A thorough understanding of magmatic plumbing systems is crucial to advance our knowledge of volcanic hazards, crustal evolution, surface deformation related to magma emplacement, as well as ore mineralisation. This session aims to investigate the multitude of key processes operating in magmatic systems at all scales, from source to surface, such as: magma generation and transport, mixing, storage and the resulting associated deformation; mineral–melt–fluid reactions and fractionation; kinetic and equilibrium elemental and isotopic exchange. We invite contributions that rely on field observations, remote-sensing and geophysical techniques (e.g., InSAR, seismicity analysis and seismic imaging, gravity and electromagnetic studies), high-resolution geochemical data (major and trace elements as well as isotope ratios), thermodynamic, numerical and analogue modelling, geochronology and diffusion chronometry, machine learning, and experimental petrology to shed light on those processes and their timescales. Studies that combine various approaches (e.g. apply experimental or computational findings to case studies of natural systems) or develop new tools for understanding the complex evolution of magmatic systems are especially welcome.
Orals: Wed, 6 May, 14:00–15:45 | Room 0.96/97
Rift zones host highly dynamic melt pathways in which magma may ascend vertically as dikes or migrate laterally to form sills, generating complex trans-crustal magma plumbing systems. While diking is a well-recognized consequence of extension, the mechanisms that promote sill emplacement during rifting remain poorly constrained. Here, we conduct high-resolution geodynamic models using ASPECT coupled with the surface process modeling code FastScape, to track the evolving lithospheric stress state over millions of years and assess its control on melt migration.
Inspired by the Main Ethiopian Rift, the reference model comprises 40 km-thick crust of intermediate strength, featuring a 25 km-thick wet quartzite upper crust and a 15 km-thick wet anorthite lower crust, and is extended at a rate of 6 mm/yr. The model spans 12 Myr and accommodates 72 km of extension. Despite the overall extensional regime, the results reveal the development of localized compressional stress. This horizontal compression arises from flexure of the mechanically competent lithosphere during rifting and is concentrated at depths of 15–20 km and 5 km. In contrast, in weak crustal configurations, compression is confined to shallower levels (<3 km).
Analysis of the temporal evolution of the stress field shows that horizontal compression initially develops in off-rift regions at the top of competent layers during early rift stages of rift-flank uplift. As extension proceeds, compression also emerges below the rift axis while it persists in some places outside the rift. We represent melt pathways as streamlines aligned with the maximum principal deviatoric stress (σ₁). Assuming that magma migration through the crust follows the direction of σ₁, vertical melt ascent occurs when σ₁ is oriented vertically, corresponding to a regime dominated by extension. Rotation of σ₁ into a horizontal orientation due to compression promotes lateral magma migration and sill emplacement beneath or within zones of compression. For intermediate orientations of σ₁, melt ascent proceeds obliquely. This approach enables melt pathways to be visualized solely as a function of the stress field: clustered streamlines indicate focused magma transport, whereas dispersed streamlines reflect more diffuse migration.
Such stress-controlled magma deflection provides a mechanism for the formation of stacked sills and multi-tiered plumbing systems observed in nature. Prolonged magma storage enhances crustal assimilation, facilitating the generation of evolved magmas from primitive melts. These results demonstrate that the evolving lithospheric stress state plays a key role on magma transport during rifting and provides a geodynamic framework for understanding plumbing-system architecture in magma-dominated rift segments, such as the East African Rift System, the Taupō Volcanic Zone, and Iceland.
How to cite: Muluneh, A., Brune, S., Rivalta, E., Magee, C., Fraters, M., Corti, G., and Pérez-Gussinyé, M.: Stress-controlled magma-plumbing system during rift evolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11102, 2026.
Magma flow through the ~10-35 km thick lower crust in Iceland is highly episodic. Half a century of crustal deformation studies in Iceland has provided indirect information on a number of magma channels in the lower crust. Geodetic modelling of volume change associated with magma accumulation in the upper crust, and extrusion rates for eruptions directly fed from the lower crust or the mantle, reveal magma flow through lower crust at rates of 0.5-50 m3/s or less (except at the Hekla and Bárðarbunga volcanoes where it is has been higher in recent eruptions). Considering the viscosity of basaltic magma flowing in such channels (~ 10-100 Pa s), driving pressure related to density difference between magma and host rock along the channel length (of about 300 kg/m3) and buoyancy in an underlying magma lens counterbalanced by viscous drag, suggests the cross-sectional area of these channels are <30 m2, corresponding to cross-sectional area of a circle with radius of about 3 m or less. Such channels have provided: (i) continuous magma flow over years to a decade to a level of about 3-6 km depth in magma domains (near the boundary between the lower and upper crust, or close to the brittle-ductile boundary), feeding repeated eruptions such as in the Svartsengi volcanic system on the Reykjanes Peninsula since 2023, in the 1975-1984 Krafla rifting episode, and caused inflation of Askja volcano since 2021 without an eruption, (ii) episodic flow directly feeding eruptions without significant accumulation of magma in the shallow crust such as at Fagradalsfjall 2021, 2022 and 2023 eruptions on the Reykjanes Peninsula and the 2010 flank eruption at Eyjafjallajökull on Fimmvörðuháls, and (iii) episodic flow to intrusions or magma domains at Eyjafjallajökull volcano in 1994, 1999 and 2009, Öræfajökull volcano in 2017-2019, and into the Upptyppingar lower crustal intrusion in 2007-2008.
The cross-sectional area of lower crustal magma channels is very minor compared to that of dikes that have formed in the upper crust in the last 50 years in Iceland, that according to geodetic modelling have allowed magma flow rates of up to >5000 m3/s. We suggest that the lack of stored tectonic stress in the ductile lower crust limits the possibilities of formation of extensive dikes there.
How to cite: Sigmundsson, F., Parks, M., Hooper, A., Geirsson, H., Drouin, V., Lanzi, C., Einarsson, P., Hreinsdóttir, S., Greiner, S. H. M., Yang, Y., Ófeigsson, B. G., Hjartardóttir, Á. R., Sturkell, E., and Sigurðardóttir, F. M.: Episodic magma flow in narrow channels through the lower crust in Iceland: geodetic evidence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20153, 2026.
Recent advances in analytical techniques, experimental studies, and computational modelling have significantly improved our ability to investigate magmatic plumbing systems. At the same time, the increasing availability of high-dimensional petrological datasets, ranging from crystal-scale chemical maps to multimodal geochemical and textural data, poses new challenges for data integration, interpretation, and physical consistency. In this context, machine learning (ML) emerges as a powerful tool to complement classical petrological approaches, offering new ways to explore complex datasets and quantify magma storage conditions and the evolution of plumbing systems.
In this contribution, we discuss how ML can be integrated into volcanology, with a particular focus on igneous petrology. We first outline the main opportunities offered by ML approaches, particularly their potential to automate tasks, enhance modelling strategies, and accelerate knowledge discovery. Then, we address key epistemological and practical challenges, such as ensuring transparency, model interpretability, calibration limits, reproducibility, and ethical considerations. These issues become especially critical in high-risk contexts such as volcanic hazard assessment, risk mitigation, and crisis management, where reliance on ML outcomes can have serious consequences for human lives (Ágreda-López & Petrelli, 2025).
Building on these considerations, we present examples of ML-based applications to reconstruct magma storage depths and plumbing system architectures. We conclude by discussing best practices for integrating ML in volcano science and by outlining future directions for combining physics-based models and data-driven approaches to improve our understanding of magmatic systems and their associated hazards.
