The organization of melts below active volcanoes plays a large role on the size, composition, and character of the ensuing eruptions. In principle it should be possible to determine the distribution of melts with geophysical data, such as inversion of seismic velocity, density, and gravity. In practice, it appears that the size and distribution of the melts have a topology that only allows for very approximate information, typically made of “hot big potatoes” where melts are likely to reside. This is specially the case for many calderas and large stratovolcanoes from subduction zones, and unfortunately such view is not good enough to address the likely size of future events. Petrological studies of erupted crystals can, also in principle, provide a view of the depth and possible variety storage areas. However, geothermobarometry data tend to have large errors on pressure, and in a similar manner to most geophysical data many calderas and stratovolcanoes show a very wide distribution of depths (transcrustal systems?). Notwithstanding, many systems show a broad agreement between the petrological and geophysical data, with three or more storage areas, roughly at 30 km (or deeper), 7-10 km, and 1-3 km. Moreover, the configuration of the distribution of the melts may change over time, and crystal-kinetic and some geophysical data suggest that in mafic volcanoes new connections and merging of melts from different environments may occur days prior to eruption, whereas large-scale amalgamation melts from multiple reservoirs to a much larger one can occur in years to decades in silicic eruptions from calderas. Yet, data from geophysical and petrological studies of several recent monogenetic dike-fed eruptions, show simpler magma plumbing configurations, with well-defined areas of isolated magma storage and connections between them near-real time, from which magmas of different compositions are erupted. In this presentation we will review the data on magma plumbing structure and dynamics from different datasets and discuss how could progress be made for their use in mitigation of volcano hazards.

How to cite: Costa, F. and Metaxian, J.-P.: Transcrustal, interconnected, or isolated magma reservoirs, can we tell the difference?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10207, https://doi.org/10.5194/egusphere-egu24-10207, 2024.

The residence timescales of antecrystic minerals contribute a key piece of information regarding the petrologic evolution of transcrustal magmatic systems and may be inferred using a combination of observations derived from microanalytical chemistry and diffusion modelling. Here, we present state-of-the-art stacked CMOS-type active pixel sensor (SCAPS) isotopographic images of tephra-hosted plagioclase microantecrysts from Tongariro Volcanic Centre in the southern Taupo Volcanic Zone, New Zealand. These crystals exhibit high-frequency Sr and anorthite zonation at sub-micron spatial resolution. We also find that all crystals display high-frequency intracrystalline Sr chemical potential variations, indicating that they have not resided at magmatic temperature for diffusive relaxation to advance significantly. To quantify crystal residence times at the well-constrained magmatic temperatures of these tephras, we first forward-modeled intracrystalline Sr diffusion over time using numerical methods. Results were then analyzed using novel spatial Fourier-transform techniques developed to understand the systematics the diffusive decay of Sr disequilibria in the spatial frequency domain. This ultimately permitted the estimation of Sr concentration profiles at crystal formation, prior to uptake into the carrier melt at the onset of eruption. Our data imply residence times of days to weeks for the studied microantecrysts. This is inconsistent with long antecryst residence times in magmatic mushes at elevated temperatures, pointing instead to a cool plutonic nature of the magmatic plumbing system beneath the southern Taupo Volcanic Zone.

How to cite: Zellmer, G., Coulthard Jr, D., Brahm, R., Lormand, C., Sakamoto, N., Iizuka, Y., and Yurimoto, H.: Plutonic Nature of a Transcrustal Magmatic System: Evidence from Ultrahigh Resolution Sr-Disequilibria in Plagioclase Microantecrysts from the Southern Taupo Volcanic Zone, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2731, https://doi.org/10.5194/egusphere-egu24-2731, 2024.

