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1. Oceanic intraplate explosive eruptions fed directly from the mantle

   https://doi.org/10.1073/pnas.2302093120  

   DeVitre, Charlotte L. ; Gazel, Esteban ; Ramalho, Ricardo S. ; Venugopal, Swetha ; Steele-MacInnis, Matthew ; Hua, Junlin ; Allison, Chelsea M. ; Moore, Lowell R. ; Carracedo, Juan Carlos ; Monteleone, Brian ( August 2023 , Proceedings of the National Academy of Sciences)

   Constraining the volatile content of magmas is critical to our understanding of eruptive processes and their deep Earth cycling essential to planetary habitability [R. Dasgupta, M. M. Hirschmann, Earth Planet. Sci. Lett. 298 , 1 (2010)]. Yet, much of the work thus far on magmatic volatiles has been dedicated to understanding their cycling through subduction zones. Further, studies of intraplate mafic volcanism have disproportionately focused on Hawaii [P. E. Wieser et al., Geochem. Geophys. Geosyst. 22 , e2020GC009364 (2021)], making assessments of the overall role of intraplate volcanoes in the global volatile cycles a challenge. Additionally, while mafic volcanoes are the most common landform on Earth and the Solar System [C. A. Wood, J. Volcanol. Geotherm. Res. 7 , 387–413 (1980)], they tend to be overlooked in favor of silicic volcanoes when it comes to their potential for explosivity. Here, we report primitive (olivine-hosted, with host Magnesium number – Mg# 78 to 88%) melt inclusion (MI) data from Fogo volcano, Cabo Verde, that suggest that oceanic intraplate silica-undersaturated explosive eruptions sample volatile-rich sources. Primitive MI (melt Mg# 70 to 71%) data suggest that these melts are oxidized (NiNiO to NiNiO+1) and very high in volatiles (up to 2 wt% CO 2 , 2.8 wt% H 2 O, 6,000 ppm S, 1,900 ppm F, and 1,100 ppm Cl) making Fogo a global endmember. Storage depths calculated from these high volatile contents also imply that magma storage at Fogo occurs at mantle depths (~20 to 30 km) and that these eruptions are fed from the mantle. Our results suggest that oceanic intraplate mafic eruptions are sustained from the mantle by high volatile concentrations inherited from their source and that deep CO 2 exsolution (here up to ~800 MPa) drives their ascent and explosivity. 

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2. Explosive Activity on Kīlauea's Lower East Rift Zone Fueled by a Volatile‐Rich, Dacitic Melt

   https://doi.org/10.1029/2021GC010046  

   Wieser, Penny E. ; Edmonds, Marie ; Gansecki, Cheryl ; Maclennan, John ; Jenner, Frances E. ; Kunz, Barbara ; Antoshechkina, Paula ; Trusdell, Frank ; Lee, R. L. ; EIMF ( February 2022 , Geochemistry, Geophysics, Geosystems)

   Magmas with matrix glass compositions ranging from basalt to dacite erupted from a series of 24 fissures in the first 2 weeks of the 2018 Lower East Rift Zone (LERZ) eruption of Kīlauea Volcano. Eruption styles ranged from low spattering and fountaining to strombolian activity. Major element trajectories in matrix glasses and melt inclusions hosted by olivine, pyroxene and plagioclase are consistent with variable amounts of fractional crystallization, with incompatible elements (e.g., Cl, F, and H₂O) becoming enriched by 4–5 times as melt MgO contents evolve from 6 to 0.5 wt%. The high viscosity and high H₂O contents (∼2 wt%) of the dacitic melts erupting at Fissure 17 account for the explosive Strombolian behavior exhibited by this fissure, in contrast to the low fountaining and spattering observed at fissures erupting basaltic to basaltic‐andesite melts. Saturation pressures calculated from melt inclusion CO₂‐H₂O contents indicate that the magma reservoir(s) supplying these fissures was located at ∼2–3 km depth, which is in agreement with the depth of a dacitic magma body intercepted during drilling in 2005 (∼2.5 km) and a seismically imaged lowVp/Vsanomaly (∼2 km depth). Nb/Y ratios in erupted products are similar to lavas erupted between 1955 and 1960, indicating that melts were stored and underwent variable amounts of crystallization in the LERZ for >60 years before being remobilized by a dike intrusion in 2018. We demonstrate that extensive fractional crystallization generates viscous and volatile‐rich magma with potential for hazardous explosive eruptions, which may be lurking undetected at many ocean island volcanoes.