References
Ágreda-López, M. & Petrelli, M. (2025). Opportunities, epistemological assessment and potential risks of machine learning applications in volcano science. Artificial Intelligence in Geosciences 6 (2). https://doi.org/10.1016/j.aiig.2025.100153
How to cite: Ágreda López, M. and Petrelli, M.: Machine learning in igneous petrology: opportunities, challenges, and insights into magmatic plumbing systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16645, 2026.
The physical and chemical evolution of magmatic systems is strongly influenced by ubiquitous reactive porous flow (RPF) during the mushy state, which has been proposed to explain the textural and chemical signatures observed in plutonic rocks. Melt–mush reactions play a key role in governing the evolution of systems containing both cumulate-forming minerals and percolating interstitial melts. In oceanic settings, RPF has been extensively investigated using volcanic and plutonic records, demonstrating its strong influence on oceanic crust, including MORB, compositions. However, most of the existing studies are qualitative, and lack strong thermodynamic constraints on the feasibility and parameters of the reactions.
Here, we used forward thermodynamic modeling with the Perple_X program to constrain the modal and chemical compositions of the phases involved in melt–mush reactions, as well as the physicochemical conditions associated with RPF signatures in plutonic rocks from oceanic ridges. Constraints on RPF-induced reactions are obtained through a parametric study that explores variations in reactive melt composition, percolated mush composition and temperature. Our results define the range of thermodynamically viable reactions and reaction products, showing that melt–mush reactions can partially reproduce the typical signatures observed in plutonic rocks (e.g., Mg#–Ti in clinopyroxene). These reactions also generate significant modal variations, primarily controlled by mush chemistry and temperature. Considering the entire mushy plumbing system, from the mushy reservoirs to seafloor-emplaced lavas, we demonstrate that reactive porous flow explains the compositions of both oceanic plutonic rocks and MORB melts. Although we herein focus on reactions occurring in oceanic magmatic reservoirs, the developed approach can be applied to any type of mush-dominated magmatic system.
How to cite: Falc'Hun, C., Bouilhol, P., and France, L.: How reactive porous flow shapes magmatic systems : A thermodynamic approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10827, 2026.
The influx of Na–F–rich fluids have the potential to shift magma compositions from peraluminous (molar [Na₂O + K₂O]/Al₂O₃ < 1) to peralkaline (molar [Na₂O + K₂O]/Al₂O₃ > 1) in silicic continental systems. The genesis of peralkaline rhyolites has long been debated, and their association with peraluminous magmas is commonly interpreted in terms of distinct magma series derived from different sources. Their contrasting compositions lead to divergent crystallization paths and mineral assemblages, often resulting in markedly different whole-rock geochemistry. At the McDermitt caldera (Nevada–Oregon, USA), both peraluminous and peralkaline rhyolites erupted between ca. 16.7 and 16.4 Ma in association with Yellowstone hot-spot activity. Peraluminous rhyolites are characterized by plagioclase, sanidine, and Fe-rich biotite (with quartz appearing in the most evolved units), whereas peralkaline rhyolites contain sanidine, quartz, and two coexisting amphibole populations (Ca-rich and Na–F-rich) within the same rocks. Despite these mineralogical differences, whole-rock compositions of the two magma types show no systematic contrasts, except for stronger negative Ba, Sr, P, Eu, and Ti anomalies in the peralkaline rhyolites, consistent with their more evolved mineral assemblages. These observations argue against distinct magma sources and instead suggest a progressive “peralkalinization” of a common parental magma, restricted to the most silicic units. Strong Mg–Fe–F zoning in biotite and the coexistence of chemically distinct amphiboles indicate a major shift in the chemical conditions of the shallow magmatic system. Previous studies have shown that Na–K–F–rich fluids can effectively modify peraluminous melts toward peralkaline compositions. Here, we use mineral chemistry, in situ and whole-crystal trace-element analyses of biotite and amphiboles, and major- and trace-element data from melt inclusions in quartz and feldspars to test and characterize this peralkalinization process. Our aim is to constrain the pre-eruptive and pre-crystallization conditions of these magmas and to assess the role of alkali–halogen-rich fluids in driving compositional evolution and metal enrichment. McDermitt thus represents a natural laboratory for investigating the magmatic–hydrothermal transition responsible for Li and other critical-metal endowments, and for evaluating whether such enrichments are primary magmatic features or are enhanced by late-stage fluid–melt interaction.
How to cite: Buian, A. and Ruprecht, P.: Fluid-driven peralkalization of silicic peraluminous magmas: evidence from the McDermitt caldera (USA), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5960, 2026.
From May 2018 to late 2021, Mayotte experienced a major volcanic crisis that produced ~6.5 km³ of nearly aphyric (<5 wt.% crystals) evolved basanitic magma (4–5 wt.% MgO) and led to the discovery of a new offshore volcanic edifice, Fani Maoré, located ~50 km east of the island. The emitted basanite is characterized by the presence of Olivine (Fo70), Titanomagnetite and Apatite assemblage which dominated throughout the eruption. Yet, in some phases of the eruption, the main mineral cargo also contained minor amounts of reversely zoned ferrous olivine from Fo55 cores to Fo70 rims, associated with ilmenite crystals partially resorbed and overgrown by titanomagnetite at their margins. Thermobarometric constraints derived from clinopyroxene antecrysts identified in the basanite indicate that the eruption was supplied by two magmatic reservoirs located at deep mantle conditions (≥37 km), in close agreement with the depths of volcano-tectonic seismicity recorded throughout the crisis. Yet, these inferred depths contrast with the origin of the dominant Ol+Mt+Ap assemblage which, according to previous studies, was formed during syn-eruptive ascent. Further, interaction of the dominant basanitic magma with a more evolved tephri-phonolitic reservoir at 17 ± 6 km could explain the reverse zoning observed in some olivines. Based on the disparity between reservoir location and mineral assemblage crystallization conditions and the large uncertainties of thermobarometric tools (100–400 MPa and ±50°C for Pressure and Temperature respectively), we conducted high-pressure crystallization experiments using a piston-cylinder apparatus at pressures of 0.7–1.3 GPa and temperatures of 1050–1100°C, exploring seismically defined magma storage depths and intensive parameters (H₂O + CO₂ contents and oxygen fugacity). Experimental results demonstrate that the transition from Olivine-dominated to clinopyroxene-bearing assemblages occurs between 0.7 and 1 GPa (~21–30 km), with clinopyroxene stable only at higher pressures. However, clinopyroxene is absent from the magmatic paragenesis and only one antecryst has been described. This inescapably implies pre-eruptive magmatic storage at depths ≤21 km, where Olivine, Titanomagnetite and Apatite are stable. The Mg/Fe ratios of experimental olivine crystals show a strong dependence on temperature and oxygen fugacity, providing robust constraints on magma storage conditions. Best-fit conditions for the final storage episode of the evolved basanite are ~1075°C and pressures ≤0.7 GPa at ~FQM buffer. At odds with previous allegations, we show here that our experiments successfully reproduce the chemical evolution of the rocks, indicating that crystallisation processes within a single reservoir remain possible. This storage depth, obtained from our experiments, contrasts with seismicity and thermobarometry that locate a reservoir at >37 km depth. This contrast implies at least two distinct levels of storage within the plumbing system, which may be related to a seismicity gap between 12 and 25 km beneath the volcano observed during the eruption. These results constrain the architecture and dynamics of the magmatic plumbing system feeding one of the largest recent submarine volcanic events.
How to cite: Guégan, S., Andujar, J., Gaillard, F., and Wawrzyniak, P.: Experimental insights on storage depth of Fani Maoré magmas (Mayotte), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21660, 2026.
