GMPV7.1 | Dynamics of crustal igneous systems from source to surface
EDI
Dynamics of crustal igneous systems from source to surface
Convener: Pascal AelligECSECS | Co-conveners: Gregor WeberECSECS, Tobias Keller, Charline LormandECSECS, Catherine BoothECSECS, Adina E. PusokECSECS, Nicolas Riel
Orals
| Tue, 16 Apr, 08:30–10:15 (CEST)
 
Room G2
Posters on site
| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00
 
Hall X2
Posters virtual
| Attendance Tue, 16 Apr, 14:00–15:45 (CEST) | Display Tue, 16 Apr, 08:30–18:00
 
vHall X1
Orals |
Tue, 08:30
Tue, 16:15
Tue, 14:00
Magmatic systems are shaped by complex dynamics, including melt generation in the mantle, transport and emplacement in the crust, and volcanic extrusion to the surface. Processes such as fractional crystallization, mixing and mingling, or melt-rock reactions may lead to differentiation, emplacement, and eruption of magma, which can also generate critical mineral resources. Geophysical tomography and monitoring, as well as geochemical analyses of volcanic and plutonic materials, provide evidence for these processes. Understanding their dynamics, hazards, and resource potential is crucial for advancing our knowledge of geological processes, mitigating natural disasters, and transitioning to a sustainable economy. This session aims to bring together researchers from various disciplines to explore the multifaceted aspects of crustal igneous systems. We invite contributions that investigate these topics across all tectonic settings, including but not limited to:
1. Computational Magma Dynamics and Thermodynamics: Research utilizing computational models to explore the mechanics, thermodynamics, and fluid dynamics of igneous and volcanic processes.
2. Geochemical and Textural Studies: Contributions that investigate the evolution of magmatic and fluid processes through the analysis of igneous and volcanic materials, including melt/fluid inclusions, crystal stratigraphy, diffusion chronometry, isotopic tracing, and geochronology.
3. Experimental Petrology: We welcome contributions sharing insights gained from high-pressure, high-temperature experiments that simulate P-T-X conditions within crustal igneous systems.
4. Physical Volcanology: Studies that advance our understanding of eruption dynamics, volcano monitoring, and the interplay between subsurface processes and volcanic events.
5. Energy and Metal Resources: Contributions on the resources associated with crustal igneous activity, including geothermal energy, mineral deposits, and ore-forming processes.
6. Data Science and Machine Learning Approaches: Contributions that leverage large datasets and computational statistics to understand igneous phenomena.
We particularly encourage studies that bridge multiple disciplines, showcasing the power of collaborative efforts in advancing our understanding of crustal igneous systems.

Orals: Tue, 16 Apr | Room G2

Chairpersons: Pascal Aellig, Gregor Weber, Tobias Keller
08:30–08:35
08:35–08:45
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EGU24-9163
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ECS
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solicited
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Highlight
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On-site presentation
Alberto Caracciolo, Edward W. Marshall, Enikő Bali, Heini H. Merill, Sæmundur A. Halldórsson, Simon Matthews, Olgeir Sigmarsson, Sóley M. Johnson, Guðmundur H. Guðfinnsson, Jóhann Gunnarsson Robin, Araksan A. Aden, and Byron F. Pilicita Masabanda