The Asal Rift, situated within the Afar region, presents a unique opportunity to study continental rifting and ongoing break-up mechanisms. Here we present a comprehensive study based on volatile element contents of magmas within the Asal rift's segment. Samples were gathered from various volcanic sub-segments within the active part of the Asal rift, and a subset was collected to document the successive steps of the recent 1978 Ardoukoba eruption. Altogether our new sampling is offering a chronological framework crucial to understanding this magmatic system and the eruptive sequences. Quenched pyroclastic deposits (scoria) were used as they are more likely to preserve the magma's volatile content without significant degassing upon cooling at surface than lava flows. By analyzing over 400 melt inclusions within plagioclase and olivine crystals of 15 new samples, we provide insight into the pre-eruptive volatile content of Asal magmas. The melt inclusions volatile contents (H₂O, CO₂, Cl, and S) were quantified through SIMS analyses at CRPG. Sample preparation for SIMS measurements was carefully achieved to avoid any contamination or volatile loss. After estimation of the volatile migration through the shrinkage bubbles of the melt inclusions by Raman spectroscopy, and correction from post-entrapment crystallization processes, we reconstructed the initial magmatic volatile content at the reservoir depth. This content, combined with detailed petrographic study, field observations, and new dating, allows us to propose a comprehensive picture of the Asal Rift plumbing system architecture, and to discuss its spatial variability and temporal evolution. The wealth of data allowed us to highlight a relative homogeneity of the reservoir volatile contents over the recent Asal rift segment erupted magmas, and to discern the depth range of the Asal igneous reservoir that spans from approximately 5 km to 25 km (based on solubility models of VESIcal (1)). Furthermore, volatile data, combined with in-situ major and trace element analysis, provides insights into magma differentiation, degassing, and into the volatile content of the mantle source. We investigate 3 potential steps of degassing and their effect on volatile, trace and major element: within the plumbing system (during the differentiation), during magma ascent, and at the surface during the eruption (unlikely given the sampling method). Finally, our study focused on the 1978 Ardoukoba eruption within the Asal rift. With a sampling of the entire eruptive sequence, we were able to highlight the evolution of the volatile content during this eruption, showing that the initial differentiated magma reservoir underwent a recharge event before eruption. In conclusion, this new in-situ high-resolution volatile, trace and major element extended dataset 1/ delineated the extensive depth range of the magmatic reservoir, 2/ allows a better understanding of the dynamics of magma reservoirs that feed continental rift systems, and 3/ provides new constraints on the magma evolution, differentiation, and degassing at depth within such a system.

(1) Iacovino, K., Matthews, S., Wieser, P. E., Moore, G. M., & Bégué, F. (2021). VESIcal Part I: An Open‐Source Thermodynamic Model Engine for Mixed Volatile (H₂O‐CO₂) Solubility in Silicate Melts. Earth and Space Science, 8(11).

How to cite: Pin, J., France, L., Chazot, G., Deloule, E., Gabrewold Birhane, Y., Pik, R., and Schimmelpfennig, I.: Plumbing system architecture, magma differentiation, and volatile element evolution in an active rift segment: Constraints from melt inclusions in Asal rift (Djibouti, Afar)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7717, https://doi.org/10.5194/egusphere-egu24-7717, 2024.

Villarrica and Osorno are two active stratovolcanoes in the Central Southern Volcanic Zone (CSVZ) of the Chilean Andes that share several geochemical characteristics: near-primary, tholeiitic parent magmas (50-53 wt. % SiO₂), overlapping major/trace element differentiation trends, and comparable storage conditions [1-4]. Yet, their current or recent eruptive styles diverge significantly. Villarrica is a steady-state, open-vent volcano with a lava lake that produced ~100 moderate-intensity, Strombolian eruptions since 1579; Osorno is a closed-vent volcano with 10x less eruptions for the same period. Our initial hypothesis proposed that differences in eruptive style and frequency could be due to a relatively higher degree of crustal permeability under Villarrica than Osorno [5]. Although preliminary data shows that some differences exist in olivine chemistry and textures between Villarrica (Fo_72-87) and Osorno (Fo_66-82) [4,5,6], both volcanoes have broadly similar compositional ranges and multimodal distributions, with comparable diffusion timescales. This suggests the degree of crustal permeability underneath both volcanoes are likely comparable, prompting us to consider other parameters, such as magma supply rate. In this contribution, we discuss and evaluate the role of magma supply rate and other parameters in modulating eruptive styles at Osorno and Villarrica, based on an updated dataset of magma storage conditions, diffusion timescales, and inferences drawn from published literature. We aim to further current understanding of subduction zone magmatism and geodynamics, with implications on volcanic hazard reduction.

1. Vergara et al. (2004). J. S. Am. Earth Sci. 17: 227-238. 2. Morgado et al. (2015). JVGR, 306: 1-16. 3. Pizarro et al. (2019). JVGR. 384: 48-63. 4. Bechon et al. (2022). Lithos. 106777. 5. Utami et al. (2023) Goldschmidt 2023 Abstract 6. Romero et al. (2022). Bull. Volc. 85 (2).

How to cite: Utami, S. B., Vander Auwera, J., Bechon, T., Fugmann, P., and Namur, O.: What modulates eruptive styles and timescales at Villarrica and Osorno volcanoes (Chile)?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7781, https://doi.org/10.5194/egusphere-egu24-7781, 2024.