Understanding the architecture of magmatic plumbing systems, including the coexistence, depth, and connectivity of magma reservoirs leading to eruption, guides where and how we probe the crust for hazardous magma bodies. Given the scarcity of volcanic events at a given volcano and challenges in resolving magmas in the subsurface with geophysical techniques, products from past eruptions provide an alternate avenue to reconstructing this architecture. We present major and trace element data from matrix glass and minerals (feldspar, biotite, zircon) from the Tuff of Elevenmile Canyon supereruption (≤5000 km3; 60-78 wt.% SiO2) in western Nevada, USA. Matrix glass geochemistry and geobarometry reveal that the eruption tapped multiple discrete, coexisting magma reservoirs within a vertically extensive magmatic system. Glasses fall into at least five compositional groups distributed over pressures ranging from ~50 to 1000 MPa (2-37 km), determined by multiple geobarometers, including rhyolite-MELTS, MagMaTaB, Al in hornblende, and the haplogranitic ternary. Glass compositions vary along at least two independent crystallization paths (Paths 1 and 2) which are associated with distinct feldspar textures and compositions. Path 1 feldspars are dominated by simple, oscillatory zoning, while Path 2 feldspars dominantly display complex resorption and exsolution-like textures (e.g., feathery lamellae at zone boundaries). Compositionally, Path 1 plagioclase records more extensive variation (An20-65) from core to rim while alkali feldspar is compositionally constrained (Or60-70). One distinctive sample group (Path 2) includes a feldspar population characterized by oligoclase and anorthoclase cores rimmed by alkali feldspar (anti-rapikivi). Biotite grains are ubiquitous and euhedral throughout the eruption, with no apparent breakdown or reaction rims. Their compositions generally fall into discrete groups associated with distinct pressure horizons in our geobarometry results. In BSE imaging, higher Mg# (47-60) biotites commonly contain dark, resorbed cores with bright rims while lower Mg# (40-45) biotites display the opposite trend and are either unzoned or oscillatory zoned. In some cases, single biotite grains may contain cores that fall into one sample group, and rims that plot in another, illuminating links between melts in different pressure horizons. Other samples bridge compositional gaps between populations. Thus, biotite captures melt interactions and dynamics not recorded by other phases. Zircon crystals from all glass compositional groups overlap in trace element composition. This suggests that this phase captures either a distinct period in the system’s evolution or an alternate process. This work highlights the power of a multiphase approach to capturing snapshots into a dynamic magmatic system’s history, leveraging both compositional and mineral textural information.
How to cite: Ruefer, A. C., Pamukçu, A. S., Chiaro, G. R., Price, M. E., Lewis, M. J., Eddy, M. P., and Desormeau, J. W.: Snapshots of a supereruption: multiphase insights into the Tuff of Elevenmile Canyon from glass, feldspar, biotite, and zircon , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15209, 2026.
Constraining magma storage conditions and pre-eruptive mobilization timescales is essential for understanding how deep-seated magmatic unrest progresses toward eruption. While these processes are increasingly well constrained in Iceland’s on-rift volcanic zones, magma dynamics in off-rift flank regions remain poorly understood, despite their potential for hazardous explosive eruptions. Here, we investigate magma storage depths and pre-eruptive timescales of magma mobilization and crystal-mush erosion in the Snæfellsnes Volcanic Zone (SNVZ), a relict Tertiary volcanic belt hosting Iceland’s most extensive off-rift volcanism. We integrate olivine Fe-Mg diffusion chronometry with fluid inclusion and clinopyroxene-based barometry to reconstruct magma storage conditions preceding the Holocene Búðahraun and Berserkjahraun eruptions. Our results identify a dominant magma storage region at ~11-15 km depth [1]. The absence of fluid inclusions recording shallow storage indicates rapid olivine entrainment and swift magma ascent from mid-crustal depths to the surface. These storage depths broadly overlap with deep seismicity (15-20 km; median ~17 km) detected in the SNVZ since August 2024, consistent with possible reactivation of a mid-crustal magma domain by ongoing mantle-derived magma intrusion. Olivine diffusion chronometry indicates that mush erosion began ~4.9 and ~1.8 years prior to the Búðahraun and Berserkjahraun eruptions, respectively, with mobilization accelerating during the final ~1.5 months before eruption. These results suggest that once magmatic unrest in the SNVZ progresses toward eruption, magma mobilization may proceed rapidly, with eruptions potentially following within weeks to months. These timescales are comparable to those documented in Icelandic on-rift systems, suggesting broadly similar magma mobilization processes in off-rift and on-rift systems. In light of ongoing seismicity, our findings provide the first quantitative lead-time constraints relevant for monitoring and hazard assessment in this historically quiet, yet potentially active, off-rift volcanic zone [1].
[1]: Kahl, M., Morgan, D.J., Wieser, P.E. et al. Crystal-mush remobilization timescales and magma storage depth in the Snæfellsnes Volcanic Zone (W-Iceland): insights from olivine Fe-Mg diffusion chronometry and fluid inclusion barometry. Bull Volcanol 87, 118 (2025). https://doi.org/10.1007/s00445-025-01892-3
How to cite: Kahl, M., Morgan, D. J., Wieser, P. E., Bali, E., Guðfinnsson, G. H., Neave, D. A., and Walshaw, R.: Unlocking the Off-Rift Record: Magma Storage and Mobilization in the Snæfellsnes Volcanic Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3774, 2026.
Magmatic plumbing systems are vertically extensive, complex, and dominated by crystal mush (Cashman et al., 2017). Across tectonic settings, distinct lithospheric architecture, magma flux and magma composition modulate the anatomy and dynamics of magma plumbing systems (Ubide et al., 2023). Understanding magmatic architecture in convergent margins is of particular interest, because volcanic arcs host explosive eruptions, build the continental crust, and can accumulate critical metals, such as in porphyry copper deposits. Magma plumbing systems in volcanic arcs are commonly transcrustal; however, differences in magma flux (Best et al., 2016) and tectonic context, which modulates magma composition (Ward et al., 2024; Bennett et al., 2025), impose notable differences that have remained underexplored.
Here, we focus on the Sunda arc (Indonesia) as a natural laboratory to constrain differences in magmatic architecture from typical calc-alkaline volcanoes in the main arc to anomalous volcanoes located off-axis, where the slab reaches depths >200 km and erupted magmas become strongly alkaline and silica-undersaturated (potassic; Ward et al., 2024; Bennett et al., 2025). By applying novel high-resolution petrology to the crystal cargo (Davidson et al., 2005; Ubide & Kamber, 2018; MacDonald et al., 2023) and the carrier magmatic liquids (rock groundmass; Ubide et al., 2023), we resolve differences in storage depths and temperatures, magma dynamics and eruption triggers across the arc. We find that relative to typical calc-alkaline volcanoes, the anomalous alkaline volcanoes are characterized by deeper storage and more mafic compositions, which can trigger eruptions rapidly filtering eruptible liquids, similar to observations in ocean island settings (Ubide et al., 2022). Our new insights aim to assist monitoring of future eruptions and improve understanding of the architecture of magmatic systems that become fertile for mineralization in critical metals.
Best et al., 2016 Geosphere
Cashman et al., 2017. Science
Davidson et al., 2005 JVGR
Edmonds et al., 2019. Philosophical Transactions A
MacDonald et al., 2023 J Petrol
Ubide and Kamber, 2018 Nature Commun
Ubide et al., 2022 Geology
Ubide et al., 2023. The Encyclopedia of Volcanoes (pre-print in EarthArXiv)
Ward et al., 2024 EPSL
How to cite: Ubide, T., Rosenbaum, G., Ward, J., MacDonald, A., Bennett, D., and Sihombing, F. M. H.: Magmatic architecture across tectonic settings – the case of calc-alkaline vs. potassic volcanoes in the Sunda arc, Indonesia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15975, 2026.
