GMPV7.3 | Linking modelling, experiments, and observations of magmatic systems from source to surface
EDI
Linking modelling, experiments, and observations of magmatic systems from source to surface
Co-organized by GD2
Convener: Tobias Keller | Co-conveners: Flavia Palummo, Adina E. Pusok, Barbara Bonechi, Nicolas Riel, Cristina Perinelli, Mattia de’ Michieli Vitturi
Orals
| Fri, 28 Apr, 16:15–18:00 (CEST)
 
Room 0.14
Posters on site
| Attendance Fri, 28 Apr, 10:45–12:30 (CEST)
 
Hall X2
Orals |
Fri, 16:15
Fri, 10:45
Magma dynamics from sources in the upper mantle and lower crust to volcanic eruption at the surface or plutonic emplacement in the shallow crust includes a range of complex phenomena. Fluid-mechanical and thermo-chemical interactions between the different phases (liquid melt, solid crystals, exsolved volatile fluid or vapour, and pyroclasts) emerge on sub-millimetre scales but give rise to interlinked systems of melt extraction, magma ascent, differentiation (e.g., fractional crystallization, magma mixing and mingling, rock assimilation, melt-rock and melt-crystal mush reactions), and storage, eruption, and mineral resource generation extending from several metres to dozens of kilometres throughout the lithosphere and crust. Evidence for these processes derives from geophysical tomography, seismic, acoustic, and ground deformation monitoring, as well as geochemical analyses of volcanic and plutonic products. Observations are complemented by study of experimental petrology, thermodynamic and mechanical properties of magmas. Most observational and experimental methods, however, only provide indirect access to the systems of interest. Computational modelling can therefore provide powerful tools for interpreting and synthesising the wealth of observational and experimental data.

This session aims to stimulate discussions on how mult-idisciplinary approaches can be used to advance the interpretation of volcano monitoring, geophysical, geochemical, and petrological observations. We therefore wish to bring together contributions on the theory and implementation of models of magmatic systems and their application in the context of experimental and observational studies. We invite contributions focusing on (but not restricted to) multiphase flow, thermodynamic phase equilibria, as well as studies on melt extraction from sources in the mantle and crust, magma ascent and storage in the crust, interaction between magma and wall-rocks, crystallization and fluid exsolution dynamics, dissolved and exsolved volatiles in magmas, effusive and explosive eruption dynamics, rheology of solid-liquid-gas mixtures, fragmentation processes, magmatic-hydrothermal interactions, and associated mineral resource genesis.

Orals: Fri, 28 Apr | Room 0.14

Chairpersons: Tobias Keller, Flavia Palummo, Adina E. Pusok
16:15–16:20
16:20–16:30
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EGU23-6783
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solicited
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On-site presentation
Milena Marjanovic, Suzanne Carbotte, Alexandre Stopin, Satish Singh, René-Édouard Plessix, Miloš Marjanović, Mladen Nedimović, Juan Pablo Canales, Hélène Carton, John Mutter, and Javier Escartín

The structure of the magmatic system beneath subaerial volcanos, including the architecture and distribution of the bodies where magma is stored and the network of conduits that transport melt between these accumulations and the surface, plays a fundamental role in all aspects of volcano construction and evolution, from igneous differentiation to hazard assessment. However, due to inaccessibility, little is known about the geometry of the magma bodies residing beneath subaerial volcanos. 

Mid-ocean ridges host the most extensive magmatic system on Earth, with 98% of its length below the ocean surface, which makes them an ideal target to be scanned by controlled-source marine seismic techniques. Beneath some portions of this vast system, the shallowest magma bodies are present and represented by long-linear Axial Magma Lenses (AML). It is at these shallow-most AMLs where dikes nucleate and connect the magma accumulations to the surface to result in an eruption. To explore the magma plumbing systems at mid-ocean ridges, we use 3-D multichannel seismic data across a mid-ocean ridge environment and apply advanced marine seismic techniques to develop the highest resolution reflection images of the AMLs so far. The data were collected across a magmatically dynamic portion of the East Pacific Rise at 9°50’N with documented dike intrusion and eruptions in 1991/1992 and 2005/06.

The observations indicate that the magma reservoirs in the shallow crust are not represented by smooth bodies, but show strongly lineated topography that is spatially linked to the distribution of eruptive fissures and erupted lavas above. In the detailed topography, we find evidence for: 1) a dike root zone beneath where a caldera-like axial eruptive fissure zone is present, 2) deep excavation of this root zone within the primary eruption site for the last documented eruption, and 3) dikes rupturing from edges as well as the center of magma lenses. We also demonstrate that the distribution of additional, off-axis crustal magma accumulations further impact the stresses and melt budget at shallow-level magma accumulations leading to more frequent eruptions. Our results show that the mechanism behind eruptions along mid-ocean ridges is predominantly bottom-up and not fundamentally different from the eruptions’ mechanism at subaerial volcanoes. Considering the fine-scale morphology of shallow magma bodies will be critical for future generations of more realistic numerical models to aid in effective global volcanic hazard assessment and mitigation.

How to cite: Marjanovic, M., Carbotte, S., Stopin, A., Singh, S., Plessix, R.-É., Marjanović, M., Nedimović, M., Canales, J. P., Carton, H., Mutter, J., and Escartín, J.: Links Between Volcanic Eruptions and Magma Body Geometry Revealed by Seismic Reflection Imaging at the East Pacific Rise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6783, https://doi.org/10.5194/egusphere-egu23-6783, 2023.