Ferro-basaltic liquids intersect a binode during fractionation, splitting into two immiscible silicate liquids, one Si-rich and the other Fe-rich. The two liquids have very different physical properties: the Si-rich liquid is more buoyant and viscous, preferentially wetting plagioclase, whereas the Fe-rich liquid preferentially wets grains of mafic minerals and Fe-Ti oxides. The density difference means that when a crystal-poor magma body intersects the binode, it is likely to undergo compositional stratification, with implications for the compositions of any eruptions. When the interstitial liquid in a crystal mush unmixes, the density difference is compounded by the differences in wetting properties, leading to complex behaviour if capillary forces act in a different direction to that of gravity. The extent and scale of differential migration of unmixed liquids may thus play an important role in the genesis of the Daly Gap, while the preferential partitioning of P, PGE and REE into the Fe-rich conjugate has significant implications for formation of economically important deposits.

The Skaergaard Intrusion of East Greenland records abundant evidence for differential migration of immiscible silicate liquid conjugates. At the intrusion scale, the roof rocks are more silica-rich than the cumulates at the floor, consistent with intersection of the binode by the bulk magma leading to the accumulation of the buoyant Si-rich conjugate in the roof mush. This is supported by the localised presence of reverse modal layering on the floor, interpreted as bodies of dense Fe-rich liquid ponded at the top of thin (<1m) mush. Large-scale lateral migration of Fe-rich liquid along fractures developing in the solidifying wall mush may have been the underlying cause of metasomatism to form localised 100m-scale patches of replacive pyroxenite. Evidence of metre-scale differential migration within the crystal mush on the intrusion floor is provided by paired silicic and mafic late-stage segregations, recording downwards penetration and disruption of the floor mush by dense Fe-rich liquid, coupled with limited upwards flow of viscous Si-rich liquid. Further evidence of metre-scale differential migration is provided by compositional rims developed on the tops and bases of (almost) fully-solidified blocks in the floor cumulates of material solidified at the roof, fragmented and released during contemporaneous seismic activity. The mafic rims at their tops formed by the ponding of downwards-moving Fe-rich liquid while the felsic rims at their bases formed by the ponding of upwards-moving Si-rich liquid against the impermeable autoliths, consistent with the extent of rim development being a function of autolith shape, rather than composition. Differential migration on the cm-scale, driven by capillarity and the differences in wetting properties of the two immiscible conjugates, is suggested as the mechanism by which poorly-defined cm-scale micro-rhythmic layering is superimposed on graded modal layering.

The Skaergaard examples of differential migration provide the opportunity to constrain the length- and time-scales of differential migration of unmixed immiscible silicate conjugates, to quantify the effects of capillarity and emulsion coarsening, and to assess the more general importance of liquid immiscibility on petrogenetic evolution.

How to cite: Holness, M., Nielsen, T., and Namur, O.: Differential migration of immiscible liquids in gabbroic crystal mush: the Skaergaard Intrusion, East Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3983, https://doi.org/10.5194/egusphere-egu24-3983, 2024.

At mid-ocean ridges, melts formed during adiabatic melting of a heterogeneous mantle migrate upwards and ultimately crystallize the oceanic crust. In this context, the lower crustal gabbros represent the first crystallization products of these melts and the processes involved in the accretion of the lowermost crust drive the chemical evolution of the magmas forming two thirds of Earth’s surface. At fast-spreading ridges, elevated melt supply leads to the formation of a ⁓6 km-thick layered oceanic crust. Here, we provide a detailed petrochemical characterization of the lowermost portion of the fast-spread oceanic crust drilled during IODP Leg 345 at the East Pacific Rise (IODP Site U1415), together with the processes involved in crustal accretion. The recovered gabbroic rocks are primitive in composition and range from olivine-rich troctolites to troctolites, olivine gabbros, olivine gabbronorites and gabbros. Although textural evidence of dissolution-precipitation processes is widespread within this gabbroic section, only the most interstitial phases record chemical compositions driven by melt-mush interaction processes during closure of the magmatic system. Yet, the occurrence of primitive orthopyroxene in most of the olivine-bearing samples indicates that reactive processes allowed for its local saturation within the percolating MORB-type melt. Comparing mineral compositions from this lower crustal section with its slow-spreading counterparts, we propose that the impact of reactive processes on the chemical evolution of the parental melts is dampened in the lowermost gabbros from magmatically productive spreading centres. Oceanic accretion thereby seems driven by in situ crystallization in the lowermost gabbroic layers, followed by upward reactive percolation of melts towards shallower sections. In addition, we here furnish a first estimate of the trace element composition of the parental melts that led to the accretion of the lower crust at Hess Deep, Atlantis Massif and Atlantis Bank; we show that the primary melts of the East Pacific Rise are more depleted in incompatible trace elements compared to those formed at slower spreading rates, as a result of higher melting degrees of the underlying mantle.