The Saurashtra region in Western India contains an extensive network of mafic dykes and lava flows, constituting a significant yet least explored part of the Deccan Flood Basalts. In contrast to the extensively studied dyke systems of the Western Ghats and Narmada–Tapi Swarm, the Saurashtra region retains indications of possibly independent and spatially variable magma plumbing systems. However, the relationships between dykes, potential feeder channels, and overlying flow units are not thoroughly understood. Previously, geochemical investigations identified both tholeiitic and alkaline magmas in this area, each characterized by distinct isotopic signatures, mineralogical compositions, and mantle origins.
This study combines structural and magnetic fabric analyses to find out if the Saurashtra dykes are separate intrusive events, localized feeder systems for nearby flows, or components of a regionally interconnected magma transport network. These insights will shed light on their emplacement dynamics and tectono-magmatic significance within the broader Deccan framework.
Various dyke parameters, like orientation patterns, dyke length, thickness variations, segmentation, and cross-cutting interactions, will be systematically mapped out as a first step in the study. These features may reveal the intrusive mechanisms and in-situ stress conditions present during magma emplacement. Particular focus will be directed towards the spatial correlations between Saurashtra dykes and lava flows to ascertain potential feeder-flow links.
Anisotropy of magnetic susceptibility (AMS) will be used to determine magma flow directions and sense within dykes and flows. Combined with structural observations, AMS will help distinguish between lateral, vertical, or complex hybrid intrusion pathways and test for multiple functioning magma sources across the region. Complementary rock-magnetic investigations (hysteresis, domain-state analysis, Curie temperatures, and mineralogical characterization) will support interpretation by separating primary cooling signatures from secondary alteration.
If possible, geochronology and magnetic polarity data will be used to find eruptive phases and figure out if the intrusions are separate magmatic pulses or part of a multi-stage system in the larger Deccan province. Expected outcomes encompass extensive structural and magnetic datasets, improved constraints on dyke–flow connection, identification of possible feeder centers, and a more comprehensive understanding of Saurashtra’s intrusive within the Deccan magmatic framework. This work aims to enhance understanding of Large Igneous Province plumbing systems and the connections between intrusive and eruptive processes in volcanic areas by combining multiple datasets.
How to cite: Shukla, G., Lakshmi, B., Mohite, P., Singh, M., Deenadayalan, K., and Dimri, A.: Emplacement Dynamics and Magma Plumbing System Structure of the Dykes and Flows in the Saurashtra Region of the Western Deccan Volcanic Province, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-926, https://doi.org/10.5194/egusphere-egu26-926, 2026.
In the upper crust, dykes are commonly assumed to propagate as elastic fractures, exhibiting thin, tapered geometries, and propagating through mode I, tensile opening at the fracture tip. In the lower ductile crust, which is often assumed to have a Maxwell-type rheology, the fast strain rates associated with dyke emplacement are thought to embrittle the host rock. This reasoning has led to the assumption that ductile deformation of the host rock is negligible during dyke emplacement in the deep crust. In Sarek National Park, northern Sweden, a dyke complex was emplaced during a ca 608 Ma continental rifting event at depths of 10–15 km and temperatures reaching ca 650 °C. The dyke swarm was emplaced into carbonate and sandstone host rocks. Detailed field observations from glacially polished outcrops demonstrate that significant ductile deformation of the host rock accommodated dyke emplacement. We quantify that approximately 25% of the dyke thickness is accommodated by ductile folding of the host rock. Thermal modelling is used to estimate magma crystallization times, which in turn allow estimating ductile strain rates on the order of 10-3 to 10-6 s-1. These strain rates are 6 to 10 orders of magnitude higher than typical tectonic ductile strain rates in the middle crust (10-12 - 10-15 s-1). Furthermore, we document how the weak rheology of the host rock influenced the shape and geometry of the mafic dykes. These results have implications for our understanding of dyke emplacement as well as general deformation and rock strength in the ductile crust, which constitute a significant part of the pathway for magma to reach the surface.
How to cite: Kjøll, H. J., Scheiber, T., and Galland, O.: Rapid viscous flow of crustal rocks controls dyke emplacement in the ductile crust, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19107, 2026.
Subsurface magma emplacement in the middle/shallow crust triggers rock-/surface-uplift, rock deformation and crustal heating. Understanding dimensions, depths and the short- to long-term evolution of such intrusions might be crucial for geothermal explorations or surveillances and monitoring of un-resting volcanic settings. Several approaches are currently applied for exploring both active and inactive blind subsurface intrusions, but commonly based on invasive, costly, and time-demanding methods which in most cases only provide a current snapshot. To overcome these limits, we test a novel linear river inversion scheme in the active geothermal field of Larderello-Travale-Magmatic-System (LTMS) in the Northern Apennines of Italy, through which we extract spatially explicit maps of rock-uplift rates from topographic and geological data. After combining our pattern of rock-uplift rates with available low shear-wave velocity anomaly (SW), imaging the current magma body beneath LTMS, we document a strong correlation in space and wavelength between surface topographic responses to subsurface magmatic processes. This exercise allows us to infer the location and depth of the magmatic system, the associated surface deformation caused by the emplacement of magma, a minimum estimate for the active volume of partial melt characterizing the geothermal system, and a preliminary estimate for the magma overpressure.
Our approach, for the first time, offers the opportunity to bridge different time scales of observations together with supporting the interpretation of geophysical analyses such as the ambient noise tomography. Eventually, with this work we demonstrate that early-stage exploration or monitoring of crustal magmatic intrusions is possible by using non-invasive, environmentally sustainable and extremely low-cost river network inversions, representing significant advantages over previous methods.
How to cite: Lanari, R., Smith, A., Stumpp, D., Bonini, M., Del Ventisette, C., Fox, M., Lupi, M., Cabrera-Perez, I., and Montanari, D.: Linking Long-Term Rock Uplift and Shear-Wave Anomalies to trace Magma Emplacement , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17946, 2026.
Magma generated at depth ascends through the crust and erupts at the surface. In this process, the magma volume creates space by deforming the crustal rock. To study this process, researchers have employed analogue experiments for decades. Conventionally, most analogue models assume the crustal rock as a purely elastic, brittle (Coulomb), or viscous material. However, natural rocks exhibit more complex visco-elasto-plastic behaviours, with rheological properties transitioning from elastic-plastic to visco-elasto-plastic with increasing depth. Conversely, magma itself behaves as a Newtonian fluid, exhibiting a range of viscosities influenced by factors such as silica and volatile content. In this study, we conducted scaled 2D analogue magma emplacement experiments using Laponite® RD (LRD), a complex visco-elasto-plastic rheological material, as a host rock analogue. The rheological properties of LRD were systematically varied by changing the curing time (tc) from tc = 30 min to tc = 240 min to simulate a broad range of crustal rheological behaviours, corresponding to different depths from viscous to visco-elasto-plastic regimes. Food-coloured water and hydroxyethyl cellulose (HEC) aqueous solutions, with concentrations of 0.50 wt% and 0.75 wt%, are used to simulate magma with varying viscosities. Polyamide seeding particles (PSPs) of 60µm diameter were incorporated inside the LRD solution to quantify host-rock deformation during magma emplacement via particle image velocimetry (PIV). Our experimental results show that magma intrusions exhibit various shapes, ranging from straight-edged fractures in the case of low-viscosity water and viscoelastic LRD of high tc to bulbous, rounded forms in high-viscosity HEC and viscous LRD of low tc. Furthermore, PIV data enabled the identification of domains exhibiting distinct deformation types, thereby delineating changes in deformation regimes attributable to variations in the rheological properties of the host rock. Finally, by integrating geometric and PIV analyses, we established a relationship between the intrusion morphology and host rock rheology, and propose a mechanical model that elucidates the deformation mechanisms operative within the host during magma emplacement across different rheological combinations of host and magma materials.
