Melt inclusion constraints on the magma source of Eyjafjallajökull 2010 flank eruption

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Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland

The 39-day long eruption at the summit of Eyjafjallajökull volcano in April–May 2010 was of modest size but ash was widely dispersed. By combining data from ground surveys and remote sensing we show that the erupted material was 4.8±1.2·1011 kg (benmoreite and trachyte, dense rock equivalent volume 0.18±0.05 km3). About 20% was lava and water-transported tephra, 80% was airborne tephra (bulk volume 0.27 km3) transported by 3–10 km high plumes. The airborne tephra was mostly fine ash (diameter <1000 µm). At least 7·1010 kg (70 Tg) was very fine ash (<28 µm), several times more than previously estimated via satellite retrievals. About 50% of the tephra fell in Iceland with the remainder carried towards south and east, detected over ~7 million km2 in Europe and the North Atlantic. Of order 1010 kg (2%) are considered to have been transported longer than 600–700 km with <108 kg (<0.02%) reaching mainland Europe

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption.We usemultiparameter geophysical and geochemical data to show that the 110-squarekilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, nearexponential decline of both collapse rate and the intensity of the 180-day-long eruption

The evolution and storage of primitive melts in the Eastern Volcanic Zone of Iceland: the 10 ka Grímsvötn tephra series (i.e. the Saksunarvatn ash)

Major, trace and volatile elements were measured in a suite of primitive macrocrysts and melt inclusions from the thickest layer of the 10 ka Grímsvötn tephra series (i.e. Saksunarvatn ash) at Lake Hvítárvatn in central Iceland. In the absence of primitive tholeiitic eruptions (MgO > 7 wt.%) within the Eastern Volcanic Zone (EVZ) of Iceland, these crystal and inclusion compositions provide an important insight into magmatic processes in this volcanically productive region. Matrix glass compositions show strong similarities with glass compositions from the AD 1783–84 Laki eruption, confirming the affinity of the tephra series with the Grímsvötn volcanic system. Macrocrysts can be divided into a primitive assemblage of zoned macrocryst cores (An_78–An_92, Mg#_cpx = 82–87, Fo_79.5–Fo_87) and an evolved assemblage consisting of unzoned macrocrysts and the rims of zoned macrocrysts (An_60–An_68, Mg#_cpx = 71–78, Fo_70–Fo_76). Although the evolved assemblage is close to being in equilibrium with the matrix glass, trace element disequilibrium between primitive and evolved assemblages indicates that they were derived from different distributions of mantle melt compositions. Juxtaposition of disequilibrium assemblages probably occurred during disaggregation of incompatible trace element-depleted mushes (mean La/Yb_melt = 2.1) into aphyric and incompatible trace element-enriched liquids (La/Yb_melt = 3.6) shortly before the growth of the evolved macrocryst assemblage. Post-entrapment modification of plagioclase-hosted melt inclusions has been minimal and high-Mg# inclusions record differentiation and mixing of compositionally variable mantle melts that are amongst the most primitive liquids known from the EVZ. Coupled high field strength element (HFSE) depletion and incompatible trace element enrichment in a subset of primitive plagioclase-hosted melt inclusions can be accounted for by inclusion formation following plagioclase dissolution driven by interaction with plagioclase-undersaturated melts. Thermobarometric calculations indicate that final crystal-melt equilibration within the evolved assemblage occurred at ~1140°C and 0.0–1.5 kbar. Considering the large volume of the erupted tephra and textural evidence for rapid crystallisation of the evolved assemblage, 0.0–1.5 kbar is considered unlikely to represent a pressure of long-term magma accumulation and storage. Multiple thermometers indicate that the primitive assemblage crystallised at high temperatures of 1240–1300°C. Different barometers, however, return markedly different crystallisation depth estimates. Raw clinopyroxene-melt pressures of 5.5–7.5 kbar conflict with apparent melt inclusion entrapment pressures of 1.4 kbar. After applying a correction derived from published experimental data, clinopyroxene-melt equilibria return mid-crustal pressures of 4±1.5 kbar, which are consistent with pressures estimated from the major element content of primitive melt inclusions. Long-term storage of primitive magmas in the mid-crust implies that low CO_2 concentrations measured in primitive plagioclase-hosted inclusions (262–800 ppm) result from post-entrapment CO_2 loss during transport through the shallow crust. In order to reconstruct basaltic plumbing system geometries from petrological data with greater confidence, mineral-melt equilibrium models require refinement at pressures of magma storage in Iceland. Further basalt phase equilibria experiments are thus needed within the crucial 1–7 kbar range.D.A.N. was supported by a Natural Environment Research Council studentship (NE/1528277/1) at the start of this project. SIMS analyses were supported by Natural Environment Research Council Ion Microprobe Facility award (IMF508/1013).This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s00410-015-1170-

Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland

Recent Icelandic rifting events have illuminated the roles of centralized crustal magma reservoirs and lateral magma transport1,2,3,4, important characteristics of mid-ocean ridge magmatism1,5. A consequence of such shallow crustal processing of magmas4,5 is the overprinting of signatures that trace the origin, evolution and transport of melts in the uppermost mantle and lowermost crust6,7. Here we present unique insights into processes occurring in this zone from integrated petrologic and geochemical studies of the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula in Iceland. Geochemical analyses of basalts erupted during the first 50 days of the eruption, combined with associated gas emissions, reveal direct sourcing from a near-Moho magma storage zone. Geochemical proxies, which signify different mantle compositions and melting conditions, changed at a rate unparalleled for individual basaltic eruptions globally. Initially, the erupted lava was dominated by melts sourced from the shallowest mantle but over the following three weeks became increasingly dominated by magmas generated at a greater depth. This exceptionally rapid trend in erupted compositions provides an unprecedented temporal record of magma mixing that filters the mantle signal, consistent with processing in near-Moho melt lenses containing 107–108 m3 of basaltic magma. Exposing previously inaccessible parts of this key magma processing zone to near-real-time investigations provides new insights into the timescales and operational mode of basaltic magma systems

Mineral diffusive and ^(226)Ra/^(230)Th timescales for the genesis of Icelandic basalts: Laki and the Grimsvötn magma system

Many Icelandic magmas are 1-3‰ lower in δ^(18)O than typical terrestrial basalts. We report oxygen isotope and trace element analyses in individual grains and bulk separates of olivine, plagioclase, and clinopyroxene phenocrysts and of basaltic glass from the1783-4 fissure eruption of Lakagigar (Laki)—the largest historic basaltic eruption—and from subsequent, smaller volume 20th century ashes from the same magma system (the subglacial Grimsvötn caldera). Previously and newly analyzed ash and lava samples of Laki basalts are homogeneous in δ^(18)O =3.1±0.1‰; 1996 and 1998 basaltic ashes are also homogeneous though slightly lower in δ^(18)O =2.9±0.1‰. In contrast, we find extreme heterogeneity in δ^(18)O in phenocrysts and disequilibrium and often reversed olivine-plagioclase and mineral-glass fractionations. Olivine phenocrysts (Fo_(89-75)) vary in δ^(18)O from 4.7‰ (typical of other low- δ^(18)O basalts from Iceland) to extremely low values of 2.5‰ (in equilibrium with the host glass). Plagioclase phenocrysts (An_(89-75)) are more uniformly low in δ^(18)O, varying from 3.28 to 2.85‰. Larger and Mg-rich olivines and Ca-rich plagioclase tend to have higher δ^(18)O values than the smaller, more Fe- and Na-rich ones, but these correlations are poor, perhaps because the phenocryst population is a mixture of grains that grew from their host magmas at different times as it varied in δ^(18)O, and/or of cumulates that precipitated from other magmas and were later entrained. Oxygen diffusion in plagioclase and olivine constrains their δ^(18)O zoning and reversed Δ^(18)O(Pl-Ol) as being transient exchange feature at ~1-2 kyr. In contrast to δ^(18)O values, fast diffusing trace element Ni, Mn, Ca in olivine, and Mg in plagioclase are consistent with equilibrium partitioning, and thus require >100 yrs. Laki lavas and plagioclase have 15% excess in (^(226)Ra/^(230)Th) that require shorter than 8kyr magma residence, but mineral diffusion age may pre- and post-date magma segregation depending on the time of their growth/entrapment. These overall fast timescales and the surprising whole-rock δ^(18)O homogeneity with low ^3He/^4He= 3.6, call for an effective magma mixing, storage, and homogenization for ~1 kyr. Mass balance requires that the initial normal δ^(18)O parental olivine tholeitic basaltic magma of the eastern rift zone, melted low- δ^(18)O Iceland crust 1000s yrs before eruption, followed by the addition of 15% of superliquidus, -10‰ silicic partial melt with 3-4wt% H_2O and 2-3wt% K_2O. Low- δ^(18)O Iceland’s anomaly is viewed as crustal in origin caused by glaciation