After 7000 years of quiescence, three eruptions occurred in 2021, 2022 and 2023 AD in the Fagradalsfjall volcanic system, in Reykjanes peninsula in southwest Iceland. Looking at the eruptive history of the peninsula in the past 4000 years, characterized by ~400-year-long rifting episodes at time intervals of 800-1000 years, the current magmatic reactivation could mark the onset of a new rifting episode. The 2021 eruption, which is a olivine tholeiite lava (mean WR MgO=9.5 wt%), was directly sourced from Moho depths, providing unique insights into the deep parts of the Fagradalsfjall volcanic system1. Furthermore, the 2021 eruption featured remarkable geochemical changes in the first 50 days, characterized by great variability in geochemical tracers used as a proxy for mantle enrichment such as K2O/TiO2  and La/Yb, in the range 0.14-0.26 and 2.1-4.51. After this period and to the end of the eruption, incompatible element ratios record only minor fluctuations2. The 2022 and 2023 AD lavas have lower WR MgO, in the range 8.4-8.7 wt%, with the 2023 eruption being slightly less differentiated. Incompatible element ratios do not change throughout the 2022 AD and 2023 AD eruptions. However, the 2022 and 2023 lavas are slightly more enriched than any 2021 lava, with K2O/TiO2 and La/Yb in the range 0.24-0.28 and 4.3-4.9 respectively. Hence, the 2022 and 2023 lavas are very similar to the most enriched 2021 lavas. The crystal cargo in the Fagradalsfjall lavas is made of plagioclase, olivine and clinopyroxene macrocrysts, with olivine and clinopyroxene becoming increasingly rare in the 2022 and 2023 products. Plagioclase macrocryst cores are in the range An84-91 throughout the 2021, 2022 and 2023 eruptions, without significant variability between eruptions. Conversely, the olivine and clinopyroxene cargo varies over the course of the Fagradalsfjall fires. In the 2021 products, they are mostly in the range of Fo86-89 and Mg#84-91, respectively—more primitive than in the 2022 and 2023 eruptions and out of equilibrium with the melts that carried them to the surface. In the 2022 and 2023 products, most of olivine and clinopyroxene crystals are in the range Fo84-87 and Mg#83-86, respectively. These are found to be in chemical equilibrium with carrier melts, suggesting that they likely represent true phenocrysts of the 2022-23 crystal cargo, as opposed to plagioclase crystals. This compositional variability of the crystal cargo suggests different mush erosion and/or incorporation processes throughout the Fagradalsfjall fires, with preferential incorporation of mush plagioclase crystals and less efficient mush erosion processes over time.

1Halldórsson, S. A. et al. Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland. Nature 609, (2022).

2Marshall, E. W. et al. Rapid geochemical evolution of the mantle-sourced Fagradalsfjall eruption, Iceland. Abstract, AGU 2021.

How to cite: Caracciolo, A., Marshall, E. W., Bali, E., Merill, H. H., Halldórsson, S. A., Matthews, S., Sigmarsson, O., Johnson, S. M., Guðfinnsson, G. H., Gunnarsson Robin, J., Aden, A. A., and Pilicita Masabanda, B. F.: The 2021-23 Fagradalsfjall fires: geochemical and petrological insights, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9163, https://doi.org/10.5194/egusphere-egu24-9163, 2024.

08:45–08:55
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EGU24-13352
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ECS
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On-site presentation
Christopher Galley, Alan Baxter, Mark Hannington, Michael King, Erin Bethell, Peter Lelièvre, Marc Fassbender, and John Jamieson

The formation and evolution of arc-backarc systems govern crustal production in some of the most volcanically and hydrothermally active environments on Earth. Geologic mapping of these systems is increasingly possible by interpretation of emerging ship-based and global geophysical datasets. Although specific rock types cannot be confidently identified from a single physical property, the relative density changes across a region can provide information about the composition of the crust and how it was formed, for example, indicating whether old crust was produced along the volcanic arc or at a back-arc spreading center. This study presents the first complete three-dimensional density model of the Lau Basin and Tofua arc-backarc system in the southwest Pacific Ocean. Seafloor density and crustal thickness maps were produced that reveal changes in crustal composition and growth rates throughout the basin and along the volcanic arc. Crustal thickness varies greatly between the different centers of accretion (indicated here by assemblages), reflecting seafloor spreading and subsurface melt accumulation below volcanic fields. Volumetric growth rates were calculated for each assemblage, corresponding to their respective contribution to basin expansion. The highest crustal density and growth rates are thought to be related to a mantle-derived melt source entering the basin from the north around the edge of the subducting Pacific Plate. The inverse modelling approach used in this study can be applied to global gravity datasets to characterize and quantify the density and thickness of the crust anywhere in the oceans.