How to cite: Biswas, U., Galland, O., and Carlson, A.: Magma emplacement mechanism in visco-elasto-plastic crustal rock: an insight from quantitative 2D analogue experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18980, 2026.
Partially molten lower-crustal domains are key features of many large hot orogens, including the Altai tract of the CAOB, Tibet, and the Altiplano–Puna, where seismic imaging reveals extensive low-velocity, high-temperature regions interpreted as crustal mush zones. These regions form and evolve under the combined influence of crustal thickening, mantle–lithosphere removal, and thermally driven weakening, which together promote melt generation, rheological softening, and decoupling between crustal levels, thereby enabling lateral and vertical redistribution of material. Yet, the feedback between melt migration, deformation, and mechanically anisotropic, layered mush systems remains insufficiently quantified.
In this contribution, we compare different types of models that approximate the crustal evolution of hot orogens: semi-scaled thermal paraffin-wax analogue models with visco-plastic finite-element numerical models that respect the laboratory scale and employ similar material properties. In addition, orogen-scale control numerical models were performed to mimic natural prototypes. The models were designed to explicitly address (i) crustal strength, shortening, and basal heating, and (ii) how these parameters govern internal deformation, melt coalescence, and plumbing-system architecture.
Analogue experiments successfully reproduced melt migration and its coalescence in buckled and folded layers, suggesting that mechanically layered mush domains can localize melt along fold hinges, shear zones, and evolving permeability pathways, with potential transitions from dominantly lateral to buoyancy-driven melt transfer as deformation proceeds. However, the analogue models lack rigorous and precise quantification of the thermal field, and melt migration is tracked approximately, using image analysis based on DIC and X-ray CT-scanning methods. Furthermore, precise dynamical scaling is currently limited by the absence of a representative rheological law based on the complex rheometry of the paraffins used, restricting us to discrete viscosity measurements for different velocities and temperatures.
The first step in the numerical approach was to reproduce the analogue model geometry and melt distribution. Simulations successfully mimic the development of melt-rich regions at both laboratory and orogen scales within a range of natural parameter values, but they do not reproduce the degree of melt coalescence within crustal layers that occurs naturally in the analogue models; nevertheless, these weak zones promote further strain distribution and strongly influence the overall crustal deformation response. An important advantage of the numerical approach is the well-constrained control on the thermal regime and temperature–melt evolution in the system. For the tested parameters, however, the numerical models yield a more homogeneously thickened crust without significant buckling of the lower crust, and a major limitation is the absence of porous melt flow, which may play a key role in melt coalescence and ascent.
The discrepancy between analogue and numerical results suggests more complex rheological coupling between deformed and partially molten crustal layers than can be captured by either method alone. This motivates a re-evaluation of the dynamical and thermal scaling of analogue experiments and the implementation of porous flow and anisotropic permeability in future numerical models.
How to cite: Krýza, O., Maierová, P., Závada, P., Zwaan, F., Schreurs, G., Schulmann, K., and Čížková, H.: Evolution of hot partially molten orogenic crust during lateral compression: Insights from numerical and analogue models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21591, 2026.
The central West Philippine Basin (WPB) comprises three contrasting geomorphologic provinces, the mantle-plume type Benham Rise in west, the volcanic arc-type Kyushu-Palau Ridge (KPR) at the east limit, and the in-between central rift hosting the deepest (~7874 m) seafloor. Their morphic transit and dynamic interactions remain elusive owing to the insufficiency of relevant data. Incorporating new and previous multibeam bathymetry data fully enveloping the central rift enables us to synthesize a 3-band, 3-segment seafloor morphic fabric of the central WPB and deduce its formation mechanisms. It features prominent across- and along-axis variations and variable landform assemblages, including: 1) overall trends of abyssal hill lineation swing counter-clockwise from ~N100/105°E at a distance of 100 km from the central rift valley to ~N85/95°E at a distance of ~30/50 km, then clockwise to ~N100/140°E in the valley, which recognizes three irregularly embedded bands reflecting a rotatory spreading fabric; 2) the valley narrows westward from ~85 km wide near the KPR to ~25 km at Centric Deep, and then fades out to further west, synchronously from shallow, volcano-rich to deep, volcano-poor then to failed, indicating a northwestward propagating rift driven by the KPR arc volcanism. Moreover, it is found in the middle segment that three major transform faults bend southwesterly in the southern band with their concaves consistently pointing to the Benham Rise. Behaving as pseudo-faults, they are interpreted as result of propagating rift triggered by the former magmatism of the Benham Rise. Lying just at the intersection of a relict nodal basin and the western tip of the later propagating rift, the depth maxima (~7874 m) might have resulted from intersection of two rifts from west and east, respectively. Thus, the geomorphic fabric featuring high spreading instability reflects strong magma-tectonic intervention by excessive magmatism of mantle plume and subduction arc.
This study was funded by the China Geological Survey Project (grant No. DD20230642), NSFC (grant No. 42574132 and U1901217).
How to cite: Yan, P. and Weidong, L.: Unstable spreading owing to extra magmatism in the central West Philippine Sea Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8572, 2026.
Layered intrusions represent the fossilised remains of mafic to ultramafic magma bodies. They host significant critical metals and are intensively studied as natural laboratories for igneous processes. The eponymous layers occur over length-scales ranging from millimetres to decametres and are typically interpreted to represent cumulates formed during fractional crystallisation of one or more parental magmas. Most natural melts crystallise several mineral phases at the liquidus to form polymineralic cumulates, but many intrusions also host layers dominated by a single mineral such as olivine, orthoypyroxene, plagioclaise or chromite.
Numerous conceptual models have been proposed to explain the formation of monomineralic layers. Most suggest that these layers form when there is restricted stability of minerals crystallising at the liquidus coupled with efficient separation of cumulate minerals and melt. During the formation of a cumulate layer, compaction of a crystal ‘mush’ contributes to melt loss once the melt fraction falls below 40 – 60 %. However, there is a lack of microstructural evidence for compaction, especially to the low melt fraction of adcumulates (<5% interstitial melt). Convective flow in the mush could replenish the melt, allowing ongoing crystallisation of a single phase, but only if the local bulk composition and temperature allow this. Alternatively monomineralic layers could crystallise from melts saturated with a single phase, but such melts are not produced by fractional crystallisation of any reasonable parental magma composition, so they are typically assumed to be sourced elsewhere.
Here we use a one-dimensional model to test the role of reactive flow in creating layering. Reactive flow can occur whenever there is relative motion between melt and crystals and the bulk composition is spatially variable. We develop a two-phase (melt and crystals) numerical model that is applicable to layered intrusions constructed incrementally or by a single batch of magma. The numerical model captures (i) the buoyancy-driven separation of melt and crystals by crystal settling at high melt fraction and percolative flow at low melt fraction; (ii) compaction of crystal mush at low melt fraction; (iii) transfer of heat by conduction and advection; (iv) transfer of chemical components in melt and crystal phases, and (v) crystal-melt component and mass exchange. We report a chemical model developed specifically for layered intrusions.
Results of our numerical model suggest that reactive flow during melt-crystal separation can explain the formation of monomineralic layers and other characteristic features of layered intrusions. Reactive flow can produce the upwards decrease in MgO usually interpreted to reflect fractional crystallisation, but also the commonly observed local decreases (‘reversals’). It can also remove an early-formed upper boundary zone and explain the lack of microstructural evidence for compaction. Our results suggest that reactive flow is an important process in which there is a relative movement of melt and crystals that can chemically react, regardless of if magma is intruded as single or multiple batches. Simple models of fractional crystallisation or compaction neglect reactive flow and can fail to fully understand the formation of layered intrusions.