16:30–16:40
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EGU23-5441
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ECS
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solicited
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Highlight
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On-site presentation
Haiyang Hu, Pablo Salinas, and Matthew Jackson

IC-FEMRES (Imperial College Finite Element Magma REservoir Simulator), is a finite-element based numerical code for simulating the 3D dynamic behaviour of a two-phase, multi-component magma reservoir with chemical reaction.  The code is built upon the open-source IC-FERST package (http://multifluids.github.io/) which includes advanced numerical features such as dynamic mesh optimization, to allow fine-scale solution features to be captured while simulating in a large domain.

The model solves for velocity using a finite-element approach, and for transport using a control-volume scheme to ensure the conservation of energy, mass, and components.  Solid, melt and volatile phases are modelled as Stokes fluids with very different Newtonian viscosities.  Individual crystals in the solid matrix are incompressible, but the solid phase is compressible to account for changes in melt fraction.  The formulation captures viscous compaction and convection of the solid matrix, and flow of melt and volatiles via a Darcy-type formulation at low melt fraction, and a hindered-settling type approach at high melt fraction.  It also captures heat transport by conduction and advection, and component transport by advection.  A chemical model is used to calculate phase fraction and composition.  The numerical package sequentially solves for: 1. Melt and solid velocity (mass and momentum conservation); 2. Enthalpy and component transport (energy and component conservation); 3. Phase fraction and composition (chemical model).  Material properties such as density and viscosity can be coupled to solution fields such as melt fraction and composition to yield a highly non-linear system of coupled equations that are solved iteratively.

We demonstrate here the validation of the formulation against well-constrained test cases, and example results for a magma reservoir in the continental crust obtained using a simple two-component chemical model created by fitting a binary phase diagram to experimental melting data.  Solutions show significant deviations from the predictions of 1- and 2D thermal models, or 1D models that include magma dynamics, and may explain some hitherto poorly understood aspects of magma reservoir formation, dynamics and chemical differentiation. 

How to cite: Hu, H., Salinas, P., and Jackson, M.: A 3D finite element magma reservoir simulator, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5441, https://doi.org/10.5194/egusphere-egu23-5441, 2023.

16:40–16:50
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EGU23-13522
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On-site presentation
John Maclennan, Xenia Boyes, and Euan Mutch

The prevalence, durability and physical significance of crystal mushes in crustal magmatic systems is a topic of current interest in igneous petrology. Fragments of mushes brought to the surface by basaltic eruptions provide a snapshot of the temporal evolution of crustal magmatic systems.  Petrographic and geochemical analysis of such fragments give valuable insights into basaltic magma reservoirs, including information about magma storage conditions and possible eruption triggers. A detailed petrological and geochemical study was carried out on gabbroic mush nodules from the Brandur, Fontur and Saxi tuff cones to understand the processes that occur before large fissure eruptions in the Bárðarbunga system, Iceland.

Petrographic studies of the mush nodules, from QEMSCAN images, reveal a bimodal phenocryst population in a glassy vesicular groundmass. Probe analyses confirm the bimodal population consists of a primitive and evolved assemblage. The former is composed of large equant crystals of high-anorthite plagioclase (An~88), high-forsterite olivine (Fo~86) and high Mg# clinopyroxene (Mg#~86) forming an interconnected solid framework. The evolved assemblage consists of low-anorthite plagioclase (An~75), low-forsterite olivine (Fo~77) and low Mg# clinopyroxene (Mg#~79) crystallising in the pore space of the mush framework and on the rims of the primitive macrocrysts. The textures and compositions seen suggest the nodules experienced two stages of crystallisation: primitive macrocrysts crystallised first and were stored in crystal mushes. Then a later event caused a change in PTX conditions and triggered relatively rapid crystallisation in the pore-spaces of the mushes.

The quenched glass in the pore spaces of the nodules has the composition of a basaltic liquid that in chemical equilibrium with the evolved assemblage of crystals. Thermobarometry based on equilibrium between this liquid and the phases indicates that the final stage of crystallisation occurred at pressures of ~2 kbar. A putative interstitial liquid composition was reconstructed under the assumption of closed system growth of the evolved assemblage by using the QEMSCAN pixel maps to add the evolved crystals to the interstitial glass composition. This reconstructed liquid is far from chemical equilibrium with the primitive crystals in the mush framework, indicating that the assumption of simple closed system crystallisation from an initial mush liquid in equilibrium with the primitive solids is not correct. Therefore, the phase mapping and compositional relationship provide constraints on open-system processes in mushes.

The failure of the closed system models to match the observations is significant in two ways. First, the lack of equilibrium between mush liquid and cumulus plagioclase is consistent with the expected sluggish diffusion of NaSi-CaAl in plagioclase. This disequilibrium poses challenges for numerical models of magmatic systems that use the assumption of crystal-melt equilibrium to link temperature, melt fraction and phase compositions.  Second, bubble expansion during pre-eruptive ascent forces mush liquid out of solid framework in the nodules and may provide observational constraints on the physics of multiphase flow in deep magmatic systems.

How to cite: Maclennan, J., Boyes, X., and Mutch, E.: Disequilibrium during mush evolution in the Bárðarbunga volcanic system, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13522, https://doi.org/10.5194/egusphere-egu23-13522, 2023.

16:50–17:00
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EGU23-2116
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On-site presentation
Curt Koenders and Nick Petford

Dispersive grain pressure (Bagnold, 1954) is commonly used to explain the observed axial concentrations of phenocrysts in dykes and sills via flow differentiation (Komar, 1972). The idea was formulated for particle fractions exceeding 0.13 by volume. A dispersive pressure is proposed that is greatest near the intrusion walls, forcing crystals to move inward, towards the centre of the magmatic flow where shear strains are low. However, Barriere (1979) argued that this phenomenological ‘Bagnold effect’ should be confined only to narrow (<<100 m) wide intrusions. His reasoning was that in larger channels, the wall effect driving the dispersive pressure diminishes swiftly, nullifying the dispersive pressure. This is true where the relevant length scale of the problem scales with the ratio W/d, where W is the full channel width and d is particle diameter.

