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

Abstract

It has been demonstrated for several years that the UPb zircon system can provide useful dating information for understanding the time-evolution of the volcanic systems. In addition, in situ techniques were successfully used for determining the formation age of young Pliocene and Pleistocene volcanic rocks and to record the spatial and temporal distribution and the lifetime evolution of the magma chambers, generally in the case of large volcanic domains.Here we show that it is possible to obtain a precision at the percent level on zircon from a short-size and late volcanic event from the Sancy stratovolcano (French Massif Central). LA-ICP-MS dating of Pleistocene magmatic zircons allow to distinguish the timescale of these late magmatic events within the complex volcanic activity of this large stratovolcano. A syenite xenolith enclosed into a trachyte pumice flow were dated at 277.6 ± 3.2 ka and 260.1 ± 3.6 ka, respectively, whereas an earlier trachyandesite dome was emplaced at 284.4 ± 4.2 ka. These different ages allow to propose a minimum evolution time of about 24 ± 8 kyrs for a differentiated magma chamber, which corresponds to a short lifetime associated with low magma volumes. The duration of this discrete volcanic event 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.