 

How to cite: Galley, C., Baxter, A., Hannington, M., King, M., Bethell, E., Lelièvre, P., Fassbender, M., and Jamieson, J.: Quantifying crustal growth in the Lau arc-backarc system through gravity inverse modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13352, https://doi.org/10.5194/egusphere-egu24-13352, 2024.

08:55–09:05
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EGU24-3858
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ECS
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Highlight
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On-site presentation
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Lisa Rummel, Alexander Bartels, Franz May, Maximilian O. Kottwitz, and Tobias S. Baumann

Future volcanic activity within or around distributed volcanic fields is difficult to determine, as many processes affect the melt formation in the mantle and the ascent of melt through the lithosphere. Depending on the external and internal forces and mechanisms, the igneous activity (i.e., shallow intrusive along with extrusive magmatism) can be long lasting or be interrupted by several phases of dormancy. To determine the long-term (i.e., next 1 Myr) relative potential of igneous activity in Germany we therefore suggest to consider the characteristics of various parameters including, among others, seismic anomalies in the mantle, earthquakes, degassing of mantle fluids, ground motion, depth of Moho and LAB, tectonic activity, modelled melt potential based on numerical simulations, and past volcanic eruptions. Thereby, numerical simulations can be used to quantify uncertainties of various parameters describing the structural and thermal state of the lithosphere and the upper mantle. Melt potential calculations including these uncertainties as well as compositional variations of mantle rocks can be used to identify areas of actual critical state with regard to possible future volcanic eruptions below Central Europe.

Based on all 20 parameters investigated, a semi-quantitative multi-criteria method was developed and finally applied to differentiate regions of relative potential for future igneous activity in Germany. Although, most parameters are not uniquely related to magmatic processes, the presence of values exceeding the defined thresholds of any single parameter enhances the potential of future igneous activity at specific locations. Parameter properties are scaled between 0 and 10 within their range of significance (above/below a defined threshold value) to allow their comparison and combination. Weighting factors for individual parameters are used based on the results of expert surveys. However, an index map with statistically determined weighting factors shows the insensitivity of the proposed method in terms of chosen weighting factors.

The results of the multi-criteria method can be used to identify suitable regions for a safe repository for high-level radioactive waste, where areas have to be excluded, which might be directly affected by future magmatic processes. In this context, we computed Germany-wide index (“hazard”) maps, where the index values represent a combination of all 20 parameters. The resulting index maps show that a higher relative potential of future igneous activity occurs not only in regions affected by Quaternary volcanism, but also in and around older Cenozoic volcanic fields or even in regions that have not been affected previously by Cenozoic volcanism. These observations indicate the possible longevity of a geodynamic framework that facilitates magmatic activity over large time scales (millions to tens of millions of years).

How to cite: Rummel, L., Bartels, A., May, F., Kottwitz, M. O., and Baumann, T. S.: Determining the relative potential of future igneous activity in Germany – a multi-criteria approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3858, https://doi.org/10.5194/egusphere-egu24-3858, 2024.

09:05–09:15
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EGU24-16851
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ECS
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On-site presentation
Janine Birnbaum, Einat Lev, Marc Spiegelman, Jackie Kendrick, and Yan Lavallée

Silicate melts have highly temperature-dependent viscosity and at low temperatures, crystalize and/ or vitrify. The development of a solid rind or carapace results in a transition in deformation mechanism from dominantly viscous to elastic or plastic. This transition has a significant impact on the rate and style of emplacement of lava flows and domes, including on the construction of channelized flows, over-steepened margins, and advance due to lava flow breakouts. These processes are especially important in subaqueous, subglacial, and extraterrestrial environments in which cooling is accelerated, resulting in a current lack of models specifically calibrated for these environments.

We develop a numerical model, Viscous-Elastic Numerically Unified Solver for Solidifying flows (VENUSS), for cooling and solidifying free surface flows. The model couples a viscous fluid interior with an elastic shell whose thickness grows in response to cooling. We use a numerically unified approach that solves for the velocity field in the viscous and elastic fields together. Interface tracking is provided using the level set method combined with an extended finite element (XFEM) approach to avoid costly remeshing. Simulations are performed in two-dimensional planar or axisymmetric conditions which allows for modeling natural geometries such as lava flows and lava domes. This approach presents an improvement upon existing models of lava flow and dome evolution that either neglect or greatly simplify the mechanical effects of a crust.

