The residence time of crystals in magmatic systems is an essential parameter to depict the dynamics of these systems and to evaluate the temporal representativeness of the mineral data used to document the physical conditions in the magmas. Uranium-series disequilibria in mineral separates from young volcanic rocks with a known eruption date provide unique insights on these residence times. We present 238U-230Th-226Ra measurements for plagioclase separates and groundmass from magmas erupted at Volcán de Colima, Mexico in 2004 and 2007. The (230Th/232Th) activity ratios in plagioclases show limited variations within the range measured in groundmasses and previously documented in whole rocks. (230Th/232Th) and (238U/232Th) activity ratios in plagioclases are predominantly controlled by glass present as inclusions in the crystals or adhering on their rims, even in high purity crystal separates with less than 2% of glass. Variations in these activity ratios are best explained by crustal assimilation during crystallization and do not require aging of the crystals. One plagioclase separate with very limited contamination by glass impurities has a demonstrable zero 230Th-238U crystal age. Precise 226Ra-230Th model ages are difficult to obtain due to the strong influences of uncertainties in the partition coefficients, the temperature of crystallization and the correction for glass impurities in crystal separates. Nevertheless, if these uncertainties are taken into account, 226Ra-230Th model ages in the range 0 to 2000 yrs are obtained for the plagioclases separates. More complex models elaborated on the basis of the compositional zoning observed in plagioclase phenocrysts suggest that the cores of the crystals are at most 8500 yrs old. Overall, these results indicate that the plagioclase phenocrysts are relatively young and not sourced from a long-lived near-solidus crystal mush as often suggested for arc volcanoes. A more dynamic system in which crystallization predominantly occurs in response to degassing during ascent of the melts is conceivable at Volcán de Colima.