How to cite: Basch, V., Sanfilippo, A., Snow, J., Loocke, M., and Zanetti, A.: Accretion of the lowermost oceanic crust at fast-spreading ridges: Insights from the East Pacific Rise (Hess Deep, IODP Leg 345), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2048, https://doi.org/10.5194/egusphere-egu24-2048, 2024.

Understanding how magmatic systems work is of interest to a wide range of Earth Scientists. One of the key components when studying magmatic systems is the ability to predict stable mineral assemblage. These predictions allow retrieving critical information such as mineral stability, fraction and composition of melt.

However, the dynamic evolution of magmatic chambers, including the cycling between magmatic recharge and extraction in and out of the reservoir, imply that compositions of crystals and melts are constantly evolving. Hence, the use of phase equilibrium parameterization or look-up-tables of fixed bulk-rock composition is inappropriate to predict the dynamic chemical evolution of magmatic systems, and we instead need methods that can take the evolving chemistry into account.

Here, we present an updated version of our in-house Gibbs energy minimization package, MAGEMin [1,2]. MAGEMin is ideally suited so simulate the chemical evolution of magmatic systems by incorporating a range of recently developed thermodynamic melting models suitable to simulate both melting of magmatic arcs and of pelitic crustal rocks. Through its Julia wrapper, MAGEMin_C, it is particularly easy to perform (parallel) pointwise computations, and couple it with other thermal or thermomechanical codes.

We have made several additions to MAGEMin which include a) adding more thermodynamic databases, b) developing a new web-based graphical user interface, MAGEMin_app, which simplifies creating publishable phase diagrams and c) coupling MAGEMin with dynamic codes.

The ability to couple MAGEMin with other codes is demonstrated by linking it with the MagmaThermoKinematics.jl Julia package [4,5] that simulates the thermal evolution of magmatic systems following the intrusion of dikes and sills, in 2D, 2D axisymmetric and 3D geometries. For this to be efficient, we develop a new system in which we dynamically create a database of pre-computed points as a function of pressure, temperature and chemistry that is updated on the fly. This allows simulating the evolving chemistry of a crustal-scale mush system.

[1] Riel, N., Kaus, B.J.P., Green, E.C.R., Berlie, N., 2022. MAGEMin, an Efficient Gibbs Energy Minimizer: Application to Igneous Systems. Geochem Geophys Geosyst 23. https://doi.org/10.1029/2022GC010427

[2] https://github.com/ComputationalThermodynamics/MAGEMin

[3] https://github.com/ComputationalThermodynamics/MAGEMin_C.jl

[4] Schmitt, A.K., Sliwinski, J., Caricchi, L., Bachmann, O., Riel, N., Kaus, B.J.P., de Léon, A.C., Cornet, J., Friedrichs, B., Lovera, O., Sheldrake, T., Weber, G., n.d. Zircon age spectra to quantify magma evolution. Geosphere 19. https://doi.org/10.1130/GES02563.1

[5] https://github.com/boriskaus/MagmaThermoKinematics.jl

How to cite: Riel, N., Kaus, B., Ranocha, H., Aellig, P., and Green, E.: Direct coupling of petrological and thermo-kinematic modelling: application to magmatic chambers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16269, https://doi.org/10.5194/egusphere-egu24-16269, 2024.