As a validation/test of our model, we simulate the advance of meter-scale experimental lava flows from the Syracuse Lava Project. We find the flow propagation is highly sensitive to the boundary conditions applied at the flow base. Under no-slip conditions, the simulated flow arrests more quickly than the experiments. No-stress conditions at the flow base produce plug-like flow that propagates too quickly. Adding an imposed ruptured condition (no solidification and viscosity appropriate to the flow interior) in a thin layer at the flow base produces a lobate morphology that qualitatively resembles observations of natural and experimental flows.

In our models, flows are slowed and stopped by the development of a coherent crust at the flow front, whereas natural flows would continue to propagate via rupture of the skin or crust, highlighting the importance of including these mechanisms in models. However, crust development and rupture are usually omitted from lava flow models, in which propagation and arrest are usually controlled by an increase in viscosity through the entire flow thickness. Our new model allows for investigation into the development and arrest of lava flows that depends on geometry, the competition between flow advance and cooling, and the mechanical properties of a solidified skin or crust. Such insight can be embedded into flow field scale models and allow for physics-based, complex flow fields impacted by breakouts, ooze-outs, channelization, and other critical crust-dominated processes.

How to cite: Birnbaum, J., Lev, E., Spiegelman, M., Kendrick, J., and Lavallée, Y.: Numerical simulation of the effect of solidifying crusts on lava propagation and arrest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16851, https://doi.org/10.5194/egusphere-egu24-16851, 2024.

09:15–09:25
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EGU24-15105
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ECS
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Highlight
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On-site presentation
Thierry Solms, Thomas Driesner, Olivier Bachmann, and Isabelle Chambefort

Exploiting high-enthalpy geothermal systems is an important component of expanding low-carbon electricity generation in volcanically active regions. One possibility to enhance power production is harnessing supercritical geothermal resources that underlay conventional high-enthalpy systems, but utilizing them requires a deeper understanding of the physical and chemical processes taking place at the magmatic-hydrothermal transition immediately below the supercritical reservoir.         
In water-rich, silicic magma bodies, the exsolution of a magmatic volatile phase (MVP) can result from magma crystallization. In a certain crystal fraction range, the MVP can be abundant enough to percolate through permeable pathways within the magma mush and coalesce at the intrusion’s apex, where fluid pressure build-up can lead to hydro-fracturing.   
For the case of a prolate, shallow-seated (situated at 4 to 7 km, 0.94 km width), water-rich silicic magma body, we conducted 2D numerical fluid flow simulations, exploring the transient patterns of MVP exsolution and flow inside and out of the cooling intrusion, and hydrothermal fluid flow outside of it. We examined the impact of varying temperature-crystallinity trends on the timing of MVP production, the formation of permeable pathways, overpressure build-up and hydro-fracturing.       
Our findings show that for silicic magmas, where crystallization primarily takes place at low magmatic temperature (near the haplogranitic solidus), permeable pathways (“channels”) form within the mush, but fluid pressures at the intrusion apex are not sufficient to expel MVPs forcefully. In contrast, for chemically less evolved melts, with crystallization shifted to higher temperatures, overpressure build-up is large enough to periodically release MVPs via hydro-fractures into the ductile carapace around the intrusion and beyond.       
This periodic MVP release from the magma contributes a small fraction of the total water in the geothermal system above the cooling intrusion, where it is mixed with meteoric water. At typical borehole depths for conventional, high-enthalpy geothermal systems (e.g. 2 km), the contribution of magmatic water is usually ≤ 5%, and its thermal effect is negligible. 
The observed degassing patterns could elucidate differences in degassing style between hydrous magmatic systems of different chemical compositions, e.g. the silicic intrusions of the Central Taupō Volcanic Zone versus the more mafic Whakaari White Island volcano (both in New Zealand). Further, these insights into the timing and extent of hydro-fracturing and the related advection of metals and ligands are key to understand the conditions relevant to the formation of magmatic-hydrothermal ore deposit such as granite-related tin-tungsten deposits and porphyry-copper deposits.