How to cite: Booth, C., Davis, S., Hu, H., Jackson, M., Virtanen, V., Kutyrev, A., and Maier, W.: Reactive flow as a mechanism to form monomineralic rocks in layered intrusions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7394, 2026.
In geochemistry, big data applications at both global and regional scales rely on compilation and aggregation of numerous smaller datasets to form a big dataset. For this reason, geochemical data compilations are vulnerable to systematic biases between the smaller datasets they are composed of. These biases relate to the analytical methods and procedures, laboratories, instruments, sample preparation, detection limits, mass interferences, sample matrices, etc. In other words, the preparation and analysis of each sample batch is unique beyond the “method” or “laboratory” bias. This uniqueness and potential offsets it might cause between analytical batches we define as inter-study bias. The only quantitative way to evaluate inter-study bias in geochemical data compilations is through metadata and specifically assessment of analytical data of geochemical reference materials. Reference materials are substances of known composition measured alongside unknown samples, as is a standard good practice during routine geochemical analyses. In an ideal world, all geochemical studies report analyses and values of reference materials and analytical methods and analyses have been refined and calibrated to match the reference material’s certified value within uncertainty. Only in this case can the inter-study bias be considered negligible. Accordingly, most geochemical big data compilations are based on this assumption and do not explicitly assess the metadata for potential inter-study bias. In the real world, perfectly calibrated analyses are often not the case and metadata uncommonly reported.
To assess the comparability, compilability and inter-study bias between geochemical datasets, we have developed several data quality and outlier-detection tools based on the Geological and Environmental Reference Material database - GeoReM. We use these tools to showcase the implications of inter-study bias for global geochemical interpretation models using two well-known geochemical big data research topics: 1) identification of compositional end-members for oceanic basalts and the origin of their source mantle components (colloquially called “the mantle zoo”) and 2) compositional signatures of zircons as tracers for the growth, reworking and evolution of the continental crust. Our take home message: Geochemical datasets must be comparable to be compilable. We therefore advocate the assessment of your inter-study bias as well as comprehensive reporting of your metadata and reference materials, so that computational geochemistry can progress as a subdiscipline of big data science.
Keywords: Reference material, GeoReM, outlier, metadata, method bias, isotopes, mantle geochemistry, zircon, GEOROC, crustal evolution
How to cite: Traun, M. K., Renno, A. D., Kallas, L., Willbold, M., Waight, T., Garbe-Schönberg, D., and Wörner, G.: How comparable are geochemical datasets really and why it matters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14861, 2026.
Amphibole is a common hydrous mineral in mafic calc-alkaline magmas that typically crystallizes via a peritectic reaction involving pre-existing minerals and melt. Its role in arc magma differentiation is fundamental, thus, constraining the amphibole-forming peritectic reaction is key to interpreting the dynamics and evolution of trans-crustal magmatic systems. Up to date, only a limited amount of experimental studies focused on the amphibole peritectic reaction in basaltic to basaltic-andesitic systems, showing that the mineral assemblage involved in this reaction varies as a function of bulk composition and pressure. Although these studies provide first insights, systematic investigations allowing the prediction of amphibole crystallization are still missing. Therefore, the aim of our contribution is to experimentally quantify the amphibole-forming peritectic reaction and to investigate how various parameters (i.e. pressure, bulk composition) influence the reaction stoichiometry.
Equilibrium crystallization experiments were performed in internally heated pressure vessels (IHPV) at mid-crustal pressures between 200 and 400 MPa and temperatures between 950 and 1050 °C employing varying initial bulk H2O contents (1-9 wt.%). Oxygen fugacity was buffered at conditions around NNO+2. To better constrain the amphibole forming reaction, a supplementary two-step experimental approach was used, involving first the synthesis of an amphibole-free crystalline assemblage and a second step at lower temperatures to trigger amphibole saturation at the expense of previously formed anhydrous phases. So far, two different basaltic starting compositions were explored covering the typical compositional range of mafic arc magmas.
Our results show that clinopyroxene systematically participates as a reactant in the amphibole-forming peritectic reaction, while olivine is frequently, but not always, involved. At low bulk water content (< 3.0 wt.%), amphibole and orthopyroxene crystallized simultaneously, thus the role of orthopyroxene as a reactant or a product in the reaction remains to be defined. From our dataset, we formulated a general preliminary stoichiometric peritectic reaction for basaltic calc-alkaline magmas valid for mid- to upper- crustal conditions (200-400 MPa): 0.62 (±0.10) melt + 0.15 (±0.02) olivine + 0.20 (±0.09) clinopyroxene + 0.03 (±0.03) oxide = 1.0 amphibole. Increasing pressure or bulk water content generally favors more melt and less clinopyroxene being involved in the reaction. These results are crucial to provide new experimental constraints that can be implemented in thermodynamic models, improving the prediction of amphibole crystallization in natural magmatic systems and offering insights into the conditions controlling amphibole fractionation in arc magmas.
How to cite: Altermatt, A., Marxer, F., and Holtz, F.: Experimental investigation of the amphibole-forming peritectic reaction in mafic calc-alkaline magmas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6305, 2026.
The Cordón Caulle volcanic graben system in the Chilean Southern Andean Volcanic Zone represents an ideal setting to study magmatic processes within an active tholeiitic arc system. Rhyolitic lavas erupted in 2011-2012 host crystal-rich basaltic enclaves with interstitial glasses that are compositionally very similar to their host rhyolitic magmas. Thus, these basaltic enclaves have been interpreted as pieces of a crystal mush where the host rhyolites represent late-stage extracted residual melts. This model suggests closed-system, in-situ rhyolite generation at Cordón Caulle, which offers a rare possiblity to investigate the formation of rhyolites in a single differentiation step from a parental basalt.
In this study, we experimentally test this petrogenetic model by performing partial melting experiments on natural rock powders of basaltic enclave samples employing bulk water contents of 0.0 to 1.0 wt.%. Experiments were run in internally heated pressure vessels (IHPV) at 75 and 150 MPa and temperatures between 800 and 1000 °C, corresponding to previously estimated pre-eruptive magma storage conditions for the 2011-2012 Cordón Caulle eruption. Our experimental setup is specifically designed to simulate a crystallisation-driven differentiation mechanism applicable to an in-situ evolving crystal mush, representing a mixture between fractional and equilibrium crystallisation regimes, where the "reactive magmatic system" is continously changing during progressive cooling.
Experimental liquids define distinct differentiation trends and show a close compositional match with the natural rock record. In particular, near-anhydrous runs at 1000 to 900 °C reproduce distinctively best the rhyolites erupted in 2011-2012 inferring rhyolite generation at rather hot and nearly dry magmatic conditions. Consequently, in-situ generation of highly-evolved liquids in a nearly-anhydrous cooling basaltic crystal mush combined with an efficient residual melt extraction mechanism represents a possible differentiation scenario for the Cordón Caulle system. Moreover, we speculate that this mechanism of nearly dry, hot, and shallow magma storage and single step rhyolite generation likely also occurs in similar arc tholeiitic systems worldwide.
How to cite: Marxer, F., Ruprecht, P., and Koch, L.: In-situ rhyolite generation in a basaltic crystal mush - an experimental study of the 2011-2012 Cordón Caulle eruption, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1743, 2026.
Silicic caldera volcanoes normally cause adverse effects on human life since they often generate some of the largest and most catastrophic volcanic eruptions and eject massive amounts of gases (e.g., H2O, CO2, S, Cl, and F) into the stratosphere, potentially leading to extreme climate conditions. Oxygen fugacity (fO2) is a vital chemical parameter controlling the geochemical behavior of multivalent elements (e.g., Fe, V, S, and C) but also influences magma degassing and magmatic evolution processes. Thus, studying the relationships between redox states and magma evolution is essential for the interpretation of mineral and residual liquid compositions in peralkaline felsic magmas.
