A recurrent magmatic pattern on observable time scales prior to Plinian eruptions from Nevado de Toluca (Mexico)

Nevado de Toluca is a stratovolcano in the densely populated Mexican Highland and the source of three late Pleistocene Plinian eruptions. While the characterization of the magmatic processes and time scales, leading to these events is crucial to evaluate potential signals of the reawakening of this volcano, they are not well constrained. Here we present insights gathered from the analysis of mineral zoning. Abrupt changes in plagioclase compositions [anorthite (An) >10 mol. %] record repeated thermochemical disturbance of a shallow magma reservoir prior to the three eruptions investigated. In particular, sudden chemical changes in the outermost crystal rims indicate that the eruptions were triggered by recharge of less evolved magma. Recalculated melt compositions reveal that magma input is chemically heterogeneous. Orthopyroxene compositions span a large range [En53‐En92, Cr2O3 of up to 0.9 wt. %] resulting from magma hybridization, which is consistent with a late‐stage temperature increase recorded by amphibole chemistry. Using diffusion chronometry, we show that this recharge typically occurs decades to centuries before Plinian eruptions and hence on time scales relevant for volcano monitoring. Additionally, modelling of Mg profiles in plagioclase constraints the duration of differentiation cycles to be millennial in order of magnitude. Our study shows that similar processes preceded explosive eruptions from Nevado de Toluca, suggesting that analogous paths of unrest should be considered when evaluating potential future activity. We emphasize that signs of deep crustal activity, such as relatively broad deformation pattern surrounding the volcano, could herald the reactivation of Nevado de Toluca