GMPV7.2 | Volcanic & Igneous Plumbing System processes and kinetics: from magma to mush to pluton
EDI
Volcanic & Igneous Plumbing System processes and kinetics: from magma to mush to pluton
Co-organized by TS5
Convener: Lydéric France | Co-conveners: Uddalak BiswasECSECS, Elena Melekhova, Stefano Urbani, Pierre Bouilhol, Nibir Mandal, Daniele Maestrelli
Orals
| Wed, 17 Apr, 14:00–18:00 (CEST)
 
Room -2.91
Posters on site
| Attendance Thu, 18 Apr, 10:45–12:30 (CEST) | Display Thu, 18 Apr, 08:30–12:30
 
Hall X1
Posters virtual
| Attendance Thu, 18 Apr, 14:00–15:45 (CEST) | Display Thu, 18 Apr, 08:30–18:00
 
vHall X1
Orals |
Wed, 14:00
Thu, 10:45
Thu, 14:00
Our vision of the architecture of volcanic and igneous plumbing systems (VIPS) has been deeply modified over the last few decades. We have more and more evidence that long lived melt dominated magma bodies are difficult to form and very challenging to maintain. Instead, physical models and geophysical observations suggest the presence of local magma bodies within a larger, transcrustal magmatic system which is dominated by crystals rather than melt. Reconstruction of long-lived magmatic system is a challenging task. Challenge is to connect processes throughout the entire magmatic system, from mantle to crust to the surface (eruption). To advance our understanding of VIPS requires studying both volcanic and plutonic complexes at various scales e.g., from a whole tomographic image of VIPS to the microscopic and potentially atomic scale of a mineral or melt inclusion. We also need to be able to relate physical and chemical properties of crystal-melt-fluid segregation and differentiation, to provide quantitative data on the kinetics of the processes and on the kinematics of magma transfers, and to understand the process of melt migration, accumulation and eruption.
Advancing our studies of these magmatic systems will provide us with better constraints and understanding of volcanic eruptions, and consequently mitigation of volcanic risk, magmatic ore deposits, building of continental crust and Earth evolution. This session aims to bring together scientists working in different fields of igneous and experimental petrology and geochemistry, structural and metamorphic geology, volcano-tectonics, geodesy, geophysics and material sciences. We would like to create a multi-disciplinary session, which will hope will generate a lot of discussion, new collaborations, and interdisciplinary knowledge transfer.
This session is sponsored by the IAVCEI Commission on Volcanic and Igneous Plumbing Systems.

Orals: Wed, 17 Apr | Room -2.91

Chairpersons: Lydéric France, Elena Melekhova, Pierre Bouilhol
Igneous processes
14:00–14:20
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EGU24-10207
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solicited
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On-site presentation
Fidel Costa and Jean-Philippe Metaxian

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.

14:20–14:30
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EGU24-2731
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On-site presentation
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Georg Zellmer, Daniel Coulthard Jr, Raimundo Brahm, Charline Lormand, Naoya Sakamoto, Yoshiyuki Iizuka, and Hisayoshi Yurimoto

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.

14:30–14:40
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EGU24-7717
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ECS
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On-site presentation
Juliette Pin, Lydéric France, Gilles Chazot, Etienne Deloule, Yafet Gabrewold Birhane, Raphaël Pik, and Irene Schimmelpfennig

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.

14:40–14:50
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EGU24-7781
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ECS
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On-site presentation
Sri Budhi Utami, Jacqueline Vander Auwera, Tonin Bechon, Paul Fugmann, and Olivier Namur

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 (Fo72-87) and Osorno (Fo66-82) [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.

14:50–14:55
14:55–15:05
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EGU24-3983
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On-site presentation
Marian Holness, Troels Nielsen, and Olivier Namur

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.

15:05–15:15
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EGU24-2048
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ECS
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On-site presentation
Valentin Basch, Alessio Sanfilippo, Jonathan Snow, Matthew Loocke, and Alberto Zanetti

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.

15:15–15:25
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EGU24-16269
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On-site presentation
Nicolas Riel, Boris Kaus, Hendrik Ranocha, Pascal Aellig, and Eleanor Green

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.

15:25–15:35
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EGU24-460
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ECS
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On-site presentation
Tahnee Otto, Gary Stevens, Jean-Francois Moyen, Matthew Mayne, and John Clemens

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.

15:35–15:45
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EGU24-15239
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solicited
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On-site presentation
Tobias Keller

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.

Coffee break
Chairpersons: Stefano Urbani, Daniele Maestrelli, Uddalak Biswas
Magmatic bodies emplacement
16:15–16:35
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EGU24-5812
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solicited
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Highlight
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On-site presentation
Craig Magee

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.

16:35–16:45
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EGU24-7511
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On-site presentation
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Matthew J. Comeau, Graham J. Hill, Svetlana Kovacikova, Jochen Kamm, Réka Lukács, Ioan Seghedi, Alexander Grayver, István Bondár, and Harangi Szabolcs

There are indications that some long-dormant or seemingly inactive volcanoes may have potentially active magma storage systems. One such system is Ciomadul volcano, which is located at the south-eastern terminus of the Carpathian volcanic chain (Romania). With the last eruption occurring at ~30 ka, this is the youngest volcano in eastern-central Europe. Understanding the nature and structure of the magma plumbing system is crucial to elucidating the evolution of the volcano and to assessing its hazard potential. This includes the depth, size, and geometry of the magma storage region, the amount and composition of the melt present, and the link between mantle and crustal processes.  

Ciomadul is situated in a geodynamically active region about 50 km from the Vrancea zone, where deep earthquakes are frequent. These earthquakes may represent the descent of a dense lithospheric slab beneath a continental collision zone and this may imply an asthenospheric upwelling due to return flow of mantle material. To the north-west of Ciomadul lies a chain of older volcanic complexes, the Călimani–Gurghiu-Harghita volcanic complex; about 40 km west of Ciomadul towards the Transylvanian Basin, a monogenetic basaltic volcanic region was developed at 1.2–0.5 Ma (Perşani volcanic field). Seismic tomography has revealed low-velocity columns through the lithosphere beneath both Ciomadul and Perşani. However, high-resolution images of the complex geometry of the system are lacking.  