Here we show that for congested magma (0.5 > Φ > 0.8), with the rheology decomposed into scalar and vector components, particle fluctuations (in velocity) are dependent critically on the distance gap (h) between nearest neighbour that imparts a particle pressure. Thus, the critical ratio becomes d/h. It is fluctuations in the interparticle gap distance arising during shear in the flowing suspension that causes migration, irrespective of the channel width. We show that for a fixed particle size, d/h scales with crystal fraction (Φ) and the migration effect is enhanced as W/d increases.   We focus here on particle (crystal) migration as opposed to segregation or particle size sorting, although the latter are both amenable to analysis through modifications to our mathematical model.    

Flow differentiation via particle migration is likely to be just as effective in wider channels (W >> 100m) than in narrow ones, eliminating the need to invoke other fluid dynamical or thermal explanations (convection, multiple intrusion, gravitational settling) to explain the central concentration of phenocrysts in dykes and sills exceeding several metres in width.  As the (multiphase) migration effect exerts a strong control on both magma rheology and composition, flowage differentiation as a mechanism for compositional variation during magma emplacement in large intrusions is open for re-evaluation. 

 

References

Bagnold, RA, (1954). Experiments on gravity-free dispersion of large solid spheres in a Newtonian fluid under shear. Proc. Roy. Soc. London 225, 49-63.

Barriere, M, (1976). Flowage differentiation: limitation of the Bagnold effect to the narrow intrusions. Contrib. Min. Pet. 55, 139-145. 

Komar, P, (1972). Mechanical interactions of phenocrysts and flow differentiation of igneous dykes and sills. Geol. Soc. Amer. Bull. 83, 973-988.

How to cite: Koenders, C. and Petford, N.: Flow differentiation in dykes and sills NOT limited by intrusion width, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2116, https://doi.org/10.5194/egusphere-egu23-2116, 2023.

17:00–17:10
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EGU23-15245
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Highlight
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On-site presentation
Joachim Ritter, Mohsen Koushesh, and Dario Eickhoff

Deep low-frequency seismic events are detected in the East Eifel Volcanic Field (EEVF) since 2013. To well detect and locate such events the Deep Eifel Earthquakes Project - Tiefe Eifel Erdbeben (DEEP-TEE) started in July 2014 which now is composed of ca. 10 permanent and 15 mobile recording stations. Up to now, the DEEP-TEE seismic dataset contains eight years of continuous seismic records and the network has been reconfigured and continuously developed to achieve an optimum configuration regarding detection and location of seismic events.

In order to detect the weak deep low-frequency (DLF) events we developed a seismic event detector and found ca. 330 localizable DLF events in 2014-2021. The DLF hypocenter distribution outlines a near-vertical structure close to the Laacher See Volcano (LSV) which erupted about 13,079 years ago. The hypocenters are as deep as ca. 45 km, close to the assumed lithosphere-asthenosphere boundary, and reach to about 5-8 km depth. Most events occur close to the Moho and in the lower crust what is interpreted as magmatic underplating and deep crustal intrusion. In the same depth range but further to the west, we find seismic reflections with a negative polarity. These are also interpreted as magmatic pockets in the lower crust and the Moho region.

We try to estimate the mass flux (magma and volatiles) which is related with the seismicity. For this we apply Aki et al.'s model (JVGR, 1977) for describing the magma movement (a so-called chain of cracks connected by narrow channels) and estimate the related magma intrusion volume rate in the EEVF lithosphere. We assume an initial set of model parameters and evaluate the sensitivity and stability of the modelling results by allowing a reasonable range of each individual input parameter. Our results give an estimate of about 2,000-16,000 cubic meters of melt per year which is transported in the lithosphere.

How to cite: Ritter, J., Koushesh, M., and Eickhoff, D.: Melt Detection and Estimation of the Current Magma Intrusion Rate beneath the East Eifel Volcanic Field, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15245, https://doi.org/10.5194/egusphere-egu23-15245, 2023.

17:10–17:20
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EGU23-14990
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On-site presentation
Mehmet Keskin, Namık Aysal, İsak Yılmaz, Nurullah Hanilçi, Avtandil Okrostsvaridze, Hayrettin Koral, Cem Kasapçı, Fatma Şişman Tükel, and Giorgi Bochenko

In NE Türkiye, an almost 30,000 km2 area is covered by young volcanic rocks, ranging in age from Miocene to Quaternary and spanning the whole compositional spectrum from basanites/tephrites to high silica rhyolites. The region exhibits a plateau morphology, known as the Erzurum-Kars Plateau,  at ~2 km above sea level. That volcanic plateau continues far beyond the state border into Georgia (ie., the Samtskhe-Javakheti plateaus). Although there are a few studies, the petrological evolution of the these volcanic plateaus is still not well known. To better understand the origin, magmatic history, and geodynamic setting of the volcanism on these plateaus, we, Turkish and Georgian researchers, have been conducting a joint cross-border research project (i.e., TÜBİTAK- SRGNSF project #118Y272) across the region. The volcanic units making up those plateaus are composed of numerous volcanic cones of different shapes and sizes, lava domes, pyroclastic layers, and widespread plateau-forming lavas.

