Colli Albani is a quiescent caldera complex located within the Roman Magmatic Province, Italy. The recent Via dei Laghi phreatomagmatic eruptions led to the formation of nested maars. Albano Maar is the largest and has erupted seven times between ca 69-33 ka. Albano maar magmas are silica-undersaturated and alkali-rich (K2O ≈ 9 wt%) and the highly explosive nature of the eruptions is at odds with the predominant relatively mafic (48-52 wt%) foiditic magmatic composition. The deposits have been previously interpreted as phreatomagmatic, however they contain large amounts (up to 30 %vol) of deep seated xenoliths, skarns and all pre-volcanic subsurface units which have been excavated from depths of up to 6 km, rather than being limited to the depth at which magma and water interaction is likely to have occurred. This suggests an alternative trigger for eruption. High precision geochemical glass and mineral data of fresh juvenile (magmatic) clasts from the small volume explosive deposits indicate that the Albano Maar magmatic system have evolved along one of two evolutionary paths towards foidite or phonolite. The foiditic melts record ca. 50% mixing between the most primitive magma and Ca-rich melt late stage prior to eruption. A major result of our study is that the generation of Ca-rich melts via assimilation of limestone may provide storage for significant amounts of CO2 that can be released during this mixing event. Differences in melt evolution are inferred to be controlled by variations in storage conditions: residence time and magma volume.