We report here on a 3-D electrical resistivity model of the region that was generated from 41 magnetotelluric measurements acquired in 2022 that form a 75 km by 75 km array. The data typically had reliable periods from 128 Hz to 4,100+ s. Choosing appropriate locations for measurement was critical, away from sources of cultural electromagnetic noise that can contaminate the signals, as was careful data processing, including applying data pre-selection schemes and manual time windows in addition to standard approaches using robust statistics.  

Phase tensor analysis suggests that the data are 3-D at all scales. The 3-D electrical resistivity model reveals conductive anomalies (<10 ohm-m) in the subvolcanic crust. These are interpreted as melt-bearing magma reservoirs distributed in the mid-lower crust (depths of ~10–25 km) and a quasi-vertical conduit extending to the near surface. The crustal reservoir is oriented north-south, has its western margin beneath the surface vent of Ciomadul, and extends ~20 km eastward. These results are consistent with the quantitative petrological models placing the upper melt-bearing silicic crystal mush reservoir at a depth of 5–20 km beneath Ciomadul, and a magma-generation area in the asthenosphere (85–105 km depth). In contrast, no strong conductive anomaly is observed in the crust below Perşani, which fits the magma evolution model, i.e. small batches of mantle-derived magmas ascend rapidly through the crustal column. Our results suggest that Ciomadul, a seemingly inactive volcano, is still underlain by a melt-bearing magma body and therefore can be regarded as having potential for reactivation and further volcanic eruptions.  

How to cite: Comeau, M. J., Hill, G. J., Kovacikova, S., Kamm, J., Lukács, R., Seghedi, I., Grayver, A., Bondár, I., and Szabolcs, H.: Imaging the magma plumbing system of Ciomadul volcano and the Perşani Volcanic Field and constraining postcollisional magma dynamics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7511, https://doi.org/10.5194/egusphere-egu24-7511, 2024.

16:45–16:55
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EGU24-14370
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On-site presentation
Graham Hill, Paul Bedrosian, Bethany Burton, Jade Crosbie, Bennett Hoogenboom, Michael Mitchell, Jared Peacock, and Erin Wallin

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 20th 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.

16:55–17:05
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EGU24-10396
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ECS
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On-site presentation
Shan Yan, Yang Li, Wei Tao, Yuanyuan Liu, and Fule Liu

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.

17:05–17:10
17:10–17:20
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EGU24-5981
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On-site presentation
Antony Morris, Andrew Parsons, Michelle Harris, Chris MacLeod, Benoit Ildefonse, Charlotte Atton, Simon Allerton, and Derya Gürer

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.

17:20–17:30
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EGU24-6145
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ECS
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On-site presentation
Alessandro La Rosa, Carolina Pagli, Hua Wang, Freysteinn Sigmundsson, Virginie Pinel, and Derek Keir

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.

17:30–17:40
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EGU24-9775
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ECS
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On-site presentation
Jade A. Hrintchuk, Janine L. Kavanagh, and Elisabetta Mariani

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.

17:40–17:50
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EGU24-12898
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solicited
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Virtual presentation
Agust Gudmundsson

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.

17:50–18:00

Posters on site: Thu, 18 Apr, 10:45–12:30 | Hall X1

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 12:30
Chairpersons: Elena Melekhova, Pierre Bouilhol, Daniele Maestrelli
X1.158
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EGU24-13447
Lydéric France, Aurore Toussaint, and Valentine Charvet

The assemblage and evolution in time through various differentiation processes of igneous reservoirs shapes magmatism expressions at depth and at surface. Our knowledge of those systems largely relies on theoretical or applied thermomechanical and kinetic models, on geophysical data from active systems, and on structural and petrological data from active and fossil systems. Petrological approaches commonly use textures, thermodynamic models, chemical compositions of major and trace elements to decipher on the dynamics of complex igneous processes. Although chemical maps are more and more common, the overwhelming of the published data reposes on punctual measurements.

Here by using the example of a basalt crystallizing from liquidus to solidus in closed system, we present a new petrological approach that couples chemical maps to thermodynamic models to provide the first maps of thermodynamic parameters with a value attributed to each pixel (e.g., temperature or melt fraction maps in plutonic rocks). If the cooling rate is quantified by other means (e.g., diffusion chronometry), then the first of its kind movies of the crystallization evolution can be built from the first crystal to form to the last melt drop crystallization. We will present such results, allowing the igneous petrologist to explore their data in a new perspective. As an example the studied samples could be observed at various stages of the crystallization path highlighting a heterogeneous interstitial melt spatial distribution during magma solidification. This result has potentially important implications on melt segregation at the scale of the igneous reservoir. The presented results highlight that such a heterogeneous melt distribution was already present at the magma/mush transition. Additional simplified numerical crystallization models suggest that this heterogeneous a melt distribution is related to an early heterogeneous nucleation process, and may be common in volcanic and igneous plumbing systems.

Overall, this new approach will eventually help to make progress in our understanding of igneous systems.

How to cite: France, L., Toussaint, A., and Charvet, V.: Advances in Igneous Petrology: Coupled chemical maps & thermodynamic models to tackle mushes crystallization dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13447, https://doi.org/10.5194/egusphere-egu24-13447, 2024.

X1.159
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EGU24-21561
Jie Li, Ling Chen, and Yan-Hui Dong

Mid-oceanic ridge basalts (MORBs) are frequently grouped as depleted (D-MORBs), normal (N-MORBs), or enriched (E-MORBs) based on the abundances of highly incompatible elements. E-MORBs, characterized by enriched in incompatible elements, were first noted near mantle plumes, so that enrichment of highly incompatible elements was initially understood as a result of infiltration of plume-related melts into the MORB plumbing system. But for E-MORBs far from plumes, it is still controversial of the lithology of enriched components of these E-MORBs. Two major explanations are proposed that the enriched components are generated by the melting of entrained recycled crust (pyroxenite) beneath ridges or by the melting of refertilized peridotites from subducted slabs. The reason for this problem is that melting of the ambient refractory peridotite along with the enriched component will dilute the signals recorded in MORB. Therefore, the in-situ analyses of minerals and/or melt inclusions will shed new light on this question.