    

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3. Linking Subsurface to Surface Using Gas Emission and Melt Inclusion Data at Mount Cleveland Volcano, Alaska

   https://doi.org/10.1029/2019GC008882  

   Werner, C. ; Rasmussen, D. J. ; Plank, T. ; Kelly, P. J. ; Kern, C. ; Lopez, T. ; Gliss, J. ; Power, J. A. ; Roman, D. C. ; Izbekov, P. ; et al ( July 2020 , Geochemistry, Geophysics, Geosystems)

   Mount Cleveland is one of Alaska's most active volcanoes, yet little is known about the magmatic system driving persistent and dynamic volcanic activity. Volcanic gas and melt inclusion (MI) data from 2016 were combined to investigate shallow magmatic processes. SO₂emission rates were between 166 and 324 t/day and the H₂O/SO₂was 600 ± 53, whereas CO₂and H₂S were below detection. Olivine‐, clinopyroxene‐, and plagioclase‐hosted MIs have up to 3.8 wt.% H₂O, 514 ppm CO₂, and 2,320 ppm S. Equilibration depths, based on MI H₂O contents, suggest that a magmatic column extended from 0.5 to 3.0 km (~10–60 MPa). We used MI data to empirically model open‐system H‐C‐S degassing from 0 to 12 km and found that a column of magma between 0.5 and 3 km could produce the measured gas H₂O/SO₂ratio. However, additional magma deeper than 3 km is required to sustain emissions over periods greater than days to weeks, if the observed vent dimension is a valid proxy for the conduit. Assuming an initial S content of 2,320 ppm, the total magma supply needed to sustain the annual SO₂flux was 5 to 9.8 Mm³/yr, suggesting a maximum intrusive‐to‐extrusive ratio of 13:1. The model predicts degassing of <50 t/day CO₂for July 2016, which corresponds to a maximum predicted CO₂/SO₂of 0.2. Ultimately, frequent recharge from deeper, less degassed magma is required to drive the continuous activity observed over multiple years. During periods of recharge we would expect lower H₂O/SO₂and measurable volcanic CO₂.

    

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4. Highly explosive basaltic eruptions driven by CO2 exsolution

   https://doi.org/10.1038/s41467-020-20354-2  

   Allison, Chelsea M. ; Roggensack, Kurt ; Clarke, Amanda B. ( January 2021 , Nature Communications)

   The most explosive basaltic scoria cone eruption yet documented (>20 km high plumes) occurred at Sunset Crater (Arizona) ca. 1085 AD by undetermined eruptive mechanisms. We present melt inclusion analysis, including bubble contents by Raman spectroscopy, yielding high total CO₂(approaching 6000 ppm) and S (~2000 ppm) with moderate H₂O (~1.25 wt%). Two groups of melt inclusions are evident, classified by bubble vol%. Modeling of post-entrapment modification indicates that the group with larger bubbles formed as a result of heterogeneous entrapment of melt and exsolved CO₂and provides evidence for an exsolved CO₂phase at magma storage depths of ~15 km. We argue that this exsolved CO₂phase played a critical role in driving this explosive eruption, possibly analogous to H₂O exsolution driving silicic caldera-forming eruptions. Because of their distinct gas compositions relative to silicic magmas (high S and CO₂), even modest volume explosive basaltic eruptions could impact the atmosphere.

    

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5. Insights for crystal mush storage utilizing mafic enclaves from the 2011–12 Cordón Caulle eruption

   https://doi.org/10.1038/s41598-022-13305-y  

   Winslow, Heather ; Ruprecht, Philipp ; Gonnermann, Helge M. ; Phelps, Patrick R. ; Muñoz-Saez, Carolina ; Delgado, Francisco ; Pritchard, Matthew ; Amigo, Alvaro ( December 2022 , Scientific Reports)

   Abstract Two distinct types of rare crystal-rich mafic enclaves have been identified in the rhyolite lava flow from the 2011–12 Cordón Caulle eruption (Southern Andean Volcanic Zone, SVZ). The majority of mafic enclaves are coarsely crystalline with interlocking olivine-clinopyroxene-plagioclase textures and irregular shaped vesicles filling the crystal framework. These enclaves are interpreted as pieces of crystal-rich magma mush underlying a crystal-poor rhyolitic magma body that has fed recent silicic eruptions at Cordón Caulle. A second type of porphyritic enclaves, with restricted mineral chemistry and spherical vesicles, represents small-volume injections into the rhyolite magma. Both types of enclaves are basaltic end-members (up to 9.3 wt% MgO and 50–53 wt% SiO 2 ) in comparison to enclaves erupted globally. The Cordón Caulle enclaves also have one of the largest compositional gaps on record between the basaltic enclaves and the rhyolite host at 17 wt% SiO 2 . Interstitial melt in the coarsely-crystalline enclaves is compositionally identical to their rhyolitic host, suggesting that the crystal-poor rhyolite magma was derived directly from the underlying basaltic magma mush through efficient melt extraction. We suggest the 2011–12 rhyolitic eruption was generated from a primitive basaltic crystal-rich mush that short-circuited the typical full range of magmatic differentiation in a single step. 

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