The Suphan stratovolcano is one of the major Quaternary eruption centers of post-collisional volcanism in eastern Anatolia, located in the zone of convergence between the Arabian and the Anatolian plates. We document the geological and geochemical evolution of Suphan in terms of volcanostratigraphy, geochronology (Ar-40-Ar-39), isotope composition (Sr, Nd, Pb) and bulk-rock geochemistry. Our new Ar-40-Ar-39 data, along with previously published K/Ar ages, indicate an age of 0 center dot 76-0 center dot 06 Ma for the eruptive products, which extend over an area of similar to 2000 km(2). The products of Suphan include transitional mildly alkaline to calc-alkaline lavas, domes and pyroclastic rocks ranging in composition from basalt to rhyolite. MELTS modeling suggests that the majority of the Suphan magmas with SiO2 contents between similar to 57 and similar to 65 wt % are the products of isobaric-isenthalpic mixing of basaltic trachyandesitic and rhyolitic magmas at a crustal pressure of 0 center dot 5 kbar. Energy-constrained assimilation and fractional crystallization modeling of trace element and isotope compositions points to 2-10% (upper) crustal contamination that accompanied differentiation. Large ion lithophile element enrichment and the presence of negative high field strength element anomalies in primitive mantle-normalized trace element patterns suggest a mantle source that was modified by subducted sediments. Light to heavy and medium to heavy rare earth element ratios and partial melting models suggest the derivation of the eastern Anatolian parental magmas from variable mixing of lithospheric and asthenospheric melts. Unlike the commonly accepted models for post-collisional volcanism that envisage an increasing contribution from asthenospheric melts with time, melting degree and contribution of the lithospheric mantle seem to have increased from Miocene-Pliocene to Quaternary times in eastern Anatolia.