Here high-precision in-situ analyses were conducted on olivine and plagioclase in the studied samples. According to the major and minor element contents of olivine phenocrysts, we found they have similar Ni, Mn and Ni/(Mg/Fe) contents with those from N-MORB at a given Fo, indicating a peridotitic source. Furthermore, in-situ Sr isotope in plagioclase phenocrysts and in-situ Pb isotope of plagioclase-hosted melt inclusions are also reported to constrain origin of parental magma. The isotopic results show that unlike the uniform whole-rock 87Sr/ 86Sr and 206Pb/204Pb ratios, the plagioclase phenocrysts record highly Sr and Pb isotopic heterogeneity. Strontium isotopic heterogeneity is observed between crystals even in a single thin section. Based on the high An contents of plagioclase phenocrysts and chemical disequilibrium between plagioclase phenocrysts and groundmass, we propose they crystallized early in the magma chamber and were most likely formed in different batches of mantle-derived melts. The enrichment of LREE and negative correlations between La/Sm and Pb isotopes melt inclusions, suggest that ancient continent lithosphere materials are likely present in the sub-ridge mantle of the east of the Melville FZ, SWIR. Collectively, we proposed that the continent lithosphere materials were slabbed into the upper mantle under MOR as refertilized peridotites.

How to cite: Li, J., Chen, L., and Dong, Y.-H.: Constraints on the mantle lithology of enriched components: evidence from E-MORB of Southwest Indian Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21561, https://doi.org/10.5194/egusphere-egu24-21561, 2024.

X1.160
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EGU24-21736
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ECS
Alex G Stewart, Margaret E Hartley, Rhian H Jones, Jon W Fellowes, and David A Neave

The redox state of magmatic systems controls important physico-chemical properties and processes on the Earth, such as the composition of volcanic gases, the rheology of magma, and the transport and deposition of critical metals. In natural silicate magma, Fe is the most abundant multivalent element, and the redox state of the system can be determined if the relationship between Fe valence and fO2 is known. Popular oxybarometers (e.g., Fe3+/FeT in glass or Fe-Ti oxide pairs) can accurately determine the redox state of magmatic systems but suffer limitations such as beam damage during analysis or the requirement of specific phases to be present.

Clinopyroxene is a common igneous mineral that plays a key role in chemical cycling on Earth and is found in igneous rocks ranging from near-primary basalts to rhyolites. Clinopyroxene can incorporate both Fe2+ and Fe3+ and may capture a record of magmatic redox state upon crystallisation. However, attempts to quantify how Fe valence varies in clinopyroxene as a function of redox state are limited, partly due to the inability to routinely measure Fe valence using electron probe microanalysis (EPMA).

To remedy this, we are exploring the utility of the “flank method” [1] and conventional stoichiometric estimates for determining Fe valence using EPMA. Using a suite of Mössbauer calibrated clinopyroxene standards, preliminary “flank method” analyses demonstrate that the FeO content of clinopyroxenes ranging from diopside (FeOT = 3 wt%) to aegirine (FeOT = 28 wt%) can be determined with a RMSE of 0.03 wt%. Additional standards with FeOT from 2 – 10 wt% are being collated to improve the performance of this method when applied to augitic clinopyroxene. Furthermore, it is possible to obtain 3σ uncertainties on Fe3+/FeT of 3-7% using conventional stoichiometric estimates if EPMA analyses are sufficiently precise [2].

Using high-precision EPMA and stoichiometric estimates of Fe3+, we demonstrate that clinopyroxene crystals in oceanic basalts from the Reykjanes Ridge, Iceland and the Canary Islands have Fe3+/FeT of 0.1 – 0.7. Olivine-glass and olivine-spinel pairs constrain the redox state of these oceanic basalts to be equivalent to FMQ, FMQ+1.5 and FMQ+2, respectively, in line with independent estimates from the literature. The partitioning of Fe3+ between clinopyroxene and melt (KD Fe3+cpx-melt) ranges from 0.50 – 1.4 in tholeiitic to alkali basalts, and we show that clinopyroxene Fe3+/FeT increases concomitantly with estimates of redox state.

However, there is currently limited experimental data in which Fe3+ has been measured with sufficient accuracy or precision to fully understand the controls on Fe3+ partitioning in basaltic systems, precluding the use of clinopyroxene as a probe for magmatic redox at present. An experimental campaign is currently underway to help refine models of Fe3+ partitioning, ultimately contributing to the development of a clinopyroxene based Fe-oxybarometer, and to shed light on the poorly defined role of Fe3+ in the chemical evolution of basaltic magmatic systems.

 

[1] Hofer & Brey, 2007. Am Min, 92, pp.873-885.

[2] Neave et al., 2024. CMP, 179, 5. doi: 10.1007/s00410-023-02080-2

How to cite: Stewart, A. G., Hartley, M. E., Jones, R. H., Fellowes, J. W., and Neave, D. A.: Fe-valence in magmatic clinopyroxene and the redox state of oceanic basalts – perspectives from natural samples and experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21736, https://doi.org/10.5194/egusphere-egu24-21736, 2024.

X1.161
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EGU24-18599
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ECS
Sumith Abeykoon, Lydéric France, Pierre Condamine, and Célia Dalou

Carbonatite deposits are rare magmas which represent the primary source of Rare Earth Elements (REE) on Earth; those are often associated with alkaline silicate magmas. A unique opportunity to investigate the natural carbonatite system exists through the study of the only active extrusive carbonatite volcano on Earth, the Oldoinyo Lengai (Tanzania). It has been proposed that carbonatites could be produced by low-degree partial melting of upper mantle domains associated with protracted differentiation that eventually form phonolite together with immiscible carbonatite melts. In such a model, the primitive magmas are proposed to be melilitites or Mg-nephelinite. However, a comprehensive study of the crystallization and immiscibility processes related to those parental melts is still missing.