Preliminary findings of our research have revealed that the composition and structure of the lithospheric domains below the plateau might have significant effects on the geochemical character and the lithological features of the volcanics. The volcanic succession covering the Pontide Block in the north is dominated by Late Miocene-Pliocene calc-alkaline andesitic and dacitic lavas, which mostly form medium-sized volcanic edifices. These edifices are partially overlain by Upper Pliocene to Quaternary aged low-viscosity, plateau-forming basic lavas which are also calc-alkaline. Notably, pyroclastics are scarce in the north.

The portion of the plateau that overly the Northeastern Iranian Block and the ophiolitic mélange in the south consists of a much wider variety of lava and pyroclastic lithologies. It starts with a ~5.5 Mys old acid pyroclastic layer at the base, consisting of rhyolitic pyroclastics, domes, and obsidian. It is overlain by the plateau-forming basic to intermediate lavas, Pliocene in age. In turn, the plateau sequence is overlain by a previously unknown caldera-like volcanic complex, which we named “the Digor volcanic complex”, located between Kars and Digor. It has a diameter of ~60 km and consists of lavas and pyroclastics of Late Pliocene to Quaternary in age, displaying both calcalkaline and alkaline character.

All those volcanics contain a clear inherited subduction signature from previous subduction events (i.e., Pontide Arc in the north). Our petrological melting modellings revealed that the magmas were possibly derived from two contrasting metasomatized lithospheric mantle sources: (1) a spinel peridotite with or without minor amphibole and, (2) a pyroxenitic mafic source with a minor amount of phlogopite. Our data indicate that the melts derived from these two sources were mixed into each other en route to the surface. Most of the plateau lavas might have been derived from the first type (i.e., spinel-peridotite) while the younger alkaline Digor volcanics were dominantly from the second type (i.e., pyroxenite). The thinning of the lithospheric mantle by delamination and the gradual increase of heat coming from the upwelling asthenospheric mantle might be responsible for these variations. Our FC and AFC models show that plateau lavas experienced intense amphibole±garnet fractionation and moderately assimilated continental crust.

How to cite: Keskin, M., Aysal, N., Yılmaz, İ., Hanilçi, N., Okrostsvaridze, A., Koral, H., Kasapçı, C., Şişman Tükel, F., and Bochenko, G.: Deep magmatic processes beneath an active collision zone: Petrological and geochemical evidence from the volcanic plateaus in northeastern Türkiye and western Georgia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14990, https://doi.org/10.5194/egusphere-egu23-14990, 2023.

17:20–17:30
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EGU23-12573
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ECS
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On-site presentation
Liying Zhang, Feng Huang, Jifeng Xu, and Xijun Liu

Central Asian Orogenic Belt (CAOB) with multiple blocks and suture zones is a key locality for understanding the process of plate tectonics. Extensive studies are mainly on the western CAOB, but less on the eastern side. Many questions remain unclear due to the lack of obvious structural records and ophiolite assemblages. In this study, we report the andesites sampled from Laolongtou Formation in the eastern CAOB with detailed geochronology and geochemistry analyses. The andesites are characterized by high Mg# values at their intermediate SiO2 contents, which are defined as typical high Mg# andesites. Zircon U-Pb ages show they erupted at the Late Triassic (~236 Ma) and the Ti-in-zircon thermometer indicates a potential high primary magma temperature. Geochemically, they show relatively high contents of Al2O3, Na2O, Cr, and Ni, with enrichment in light rare earth elements and depletion in high field strength elements. Besides, they are markedly depleted in Nb and Ta, enriched in Sr, Ba contents, and significantly differentiated in Th and U contents. They have homogeneous depleted Sr-Nd isotopic compositions that fall into the range of MORB and mantle-derived ranges. Together with the depleted zircon Hf isotopic compositions, showing the possible addition of a hot and depleted component. We propose that they were formed by interactions of components derived from a subducting slab and the overlying mantle wedge. The slab-derived components are most likely a low degree of partial melting of subducted oceanic crust that was able to stabilize garnet and rutile, without plagioclase in the melt residue. They subsequently interacted with the overlying mantle wedge, which resulted from an post-collisional setting related to the final closure of Paleo-Asian Ocean. The upwelling of the upper mantle triggered by the oceanic slab break-off may explain the genesis of the high Mg# andesites and the formation of the continental crust in northeast China.

 

How to cite: Zhang, L., Huang, F., Xu, J., and Liu, X.: Post-collision Extension in the Eastern Central Asian Orogenic Belt: Insight from the Late Triassic High-Mg Andesites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12573, https://doi.org/10.5194/egusphere-egu23-12573, 2023.

17:30–17:40
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EGU23-12617
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ECS
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On-site presentation
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Martha Papadopoulou, Tiffany L. Barry, Batulzii Dash, Alison M. Halton, Sarah C. Sherlock, and Alison C. Hunt

The closure of the Mongol-Okhotsk Ocean in Jurassic – Cretaceous times led to the final amalgamation of the interior of Eastern Asia, thus placing Mongolia in an intraplate tectonic setting. Small and widespread volcanic fields of Mesozoic and Cenozoic age are known through Eastern Asia, attributed to both post-collisional and intraplate mechanisms. In Mongolia, intraplate volcanic fields are scattered across the central and eastern parts of the country. Although several models have been proposed to explain the origin of this late Mesozoic – Cenozoic intraplate magmatism in Mongolia, there is still on-going debate about the process(es) that lead to it. Moreover, there are no temporal reconstructions on the extent of post-collisional magmatism in the area preceding intraplate magmatic activity, nor any hypotheses on the timing of the onset of the latter. In this study, we differentiate between post-collisional and intraplate magmatism in Mongolia using a set of geochemical, isotopic, palaeomagnetic and zircon data, and define the onset of intraplate magmatic activity at 107 Ma. Through evaluation of nearly 700 published radiometric data from the various volcanic fields across Mongolia along with newly-obtained age constraints, we reveal a complex temporal and spatial evolution of the magmatism that runs parallel in different volcanic fields through time, and we identify the extent of hiatuses in the magmatic activity. Based on the assessed data we discuss the source of bias in our understanding of the magmatic history of Mongolia and evaluate the various proposed models for the origin of the Mongolian magmatism. Finally, we suggest that asthenospheric upwellings were induced through a delamination event beneath Mongolia in the late Mesozoic. This initiated the intraplate magmatism, the temporal evolution of which is prolonged due to enhanced mantle flow related to northward progression of Tethys and the Indian plate.

