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The 2021 Tajogaite eruption (La Palma, Canary Islands) provides a unique opportunity to investigate magma dynamics in magmatic systems where developed and monogenetic volcanoes coexist. Here, we present an integrated, interdisciplinary study combining petrological, geochemical, and geophysical data to reconstruct the pre- and syn-eruptive processes that controlled the evolution of the eruption. Whole-rock and mineral chemistry, diffusion chronometry in olivine crystals, gas geochemistry, GNSS, InSAR, seismicity and eruptive column height monitoring were jointly analyzed to constrain magma storage conditions, magmatic processes and the temporal evolution of the plumbing system. Our multidisciplinary results reveal a multi-stage magmatic history, involving at least three pre-eruptive intrusions (2017-2018, 2020, and in the weeks before the 2021 eruption) that progressively revived the system. Olivine diffusion modeling indicates that the 2021 eruption was triggered by a late-stage intrusion in early September, with ascent times of 10-30 days. Throughout the eruption, additional deep magma injections were recorded through changes in crystal chemistry, ground deformation, and eruptive dynamics. The earliest erupted magmas of the 2021 eruption were more evolved and hosted olivine crystals with oscillatory zoning, reflecting conduit opening and rapid ascent. During the second half of the eruption, the system transitioned to a regime marked by the development of a crystal mush zone, where magma accumulated without immediate eruption. This evolution was evidenced by prolonged olivine residence times and a characteristic 5-day lag between deformation peaks and maximum eruptive column heights during this period. Therefore, to further improve eruption forecasting in monogenetic systems and to resolve the formation of transient magma storage zones in the upper crust that might control the eruption dynamics, we highlight the critical importance of integrating petrological and geophysical monitoring.

Reworking of limestone (CaCO3) by magma is an important source of carbon in volcanic arc emissions. However, while it is broadly understood that CO2 is liberated during magma-limestone interaction, the degassing behaviour of calcite in silicate melts is less well constrained. In this study, we carried out microspectroscopic analysis of volatiles within fluid inclusions and glass (former melt) in the products of short-term experiments simulating limestone assimilation in mafic arc melt (T = 1200 degrees C, P = 0.5 GPa, runtimes of 0 to 300 s). The experimental products consist of partly to wholly assimilated limestone xenoliths enveloped by CaO-rich silicate glass (reacting melt) that grades into mafic glass (host melt). Micro-to milli-metric sized fluid-filled bubbles permeate the experimental products. This study reveals that limestone assimilation induces extremely fast apparent diffusivity of CO2 (DCO2 greater than or similar to 10-7 m2/s) through both the reacting melt and the host melt. Volatile saturation is thus quickly reached, triggering nucleation of bubbles mainly containing CO2 +/- CO, CH4, N2, H2, and H2O. Crucially, we find that the host melt contains dissolved CO2 from limestone, despite showing no other compositional evidence for limestone assimilation. Mafic melts in volcanic regions underlain by limestone may therefore mobilise and transport more carbon than previously thought, with implications for eruptive behaviour, volcanic CO2 inventories, and long-term climate warming.

The term "xenopumice" describes a pumice-like xenolith of low density, frothy, highly vesiculated, partially molten, silicic crustal material found in mafic volcanic eruption products that usually serves as an indicator of magma-crust interaction. In this study we describe the occurrence of xenopumice in Quaternary eruption sequences at Harrat Rahat, in Saudi Arabia. Harrat Rahat is an intraplate volcanic field, whose last eruption was in 1256 C.E. in proximity to the city of Al-Madinah, and is characterized by a range of volcanic products from basalts to trachyte. This chemical variation found in the volcanic field, has been suggested to be reflective of closed system fractional crystallization with little to no crustal influences. To examine whether xenopumice samples collected indicate crustal assimilation and the extent to which open system processes play a role in the compositional diversity of Harrat Rahat magmas, we analyzed the mineralogy, textural features, whole-rock geochemistry and oxygen isotopes of a set of xenopumice samples and their host basalts. Their subalkaline character with high Si-contents, enriched but variable trace element contents and elevated delta O-18 (>9.8 parts per thousand) values exclude a plutonic cumulate or lower crustal origin for the xenopumice. Instead, their chemistry and textures overlap with metamorphosed granites of upper Arabian crust and/or (meta-)sedimentary rocks of the Proterozoic Arabian Shield. The delta O-18-isotopes of host basaltic magmas (5.1 to 6 parts per thousand) document assimilation of xenopumice material by magmas in some cases. The xenopumices found are an indicator of magma-crust interaction in upper crustal magma reservoirs, emphasizing the importance of evaluating the role of crustal assimilation in the Saudi Arabian Harrats.

