-silica rhyo-lites to rhyodaciles. Trace element fractionation trends suggest that these felsic and basic btmodal products were generated from the same parental magma by means of fractional crystallisation of POAM (anhydrous) minerals and hence they should have evolved in the same magma chamber. K/Ar radiometric age determination of a sample from the base of the sequence indicates that volcanism on the plateau initiated about 7.8 Ma. Al-in-amphibole geobarometry, on the other hand, implies that the magma chamber which fed the volcanism on the plateau was lo¬cated around a depth of 11-13 km. Modelling of Rayleigh fractionation vectors especially those of Sr, Ba, Sc and Ni indicate that the basic magma in this chamber fractionated a mineral assemblage consisting of plagioclase, cli-no-pyroxene and olivine until SiCb of the melt reached 65-67% at which the temperature decreased down to 700-800°C. From this point onwards, fractionation of alkali-feldspar together with plagioclase dominated the crystallising phase. It appears that this phenocryst phase was separated from the melt via infiltration and following zonation and consequently produced crystal-free high-silica magma.