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

Abstract: 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 low Vp/Vs anomaly (∼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

Reconstructing Magma Storage Depths for the 2018 Kı̄lauean Eruption From Melt Inclusion CO ₂ Contents: The Importance of Vapor Bubbles

The 2018 lower East Rift Zone (LERZ) eruption and the accompanying collapse of the summit caldera marked the most destructive episode of activity at Kı̄lauea Volcano in the last 200 years. The eruption was extremely well-monitored, with extensive real-time lava sampling as well as continuous geodetic data capturing the caldera collapse. This multiparameter data set provides an exceptional opportunity to determine the reservoir geometry and magma transport paths supplying Kı̄lauea’s LERZ. The forsterite contents of olivine crystals, together with the degree of major element disequilibrium with carrier melts, indicates that two distinct crystal populations were erupted from Fissure 8 (termed high- and low-Fo). Melt inclusion entrapment pressures reveal that low-Fo olivines (close to equilibrium with their carrier melts) crystallized within the Halema’uma’u reservoir (∼2-km depth), while many high-Fo olivines (>Fo81.5; far from equilibrium with their carrier melts) crystallized within the South Caldera reservoir (∼3–5-km depth). Melt inclusions in high-Fo olivines experienced extensive post-entrapment crystallization following their incorporation into cooler, more evolved melts. This favored the growth of a CO2-rich vapor bubble, containing up to 99% of the total melt inclusion CO2 budget (median = 93%). If this CO2-rich bubble is not accounted for, entrapment depths are significantly underestimated. Conversely, reconstructions using equation of state methods rather than direct measurements of vapor bubbles overestimate entrapment depths. Overall, we show that direct measurements of melts and vapor bubbles by secondary-ion mass spectrometry and Raman spectroscopy, combined with a suitable H2O-CO2 solubility model, is a powerful tool to identify the magma storage reservoirs supplying volcanic eruptions. Key Points Petrological, gaseous and geophysical observations can be reconciled by a model where Fissure 8 was supplied from two summit storage reservoirs (∼1–2- and 3–5-km depth) Extensive post-entrapment crystallization of melt inclusions within high-Fo olivines (Fo > 81.5) caused ∼90% of the CO2 to enter the vapor bubble Raman analyses of vapor bubbles combined with choice of a suitable H2O-CO2 solubility model is required to accurately determine magma storage depths Plain Language Summary Pockets of frozen magma trapped within olivine crystals, termed “melt inclusions,” can provide information about the depths at which magma is stored beneath the surface prior to a volcanic eruption. This is because the amount of CO2 and H2O that can be dissolved in a melt is dependent on the pressure, and therefore the depth. We examine melt inclusions from lava flows produced during the 2018 eruption of Kı̄lauea Volcano. Previous work, based on geophysics, has shown that magma is stored in two main reservoirs at Kı̄lauea, located at ∼1–2- and ∼3–5-km depth. However, because many melt inclusions host almost all of their CO2 within a vapor bubble, which is rarely measured, previous petrological estimates of magma storage depths at Kı̄lauea do not align with the depths of the two reservoirs identified by geophysics. In this study, we measure the amount of CO2 in the glass and the bubble using secondary-ion mass spectrometry and Raman spectroscopy, respectively. By adding these two measurements together, we can reconstruct the amount of CO2 that was present when melt inclusions were trapped. Calculated depths align remarkably well with geophysical estimates, and demonstrate that the 2018 eruption was supplied by both magma storage reservoirs

EPSL 4oAr/ 39Ar geochronology of rhyolites erupted following collapse of the Yellowstone caldera, Yellowstone Plateau volcanic field: implications for crustal contamination

Abstract Single-crystal laser-probe "OAr/39Ar dating of 133 grains of sanidine and plagioclase has enabled us to resolve the eruption ages of the Upper Basin Member rhyolites -the lava flows and related tuffs that erupted within the Yellowstone Caldera shortly after its collapse 630 ky ago on eruption of the Lava Creek Tuff. Two lavas and a tuff that erupted from the eastern ring-fracture zone yield an eruptive age of 481 f 8 ka, whereas two flows from the western ring-fracture zone yield eruptive ages of 516 f 7 and 198 f 8 ka. Most of the units contain old xenocrysts, explaining why previous attempts at dating these earliest post-caldera units by the conventional K-Ar method yielded poorly resolved and, in some cases, anomalous ages. The tuff shows the most severe contamination. Grains from a single pumice lapilli in the tuff show as large an age range as those from bulk vitrophyre, indicating that the xenocrysts were incorporated in the magma prior to its near-surface explosive fragmentation. Diffusion calculations indicate that the xenocrysts could not have remained in the magma for more than a few years without degassing and giving ages indistinguishable from the phenocrysts. Thus, the contamination represented by the xenocrysts probably occurred during fracturing and conduit propagation, rather than during caldera collapse, which took place more than 100 ky earlier. The apparent ages of xenocrysts and their compositions as determined by electron microprobe suggest that the Eocene Absaroka volcanics are the main contaminant, with a single xenocryst probably coming from Precambrian basement rocks. Most of the xenocrysts are difficult to distinguish optically or chemically from feldspar phenocrysts, illustrating the necessity of single-crystal analysis to date many young volcanic rocks accurately

Trace elements in olivine fingerprint the source of 2018 magmas and shed light on explosive-effusive eruption cycles at Kīlauea Volcano