Ocean island basalt (OIB) magmas are generally water poor and usually contain less than 1 wt.% of H2O. Explosive eruption styles are therefore rare. When explosive eruptions occur, they are thought to be driven by either volatile-enriched mantle sources or by gas segregation processes during magma differentiation. Here we report on crystal- and water-rich porphyritic basanites and ankaramites from El Hierro in the Canary Islands, Spain, that erupted inside the El Golfo giant landslide collapse embayment that formed at >= 39 ka. Using rock and mineral chemistry in combination with H2O contents of nominally anhydrous minerals (olivine and clinopyroxene), we show that despite their relatively primitive composition, the post-collapse ankaramites are not primary mantle melts. Instead, they record high crystal contents as well as unusually high water contents of up to 3.20 +/- 0.64 wt.% H2O, and likely represent a normally inaccessible snapshot of dense crystal-rich magma compositions that reside in the sub-island underplating zone. We hypothesize that their eruption was facilitated by sudden decompression from crustal unloading, implying that the El Golfo landslide may have affected the deeper portions of the plumbing system and triggered the ascent of volatile-rich, crystal-laden magmas from the underplating zone. We propose that some "wet" and explosive ocean island eruptions might result from the ascent of deep-seated water-rich magmas in the aftermath of vertical unloading and associated decompression.

Liquid immiscibility is one of the viable genetic models to generate carbonatites. Experimental studies have demonstrated that lighter Fe isotopes are enriched in carbonatite melts, whereas heavier Fe isotopes preferentially enter silicate melts during liquid immiscibility. However, this observation has not been substantiated by natural samples, and the mechanism behind Fe isotope fractionation during silicate-carbonatite immiscibility remains unclear. Here, we present high-precision Fe isotope data, combined with petrography, whole-rock elemental and Sr-Nd isotopic compositions, for ultramafic lamprophyres (UML) and carbonatites from the Alno<spacing diaeresis> complex in central Sweden, to elucidate the Fe isotope fractionation during silicate-carbonatite immiscibility processes. The presence of various carbonate spherules in UML, coupled with enrichments in Sr and Ba and depletion in high field strength elements in carbonatites, as well as their overlapping Sr-Nd isotope compositions, supports a petrogenetic relationship involving liquid immiscibility between the UML and carbonatites. The mean δ⁵⁷Fe of UML (0.16 ± 0.08 ‰) is higher than that of carbonatites (0.03 ± 0.04 ‰), with ∆⁵⁷Fe_sil−carb of 0.13 ‰ (± 0.05, 2SD By excluding the effects of low temperature alteration and magmatic processes, we conclude that silicate-carbonatite immiscibility imparts significant Fe isotope fractionation. This fractionation may be influenced by different Fe bond strengths provided by the distinct polymer networks of silicate and carbonatite melts, as well as the varying degrees of Fe enrichment in minerals and melts. This leads to light Fe isotopes being preferentially enriched in the carbonate melt, while heavy Fe isotopes become enriched in the coexisting silicate melt.