In this study, we performed equilibrium and fractional crystallization experiments in order to understand the differentiation behaviour of carbonatites' parental magmas at high-pressure, and to decipher on the role of both melilitites or Mg-nephelinite in carbonatite genesis. Volatiles were introduced to both melilitite and Mg-nephelinite starting compositions, and the initial volatile contents (1.2 wt.% of H2O and 0.6 wt.% of CO2) were referred to the previous melt inclusion study by Mourey et al. (2023). The conditions of the first fractional crystallization experiments were established to be just below the liquidus temperature of each composition, i.e., for melilitite = 1250 °C and for Mg-nephelinite = 1200 °C and the subsequent experiments are performed by decreasing the temperature by 15 to 30 °C in each step. At each step, the melt composition in equilibrium with crystallized minerals is determined using an electron microprobe and, mass balance calculations for volatiles. All the experiments were performed at a nominal pressure of 1 GPa (relevant for lower crustal conditions in the Oldoinyo Lengai system), using a piston-cylinder apparatus. A double capsule setup made of AuPd was used to avoid iron and volatile losses during the experiments.

Equilibrium crystallization has not been able to produce phonolite magmas, the evolved term that is observed in the natural system in equilibrium with immiscible alkaline carbonatites. The fractional crystallization experiments of Mg-nephelinite composition highlight an evolution towards the alkaline-rich phonolites after 60% of fractionation, while the evolution of melilitite experiments seems to follow chemical trends that are not consistent with the natural liquid line of descent. The alkaline silicate melt remains abundant in all the fractional crystallization experiments (>65%), which facilitates an efficient equilibrium with silicate minerals and oxides, such as olivine, spinel, clinopyroxene, magnetite, perovskite, phlogopite, melilite and garnet. Mineral assemblages present along the liquid line of descent are consistent with the natural record that has been documented at Oldoinyo Lengai by cognate plutonic samples. Experiments are still ongoing to explore the potential occurrence of carbonatite-silicate melt immiscibility at later stages of the crystallization sequence.

How to cite: Abeykoon, S., France, L., Condamine, P., and Dalou, C.: Fractional crystallization of melilitite and Mg-nephelinite at 1 GPa: An experimental study on the petrogenesis of phonolite and related immiscible carbonatite magmas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18599, https://doi.org/10.5194/egusphere-egu24-18599, 2024.

X1.162
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EGU24-14687
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ECS
Angus Rogers, Oliver Nebel, Hugh O'Neill, Greg Yaxley, Yona Nebel-Jacobsen, and Xueying Wang

Aitutaki is a basaltic Ocean Island in the South-Central Pacific Ocean, a region densely populated with age-progressive islands and seamounts considered to be a result of three or more overlapping mantle plumes. Recent (~1.9 Ma) volcanic activity at Aitutaki is difficult to reconcile with direct melting of a mantle plume, and may instead be an example of rejuvenation, whereby volcanism reappears after an extended hiatus. We have analysed samples of 21 lavas collected from Aitutaki for whole-rock major and trace elements and radiogenic isotopes, with electron probe microanalysis (EPMA) of olivine crystals and xenocrysts. Whole-rock MgO in these samples ranges from 10.3 to 13.9 wt. %. Petrographic examination and EPMA data indicate olivine accumulation is not the cause of these high values. Evidently, very little fractionation occurred during melt ascent through the volcanic plumbing network. Direct eruption of high-MgO (>10 wt.%) primitive magma is unusual in Ocean Island basalts, except among rejuvenated volcanics.

Our radiogenic isotope data closely overlap in Pb-isotope space with the nearby Samoan rejuvenated lavas from Savai’i and Tutuila, and otherwise have an EM1-FOZO signature. The major elements, trace elements and radiogenic isotopes all distinguish two populations of lavas, indicating the lavas are sourced from different regions or source materials in the asthenosphere. By analysing the spatial distribution of these chemical anomalies on the island, we observe the least evolved and most trace-element enriched samples (lowest SiO2, highest Th/Y) concentrate in geographically distinct regions on the island. Without a geochemical continuum between these two populations, we suggest the surface distribution of the enriched and depleted lavas may reflect spatial isolation of the mantle sources. Aitutaki produced multiple pulses of geochemically diverse lavas with extreme compositions throughout a short-lived (~50 ka) rejuvenated eruption cycle, exemplifying the processes responsible for producing rejuvenated lavas and challenging our understanding of the petrogenesis of such volcanism.

How to cite: Rogers, A., Nebel, O., O'Neill, H., Yaxley, G., Nebel-Jacobsen, Y., and Wang, X.: The geochemical evolution of an extreme rejuvenated lava: A case study on Aitutaki of the Cook-Austral island chain  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14687, https://doi.org/10.5194/egusphere-egu24-14687, 2024.

X1.163
|
EGU24-408
Jianfeng Ma, Xiaolei Wang, Alexandra Yang Yang, and Taiping Zhao

The genesis of intermediate intrusions is highly controversial, and one of the hot topics is whether they represent frozen melts or cumulates in the evolution of magmatic systems. Distinguishing accumulation from crystallization melt differentiated along the liquid line of descent is the key issue. The Paleoproterozoic intermediate intrusions in southern North China Craton provide an excellent case to decipher this issue. Multiple lines of evidence, including mineral textures, geochemistry as well as alphaMELTS modeling, indicate disequilibrium between whole-rock and minerals, with melt extraction occurring at temperatures of 760°–820°C and with 10–40 wt.% of trapped melts. Effective water storage, revealed by amphibole and clinopyroxene hygrometers, plays a crucial role in promoting crystal-melt segregation in pluton-sized reservoirs in the upper crust. This study demonstrates that the accumulation in intermediate magmas can be identified even without evident complementary initial and extracted melts and provides deep insights into the genesis of intermediate continental crust.

How to cite: Ma, J., Wang, X., Yang, A. Y., and Zhao, T.: Tracking Crystal-Melt Segregation and Accumulation in the Intermediate Magma Reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-408, https://doi.org/10.5194/egusphere-egu24-408, 2024.