International audienceUnderstanding magma genesis and the evolution of intensive parameters (temperature, pressure, composition, degree of melting) in the mantle source of highly active volcanic systems is crucial for interpreting magma supply changes over time and recognizing cyclic behavior to anticipate future volcanic behavior. Major and trace elements in olivine are commonly used to study variations in mantle lithologies and melting conditions (e.g., temperature, pressure, oxygen fugacity) affecting the mantle over time. Here, we track the temporal evolution of primary melts through the most recent cycle of explosive and effusive eruptions at Kīlauea (Hawai'i), which spans the last ∼500 years. We report major and trace elements in olivine from the last explosive period (∼1500 - early 1820's Keanakāko'i Tephra) and the most recent decade of the current effusive period (2018 LERZ, 2015-2018 Pu'u'ō'ō, 2008-2018 lava lake and 2020 eruption in Halema'uma'u). Scandium concentrations in olivine allow characterizing changes in mantle source between 1500 and 2018, and suggest that the recent (2015-2018) magma feeding the Pu'u'ō'ō cone did not significantly interact with the magma that erupted in the LERZ in 2018. The evolution of olivine and melt compositions over the past 500 years is not easily reconcilable with variations in mantle potential temperature, pressure of mantle melt pooling and storage, or oxygen fugacity. Instead, Sc, Mn, and Co concentrations and Ni/Mg ratio in high forsterite (Fo >87) olivine advocate for an increase in the proportion of clinopyroxene in the mantle source associated with a slightly higher degree of partial melting from 1500 to 2018. Changes in primitive melt compositions and degrees of mantle melting may well modulate magma supply to the crust and formation-replenishment of steady or ephemeral summit reservoirs, and thereby control transitions between explosive and effusive periods at Kīlauea. Analyzing trace elements in olivine at Kīlauea and elsewhere could therefore provide important clues on subtle changes occurring at the mantle level that might herald changes in volcanic behavior

Reconstructing Magma Storage Depths for the 2018 Kı̄lauean Eruption From Melt Inclusion CO<inf>2</inf> Contents: The Importance of Vapor Bubbles

The 2018 lower East Rift Zone (LERZ) eruption and the accompanying collapse of the summit caldera marked the most destructive episode of activity at Kīlauea Volcano in the last 200 years. The eruption was extremely well-monitored, with extensive real-time lava sampling as well as continuous geodetic data capturing the caldera collapse. This multi-parameter dataset provides an exceptional opportunity to determine the reservoir geometry and magma transport paths supplying Kīlauea’s LERZ. The forsterite contents of olivine crystals, together with the degree of major element disequilibrium with carrier melts, indicates that two distinct crystal populations were erupted from Fissure 8 (termed High- and Low-Fo). Melt inclusion entrapment pressures reveal that Low-Fo olivines (close to equilibrium with their carrier melts) crystallized within the Halema’uma’u reservoir (~2 km depth), while many High-Fo olivines (>Fo81.5; far from equilibrium with their carrier melts) crystallized within the South Caldera reservoir (~3--5 km depth). Melt inclusions in High-Fo olivines experienced extensive post-entrapment crystallization following their incorporation into cooler, more evolved melts. This favoured the growth of a CO2-rich vapor bubble, containing up to 99% of the total melt inclusion CO2 budget (median=93%). If this CO2-rich bubble is not accounted for, entrapment depths are significantly underestimated. Conversely, reconstructions using equation of state methods rather than direct measurements of vapor bubbles overestimate entrapment depths. Overall, we show that direct measurements of melts and vapor bubbles by SIMS and Raman Spectroscopy, combined with a suitable H2O-CO2 solubility model, is a powerful tool to identify the magma storage reservoirs supplying volcanic eruptions

Storage conditions and longevity of rift zone magmas at Kilauea volcano, Hawai’i: melt incusions insights from 2018 Lower East Rift Zone eruption

International audienc

Research Data Supporting: Reconstructing Magma Storage Depths for the 2018 Kīlauean Eruption from Melt inclusion CO2 Contents: The Importance of Vapor Bubbles

This dataset contains melt inclusion, host crystal, and matrix glass data, as well as bubble growth models

Reconstructing Magma Storage Depths for the 2018 Kı̄lauean Eruption from Melt inclusion CO2 Contents: The Importance of Vapor Bubbles

The 2018 lower East Rift Zone (LERZ) eruption and the accompanying collapse of the summit caldera marked the most destructive episode of activity at Kı̄lauea Volcano in the last 200 years. The eruption was extremely well‐monitored, with extensive real‐time lava sampling as well as continuous geodetic data capturing the caldera collapse. This multi‐parameter dataset provides an exceptional opportunity to determine the reservoir geometry and magma transport paths supplying Kı̄lauea’s LERZ. The forsterite contents of olivine crystals, together with the degree of major element disequilibrium with carrier melts, indicates that two distinct crystal populations were erupted from Fissure 8 (termed High‐ and Low‐Fo). Melt inclusion entrapment pressures reveal that Low‐Fo olivines (close to equilibrium with their carrier melts) crystallized within the Halema’uma’u reservoir ( ∼2 km depth), while many High‐Fo olivines ( > Fo81.5; far from equilibrium with their carrier melts) crystallized within the South Caldera reservoir ( ∼3–5 km depth). Melt inclusions in High‐Fo olivines experienced extensive post‐entrapment crystallization following their incorporation into cooler, more evolved melts. This favoured the growth of a CO2 ‐rich vapor bubble, containing up to 99% of the total melt inclusion CO2 budget (median=93%). If this CO2 ‐rich bubble is not accounted for, entrapment depths are significantly underestimated. Conversely, reconstructions using equation of state methods rather than direct measurements of vapor bubbles overestimate entrapment depths. Overall, we show that direct measurements of melts and vapor bubbles by SIMS and Raman Spectroscopy, combined with a suitable H2 O −CO2 solubility model, is a powerful tool to identify the magma storage reservoirs supplying volcanic eruptions