Basaltic eruptions produce a wide variety of volcanic products that show a range of different textures and physical properties, from massive lava to extremely light and aerated reticulite. While the mechanical properties of various lavas and tuffs have already been studied in more detail, volcanic bombs have received almost no attention. We characterised the mechanical and physical properties of bombs from the Plio-Pleistocene Uhl & iacute;& rcaron;sk & yacute; vrch in the Brunt & aacute;l Volcanic Field (Czech Republic) to better define their geomechanical behaviour compared to the wider range of volcanic eruption products. The cylindrical specimens showed a highly variable internal structure which resulted in scattered individual peak strength values. In contrast, the residual strength values were less variable, and thus we devised a system using the Hoek-Brown criterion for the whole bomb mechanical characterisation. This approach assigns different geological strength index (GSI) values to the specimens based on their internal structure. The bombs combine the generally low cohesion and strength of tuffs with a higher internal friction angle and a material constant akin to lava samples. The bombs may therefore be treated as a lava-like material albeit with a pyroclastic origin. From a geotechnical point of view, the presence of bombs embedded in other rock types could affect the general stability of a volcanic structure. Here we identify possible scenarios (i.e. bombs embedded in pyroclastic rock versus bombs buried in lava; bombs distributed randomly versus bombs forming a loosely connected horizon) and describe the possible outcomes. Finally, the cracked and porous structure of bombs locally increases permeability, thereby promoting hydrothermal alteration and further affecting general slope stability. However, the porous structure of bombs could also have a potential positive societal impact as it may allow for local sequestration of carbon dioxide.

The study of recent eruptions in Ocean Islands (OIs) provides a unique window into the magma dynamics governing their plumbing systems and the mechanisms leading to eruptions. Here we present an integrated approach to unravel the dynamics of magmatic plumbing systems through detailed spatial, petrological, and geochemical characterisation of volcanic products ranging from crystal-rich ankaramitic lavas to trachytic tephras. We focus on the textural and geochemical spatial variations of 42 Holocene subaerial eruptions at the OI of El Hierro (Canary Islands), as well as on their petrogenetic significance for magmatic evolution and plumbing system architecture. Integrating geochemical data within fractional crystallisation modelling and mass balance calculations reveals that ankaramitic and porphyritic lavas with phenocryst modal abundances > 10 vol% result from melt extraction and crystal accumulation. Aphyric to sub-aphyric eruption products and porphyritic lavas with phenocryst modal abundances < 10 vol% usually follow fractional crystallisation trajectories that start at similar to 10 wt% MgO. Periodic extraction of evolved melt from crystal mushes likely led to the occurrence of minor trachytic eruptions, which are difficult to reconcile with simple closed system fractional crystallisation trends. A complex, heterogeneous crustal mush system beneath El Hierro is, in fact, the most reliable scenario to explain the wide range of textures, whole-rock and mineral compositions, and the overall surface distribution of vents and eruptive styles displayed by the Holocene volcanism on the island. Our integrated findings highlight the importance of a combined field, petrological, and geochemical study to decipher plumbing system dynamics of OI magmatism. The results allow us to put forward an updated conceptual model of the current plumbing architecture of El Hierro's volcanic system during the Holocene.

The Katla volcano is a bimodal caldera complex within Iceland's basalt-dominated Eastern Volcanic Zone. To unravel the petrogenesis of silica-rich rocks from Katla, we provide new δ¹⁸O values for almost 60 basaltic, intermediate, and high-silica eruptive rocks, including a number of partially melted felsic xenoliths. The basaltic samples display a range in bulk-rock δ¹⁸O values from +4.3 to +8.5‰ (n = 17) and the sparse intermediate samples from +4.1 to +5.9‰ (n = 3). In turn, silicic rock samples and feldspar separates range from +2.7 to +6.4‰ (n = 38), whereas felsic xenoliths yield the lowest values from −4.9 to −2.3‰ (n = 4). The majority (95%) of the Katla silicic volcanics have δ¹⁸O values below typical MORB (i.e., ≤5.0‰), ruling out an origin via closed-system fractional crystallization from the basaltic magmas. We utilized the new δ¹⁸O values to model possible assimilation and fractional crystallization (AFC) scenarios. The results indicate an early stage of FC/AFC at deep- to mid-crustal levels, followed by assimilation of low-δ¹⁸O hydrothermally altered sub-volcanic materials similar to the low-δ¹⁸O felsic xenoliths at shallow crustal levels. Such a two-stage magma evolution is consistent with available geophysical and geobarometry studies at Katla, indicating mid- to deep-crustal and shallow-crustal magma domains. Importantly, mafic rocks dominantly show MORB-like δ¹⁸O values, whereas low δ¹⁸O values occur essentially in silicic rocks only. This implies that the low-δ¹⁸O values at Katla are imposed by interaction with the Icelandic crust rather than reflecting low δ¹⁸O mantle sources.