The mechanisms responsible for the formation of the mineral deposits and complex layered stratigraphy in layered mafic intrusions from cratonic environments have remained elusive, largely because the nature of the mantle melting processes that generated the parental magmas are poorly understood. The largest chromium deposits reside within the mafic-ultramafic Rustenburg Layered Suite (RLS) of the Bushveld Complex, South Africa, as laterally continuous layers of chromitite. The RLS has complex, small-scale chemical stratigraphy (Mg#, An#, Sr(i), etc.) and has surprisingly evolved Sr-isotopic compositions. Due to the low solubility of chromium in the basaltic melts theorised as parental to the suite, several models attempt to explain the chromium enrichment. Perhaps the most plausible hypothesis yet proposed to account for the origin of the RLS chromitites, as well as the associated ferromagnesian silicate layered package, is that the suite was produced from hybrid magmas that formed though the assimilation of Kaapvaal craton rocks by komatiitic magmas. As komatiites arise by high degrees of mantle melting, they carry high concentrations of all strongly compatible elements that are enriched in the mantle, but have very low abundances in crustal rocks. However, average RLS compatible trace-element ratios are not similar to mantle values, with Cr/Ni and V/Ni indicating massive enrichment of chromium and vanadium over nickel. Using phase-equilibrium modelling techniques, this study investigated the possibility that the layering and chromitite formation in the RLS are a consequence of the entrainment of components of the magma source rocks. Results reveal a wedge-shaped domain in pressure-temperature space in the subcratonic mantle in which chromium-bearing orthopyroxene is produced as a peritectic product of incongruent melting of various fertile mantle source compositions. Given the ease of orthopyroxene nucleation and the high rates of plume-driven melt production apparent in the formation of large igneous provinces, entrainment of this orthopyroxene in the melts, on extraction from their mantle sources, seems unavoidable. During ascent, magmas with entrained peritectic orthopyroxene crystallise peritectic olivine and chromite due to reaction of the orthopyroxene with melt – a double-peritectic mechanism. These chromite- and olivine-bearing magmas intrude the upper continental crust as sills of crystal-melt slurry and can produce chromite and dunite layers by density separation immediately after emplacement, even if no further cooling occurs before melt drainage. If metasomatism of the mantle source by crustally-derived fluids (ideally ancient and of low volume) is accepted as plausible, then the very high ratios of chromium and vanadium to other compatible elements for average RLS is a superior fit with the formation of the suite by broadly basaltic melts that entrained peritectic orthopyroxene, rather than formation by reactive assimilation of crust by komatiitic magmas. Thus, this study presents a novel, chemically and thermodynamically constrained model that is a simple, first order, source-dependent alternative to the complex petrogenetic models of the current paradigm.

How to cite: Otto, T., Stevens, G., Moyen, J.-F., Mayne, M., and Clemens, J.: Source peritectic crystal entrainment to mantle magmas produced Earth’s largest chromite deposit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-460, https://doi.org/10.5194/egusphere-egu24-460, 2024.

Magmatic systems in the Earth's mantle and crust range from melt-poor partially molten rock, to mush bodies at intermediate melt fractions, and lenses of melt-rich, eruptible magma suspensions. Previous process-based models, however, have represented magmatic systems as either porous flows at low melt fractions (<20%) or suspension flows at high melt fractions (>60%). A lack of theoretical basis to represent mush flows at intermediate phase fractions has thus far hindered investigations into the dynamics of crustal mush bodies. Previous theories were formulated specifically for two-phase flows of melt-solid mixtures, hence not allowing for the inclusion of a third, volatile or other fluid phase. My contribution addresses this gap by presenting a comprehensive theoretical model [1] of magmatic multi-phase flows across all phase fractions at the system scale, rooted in mixture theory. I substantiate its applicability with a numerical implementation utilising a finite-difference staggered-grid approach [2]. 

Numerical experiments replicate expected behaviours for two-phase flows including rank-ordered porosity wave trains in 1D, and porosity wave breakup in 2D in the porous flow regime, as well as particle concentration waves in 1D, and mixture convection in 2D in the suspension flow regime. In the mush regime, numerical experiments show strong melt localisation into lenses and stress-aligned melt-shear bands. A further application to a three-phase flow problem of immiscible melt segregation from a crystallising magma body demonstrates the versatility of the theoretical model and its numerical implementation. The model code is available open source at github.com/kellertobs/pantarhei.

References

[1] Keller & Suckale, GJI, 2019. https://doi.org/10.1093/gji/ggz287.

[2] Wong & Keller, GJI, 2022. https://doi.org/10.1093/gji/ggac481.

How to cite: Keller, T.: Modelling multi-phase flows in magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15239, https://doi.org/10.5194/egusphere-egu24-15239, 2024.

Significant advances have been made in using a wide variety of geophysical techniques to track melt migration, image the structure of active and ancient magma plumbing systems, and constrain emplacement mechanics. In particular, integrating traditional petrological and geochemical results with such geophysical data and modelling has afforded exciting insights into the development of entire magmatic systems. However, divisions between the scales and physical settings over which these methods are applied remain. To characterise these differences and promote the benefits of further combining geophysical, petrological, and geochemical datasets, I discuss how geophysical techniques can be utilised to provide structural context and place physical constraint to the chemical evolution of magma plumbing systems. I am no expert in many geophysical techniques and thus lean on the work of many others, showcasing the importance of collaboration to pushing the boundaries of our science. Here, I will examine on what we can do with some geophysical and geodetic techniques, whilst importantly highlighting what we cannot do with them, and discuss how their application can help us solve some of the key questions within our field. Overall, I hope to show that approaching problems concerning magma plumbing systems from an integrated petrological, geochemical, and geophysical perspective, brought together with various modelling methods, will yield important scientific advances and provide exciting future opportunities for the entire volcanological community.