X1.164
|
EGU24-2182
|
ECS
Wet calc-alkaline magmatic fractionation in the middle-upper crustal sections of continental arc: Insights from Neoproterozoic Nanba intrusive complex, western Yangtze Block, South China
(withdrawn)
Yu Zhu and Shao-cong Lai
X1.165
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EGU24-490
Generation of Neoproterozoic high-silica granites by crystal-melt segregation in the northern Yangtze Block, South China: Implications for the evolution of Precambrian continental crust
(withdrawn)
Wenbin Xue and Shaocong Lai
X1.166
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EGU24-20364
|
ECS
Nicolas Esteves, Lyderic France, Pierre Bouilhol, and Michel Cuney

To better constrain the assembly, evolution and magmatic differentiation associated kinematics of granitic intrusions, we took advantage of a 1 km long drilled core of the Echassières-Beauvoir rare metal granite, allowing a high resolution sampling of a fully recovered plutonic body. Structural and textural data, coupled with high-resolution major and trace element composition of the mineral phases (in-situ measurements and chemical map), provide constraints on the differentiation processes and its dynamics. As Li-mica (lepidolite) is a liquidus phase present all along melt evolution, their compositions allow tracking melt batches and their differentiation state. We show that the granite formed through the stacking of deca- to hectometric crystal-poor sills, defining different sub-units within the granite. As each sub-units are compositionally different, the detailed study of mineral composition provides a dynamic record of the pluton assembly: although globally constructed from bottom to top, sill emplacement can also occur through off-sequence intrusion within or beneath partly crystallized sub-units. Those sub-units seem to be the result of the amalgamation of smaller sills; the latter displaying similar mineral composition from one to the other.

Once intruded these sills crystallize an assemblage of quartz-topaz-mica and alkali-feldspar, recording differentiation trends from core to rim. This differentiation leads to the formation of a quartz-rich mush and associated albite-saturated interstitial residual melts enriched in incompatible elements (e.g. Li, F, P). A part of these residual melts has been extracted from the quartz-rich mush under the form of differentiated magma channels. Now fully crystallized, those channels correspond to albite-rich segregates, forming lobate contacts with the surrounding granite. Locally, these albite-rich segregates are accumulated beneath the overlying subsequently intruded sill, indicating a protracted plutonic construction faster than the solidification of a single sill. Ultimately, the protracted differentiation of the last and upper sub-unit (≈130 m thick) has led to the accumulation of weakly-viscous evolved melt in the upper-part of magmatic reservoir. This newly formed liquid-rich lens could then be mobilized as erupted silica-rich magma, potentially corresponding to rhyolitic intruding the surrounding host-rocks.

How to cite: Esteves, N., France, L., Bouilhol, P., and Cuney, M.: Plutonic formation through sills stacking and amalgamation: The case of Beauvoir rare-metal granite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20364, https://doi.org/10.5194/egusphere-egu24-20364, 2024.

X1.167
|
EGU24-7580
Multiple extractions of the Cretaceous silicic magma plumbing system beneath the Baiyunzhang-Lianhuashan Basins, eastern Guangdong, SE China
(withdrawn)
Yan Xia, Jianqiang He, and Xisheng Xu
X1.168
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EGU24-4426
J. Brendan Murphy, Christopher J. Spencer, Donnelly B. Archibald, and William J. Collins

Appinite plutonic rocks range from ultramafic to felsic in composition, are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies, and by spectacularly diverse textures, including planar and linear magmatic fabrics, multiple comb layers, mafic pegmatites and widespread evidence of mingling between mafic and felsic compositions. These features suggest that they are anomalously water-rich mafic magmas.  

The ca. 607 Ma Greendale Complex in the Antigonish Highlands of Nova Scotia is typical of appinite complexes which commonly occur as small (~2 km diameter) plutons adjacent to major deep crustal faults along the periphery of voluminous granitoid plutons emplaced in the waning stages of regional arc activity. Isotopic data from hornblendes in the Greendale Complex yield δD values ranging from -61 to -72 and δO18 from 3.7 to 7.0, indicating the water in the appinite magma has a strong mantle component. These data suggest the appinites may represent aliquots of hydrous basaltic magma derived from mafic underplates originally emplaced along the base of the crust during protracted subduction. Transfer of heat and fluids to the base of the crust triggered generation of coeval (615-604 Ma) granitoid magmas by partial melting in the overlying MASH zone. The granitoid magmas were emplaced in the shallow crust when transient stresses activated favourably-oriented structures which became conduits for magma transport. The ascent of late mafic magmas within the Antigonish Highlands was impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magmas that form the Greendale Complex evaded those rheological barriers because they preferentially exploited the deep crustal Hollow Fault that bounded the plutonic system.

Collectively, these mineralogical, textural and geochemical features suggest a complex magmatic history involving repeated water saturation episodes within the plumbing system as mafic, mantle-derived magmas ascended and differentiated at mid-to-upper crustal levels (ca. 3-5 kbar). More generally, the most mafic components of appinite complexes may provide a window into the composition of the mafic underplate and insights into processes that generate granitoid batholiths and crustal growth in arc systems.

 

How to cite: Murphy, J. B., Spencer, C. J., Archibald, D. B., and Collins, W. J.: A mantle source for water in Appinite complexes: implications for genesis of granitoid batholiths and crustal growth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4426, https://doi.org/10.5194/egusphere-egu24-4426, 2024.

X1.169
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EGU24-5671
|
ECS
Wafa AL-Hakimi, Sabyasachi Chattopadhyay, Faris Sulistyohariyanto, Scott A. Whattam, Hossein Azizi, Keewook Yi, and Fatemeh Nouri

 The 900–550 Ma Arabian-Nubian Shield (ANS) represents the northern part of the East African Orogen (EAO) and was generated by Neoproterozoic juvenile crust addition and ultimately, collision of eastern and western Gondwana ca. 600 Ma. The ANS  encompasses the greatest volume of Neoproterozoic juvenile crust preserved on Earth and embodies over 610,000 km2 across NE Africa and the western part of the Arabian Peninsula. The ANS comprises stacks of thin-skinned nappes resulting from oblique convergence of bounding plates and resulting amalgamation of intra-oceanic arcs generated within the Mozambique Ocean. As such, the ANS is a classic example of an accretionary orogen. Final accretion and ANS consolidation were accompanied and followed by emplacement of within-plate alkaline plutons c. 640–550 Ma, which represent the largest volume of alkaline granitoids on the planet. Overall, ANS tectonic evolution encompasses an orogenic cycle beginning with the fragmentation of Rodinia (870–800 Ma) and ending with amalgamation of eastern and western Gondwana in the Cambrian.