How to cite: Solms, T., Driesner, T., Bachmann, O., and Chambefort, I.: Impact of crystallinity evolution on volatile phase transport in hydrous magmatic intrusions during the magmatic-hydrothermal transition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15105, https://doi.org/10.5194/egusphere-egu24-15105, 2024.

09:25–09:35
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EGU24-1730
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ECS
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On-site presentation
Simon Hector, Qasid Ahmad, Clifford G. C. Patten, Massimo Chiaradia, Stephanos Kilias, Paraskevi Nomikou, and Jochen Kolb

Gold-rich seafloor massive sulfides (SMS) form in various marine hydrothermal environments, including continental volcanic arcs, where magmatic fluids may contribute significantly to the metal budget of the hydrothermal system. To track the origin of metals and unravel the mineralising processes at play in Au-rich SMS formation (i.e. hydrothermal leaching of country rocks or magmatic degassing), we investigated the volcanic/basement rocks and Au-rich SMS of the Kolumbo submarine volcano (Greece). We combine in-situ Pb isotope analysis of the sulphide mineralisation and whole rock Pb isotope analysis of volcanic and basement rocks. During magmatic evolution, crustal material assimilation slightly shifts Pb isotope ratios toward more radiogenic values defining a differentiation trend from andesite to rhyolite. The mineralisation, dominated by pyrite with episodic galena, sphalerite, chalcopyrite and Sb-Pb sulfosalts formation, has Pb isotopes ratios pointing toward an igneous source. Galena and Sb-Pb sulphosalts have Pb isotopes ratios similar to volatile-saturated trachytic magma indicating Pb mobilisation during magmatic degassing, while Pb isotopes ratios in pyrite matches volatile-poor post-degassing rhyolite, suggesting Pb mobilisation by hydrothermal leaching of rhyolite. Lead isotope ratios reveals that Pb at Kolumbo is sourced from igneous rocks but the mechanisms for metal transfer vary from rhyolite leaching by hydrothermal fluid circulation to episodic input of magmatic fluid able to provide Ag, As, Au, Cu, Hg, Pb, Sb, Tl in addition to Pb. The magmatic evolution of Kolumbo highlights the diversity and complexity of metal mobilising magmatic-hydrothermal processes involved in Au-rich SMS formation.

How to cite: Hector, S., Ahmad, Q., Patten, C. G. C., Chiaradia, M., Kilias, S., Nomikou, P., and Kolb, J.: Unravelling metal mobilising processes in the Kolumbo volcano Au-rich SMS using Pb isotopes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1730, https://doi.org/10.5194/egusphere-egu24-1730, 2024.

09:35–09:45
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EGU24-13197
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ECS
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On-site presentation
Manfredo Capriolo, Sara Callegaro, Frances Deegan, Renaud Merle, Heejin Jeon, Martin Whitehouse, László Aradi, Malte Storm, Paul Renne, Don Baker, Jacopo Dal Corso, Robert Newton, Csaba Szabó, Bruna Carvalho, Nasrrddine Youbi, and Andrea Marzoli

