A Recurrent Magmatic Pattern on Observable Timescales Prior to Plinian Eruptions From Nevado de Toluca (Mexico)

Abstract

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 timescales, 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 (En 53 -En 92 , Cr 2 O 3 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 timescales relevant for volcano monitoring. Additionally, modeling 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.

The Long-Term Life-Cycle of Nevado de Toluca Volcano (Mexico): Insights Into the Origin of Petrologic Modes

“…The long-term mineral record of Nevado de Toluca reveals that strongly zoned pyroxene crystals, similar to those found in the Plinian deposits (Weber et al, 2019), are a characteristic feature in eruptive products throughout the volcano's history ( Figure 6). Most remarkable about these crystals are elevated Cr 2 O 3 contents of up to 1.2 wt% in clinopyroxenes and up to 0.91 wt% in orthopyroxenes at En fractions typically between 0.4 and 0.5 for cpx and 0.7 and 0.9 for opx.…”

“…Isotopic (Sr, Nd, Pb) and trace element data shows that even though Nevado de Toluca sits on thick continental crust of about 50 km, crustal melting plays only a marginal role in silicic magma genesis (Martínez-Serrano et al, 2004). The shallow part of the magmatic system prior to the Plinian events has evolved as an open system, where fresh pulses of recharge magma enter the preexisting more silicic reservoirs (Smith et al, 2009;Weber et al, 2019).…”

“…Intermediate and silicic arc magmas are widely believed to originate by a combination of processes including fractional crystallization (Grove et al, 2005;Lee and Bachmann, 2014;Müntener and Ulmer, 2018), reactive melt flow through porous cumulates (Solano et al, 2012;Cooper et al, 2016;Jackson et al, 2018), assimilation of crustal rocks (Hildreth and Moorbath, 1988), and hybridization of evolved and mafic magmas (Nixon and Pearce, 1987;Eichelberger et al, 2000;Tepley III et al, 2000;Witter et al, 2005;Reubi and Blundy, 2009;Straub et al, 2011;Kent, 2014), with the relative importance of these processes being still widely discussed and possibly changing from one system to another. Plagioclase and orthopyroxene crystals from three Plinian eruptions in the younger (<26 ka) history of Nevado de Toluca have previously been used to show that interaction of a resident shallow crustal silicic magma with two distinct more mafic melts is the dominant mechanism that produced the Plinian eruptive products (Smith et al, 2009;Weber et al, 2019). Our much extended dataset of mineral and bulk-rock geochemistry for 19 additional eruptions, spanning the entire 1.5 Ma history of the volcano, allows us to evaluate the configuration of the plumbing system and pre-eruptive conditions through time.…”

“…Predictions of existing numerical models, relating magmatic processes and the spectrum of chemical compositions erupted by volcanoes can be tested based on long-term eruptive records, but can also help to illuminate physical controls on geochemical distributions and temporal trends. Here we present a dataset of 52 new and 45 previously published (Weber et al, 2019, Weber et al, 2020 whole-rock analyses and 6247 new spot analyses on minerals of temporally resolved bulk-rock major and trace element analyses and mineral chemistry spanning the 1.5 Ma life cycle of the dacitic Nevado de Toluca volcano in Central Mexico. We use mineral zonation systematics and thermo-barometric FIGURE 3 | Compilation of stratigraphic relations for Nevado de Toluca volcano.…”

Magma diversity reflects recharge regime and thermal structure of the crust

“…To establish the link between magma recharge rates and the evolution of eruptible magma chemistries in mid crustal reservoirs, we developed a numerical model that couples heat transfer and phase petrology. The design of our model is motivated by geophysical 21,22,23 and petrological 14,24,25,26,27,28,32,52 data, which show that magmas acquire their chemistry mostly at mid to lower crustal depths, before being erupted. We do not simulate magma extraction and eruption, but we trace the evolution in the chemistry of potentially eruptible magma over time, using this as a proxy for what is likely be sampled in eruptions.…”