This study combines field observations, petrography, whole rock major-and-trace element chemistry, along with U-Pb zircon geochronology and Sr-Nd-Pb isotope data of four granitoid suites of the northwestern part of the Midyan terrane (Ifal, Muwylih, Midyan, and Lawaz), that provides an excellent opportunity for further understanding of the factors influencing the shift from A- to I-type granitoids. Samples are mostly granite-granodiorite-diorite with subordinate gabbro and gabbro diorite. Seven samples are A-type, while the remaining 26 are I-type. Petrographically, I-type rocks consist of K-feldspar, quartz, albite, mica, amphiboles, and sodic-pyroxene as major minerals with a variety of accessory minerals, including Fe-oxides and zircon. Major oxide abundances such as CaO, TiO2, and P2O5 manifest a clear decrease with increasing SiO2 content, except for K2O, which indicates fractionation of, for example, plagioclase, Fe-Ti oxides, and apatite. Whole rock data shows clearly distinct characters of the A-type being metaluminous, enrchied in ∑REE with an average of 355 µg/g. In contrast, the I-type is meta-luminous-peraluminous, which only has an average of ∑REE 197 µg/g. The chondrite-normalized patterns of the A-type show lower negative Eu anomalies (Eu/Eu*=0.61) in comparison to the I-types (Eu/Eu*=0.86), depicting the different degrees of plagioclase fractionation. The primitive-mantle normalized patterns show depletions in  Sr and Ti, indicating fractionation of feldspar and Fe-Ti phases in both types. The U-Pb zircon ages indicate two distinct pulses of granitoid magmatism.  The first pulse is attributed to A2 (post collision)-type ca. 634–640 Ma, followed by a second pulse of I-type in nature ca. 618–598 Ma. The A and I-type Sr-Nd isotope data attest to the juvenile nature of the crust from the ANS (εNd =4.88–5.15), while some I-types (εNd =3.91) are derived from partial melting of a pre-existing crust. We conclude that the magmatism in the Midyan terrane area is shown to have shifted from a within-plate setting associated with orogenic collapse and partial melting of the lower crust into volcanic arc affinity with a more depleted source.

 

How to cite: AL-Hakimi, W., Chattopadhyay, S., Sulistyohariyanto, F., Whattam, S. A., Azizi, H., Yi, K., and Nouri, F.: Geochemistry and geochronology of Midyan terrane granitoids, NW Saudi Arabia: Implications for growth of the Arabian-Nubian Shield, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5671, https://doi.org/10.5194/egusphere-egu24-5671, 2024.

X1.170
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EGU24-673
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ECS
Gökçenur Bayram, Esra Tükel, Işıl Nur Güraslan, Alp Ünal, and Şafak Altunkaynak

One of the least studied plutons in NW Anatolia, the Esenköy pluton intruded into the Palaeozoic Armutlu metamorphics. Along its southwestern boundary with the Esenköy pluton, basement rocks are found as "roof pendants". Both the Esenköy pluton and the Armutlu metamorphics are cut by aplite and diorite porphyry dykes. The pluton is mainly granodioritic in composition and is made up of 45-50% plagioclase, 25-30% quartz, 12-15% alkali feldspar, 6-9% hornblende, and 3-5% biotite. It exhibits predominantly holocrystalline porphyritic texture, and graphic-granophyric textures are also widespread throughout the main plutonic body. Diorite porphyry dykes display micro-granular porphyritic texture, while aplite dykes commonly show micro-granular texture.

Chemical analyses of plagioclase and amphibole minerals in granodiorite samples reveal that plagioclases are predominantly andesine (An35-50) in composition. Zoned plagioclases generally show normal zoning with a decrease in calcium ratios from the core to the rims of the crystals. Amphiboles are all calcic in composition and are represented by magnesio-hornblende. Geothermobarometric calculations, using the chemistry of amphiboles and plagioclases from the same samples, yield pressure values ranging from 1.12 to 1.41 kbar and temperature values ranging from 741 to 787 °C. These temperature and pressure conditions suggest that the Esenköy pluton is emplaced at depths of 3.37-4.23 km within the crust. Contact relationships, textural properties and geothermobarometric calculations collectively indicate that the Esenköy pluton is an epizonal pluton that was emplaced into shallow levels of NW Anatolian crust.

How to cite: Bayram, G., Tükel, E., Güraslan, I. N., Ünal, A., and Altunkaynak, Ş.: Geology, petrography and emplacement conditions of the Esenköy Pluton (NW Anatolia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-673, https://doi.org/10.5194/egusphere-egu24-673, 2024.

X1.171
|
EGU24-2959
Jiyuan Yin, Tao Wang, and He Huang

Understanding the processes involved in the transformation of juvenile basaltic oceanic arc crust into mature continental crust remains a key challenge in Earth sciences. In this contribution, we present a comprehensive synthesis of in situ zircon U-Pb age and Hf-O isotope data for Paleozoic intrusions within the West Junggar oceanic arc, NW China. Our study reveals four distinct pulses of magmatic activity: Early Cambrian to Early Ordovician (515 to 486 Ma); Late Ordovician to Middle Devonian (445 to 392 Ma); Early Carboniferous (343 to 310 Ma) and Late Carboniferous to Middle Permian (309 to 259 Ma). These pulses have varied spatial and temporal distributions. All magmatic rocks display consistently high zircon Hf and whole-rock Nd isotope values, but substantial variations in zircon O isotopes. There are two groups of intrusions: those with high zircon δ18O (>6.5‰) and those with mantle-like zircon δ18O (ca. 5.5‰). The high zircon δ18O intrusions are predominantly concentrated in the southern West Junggar and their Hf and Nd isotopes indicate the involvement of supracrustal material and juvenile basaltic crust in their petrogenesis. Binary mixing calculations indicate a contribution from the supracrustal rocks ranging from 10% to 50%. The intrusions with mantle-like zircon δ18O are found primarily in northern West Junggar with a small amount occurring in southern West Junggar. The intrusions record a variety of magma sources and processes as demonstrated by Hf-O isotope and geochemical data. These data indicate partial melting of metasomatized depleted mantle, mixing of depleted mantle and juvenile crust, and partial melting of trapped juvenile oceanic crust or mafic lower crust. Hf model ages reveal significant crustal growth in the West Junggar, characterized by three distinct episodes of crust formation occurring at approximately 656-684 Ma, 524-536 Ma, and 441-471 Ma, involving periodic remelting of igneous material derived from a depleted mantle source. This newly-formed crust maintains a mantle-like oxygen isotope composition despite being repeatedly sampled by magmas for up to 0.26 Ga. Since the timing of crustal growth occurred independently of the major magmatic pulses, the latter reflect primarily reworking and remelting processes. Two significant episodes of magmatic activity, the late Silurian to early Devonian and the late Carboniferous to early Permian, preserve a signature of ocean ridge subduction. High-temperature magmatism during these periods promoted extensive melting of the mafic lower crust, oceanic crust, and supracrustal rocks, leading to the compositional transformation from basaltic to felsic continental crust. This comprehensive compilation provides valuable insights into granite petrogenesis, crustal evolution, and the diverse processes involved in the maturation of oceanic arc crust and its contribution to continental crust formation and evolution.