How to cite: Magee, C.: Visualising magma plumbing systems in 4D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5812, https://doi.org/10.5194/egusphere-egu24-5812, 2024.

The Katmai volcanic group (KVG) within the Alaskan Aleutian arc is an unusually dense group of active volcanic centres (Mounts Martin, Mageik, Trident, Katmai, Griggs, Snowy, and Novarupta). The KVG was the locus of the largest eruption of the 20^th century. During the 1912 eruption, rhyolite was erupted from a new vent (Novarupta) contemporaneous with the collapse of nearby Mount Katmai (10 km away). A hydraulic connection has been hypothesized between the two vents based on the above observation and on a small volume of juvenile andesitic magma with the geochemical signature of Mount Katmai that erupted from Novarupta at the onset of the three-day eruption. Unanswered questions about the structure and dynamics of the KVG include the origin and storage zone for the 1912 erupted rhyolite, its connection (if any) to the dense group of andesitic stratovolcanoes surrounding the Novarupta vent, the cause for off-arc centres such as Mount Griggs, and the reason for enhanced magmatic flux beneath the KVG relative to other segments of the arc. Our recent wideband (1 kHz – 1 mHz) magnetotelluric survey of the region encompasses the entire Katmai group of volcanoes (110 sites) and is bisected by an arc-perpendicular profile crossing the Alaska Peninsula (18 sites) and spanning subducting slab depths of 60-200 km. Coast effects are present in the magnetotelluric data; however, qualitative analysis of the data indicates the Jurassic sedimentary section upon which the arc is built, the highly resistive arc itself, and a swath of elevated conductivity beneath the arc axis that likely reflects melt storage. 3D inversion of the data is ongoing.

How to cite: Hill, G., Bedrosian, P., Burton, B., Crosbie, J., Hoogenboom, B., Mitchell, M., Peacock, J., and Wallin, E.: Magmatic Structure and Melt Storage beneath the Katmai Volcanic Group, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14370, https://doi.org/10.5194/egusphere-egu24-14370, 2024.

The Qinling Orogen, as the most prominent mountain belt in the central part of China, has experienced multiple tectonic-magmatic thermal events. Abundant granitoids were developed in response to the tectonic regime transformation during Mesozoic. These granitoids serve as valuable indicators to reflect the process and dynamic mechanism of the orogeny, as their growth process hold important structural information about the tectonic evolution. Although some geochronological and geochemical data exist from this region, it lacks systematic and sufficient tectonomagmatic information to develop a regionally coherent and viable geodynamic model for the Mesozoic magmatic evolution of the Qinling Orogen.

This study strategically focuses on the Mesozoic Taibai pluton in the Qinling Orogen, aiming to investigate the relationship between tectonics and magmatism and their variation in time and space during Mesozoic. Through multiscale structural analysis and geochronology methods, we have delineated three deformation phases, with representative rock samples reflecting mid-high temperature deformation conditions, evident in both microscopic observations and EBSD analysis, The quartz’s dynamic recrystallization and c-axis fabric analysis revealed that the Houzhenzi Shear Zone (HSZ, south of the Taibai pluton) experienced deformation under green-schist facies conditions at ∼400–550 °C. The results of Anisotropy of Magnetic Susceptibility indicate that the HSZ deformed in response to pure shear-dominated transpression and top-to-NW shear sense, exhibiting two superimposed phases of shear deformation. Together with previously published data, our results concluded the relationship between the Taibai pluton and the structural features of shear zones. The research indicates that the Qinling Orogen was dominated by compressional tectonics during the Late Mesozoic, Taibai pluton was obliquely extruded under the influence of surrounding shear zones. This research contributes to a more comprehensive understanding of the complex processes involved in continental tectonics and magmatic evolution. This work was financially supported by NSFC projects (grants 4217020371, 4180020120).

How to cite: Yan, S., Li, Y., Tao, W., Liu, Y., and Liu, F.: Structural Study of the Taibai Pluton in the Qinling Orogen, Central China: Implications for Relationship between Tectonics and Granite Magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10396, https://doi.org/10.5194/egusphere-egu24-10396, 2024.

