Precise dating of very young (≤10 000 yr) silicic volcanic rocks can be achieved by measurements of 230Th-238U disequilibria in accessory minerals such as apatite and zircon. It is illustrated here by the isochron age of 12 000 ± 1000 yr obtained on a trachyte from the Puy de Dôme (French Massif Central). The crystallization age is virtually the same as the eruption age determined by thermoluminescence and 14C dating. This indicates a short time interval (a few centuries at most) between crystallization and eruption in such small volume silicic magmas.

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