H2O and CO2 evolution in the Bandelier Tuff sequence reveals multiple and discrete magma replenishments

Abstract

The sequence of eruptions in the Bandelier magmatic system provides an opportunity to study volatile evolution through different stages of a large silicic magma chamber. The Lower Bandelier Tuff (LBT) and Upper Bandelier Tuff (UBT) eruptions offer a snapshot of a pre-eruptive magma chamber primed for eruption, while the sequence of Valle Toledo Member (VTM) eruptions open a window into the temporal evolution of the chamber's upper regions between the two super-eruptions. We measured H 2 O and CO 2 concentrations in melt inclusions from the entire sequence of eruptions and identified three peaks in CO 2 concentrations: (1) in the middle of the LBT plinian airfall (increase in mean CO 2 concentrations from 27 ± 5 ppm at the base of the plinian to 173 ± 5 ppm in the mid-plinian); (2) in VTM group III (mean of 197 ± 5 ppm); and (3) in the middle of the UBT plinian airfall (mean of 54 ± 5 ppm at the base of the plinian to 101 ± 5 ppm in the mid-plinian). We propose that these increased CO 2 concentrations are due to injections of fresh magma into the system, whereby CO 2 -rich vapours exsolved from the injected magma percolated through the magma chamber to increase CO 2 levels. Although the sharp increase in the LBT plinian indicates a rapid succession of recharge events in a short period of time, the gradually increasing CO 2 levels through the final VTM phase and the UBT plinian indicate that recharge events may have been spread over a longer period of time before the UBT eruption. Based on the theoretical and observed gradients in H 2 O and CO 2 through the LBT and UBT sequence, we calculate a vapour phase equivalent to maximum 6.7 wt% of the magma body was exsolved from the LBT magma chamber; for the less degassed UBT, the exsolved vapour phase was maximum 4.2 wt% of the magma body. Our results indicate that the volatile composition of magmatic systems, with a particular focus on CO 2 , can record evidence of magmatic recharge into the system and be an important tool in deciphering recharge events.

Shear Velocity Evidence of Upper Crustal Magma Storage Beneath Valles Caldera

“…If the seismic properties are influenced by magmatic volatiles that could bias our interpretation of the melt‐fraction toward over‐estimation. Valles magmas may have several percent dissolved volatiles based on past eruptions (Boro et al., 2020; Waelkens et al., 2022). As magma cools in the upper crust buoyant volatiles may accumulate in a thin low‐velocity layer atop the magma reservoir (e.g., Seccia et al., 2011).…”

Shear velocity evidence of upper crustal magma storage beneath Valles Caldera

“…If the seismic properties are influenced by magmatic volatiles that could bias our interpretation of the melt-fraction toward over-estimation. Valles magmas may have several percent dissolved volatiles based on past eruptions (Boro et al, 2020;Waelkens et al, 2022). As magma cools in the upper crust buoyant volatiles may accumulate in a thin low-velocity layer atop the magma reservoir (e.g., Seccia et al, 2011).…”

Geochemistry, Magmatic Processes and Timescales of Recent Rhyolitic Eruptives of the Ōkataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa/New Zealand

“…This also holds true when comparing volatiles contents in the young Ōkataina magmas (Johnson et al 2011; this thesis) with those of other silicic eruptives, including Bandelier and Yellowstone (Myers et al 2016(Myers et al , 2018Waelkens et al 2017Waelkens et al , 2022Saalfeld et al 2022).…”

“…The young Ōkataina eruptives also have a similar range in H2O contents to other silicic (daciticrhyolitic) volcanoes worldwide (Figure 5.13), including the Bishop eruption from Long Valley (Wallace et al 1999;Myers et al 2019), the Altiplano-Puna volcanic complex in the Andes (Schmitt 2001), Crater Lake in Oregon (Bacon et al 1992), Sumisu volcano in the Izu-Bonin arc (Allen et al 2010), the Bandelier Tuff from Valles Caldera, New Mexico (Waelkens et al 2022), Volcán Chaitén in Chile (Castro and Dingwell 2009), and Mt. Pinatubo in the Philippines (Wallace and Gerlach 1994).…”

“…Bowyer 2001;Deering et al 2011;Barker et al 2015;Cooper et al 2017) and worldwide (e.g. Martin et al 2008;Simon et al 2014;Swallow et al 2019;Klug et al 2020;Tierney and Reid 2021;Waelkens et al 2022). Some of these comparisons and contrasts are outlined below, to place Ōkataina and the research in this thesis into a wider context.…”