The magma plumbing system throughout the entire transcrustal section of Large Igneous Provinces (LIPs) is still poorly understood. Among the most voluminous LIPs, the Central Atlantic Magmatic Province (CAMP [1], ca. 201 Ma) and the Deccan Traps (DT [2], ca. 66 Ma) coincided in time with end-Triassic and end-Cretaceous mass extinctions, respectively. Glomerocrysts containing abundant primary melt inclusions from both CAMP and DT basaltic lava flows were investigated via a multi-analytical approach (confocal Raman microspectroscopy for volatile species within bubbles, electron microprobe for major element compositions, secondary ion mass spectrometry for oxygen isotope compositions, Synchrotron X-ray microtomography and optical microscopy for microstructural analysis). The analysed glomerocrysts are dominated by augitic clinopyroxenes, and represent portions of crystal mushes. The analysed melt inclusions consist of an intermediate to felsic composition glass and CO2-bearing bubbles, and represent relics of interstitial melts and fluids entrapped during the evolution of these crystal mushes. The different volume proportions in terms of bubbles within melt inclusions indicate a heterogeneous entrapment, implying that melts were entrapped along with already exsolved fluids. The MgO-rich composition of glomerocrysts and whole rocks is in contrast with the SiO2-rich composition of melt inclusions, unveiling disequilibrium conditions of entrapment, as supported by thermodynamic modelling too. The oxygen isotope compositions of clinopyroxene in glomerocrysts indicate that they crystallized from mafic melts with normal (i.e., mantle-like) to mildly low δ18O values. However, the oxygen isotope compositions of glass in melt inclusions indicate that they entrapped distinct, intermediate to felsic melts with normal to extremely high δ18O values, which may be explained by variable degrees of crustal assimilation and partial mixing in an open system. Hence, the oxygen isotope compositions of glass in melt inclusions also suggest that the CO2 within their coexisting bubbles may be derived partly from the mantle and partly from assimilated crustal melts as well. Overall, geochemical data and microstructural observations reveal the presence of multiphase (i.e., solid + liquid + gaseous phases) crystal mushes within the magma plumbing system of both CAMP and DT, and shed light on the origin of carbon and its transfer from the mantle to Earth’s surface.

 

[1] Marzoli et al. (1999), Science 284, 616–618.

[2] Sprain et al. (2019), Science 363, 866–870.

How to cite: Capriolo, M., Callegaro, S., Deegan, F., Merle, R., Jeon, H., Whitehouse, M., Aradi, L., Storm, M., Renne, P., Baker, D., Dal Corso, J., Newton, R., Szabó, C., Carvalho, B., Youbi, N., and Marzoli, A.: The transcrustal plumbing system of Large Igneous Provinces: Insights from glomerocrysts and melt inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13197, https://doi.org/10.5194/egusphere-egu24-13197, 2024.

09:45–09:55
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EGU24-530
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ECS
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On-site presentation
Haitao Ma, Jingsui Yang, Pengjie Cai, Mudlappa Jayananda, Dongyang Lian, and Krishnasamy Ravindran Aadhiseshan

Chromitites, found in Archean greenstone belts as the oldest ultramafic rocks, offer critical insights into the early Earth's evolution. Water plays a fundamental role in aggregation and mineralization of chromite, yet the water content of parental magma of chromitite remains unclear. This study present petrologic and elemental data on chromitites from the 3.3-3.1 Ga Nuggihalli greenstone belt, Western Dharwar craton (India), and address origin of chromitites in Archean greenstone belts particularly water contents in primary magmas. Major and trace element data of chromites and clinopyroxenes from chromitites coupled with thermobarometry, and hygrometry calculation, as well as numerical modeling reveal that the chromites are high-Cr chromites (Cr# 68.1-78.6) with low TiO2 (0.19%-0.29%), Al2O3 (9.10%-13.13%), and Ga (4.24-10.37 ppm), similar to the parental melts of high-Cr podiform chromites and boninites in modern ophiolites. The clinopyroxenes are augites with high Mg# (93-95) which corresponds to equilibrated melts with the Nuggihalli chromitites having high Mg# values (79-86), resembling ancient komatiitic or picritic magmas (75-90), crystallized in a primary magma environment. Thermobarometry and hygrometry calculation suggest that the clinopyroxenes could form at temperatures of 1194-1221℃ and pressures of 0.7-5.8 kbar with high water contents (~2.4-2.6 wt.%), exceeding water contents in mid-ocean basalts (MORB) and oceanic island basalts (OIB) source. Numerical modeling of rare earth elements indicates that moderate degrees of partial melting (1%~20%) of hydrated spinel lherzolite mantle (water content: ~478-5408 ppm). The primary magmas of the 3.3-3.1 Ga Nuggihalli chromitites are characterized by enrichment of water contents (~2.4-2.6 wt.%) and high field strength elements (HFSEs, e.g., Nb and Hf), demonstrating high comparability with boninites and arc magmas. Furthermore, the rock associations including ultramafic rocks with chromitites, high-Mg basalts and sheets of gabbro-anorthosites in the Nuggihalli greenstone belt may represent the relic of oceanic lithosphere. This declares that the 3.3-3.1 Ga Nuggihalli chromitites could have formed at a forearc basin on a subduction system.