How to cite: Papadopoulou, M., Barry, T. L., Dash, B., Halton, A. M., Sherlock, S. C., and Hunt, A. C.: Evidence for long-lived continental intraplate magmatism: A case study from Mongolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12617, https://doi.org/10.5194/egusphere-egu23-12617, 2023.

17:40–17:50
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EGU23-177
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ECS
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On-site presentation
Xing Cui, Min Sun, Guochun Zhao, Yunying Zhang, Jinlong Yao, and Jean Wong

The chemical differentiation of mantle-derived magmas in subduction zones during the generation, transport, and emplacement has always been a concern, which is closely related to the petrogenesis of calc-alkaline granitoids. A systematic study of petrography, mineralogy, and geochemistry is conducted on typical arc granitoids and associated mafic microgranular enclaves (MME) from the Chinese Altai, Central Asian Orogenic Belt. Magma hybridization modeling using major and trace element compositions suggests that the parental magma of granitoids is a mixture of a mafic and a felsic endmember. The sharp decrease of plagioclase An values from cores to rims (e.g., from ca. 80 to 40) implies polybaric crystallization of water-saturated magmas accompanied by degassing. Petrographic evidence and plagioclase in situ Sr isotopic compositions ((87Sr/86Sr)i = 0.7053–0.7071) show the involvement of isotopically different magmas during the mineral crystallization. The positive zircon εHf(t) values of MME (+2.3 to +5.4) and granitoids (+0.6 to +4.6) further show that the mafic melts are mantle-derived, while felsic melts should originate from juvenile lower crust with the slightly more evolved isotopic composition. An evolution scenario of the mantle-derived mafic magma and formation of enclave-bearing calc-alkaline plutons in arc settings is demonstrated: Hydrous mantle melts rose to the deep crustal-mantle boundary, where they effectively mixed with juvenile lower crustal melts to form the hybrid parental magma of the granitoids. In the high crustal-level chambers, decompression-dominated crystallization, mingling, and limited mixing of mafic magma blobs and enclosing granitic melts ultimately determined the rock texture, mineral composition, and enclave morphology. This work was financially supported by Hong Kong RGC GRF (17302317), National Key R&D Program of China (2017YFC0601205), NSFC Projects (41730213, 42072264, 41902229, and 41972237).

How to cite: Cui, X., Sun, M., Zhao, G., Zhang, Y., Yao, J., and Wong, J.: Petrogenesis of the enclave-bearing granitoids from the Chinese Altai: implications for the differentiation of mantle-derived magmas and formation of calc-alkaline plutons in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-177, https://doi.org/10.5194/egusphere-egu23-177, 2023.

17:50–18:00
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EGU23-8045
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On-site presentation
Jacob Hanley, Daniel Meagher, Kevin Neyedley, Patrick Mercier-Langevin, and Zoltan Zajacz

Silicate melt inclusions (SMI) in rhyolitic volcanic rocks in the ~2699 – 2697 Ma Bousquet Formation, Subprovince, Québec were studied through integration of a variety of microanalytical methods (petrography, laser Raman microspectroscopy, LA-ICP-MS) to explore links between magmatic metal/volatile endowment and the high gold content of mineral deposits in the world-class Doyon-Bousquet-LaRonde mining district. The study is the first to present melt inclusion data from felsic volcanic rocks of Archean age.

Rhyolitic SMI of primary origin were characterized from magmatic quartz phenocrysts from tholeiitic rhyolite sills and calc-alkaline flows near gold-rich volcanogenic massive sulfide deposits. Silicate melt inclusion trace element chemistry records a continuous transition from ocean ridge to volcanic arc tectonic affinity. SMI Sr-Y-La-Yb systematics are  inconsistent with Archean tonalite-trondhjemite-granodiorite (TTG; “adakitic”) compositional domains; rather, they are consistent with post-Archean TTG (“calc-alkaline”) suggesting significant compositional modification of TTG magmas through contamination and/or plagioclase fractionation during magma storage and ascent.  Thermobarometry suggests prolonged phenocryst residence at depth prior to eruption with SMI entrapment at ~10-12 km depth. Concentrations of Au in the SMI are variable and up to two orders of magnitude higher than in the host bulk volcanic rocks. This demonstrates that whole rock data are not representative of the composition of the original magmatic liquids and, thus, cautioning the traditional use of whole rock data as a proxy for volcanic assemblage fertility in such Archean environments. Moreover, SMI show melt co-entrapment with an immiscible, high density, carbonic fluid (CO2-dominant), indicating that rhyolitic melts were saturated in CO2. Saturation of this fluid phase may explain, in part, the variability observed in SMI metal contents, and demands consideration of the relative importance of early separation of magmatic volatile phases versus seafloor hydrothermal leaching of volcanic products in controlling the magmatic metal endowment of Archean exhalative ore-forming systems.  

