LA-ICP-MS U/Pb zircon timescale constraints of the Pleistocene latest magmatic activity in the Sancy stratovolcano (French Massif Central)

Co-auteur étrangerInternational audienceIt has been demonstrated for several years that theU\\Pb zircon systemcan provide useful dating information forunderstanding the time-evolution of the volcanic systems. In addition, in situ techniques were successfully usedfor determining the formation age of young Pliocene and Pleistocene volcanic rocks and to record the spatial andtemporal distribution and the lifetime evolution of the magma chambers, generally in the case of large volcanicdomains.Herewe showthat it is possible to obtain a precision at the percent level on zircon froma short-size and late volcanicevent from the Sancy stratovolcano (FrenchMassif Central). LA-ICP-MS dating of Pleistocenemagmatic zirconsallowto distinguish the timescale of these latemagmatic eventswithin the complex volcanic activity of thislarge stratovolcano. A syenite xenolith enclosed into a trachyte pumice flow were dated at 277.6 ± 3.2 ka and260.1±3.6 ka, respectively,whereas an earlier trachyandesite dome was emplaced at 284.4±4.2 ka. These differentages allowto propose aminimumevolution time of about 24±8 kyrs for a differentiatedmagma chamber,which corresponds to a short lifetime associated with lowmagma volumes. The duration of this discrete volcanicevent should be compared to the hundreds of thousands of years reported for the large volcanic systems. Interestingly,the zircon crystals from the pumices were embedded into a thin layer of glass of trachytic composition,demonstrating that these zircons crystallized into the melt only a short time before eruption