Primary textural and structural features from the Fabian-Kapten ore body in the metamorphosed (amphibolite facies) Malmberget IOA deposit in northern Sweden are reported here. The primary features of the massive ore were grouped into: 1) several types of primary layering, 2) jigsaw-brecciated fine-grained magnetite, 3) skeletal amphibole with interstitial magnetite, 4) disturbed primary layering, 5) net-textured magnetite. Some of these features have not previously documented in IOA deposits. In combination, these rare but well-preserved features provide direct physical evidence of the ore forming processes in the Fabian-Kapten ore body. Our observations suggest a combination of magnetite sedimentation and magmatic crystallization processes during the formation of the Fabian-Kapten ore body and are consistent with the emplacement of a Fe-Ca-Mg-SiO2-oxide melt in, or on top of, sedimented magnetite.

Hydrothermal alteration and mineralization processes can affect the physical and chemical properties of volcanic rocks. Aggressive acidic degassing and fluid flow often also lead to changes in the appearance of a rock, such as changes in surface coloration or intense bleaching. Although hydrothermal alteration can have far-reaching consequences for rock stability and permeability, limited knowledge exists on the detailed structures, extent, and dynamic changes that take place near the surface of hydrothermal venting systems. By integrating drone-based photogrammetry with mineralogical and chemical analyses of rock samples and surface gas flux, we investigate the structure of the evolving volcanic degassing and alteration system at the La Fossa cone on the island of Vulcano, Italy. Our image analysis combines principal component analysis (PCA) with image classification and thermal analysis through which we identify an area of approximately 70 000 m(2) that outlines the maximum extent of hydrothermal alteration effects at the surface, represented by a shift in rock color from reddish to gray. Within this area, we identify distinct gradients of surface coloration and temperature that indicate a local variability in the degassing and alteration intensity and define several structural units within the fumarole field. At least seven such larger units of increased activity could be constrained. Through mineralogical and geochemical analysis of samples from the different alteration units, we define a relationship between surface appearance in drone imagery and the mineralogical and chemical composition. Gradients in surface color from reddish to gray correlate with a reduction in Fe2O3 from up to 3.2 % in the unaltered regime to 0.3 % in the altered regime, and the latter coincides with the area of increased diffuse acid gas flux. As the pixel brightness increases towards higher alteration gradients, we note a loss of the initial (igneous) mineral fraction and a change in the bulk chemical composition with a concomitant increase in sulfur content from close to 0 % in the unaltered samples to up to 60 % in samples from the altered domains. Using this approach of combined remote-sensing and in situ analyses, we define and spatially constrain several alteration units and compare them to the present-day thermally active surface and degassing pattern over the main crater area. The combined results permit us to present a detailed anatomy of the La Fossa fumarole field, including high-temperature fumaroles and seven larger units of increased alteration intensity, surface temperature, and variably intense surface degassing. Importantly, we also identify apparently sealed surface domains that prevent degassing, likely as a consequence of mineral precipitation from degassing and alteration processes. By assessing the thermal energy release of the identified spatial units quantitatively, we show that thermal radiation of high-temperature fumaroles accounts for < 50 % of the total thermal energy release only and that the larger part is emitted by diffuse degassing units. The integrated use of methods presented here has proven to be a useful combination for a detailed characterization of alteration and activity patterns of volcanic degassing sites and has the potential for application in alteration research and for the monitoring of volcanic degassing systems.