 

How to cite: Yin, J., Wang, T., and Huang, H.: Ocean arc to continental crust: zircon Hf-O isotopes and crustal evolution of West Junggar, NW China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2959, https://doi.org/10.5194/egusphere-egu24-2959, 2024.

X1.172
|
EGU24-6844
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ECS
Dmitrii Zastrozhnov, Sverre Planke, John Millett, Rafael Horota, Agnes Kontny, Kim Senger, Sebastian Tappe, Anniken Helland-Hansen, Maria Telmon, Peter Betlem, Alexander Minakov, and Horst Kaempf

Sverrefjellet is the remnant of an extinct alkali basaltic stratovolcano located in NW Svalbard, representing a distinctive phase of Quaternary magmatism in the High Arctic. It is part of the Bockfjorden Volcanic Complex, which consists of several eruption centers within the Woodfjorden-Bockfjorden area. The volcanism occurred during the northern hemisphere’s glaciations and reveals evidence for magma interactions with glaciers. The Quaternary eruption centers are localized along the Breibogen Fault and were probably linked to the evolution of the Knipovich mid-oceanic ridge, yet the exact age of the magmatic activity remains uncertain. Sverrefjellet is renowned for its high abundance of mantle-derived xenoliths, which have become a focal point in most publications on this volcano to date. However, the magmatic architecture and physical volcanology of Sverrefjellet have received only limited attention after the initial mapping by Skjelkvåle et al. (1989).

In July 2023, an international multi-disciplinary geoscientific expedition to Woodfjorden-Bockfjorden was undertaken. One of the primary objectives was to perform detailed mapping and systematic sampling of volcanic-related units within Sverrefjellet volcano, with the aim of exploring and refining magma emplacement processes. To facilitate this, drones were utilized to acquire high-resolution 3D digital textured models over the best-exposed outcrops of the volcano. The in-field sampling of the main volcanic units was accompanied by extensive (∼100) magnetic susceptibility measurements with a hand-held Kappameter (SM-30). In total, 20 rock samples have been prepared for petrographic, SEM and EPMA analyses.

We observed the presence of mantle-derived xenoliths in all volcanic units, which include dyke intrusions, pillow basalts with associated lava tubes, basaltic lava flows, and various volcanogenic sediments. The slopes of the extinct volcano display predominant frost weathering, with the southern slope adorned with olivine sand and gravel sourced from 'bomb-shaped' nodules or clasts that typically contain peridotite xenoliths as their cores. The presence of pillow lavas and associated 1 to 2 meter large lava tubes suggests subglacial magma emplacement. This is supported by their relatively high elevation at 200-300 meters above sea-level, which makes interaction with seawater highly unlikely.

In between lava flows and dykes, texturally distinctive zones characterized by platy tops and bottoms as well as numerous flattened boulder-sized xenolithic nodules were observed. Petrographic and SEM analyses of xenoliths and host basalts revealed no preferred alignment of crystals within the platy zones, suggesting that these schistose textures developed due to rapid magma cooling and subsequent freeze-thaw action rather than tectonic shearing. The basalts display typical ferrimagnetic susceptibilities (average: 3.24 × 10-3 SI), whereas the volcanogenic sediments exhibit low paramagnetic susceptibility (0.38 × 10-3 SI), indicating rapid magma quenching during fragmentation, which is characteristic of subglacial emplacement.

Our preliminary results support a subglacial origin for the Sverrefjellet eruptions. Ongoing detailed mapping and thorough magnetic mineralogy analyses, coupled with geochronological and geomorphological studies, will enhance our understanding of subglacial volcanic processes at the extinct Sverrefjellet volcano and more broadly. Additionally, these findings will contribute to a better understanding of the nature and origin of High Arctic Quaternary magmatism and its paleogeographic setting.

How to cite: Zastrozhnov, D., Planke, S., Millett, J., Horota, R., Kontny, A., Senger, K., Tappe, S., Helland-Hansen, A., Telmon, M., Betlem, P., Minakov, A., and Kaempf, H.: Quaternary Magmatism in NW Svalbard: Refining the Architecture and Evolution of Sverrefjellet Volcano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6844, https://doi.org/10.5194/egusphere-egu24-6844, 2024.

X1.173
|
EGU24-1144
Hydrodynamic modelling of bubble interactions inside conduits: insights for volcanic eruption behaviour
(withdrawn)
Amiya Baruah, Pallab Jyoti Hazarika, and Nibir Mandal
X1.174
|
EGU24-9055
|
ECS
Birhan Kebede, Carolina Pagli, Derek Keir, Alessandro La Rosa, and Freysteinn Sigmundsson

Axial rift volcanoes characterised by an active magmatic and hydrothermal system offer a unique opportunity to study the interaction between these processes. The Dallol volcanic and hydrothermal area is situated in the Afar rift, on the axis of Erta Ale ridge, in a depressed salt plain. Dallol has been experiencing deformation at least since the first dike intrusion observed by InSAR in 2004. Here, we present the results of a new InSAR analysis of Dallol between 2014 and 2023, and inverse modelling of the observed deformation. We used SAR data from the ESA´s Sentinel 1A/B ascending (014) and descending (079) orbits to produce over 651 interferograms. Then we obtained InSAR average velocity maps revealing the presence of three closely spaced and concentric deformation signals of a range increase, consistent with subsidence, of up to 40 mm/yr in the satellite Line-of-Sight (LOS). The main deformation signal corresponds to the Dallol crater, while the two smaller maxima occur on the bishophite precipitating Black Mountain area south of Dallol and at the location of a circular pool at the edge of the salt plain, west of the crater. Our modelling results indicate that the deformation sources can be explained by contractions of three Okada tensile dislocation sources situated at different shallow depths, ranging between 0.7-1.7 km, with a length of 1-3 km and volume decrease of 1-3x10-4 km3/yr. Time series analysis also shows that the subsidence pattern was about linear while small seasonal fluctuation patterns are identified at the two smaller maximas. We interpret that the main subsidance at the Dallol crater is likely caused by the depressurisation of shallow sills, while a possible contribution to the defomration from the hydrothermal system due to seasonal flooding is envisaged for the other two maximas.

