Insights into magma reactivation times prior to a catastrophic highly explosive event: the Campanian Ignimbrite eruption (Campi Flegrei, Italy)

Timing and dynamic processes forming eruptible magma in crustal magma systems that feed highly explosive volcanic eruptions are encoded in compositional variations of magmatic crystals. The ca. 40 ka Campanian Ignimbrite deposit, the product of the most voluminous explosive eruption in the Campi Flegrei volcanic field, contains a variety of compositionally zoned sanidine pheno- and antecrysts. Barium diffusion chronometry was applied to 79 zoned sanidine crystals from different units and types of pumice clasts from the deposit. We focused on the compositional boundaries at the outermost rims of sanidine crystals considered to indicate mingling/mixing and recharge processes shortly prior to the eruption. Grey-scale swath profiles extracted from accumulated back-scattered electron images across these compositional discontinuities return diffusion times of mostly < 60 years at 902 °C that is the most appropriate estimated temperature. At ca. 850 °C, most times are between ca. 380 and 8 years; at ca. 970 °C, most estimates result to be < 4 years till 1 month. Our results indicate that resident magmas even in large, long-lived reservoirs such as the one that fed the Campanian Ignimbrite at Campi Flegrei, can be activated and become eruptible in relatively short timescales, comparable to those obtained for similar large silicic eruptions.