Miocene to Pleistocene calc-alkaline volcanism in the East Carpathian arc of Romania was related to the subduction of a small ocean basin beneath the continental Tisza–Dacia microlate. Volcanic products are predominantly andesitic to dadtic in composition, with rare basalts and rhyodacites (51–l71% SiO₂; mg-number 0.65–0.26) and have medium- to high-K calcalkaline and shoshonitic affinities. Mg, Cr and Ni are low in all rock-types, indicating the absence of primary erupted compositions. Detailed trace element and Sr, Nd, Pb and 0 isotope data suggest that magmas were strongly crustally contaminated. Assimilation and fractional crystallization (AFC) calculations predict the consumption of 5–35% local upper-crustal metasediments or sediments from the palaeo-accretionary wedge. Variations in the isotopic composition of the contaminants and parental magmas caused variations in the mixing trajectories in different parts of the arc The most primitive isotopic compositions are found in low-K dacites of the northern Cdlimani volcanic centre and are interpreted as largely mantle derived. A second possible mantle reservoir of lower ¹⁴⁹ Nd/¹⁴⁴ Nd and lower ²⁰⁶ Pb/²⁰⁴ Pb is identified from back-arc basic calc-alkaline rocks in the south of the arc Both magmatic reservoirs have elevated isotopic characteristics, owing either to source bulk mixing (between depleted or enriched asthenosphere and <1% average subducted local sediment) or lower-crustal contamination.