How to cite: Hanley, J., Meagher, D., Neyedley, K., Mercier-Langevin, P., and Zajacz, Z.: First insight into gold enrichment associated with Archean magmatic processes in the deep crust through melt inclusion studies: an example from the Abitibi Subprovince, Québec, Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8045, https://doi.org/10.5194/egusphere-egu23-8045, 2023.

Posters on site: Fri, 28 Apr, 10:45–12:30 | Hall X2

Chairpersons: Barbara Bonechi, Nicolas Riel, Cristina Perinelli
X2.71
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EGU23-12867
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ECS
Dániel Kiss, Evangelos Moulas, Boris Kaus, Nicolas Berlie, and Nicolas Riel

One of the continuing trends in geodynamics is to develop codes that are suitable to model magmatic processes with an increasing level of self-consistency. Developing such models is particularly challenging as most magmatic processes are multiphysics problems, and require coupling between thermal, porous, mechanical and chemical processes.

Here we consider reactive flow in a deformable porous medium coupled to thermo-mechanical processes. We present a thermodynamically self-consistent set of governing equations, describing such processes. The governing equations consists of the conservation of mass, momentum, and energy in two phases. One phase represents the solid skeleton, which deforms in a poro-visco-elasto-plastic manner. The second phase represent low viscosity melts, percolating through the solid skeleton, that is described by Darcy’s law. As melt migrates through the rock skeleton we can quantify the chemical evolution of melts due to partial melting and crystallization. The system of equations is solved numerically, using the pseudo transient method, that is well suited to solve highly non-linear problems. We are going to discuss a few key end-member results, such as melt migration along dykes and fractures, along self-localized channels or by magmatic diapirism. We will discuss how the coupling between thermo-mechanical processes and melt migration might affect the chemical evolution of percolating melts.

All the codes presented here are written within a modular Julia framework, developed within the MAGMA ERC project, that permits easy future integration of the currently stand-alone software.

How to cite: Kiss, D., Moulas, E., Kaus, B., Berlie, N., and Riel, N.: Numerical modeling of magmatic transport processes, using the pseudo-transient method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12867, https://doi.org/10.5194/egusphere-egu23-12867, 2023.

X2.72
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EGU23-7627
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ECS
Pascal Aellig, Tobias Keller, Olivier Bachmann, and Juliana Troch

The discovery of 18O-depleted igneous rocks at Krafla, Iceland, suggests that the system interacted with crustal rocks that experienced high-temperature hydrothermal alteration by a meteoric fluid to deviate from the expected mantle signature (δ18O = 5.5 ‰). Such assimilation is documented in low-δ18O settings worldwide, however, the mechanisms of this dynamic process remain poorly understood.  Due to intense drilling activity and exploration at Krafla, both hydrothermally altered crustal rocks and parental magma are comparably well characterized, making Krafla a great case study for the application of a numerical model that can further advance the understanding of the formation process of low-δ18O magmas. In this study, we use a new three-phase two-component thermo-chemical-mechanical model to simulate the effect of variable crustal compositions on the assimilation process and the magma chamber dynamics.  We define the simplified square-shaped magma chamber (10 x 10 m) of magma with initially basaltic composition (1250 °C) that assimilates the crustal rock (500 °C) at the top and bottom. Our results indicate that convective behaviour and the formation of cumulate layers can significantly hinder the assimilation process. While the crystal settling Stokes speed scale is the dominant driver for the formation of this boundary layer, depending on the assimilation timescales, the mushy chamber margins are able to grow to sufficient thickness to prohibit additional assimilation of low-δ18O crustal material. Density and buoyancy contrasts produce three types of convection: chamber convection, layered convection and plume driven convection. Final magma compositions in our preliminary model outputs range from mafic to intermediate but are not able to reach the felsic compositions encountered at Krafla. This suggests that evolution towards the erupted low-δ18O rhyolitic products involved multiple stages or included additional factors not yet accounted for in our model. Further refining of this and similar thermo-chemical-mechanical model setups may provide important new insights into the assimilation dynamics in the Krafla volcanic field and other low-δ18O settings worldwide.

 

How to cite: Aellig, P., Keller, T., Bachmann, O., and Troch, J.: Modelling three-phase magma dynamics during assimilation: Insights into the formation of low-δ18O rhyolites at Krafla, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7627, https://doi.org/10.5194/egusphere-egu23-7627, 2023.

X2.73
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EGU23-7287
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ECS
Annalena Stroh, Evangelos Moulas, and Roman Botcharnikov

Xenocrysts in magmatic rocks are often found having gradients in their composition. These compositional gradients are commonly interpreted as the result of mass fractionation during crystal growth and it is quite common that these gradients are also influenced by intra-crystalline chemical diffusion. Since the interplay between element diffusion and crystal growth in the magma controls the final composition of magmatic minerals, it is not possible to uniquely constrain the high-temperature history of a zoned crystal. To address this problem, we present a numerical model that can be used in an inverse manner to constrain the rate of olivine growth in basaltic magma. The model addresses a classic moving boundary problem, whilst solving the intra-crystalline diffusion of Ca in olivine. Our model is created to account for the growth of a spherical olivine crystal in a finite (or infinite) reservoir. The diffusion equation is solved with a forward Euler scheme and we use a conservative, regridding approach to account for changes in crystal size. The model was tested against experimentally determined olivine growth rates. Our results show that the inferred growth rates agree within an order of magnitude to the results from experiments at fixed pressure, temperature and oxygen-fugacity conditions.

How to cite: Stroh, A., Moulas, E., and Botcharnikov, R.: Constraining the rates of olivine crystal growth with diffusion chronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7287, https://doi.org/10.5194/egusphere-egu23-7287, 2023.

