This study is concerned with volcanostratigraphic and petrologic evolution of the S&uuml / phan, which is a 4050 m high Quaternary stratovolcano in eastern Anatolia. The eruptive products of S&uuml / phan Stratovolcano, including transitional mildly alkaline to calc-alkaline rocks, are lavas, domes and pyroclastics ranging in composition from basalts to rhyolites. Ar-Ar age data from different levels of the volcanostratigrafic succession yield a range of 0.76-0.06 Ma. Textural features, wide temperature ranges obtained for intermediate members, and the linear trends of whole-rock geochemistry are strongly suggestive of magma mixing in the evolution of S&uuml / phan volcanics. Presence of crystal clots in many lavas suggests that cogenetic plutonic rocks were also involved in the mixing process. Comparison of whole-rock, melt inclusion and glass chemistry data of S&uuml / phan to data from experimental studies reported in literature indicate that the melt inclusions describe true liquid lines of descent from a common hydrous parent at pressures of ~500 MPa. EC-AFC modeling of trace element and isotopic compositions reveals 2-8% crustal contamination in the differentiated lavas. REE modeling indicates that primitive rocks of S&uuml / phan volcanics were products of mixing of melts from spinel and garnet lherzolite sources, with contributions of 60% and 40%, respectively, in the mixture. A two-stage petrogenetic model is proposed for Suphan stratovolcano. Mantle- derived melts stall and undergo chemical differentiation in a deep hot zone in lower to mid-crust / variably evolved melts ascending from this zone are arrested and mixed at a shallow level where they construct a sub-volcanic magma reservoir beneath Suphan.