Changbaishan is located on the border between the Democratic People’s Republic of Korea and China and has violently erupted large-volume volcanic lavas and ashes in the past 250,000 years. Previous works have shown that the eruptions of Changbaishan volcano produced a large variety of different rocks ranging from basalt over trachyte to rhyolite. Up to now, only few studies focused on the pre-eruptive fO2 range of the highly evolved magmas of Changbaishan volcano and on the possible impact of redox state on eruption explosivity and liquid lines of descent.
In this study, we evaluated the redox states of Changbaishan magmas using Fe-Ti oxide and magnetite-melt oxybarometry. Our results reveal that trachyte and rhyolite magmas exhibit a broad range in oxygen fugacity spanning from FMQ+1 to possibly FMQ-3, where rhyolitic magmas indicate more reducing conditions than trachytic magmas. Different possible hypotheses are discussed to explain this feature, including degassing of sulfur species (notably SO2), magma mixing or crustal contamination. This work provides new insights into the evolution of pre-eruptive redox states in magma reservoirs of Changbaishan volcano and potential critical factors controlling eruption explosivity.
How to cite: Liu, Y., Zhang, C., Marxer, F., and Holtz, F.: Multiple constraints on oxygen fugacity of the highly evolved magmas of Changbaishan volcano (China/North Korea), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22957, 2026.
Axial Seamount is the most extensively monitored submarine volcano, located in the Pacific Ocean on the Juan de Fuca Ridge. Its voluminous edifice is related to the interaction of a hotspot with a convergent margin. Axial Seamount had recent eruptions occurring in 1998, 2011, and 2015 from a 3 km × 8 km caldera. Recent 3D seismic reflection imaging (Kent et al., 2025) has highlighted funnel-shaped structures beneath the axial magma lens, interpreted as magma assimilation fronts. These structures are thought to result from the assimilation by Axial Seamount magmas of hydrothermally altered sheeted dykes and gabbroic rocks. The assimilation fronts are produced during periods of high magmatic activity, whereas their solidification and accretion occur during low magmatic phases, implying cyclicity in the magmatic activity of Axial Seamount.
Here, we present new high-resolution petrological data focused on olivine phenocrysts from Axial Seamount lavas to better constrain the organisation of its magmatic reservoir and its associated assimilation dynamics. We conducted major and trace element mapping (Mg, Cr, Ni, Al, Ca, and P) of olivine grains using electron probe microanalysis (EPMA) specifically optimized for trace element measurements. These elemental maps were coupled with high spatial and analytical resolution in situ oxygen isotope measurements performed on the same grains using secondary ion mass spectrometry (SIMS).
Elemental mapping of olivine grains allows investigation of specific magma dynamics such as differentiation, early rapid growth events, and the presence and potential destabilization of long-lived mushy environments, which are notably recorded by slowly diffusing elements such as phosphorus and aluminum. In contrast, oxygen isotopic composition is a powerful tracer of the nature of potential assimilated components. We therefore use oxygen isotopes to search for additional evidence of assimilating phases inferred from geophysical data at Axial Seamount and link these observations to reservoir dynamics by coupling isotopic data with elemental crystal mapping.
Our results provide the first ultra-high spatial resolution measurements of oxygen isotopic compositions within single olivine grains, with analytical uncertainties below 0.25‰. Across the full range of magmatic processes recorded by olivine trace element compositions, we find no evidence for assimilation of hydrothermally altered components. Although the analyzed samples span a wide range of ages, none of them are from the historical eruptions. This may indicate that the samples record periods of former relatively low magmatic activity at Axial Seamount. Alternatively, they may represent different magmatic styles that have not been described yet, or assimilation may occur at depths or under conditions that are not recorded by olivine crystallization.
Kent, G.M., Arnulf, A.F., Singh, S.C. et al. Melt focusing along lithosphere–asthenosphere boundary below Axial volcano. Nature 641, 380–387 (2025).
How to cite: Pin, J., Ruprecht, P., France, L., Gurenko, A., and Kent, G.: Coupling trace element mapping and high resolution in-situ oxygen isotopic measurement in olivine crystals to constrain magmatic conditions at Axial Seamount (Juan de Fuca Ridge), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2468, 2026.
The Beerenberg volcano lies on the island of Jan Mayen and represents the northernmost active surface volcano in the world. Jan Mayen island is situated in the Arctic north-Atlantic Ocean, just south of the junction between the Mohn’s ridge and the Jan Mayen fracture zone, where the mid-ocean ridge transitions to the Kolbeinsey ridge further west. The Beerenberg volcano has gently dipping flanks and a more prominent central crater, reaching a maximum altitude of 2272 m a.s.l.
The geology of the Jan Mayen island was studied extensively in the 1970s and 1980s and three primary magma types were identified: primitive basalts, ne-normative basalts and trachytes. The volcanism from the Beerenberg central volcano is limited to primitive basalts, and alkaline basalts, with some more intermediate volcanics near the central crater. Most of, if not all, the recent eruptions of Beerenberg have been in the form of flank eruptions of primitive basaltic and trachybasaltic compositions. However, the shallow magma storage systems of the Beerenberg volcano remain unstudied, and geophysical data from past eruptions are lacking, limiting our insights into this.
In this study we investigate the shallow magma storage systems under Beerenberg by analysing a selection of samples from Jan Mayen and the surrounding seas: tephra from soil sections on the flanks of Beerenberg, rock samples from the summit crater and tephra from sediments in the seas around Beerenberg. These samples have been analysed using EPMA on glass shards, olivine, pyroxene and feldspar crystals, and we present the results from these analyses along with geothermobarometric calculations to infer the shallow magma storage conditions under the Beerenberg volcano. Our findings give new insights into the magmatic process and plumbing beneath Beerenberg that can be valuable during future volcanic unrest.
How to cite: Gjerløw, E. and Höskuldsson, Á.: Shallow magma storage and volcanism at Beerenberg volcano, Jan Mayen, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20542, 2026.
Field studies were conducted on Greenwich Island (South Shetland Islands, West Antarctica) as part of the 8th Turkish Antarctic Expedition (TAE-IV) and the Türkiye–Ecuador Bilateral Cooperation program. This study combines field observations, two-pyroxene geothermobarometry, and crystal size distribution (CSD) analysis to constrain the emplacement depth and cooling history of gabbroic stocks around Fort Williams Point, Greenwich Island.
Field investigations documented that Fort Williams Point hosts basaltic volcanic rocks and gabbroic to microgabbroic intrusions exposed across the area. The gabbroic bodies crop out as isolated stocks and dikes forming independent ridges and hills. Contacts between these intrusive bodies and volcanic rocks is not observable in the field. Petrographically, the gabbroic rocks are dominated by plagioclase, clinopyroxene, and orthopyroxene and minor amounts of olivine. They display holocrystalline porphyritic texture in which larger crystals are embedded in a relatively fine-grained groundmass. Two-pyroxene geothermobarometric calculations based on the mineral chemistry data of the intrusions indicate crystallization temperatures of approximately 1020–1035 °C and pressures in the range of 1.8–2.2 kbar which point to emplacement at shallow crustal levels.
Crystal Size Distribution (CSD) analysis of plagioclase was performed on approximately 300 crystals from two samples and displays a multi-segmented pattern, characterized by high population densities at small crystal sizes and a distinct break in slope toward larger sizes. The fine-size segment is interpreted to reflect an early stage dominated by high nucleation rates, likely triggered by rapid cooling following the emplacement. The change in CSD slope indicates a shift towards growth-dominated crystallization as cooling rates decreased and the system approached thermal stabilization. This evolution in crystallization regime suggests that the intrusions experienced initially rapid cooling consistent with shallow-level emplacement followed by progressively slower cooling within small intrusive bodies.