X2.74
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EGU23-9712
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ECS
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Olaya Dorado, John A. Wolff, Frank Ramos, and Joan Marti

The behaviour of Group I and II elements during the petrogenesis of felsic igneous rocks is largely controlled by feldspar-liquid relationships and processes. Numerous experimental studies have addressed plagioclase/melt element partitioning, with fewer studies devoted to potassium feldspar, and very few to albite-rich ternary-composition feldspar (An ~ Or < Ab). However, the partition coefficient for Ba is known to increase at least 10-fold through the crystallization sequence sodic plagioclase – anorthoclase – potassium feldspar that is typical of sodic alkaline suites. Consequently, melt Ba concentrations may drop by orders of magnitude along such a liquid line of descent. Feldspars, glasses and whole rocks in such suites may exhibit strong enrichments and depletions in Ba that can be used to track processes of crystal fractionation, cumulate formation, and cumulate recycling.

Here, we review experimental feldspar/melt partitioning data for Ba, Sr and Rb as a function of feldspar composition. Regression of available experimental data offers the basis for expressions that appear to provide a working description for the compositional dependence of partition coefficients for albite-rich compositions. We have applied this model to feldspar and melt compositions of the products of several Holocene eruptions (Pico Viejo C, Pico Viejo H, Teide J2, Lavas Negras, Arenas Blancas, Montaña Rajada and Montaña Reventada) of the basanitic-phonolitic suite of the Teide-Pico Viejo volcanic system (Tenerife, Spain). Comparing feldspar/groundmass pairs obtained by EMPA and LA-ICP-MS analyses with predicted partition coefficients obtained with the models allows us to attribute an antecrystic or xenocrystic origin to some of the feldspars. The results confirm the existence of a distinct population of cumulate feldspars, that had undergone multiple fusion and recrystallization events, in Lavas Negras and Arenas Blancas flows. In addition, the trachytic composition of Montaña Reventada is due to melting of a feldspar-dominated cumulate. Application of these techniques to active magmatic systems will allow us a better understanding of different pre-eruptive processes, and ultimately improve volcanic hazard assessment.

This research was funded by the Intramural CSIC grant MAPCAN (Ref. 202130E083). OD was supported by an FPU grant (FPU18/02572) and a complementary mobility grant (EST19/00297) from the Ministry of Universities of Spain.

How to cite: Dorado, O., Wolff, J. A., Ramos, F., and Marti, J.: Ba, Sr and Rb feldspar/melt partitioning in the basanite-phonolite suite from Teide-Pico Viejo volcanic complex, Tenerife., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9712, https://doi.org/10.5194/egusphere-egu23-9712, 2023.

X2.75
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EGU23-7430
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ECS
Daniel Gómez Frutos and Antonio Castro

Mafic microgranular enclaves (MME) appear associated with most post-collisional batholiths around the world. Together with the mafic-intermediate (sanukitoid) and granitic suites, it constitutes one of the most common features of post-collisional magmatism. MME are considered to represent a mafic endmember with mantle affinity related to granite petrogenesis. Hence, they constitute an ideal tracer of the mantle involvement in crustal-scale processes. However, their exact relationship with the host granitic post-collisional suite and the role of such mantle remains unclear. In this regard, abundant MME in Los Pedroches batholith (Iberian Massif) can provide valuable constrains to this problem. Using new MME data, we provide a comparative study between MME and the mafic-intermediate (sanukitoid) suite of post-collisional batholiths, revealing an accurate overlap between the two groups. A common geochemical signature consisting of high MgO and K2O and low CaO is evidenced, pointing to a potential genetic link between MME and the sanukitoid suite in a modified mantle source. Further information provided by cotectic experimental liquids and petrographical evidence point to cotectic differentiation and orthopyroxene restite self-contamination as the main responsible mechanisms for the particular geochemistry of the series. Once the role of the mantle in MME formation and their magmatic evolution are characterized, their potential relationship with the host granites is established using isotopic criteria. Implications for post-collisional batholith petrogenesis is then discussed in a qualitative manner, suggesting a heterogeneous yet common origin for all post-collisional magmatism.

How to cite: Gómez Frutos, D. and Castro, A.: Mafic microgranular enclaves trace the origin of post-collisional magmatism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7430, https://doi.org/10.5194/egusphere-egu23-7430, 2023.

X2.76
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EGU23-13409
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ECS
Mérédith Morin, Benoît Petri, and Marc Ulrich

Keywords: magmatic system, crustal contamination, diffusion, hybridization, partial melting

Magmatic differentiation requires a variable combination of fractional crystallization and/or crustal contamination that influences the liquid line of descent, as well as the composition and the final paragenesis of resulting magmatic rocks. However, the vectors of crustal contamination and how they influence the magmatic differentiation remain poorly constrained, notably because the depth at which they are active are usually hardly accessible. Several processes have been invoked in the literature: (1) small-scale diffusion; (2) energetically costly partial melting of crustal material coupled with magma hybridization; (3) The dissolution of crustal rocks by reactive bulk assimilation. Instead of focusing on the deepest crustal levels, we here explore crustal contamination processes active in the intermediate continental crust. We use the example of the Sondalo gabbroic complex that intruded the metasedimentary Campo unit, both exposed in the Central Alps.