At fast-spreading oceanic ridges such as the East Pacific Rise, divergence between tectonic plates is accommodated almost exclusively by magmatic accretion. A robust understanding of magmatic accretion during seafloor spreading is therefore necessary to model the structure and composition of oceanic lithosphere and exchanges in heat and mass at a global scale over geological time. Whereas most models consider magmatic accretion in 2D, variations in ridge axial morphology and magmatic compositions highlight the occurrence of ridge-parallel variations in magmatic processes along fast-spreading systems. This suggests that magmatic accretion may be a 3D process involving significant ridge-parallel magma transport.

To constrain the process of magmatic accretion at fast-spreading ridges, we present our on-going investigation of magma transport in the Oman ophiolite. The first order structure and composition of the ophiolite, defined by a sheeted dyke complex with an underlying axial melt lens of variable thickness on top of foliated gabbro, is analogous to the East Pacific Rise. This provides a unique opportunity to investigate magmatic accretion processes above and below an axial melt lens system in three dimensions at ridge segment- to grain-scales for the first time.

We present new data constrains the directions of magma transport in the crust of the Oman ophiolite. This includes analyses of foliated gabbros and sheeted dyke complexes from the Fizh, Salahi, and Sarami blocks, which define a complete ridge segment. Using anisotropy of magnetic susceptibility (AMS), we report the orientations of magnetic fabrics that serve as proxies for magmatic flow directions. Combining AMS data with paleomagnetic analyses of magnetic remanence directions allows us to restore magmatic flow directions to their paleo-ridge orientation, prior to obduction. Our results indicate that magmatic flow directions vary along the length of the ridge segment and cannot be explained by simple 2D models. Our data show that ridge-parallel lateral flow is a common phenomenon in both the sheeted dykes and foliated gabbros over the length of a ridge segment. Our results also have important implications for competing models of crustal accretion.

How to cite: Morris, A., Parsons, A., Harris, M., MacLeod, C., Ildefonse, B., Atton, C., Allerton, S., and Gürer, D.: The 3D anatomy of magma transport in fast-spreading oceanic crust of the Oman ophiolite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5981, https://doi.org/10.5194/egusphere-egu24-5981, 2024.

During plate spreading, large volumes of magma can be extracted from the upper mantle and intrude the crust. Geophysical and geochemical studies at active magmatic rifts and passive margins show that crustal intrusions mainly occur in the form of transient sill-like bodies. The sills pond at various crustal levels, potentially feeding shallower plumbing systems, dike intrusions and surface eruptions. Trans-crustal magma migration and intrusion thus have a key role in controlling extension, strain localization and subsidence during rifting. However, a clear understanding of the mechanisms of sill intrusion, their connection to upper mantle processes, as well as the spatial and temporal response of the sills to a new arrival of magma is still limited by the paucity of direct observations. In this study, we provide one of the few direct InSAR observation of rift-scale deformation caused by magma inflow from the upper mantle to multiple crustal sills in the Central Afar (CA) rift.

We used InSAR time-series from 255 ESA Sentinel-1 interferograms during 2014-2021 and combined them with available GNSS measurement to retrieve the 3D velocity field and the temporal evolution of surface deformation in CA. We observed four uplift patterns with rates of ~5 mm/yr, that we inverted using four inflating Okada tensile dislocation sources (sills). Our best-fit model shows four sills elongated in a NW-SE direction, similar to the rift trend, and opening rates ranging between 16 and 44 mm/yr. The sills are located at various crustal depths but mainly in the mid-to-lower crust, following the thinning of the crust imaged seismically in CA. Cross-correlation of time-series also show that the uplift above the four sills starts simultaneously in December 2016 and continue until March 2021.

We interpreted the simultaneous inflation of four distant sills as the result of a shared pressurization event caused by an episodic magma inflow from a common source in the upper mantle. Our results show that magma supply from the mantle beneath continental rifts is episodic, and occurs across large spatial scales but short temporal scales over which deep crustal magma ponding takes place. Such process could explain how the thick intruded crust common at magma-rich rifted margins is created and could help in understanding the long-term dynamics of rifting episodes and volcanism.

How to cite: La Rosa, A., Pagli, C., Wang, H., Sigmundsson, F., Pinel, V., and Keir, D.: Geodetic observations of simultaneous rift-scale magma inflow in multiple sills in the Central Afar rift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6145, https://doi.org/10.5194/egusphere-egu24-6145, 2024.