How to cite: Kebede, B., Pagli, C., Keir, D., La Rosa, A., and Sigmundsson, F.: Continuous Subsidence of Dallol Volcano (Danakil Depression) as a result of magmatic and hydrothermal interaction: Insights from InSAR Observation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9055, https://doi.org/10.5194/egusphere-egu24-9055, 2024.

X1.175
|
EGU24-744
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ECS
Uddalak Biswas, Atin Kumar Mitra, and Nibir Mandal

The laboratory modelling of upper and lower crustal rocks has been challenging in terms of rheological scaling for geologists. Upper and lower crusts have been considered as coulomb-brittle or elastic and viscous rheological material, respectively, by the analogue modeller in simulating several deformation related phenomena. However, in nature, they are not purely viscous or elastic, or plastic. Rather, they behave visco-elasto-plastically. This work introduces two new materials of complex visco-elastic and visco-elastoplastic rheology i) Gel wax and, ii) Ultrasound Transmission Gel (USTG). Gel wax is a commercial wax which is composed of mineral oil and hydrocarbon-based polymer. It is used for making transparent, long-lasting candles with melting temperatures of 70-80°C. On the other hand, USTG is a gel-like substance made mainly of Carbopol powder and water.

In this present work, we performed amplitude and frequency sweep tests in a rheometer for both the Gel wax and USTG to understand their complex rheology. The results suggest that Gel wax can be an appropriate analogue material to simulate upper crustal experiments. Similarly, visco-elastoplastic rheology of USTG is analogous to lower crustal rocks.

Considering these materials as crustal analogues, we conducted a few dike emplacement experiments following proper geometric, kinematic and dynamic scaling. The experimental results revealed remarkable 3D dike geometry as both the materials are transparent. Finally, we matched these patterns with a few exposed dikes observed in the field, which supports the applicability of Gel wax and USTG as crustal rock analogues.

How to cite: Biswas, U., Mitra, A. K., and Mandal, N.: Gel wax and Ultrasound Transmission Gel as upper and lower crustal rheology analogue, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-744, https://doi.org/10.5194/egusphere-egu24-744, 2024.

X1.176
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EGU24-10782
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ECS
Stefano Urbani, Janine Kavanagh, Tegan Havard, Dawid Rybak, Katharine Gilchrist, Simon Martin, Andrew Biggin, Elisabetta Mariani, and Steffi Burchardt

Since dykes represent the main mechanism for magma movement from the Earth’s crust to the surface, understanding how they generate a path to feed an eruption is crucial for volcanic hazard assessment. To this purpose, key information can be obtained by studying fossil dykes in extinct and eroded volcanic systems where dykes show a variety of shapes, segmentation, and propagation paths due to a suite of pre-, syn- and post-emplacement physical processes (e.g. heat transfer, host rock layering, local stress variations).

To discern the factors that control these complex geometries and reveal how they affect the dynamics of magma transport, we used a multi-method approach on a N-S trending fossil dyke from the Reyðarfjörður dyke swarm (eastern Iceland). We collected meso-scale geometric data from drone photogrammetry, and rock magnetic, petrographic and microstructural laboratory analyses were conducted on oriented rock cores and samples to reveal microscopic magma flow indicators (e.g., magnetic fabrics and crystal alignment). Rock cores were sampled both across the thickness and along the breadth of the dyke segments, also recording the core position relative to different cooling surfaces (i.e. from the dyke margin to its interior).

The studied dyke is exposed for ˜900 m across its breadth in ˜300 m height. It comprises several segments showing different shapes (from straight to curved paths), thickness (spanning from 0.5 to 5 m) and linkage pattern (i.e. connected or not connected segments). The photogrammetry and geological field observations show the curved segments are more frequent in the shallower and thicker portions of the dyke, whereas the amount of offset, overlap and spacing between the segments is higher in the shallower portions of the dyke exposure. Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) were used to identify magnetic fabrics that may be related to magma flow in the rock cores. These results show that the magnetic data record complex magma flow dynamics spanning from sub-horizontal to subvertical along the dyke path, which is inferred for adjacent connected segments and from the dyke margin to its interior.

We relate the geometrical variability of the dyke segments to the far-field stress (controlled by regional extension) versus the near- field stress (controlled by local magma overpressure), the latter being dominant in the shallower (and thicker) portions of the dyke. This generates a mixed mode fracturing during dyke propagation, reflecting its geometrical variability, that also controls a complex magma flow pattern within the dyke. Microstructure analysis is in progress and it is expected to complement magnetic fabric analysis and fieldwork in the interpretation of magma flow dynamics. Current results already show that a multimethod approach aimed at linking observations from the mesoscale to the microscale is required to better capture small scale and complex propagation paths and magma flow patterns providing more reliable insights on dyke propagation.

How to cite: Urbani, S., Kavanagh, J., Havard, T., Rybak, D., Gilchrist, K., Martin, S., Biggin, A., Mariani, E., and Burchardt, S.: Complex magma flow dynamics within fossil dykes: linking multi-method observations across scales from the Reyðarfjörður dyke swarm, eastern Iceland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10782, https://doi.org/10.5194/egusphere-egu24-10782, 2024.

Posters virtual: Thu, 18 Apr, 14:00–15:45 | vHall X1

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 18:00
Chairpersons: Lydéric France, Stefano Urbani, Elena Melekhova
vX1.20
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EGU24-2316
Litho-bound basin scale thin sill emplacement, Raton Basin, USA. 
(withdrawn)
Chris Cornelius