The Sondalo gabbroic complex is a Permian intrusion of tholeiitic affinity (troctolite and norite, 300±12 and 280±10 Ma by Sm-Nd) that evolved towards calc-alkaline intermediate bodies (diorite and granodiorite, 289±4 - 285±6 Ma by U-Pb on Zrn). Mafic melts intruded the Campo unit composed of fertile amphibolite-facies micaschist and paragneiss (Ms-Bt-St-Grt-Pl stable), attesting of a (supposed) Carboniferous prograde P-T paths (5.5 - 6 kbar/600°C-650°C). The emplacement of this intrusion caused a HT-contact metamorphism reaching partial melting of host rocks at 289±4 – 288±5 (U-Pb on Zrn) Ma and in-situ formation of Crd-Grt-Sil-Spl granulite-facies restite composing large septa. Field and petrological observations coupled with geochemical bulk rock major and trace element analyses show the contribution of host-rock contamination, by: (1) mafic magmas of tholeiitic affinity becoming progressively calc-alkaline; (2) the increase in modal amount of garnet, biotite and cordierite in magmatic rocks around metasedimentary septa, stabilized by the influx of some major elements (e.g., SiO2, K2O, Al2O3 and H2O) in the noritic mush; (3) liquid line of descent departs from theoretically predicted compositions (with both equilibrium and fractional crystallization) with enrichment in elements typical for crustal rocks (i.e., K2O and Al2O3 at high Mg#).

Field observations and bulk rock major and trace elements composition highlight that crustal contamination is achieved through a combination of vectors having a variable spatial extent. Their respective weight is, however, still difficult to constrain. The middle crust seems to be the ideal location for crustal assimilation because host-rocks are fertile and the mafic magmas benefit from a high and durable thermal regime that appears to favor physical and chemical interactions. Further constraints will be brought by in-situ trace element analyses and Sr-Nd isotopes to estimate their respective influence on hybridization.

How to cite: Morin, M., Petri, B., and Ulrich, M.: Modes and impact of crustal contamination: Example of the Sondalo gabbroic complex (Central Alps, SE Switzerland - N Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13409, https://doi.org/10.5194/egusphere-egu23-13409, 2023.

X2.77
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EGU23-16113
Axel K Schmitt, Carlos Angeles-De La Torre, Oscar M Lovera, Henja Gassert, Axel Gerdes, and Janet C Harvey

One the world’s largest geothermal reservoirs, “The Geysers” in the California Coast Ranges, is underlain by a composite granitic pluton at shallow depth (~1–3 km, based on geothermal well penetration). Published U-Pb zircon geochronology indicates that this Geysers Plutonic Complex (GPC) intruded between c. 1.8 and 1.1 Ma in three major pulses: the oldest formed a cap of orthopyroxene-biotite microgranite porphyry, followed by orthopyroxene-biotite granite and hornblende-biotite-orthopyroxene granodiorite dominating at deeper levels. Lavas and minor pyroclastic deposits of the overlying Cobb Mountain Volcanic Center erupted between c. 1.2–1.0 Ma. The Geysers-Cobb Mountain plutonic-volcanic association shares common magmatic origins rooted in asthenospheric upwelling into a migrating slab window, where lower-crustal hybridization of mantle-derived magmas was followed by upper-crustal intrusion and differentiation. When and how shallow intrusions or eruptions were fed from this common source, however, remains unclear. This can be reconstructed from crystal-scale analysis of trace elements, oxygen and hafnium isotopes in zircon that can uniquely track magmatic processes in an evolving, long-lived magma system.

GPC microgranite zircons display strongly negative Eu anomalies, high levels of incompatible trace elements, and near-solidus Ti-in-zircon temperatures (~670 °C for aTiO2 = 0.55 and aSiO2 = 1). This is distinct from zircons from GPC granite and granodiorite that have moderately negative Eu anomalies, inconspicuous trace element enrichments, and variable Ti-in-zircon temperatures (~850–700 °C). Unlike trace elements, O and Hf isotopes in zircon are indistinguishable between GPC microgranite porphyry and the main population of granite-granodiorite zircons (δ18O = +4.76 to +9.18; εHf = +1.4 to +10.7). There is, however, a subgroup of zircon in GPC granite and granodiorite with elevated δ18O (~8.05) and lower εHf (~4.4) indicating that some late-stage melts experienced higher degrees of assimilation compared to the other magma types. Zircons from Cobb Mountain lavas are similar to those from the GPC granite and granodiorite, but distinct from the granophyre.

We set up a thermal model for zircon crystallization to satisfy the following observations: (1) evolved magma from which zircon crystallized was continuously present between c. 2.1 and 1.1 Ma, and (2) crystal recycling from the GPC microporphyry stage in subsequent intrusive or eruptive pulses was negligible. A magma reservoir at ~7 km depth which incrementally grew in three stages matches requirements imposed by zircon ages and compositions: (1) initial magma accumulation at low recharge fluxes starting at 2.1 Ma (0.1 km3/ka), (2) a brief flare-up at 1.6 Ma (4 km3/ka for 50 ka), (3) a return to low recharge fluxes (0.1 km3/ka) between 1.3 and 1.1 Ma. The total injected magma volume amounts to ~300 km3, three times the volume of the GPC as constrained by geothermal wells. According to this model, magma accumulation was long-lived, thus capable of sustaining protracted geothermal activity, but the main igneous growth occurred almost instantaneously. One implication is that accumulation of large volumes of magma can be rapid, and may require special circumstances that are only realized ephemerally despite overall long-lived magmatic activity.

How to cite: Schmitt, A. K., Angeles-De La Torre, C., Lovera, O. M., Gassert, H., Gerdes, A., and Harvey, J. C.: The construction of a composite magma intrusion underneath “The Geysers” geothermal reservoir (California) based on zircon ages, trace elements, and isotopic compositions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16113, https://doi.org/10.5194/egusphere-egu23-16113, 2023.