To understand the style, longevity and hazards of volcanic fissure eruptions, we need to understand the magma flow dynamics governing their feeder dykes. Microstructural analysis through optical microscopy and electron backscatter diffraction (EBSD) can be used to observe crystal alignment, shape and size from dyke samples to investigate magmatic fluid flow and deformation processes during the ascent of magma. Plagioclase is a mineral ubiquitously found in volcanic rocks that forms throughout magma crystallisation at a wide range of temperatures (~1300-400°C), and is therefore a mineral commonly used to investigate magma flow dynamics in dykes and sills. In particular, microlites of plagioclase (<0.1 mm) are amongst the last crystals to form at shallow crustal depths so have the potential to record the near surface flow behaviour and deformation processes that can lead to eruption.

Here we examine elongate plagioclase microlites from oriented samples of a basaltic dyke from the Budj Bim Volcanic Complex, the only known fissure-fed eruption in the Newer Volcanics Province, south east Australia. Extensive quarrying of the Little Mount scoria cone has provided excellent exposure of the internal architecture of its feeder dyke. Optical microscopy observations show the dyke is comprised of zoned olivine phenocrysts (20%, <0.5 mm diameter), pyroxenes (20%, <0.1 mm diameter) and a fine-grained plagioclase-rich groundmass with minor oxides (5%, <0.05 mm diameter). EBSD of the plagioclase microlites shows they share a strong shape preferred orientation (SPO) and crystallographic preferred orientation (CPO). Plagioclase microlite orientation can be used as an indicator of magma flow, as elongate crystals may reorient due to flow and/or pure shear within the ascending magma. Using these novel data, we propose a model for plagioclase orientation, and therefore potential magma flow dynamics in the Little Mount dyke. Understanding the physical and chemical processes governing historic fissure eruptions such as the Budj Bim Volcanic Complex enables us to inform hazard mitigations for future fissure eruptions worldwide. 

How to cite: Hrintchuk, J. A., Kavanagh, J. L., and Mariani, E.: Plagioclase preferred orientation provides insights into magma flow dynamics of a basaltic dyke from the Budj Bim Volcanic Complex, Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9775, https://doi.org/10.5194/egusphere-egu24-9775, 2024.

Dikes supply magma to most volcanic eruptions. Understanding under what conditions propagating dikes reach the surface to erupt or, alternatively, become arrested (stop their propagation) or deflected so as to propagate primarily laterally or change into sills, is thus one of the fundamental tasks of volcanology. Many dike segments injected from magma sources do not reach the surface to feed volcanic eruptions. Instead, the dike segments become arrested, commonly at or close to contacts between mechanically dissimilar layers/units, at various crustal depths. This means that many and perhaps most volcanic unrest periods with dike injections do not result in eruptions. There are several conditions in the crust that make dike arrest likely, but the main one is layering where the layers have contrasting mechanical properties. Such layering means that local stresses are heterogeneous and anisotropic and thus in some layers unfavourable (e.g., because the layers act as stress barriers) for vertical dike propagation, resulting in dike arrest, lateral dike propagation beneath the stress barrier, or dike deflection into a sill. Here I show that once a dike has formed, its very existence tends to make the local stress field along the dike homogeneous (with invariable orientation of principal stresses) and favourable (with dike-parallel orientation of the maximum compressive principal stress) for later dike injections. This means that a later-injected dike may use an earlier-injected dike as a path, either along the margin or the centre of the earlier dike, thereby generating a multiple dike. Because earlier feeder-dikes form potential paths for later-injected dikes to the surface, many volcanic eruptions are fed by multiple dikes. Multiple dikes thus tend to favour dike propagation to the surface, thereby facilitating dike-fed eruptions. Examples of multiple-dike-fed eruptions include recent ones in Etna (Italy) and Kilauea (Hawaii), as well as in the Icelandic volcanoes Krafla and Hekla. Here, however, the focus is on several eruptions in the past few years on the Reykjanes Peninsula, Iceland. In particular, I discuss the eruptions of 2021, 2022, and 2023 in the volcano Fagradalsfjall as well as the 2023 eruption along the volcanic fissure Sundhnukar (close to the town of Grindavik), all the eruptions occurring on the Reykjanes Peninsula.

Gudmundsson, A., 2022. The propagation paths of fluid-driven fractures in layered and faulted rocks. Geological Magazine, 159, 1978-2001.

Gudmundsson, A., 2023. Multiple dikes make eruptions easy. EarthArXiv, https://doi.org/10.31223/X5M67Q

How to cite: Gudmundsson, A.: How multiple dikes facilitate volcanic eruptions, with application to recent events on the Reykjanes Peninsula, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12898, https://doi.org/10.5194/egusphere-egu24-12898, 2024.