Overall, the combined geothermobarometric results and CSD patterns suggest that the gabbroic stocks of Fort Williams Point, Greenwich Island were emplaced within small and shallow magma storage zones and experienced rapidly changing thermal conditions during crystallization.
How to cite: Ünal, A.: Emplacement depth and cooling evolution of gabbroic stocks on Greenwich Island, Antarctica: an integrated approach using crystal size distribution (CSD) and two-pyroxene geothermobarometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7702, 2026.
The crystal content of lavas can be used to interpret their magmatic histories and to infer both the structure of magma reservoirs and the nature of the processes that operate within them. Magma reservoirs are increasingly viewed as complex, crystal-rich systems, often expressed in terms of a crystal mush paradigm, where melt is distributed within vertically extensive crystal frameworks [1]. Crystal mush models were primarily developed at volcanic arc systems, where magma flux and volatile content are high, sustaining trans-crustal mushes. It is uncertain whether such trans-crustal mushes are viable at ocean island volcanic systems, due to their generally lower magma fluxes and volatile contents. In some ocean island systems, such as the Eastern Volcanic Zone (EVZ) of Iceland, spatially and temporally proximal samples have a wide range of crystal contents. In the EVZ, plagioclase-phyric magmas are erupted alongside crystal-poor magmas. It is possible that the variation in crystal content reflects the level of interaction between the magma and a crystal mush structure, as portions of the mush are entrained during magma ascent [2].
In this study, we use the geochemistry and petrology of 32 basalt samples from the EVZ, which were mostly erupted beneath ice, to investigate the nature and cause of variation in crystal abundances and proportions. We combine whole-rock analyses from X-ray fluorescence, thin section textural observations from optical and electron imaging (backscattered electron imaging and scanning electron microscope energy dispersive spectroscopy), and geochemical microanalysis (electron probe microanalysis) to constrain magma storage conditions and examine the processes controlling crystal content. Our goal is to evaluate magma storage models of ocean island systems, using the EVZ as a case study of an ocean island system with relatively high magma flux.
References
[1] Sparks et al. (2019). Phil Trans R Soc A 377: 20180019; [2] Neave et al. (2014). J Pet 55(12): 2311-2346
How to cite: Pierce-Jones, T., Hartley, M. E., Namur, O., Vander Auwera, J., and Neave, D. A.: Variations in the crystal content of basalts from the Eastern Volcanic Zone of Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1420, 2026.
Magma intrusion and the generation of silicic magmas are fundamental processes controlling volcanic behaviour and continental crust formation. Exposed plutons provide key constraints on these processes; however, the geological context of silicic plutonic systems, particularly in oceanic rift environments, remains poorly resolved. Southeast Iceland hosts exceptionally exposed large Miocene plutonic complexes, due to a combination of higher erosion and crustal accretion rates. This setting provides a unique insight into the evolution of Iceland’s geodynamics, making it a prime natural laboratory for investigating silicic magma generation within anomalously thick (>40 km) basalt-dominated, plume-influenced, oceanic crust setting.
Recent geological mapping in Southeast Iceland has revealed four previously unknown, and unmapped, silicic formations preserved as caldera-bounded pyroclastic successions, conduit facies, and shallow intrusions: Kvosir, Þórgeirsstaðurdalur, Kapaldalur, and Hvammsheiði These formations surround the 8–10 km³ Slaufrudalur granite pluton and bound it to the south, east, and northwest, appearing structurally linked to its emplacement. This discovery is significant because the Slaufrudalur pluton is the largest granitic intrusion exposed in Iceland, yet its relationship with surrounding rocks remains poorly constrained.
The aim of our research is to constrain the processes that govern the petrogenesis and temporal evolution of large silicic volcanic centres in Iceland. We integrate high-resolution field mapping, photogrammetry, structural analysis, petrography, geochemical and geochronological data on key stratigraphic units to examine how these volcanic formations relate to pluton emplacement and shallow (<5 km) crustal magma storage.
Preliminary zircon U-Pb ages of both plutonic and the newly identified silicic caldera formations indicate that silicic magmatism in the area spans a near continuous 5 million-year period, from 9–<4 Ma, starting with the Hvammsheiði formation. Within the pluton, zircon crystallisation ages reveal a resolvable age difference between an older roof unit and younger units beneath it. This is consistent with previous studies that suggest a top-down magma batch emplacement (Carmody, 1991; Burchardt et al. 2012; Quintela et al. 2025). The data further reveal a complex temporal and structural interplay between pluton growth and surrounding volcanism:
(1) Early magma injections forming the pluton roof are broadly coeval with the largest silicic centre, the Kvosir caldera, whose bounding fault straddles the pluton.
(2) Þórgeirsstaðadalur bimodal volcanism predates pluton emplacement, potentially creating a structural weakness that localized granitic magma intrusion. This lineament remained a focus of magmatic injection after pluton construction.
(3) The Kapaldalur formation represents a younger explosive center emplaced along a pluton wall fault. A pyroclastic unit containing plutonic lithics records two zircon populations: one coeval with, and one younger than, the pluton.
These findings offer new insights into possible geodynamic scenarios in Iceland during the Miocene. This work also contributes to a broader understanding of crustal accretion and crustal recycling processes in long lived silicic volcanic centers. This framework provided also opens for new constraints on silicic magma generation and pluton emplacement in oceanic rift environments and has implications for understanding the formation of continental crust.
How to cite: Gallagher, C., Askew, R., Burchardt, S., Popa, R., Halldórsson, S., Óskarsson, B., Bachmann, O., and Jónsson, K.: Temporal and Structural Interactions Between Silicic Volcanic Centers and the Slaufrudalur Pluton, Southeast Iceland., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21601, 2026.
The 2009 intersection of molten rhyolitic magma at ~2.1 km depth by the IDDP-1 well revealed an active shallow magmatic system - shallower than initially believed - beneath the Krafla caldera (NE Iceland), challenging the prevailing assumption that shallow bodies should rapidly solidify. Close to aphyric molten rhyolite was found directly below nearly completely solidified felsite, while a crystal mush was not found, contradicting current views.
We have developed a thermomechanical numerical model to investigate the dynamics, thermal evolution, and longevity of this magma pocket. The model couples partially compressible Stokes flow with heat transport, explicitly accounting for latent heat during crystallization. Magma is treated as a multicomponent mixture of melt, crystals, and volatiles, with thermophysical properties evolving self-consistently with temperature, pressure and composition. Conductive heat exchange with the host rocks leads to cooling of the magma chamber. We have implemented this new framework in the finite element code GALES (Garg and Papale, Frontiers in Earth Sciences 2022).
Numerical simulations, constrained by IDDP-1 observations (initial T ≈ 900 °C, P ≈ 45 MPa), show an initial rapid cooling phase followed, after ~50 years, by a quasi-stationary cooling characterized by thermal oscillations. This behavior is driven by latent heat release during crystallization and it delays solidification, maintaining a largely molten state for several hundred years. In addition, cooling and crystallization -induced convection redistributes heat and remobilizes marginal crystal accumulations, preventing the formation of a stable crystal mush at the chamber roof and walls.
These processes provide an explanation for the direct encounter with molten magma in the IDDP-1 borehole and indicate that small, shallow rhyolitic magma bodies can persist in a molten state over much longer timescales than commonly tought. The results have direct implications for future drilling-to-magma initiatives such as KMT (Krafla Magma Testbed).
How to cite: Girela Arjona, G., Garg, D., Longo, A., and Papale, P.: Longevity and crystal mush stability of the IDDP-1 magma body at Krafla, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12602, 2026.