How to cite: Ma, H., Yang, J., Cai, P., Jayananda, M., Lian, D., and Aadhiseshan, K. R.: Water content in primary magma compositions and mantle source of chromitites in Mesoarchean Nuggihalli greenstone belt (India), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-530, https://doi.org/10.5194/egusphere-egu24-530, 2024.

09:55–10:05
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EGU24-7044
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ECS
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On-site presentation
Xiaofang He, Martin Hand, Laura J. Morrissey, and William J. Collins

Crustal melting leading to the formation of S-type granite is typically considered a characteristic of collisional regimes. However, the formation of S-type granites does not necessarily require overt crustal thickening. Instead, voluminous granite generation can occur where burial of fertile H2O-rich material occurs in high heat flow environments. One obvious setting that has these attributes is rapidly developing back arc regimes. Settings such as these are ideal to generate large volumes of S-granite without necessarily requiring appreciable crustal thickening.

The Bundarra and Hillgrove granite intrusions in the southern New England Orogen, eastern Australia are part of an Early Permian garnet/cordierite-bearing S-type granite batholith (>1800km2) generated in a back-arc setting linked to the easterly (outboard) migration of a W-dipping subduction zone. This setting facilitated rapid and thick accumulation of compositionally immature detritus from the active arc and the inboard continent, creating a fertile system for granite genesis driven by back arc high heat flow. Deposition of the precursor sedimentary volume occurred between 360 and 300 Ma, with partial melting and batholithic-scale melting and granite accumulation occurring between ca. 298-288 Ma. Seismic reflection data suggests the currently preserved crustal column in places comprises ~30% granite, with the current level of denudation ranging between ~ 3-5kbar.

Ti in zircon and quartz, and zircon saturation temperatures suggest granite-formation temperatures may have been as low as 700-750 °C. Mineral equilibria modelling using protolith compositions considered presentative of the sedimentary protoliths suggest melting at the scale indicated by regional mapping and geophysics is only possible in a water rich environment, either from trapped water that was not expelled during burial in the back arc, or for an external source.

The geochemistry of the Bundarra and Hillgrove suites shows significant variability in their maficity. When comparing the modelled magma/melt compositions at different water contents the variation in maficity shows the granites are more mafic than the modelled melt compositions, suggesting much of the mafic content is entrained from the source. This is supported by the occurrence of hexagonal shaped biotite aggregates which contain occasional garnet relics.

We interpret that water-fluxed melting played an important role in the genesis of back arc hosted S-type granites in eastern Australia, and it may apply to the genesis of many other S-type granite batholiths. Variable entrainment of the residual mineral assemblage within a cool, hydrous silicic melt can probably explain the compositional range of New England and other S-type granite batholiths.

How to cite: He, X., Hand, M., Morrissey, L. J., and Collins, W. J.: Voluminous low-temperature S-type granite formation in the New England Orogen, eastern Australia during back arc evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7044, https://doi.org/10.5194/egusphere-egu24-7044, 2024.

10:05–10:15
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EGU24-18369
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On-site presentation
Elena Melekhova

Water-rich high-alumina basalts are widely implicated in models of subduction zone magma genesis and porphyry copper mineralisation, yet their phase relationships at high pressures have been very little studied since the pioneering work of Yoder and Tilley (1963). To fill this gap an experimental study has been carried out on water-saturated phase relationships of a high-alumina basalt (HAB) from St. Kitts, Lesser Antilles volcanic arc (Eastern Caribbean), in the pressure range 1.5 to 20 kbar. Experimentally produced glasses, mineral compositions and mineral assemblages match whole rock data of Lesser Antilles high-alumina basalts and high-alumina basaltic andesites, phenocryst assemblages and mineral chemistry. I show that the liquidus silicate mineral phase changes from olivine and plagioclase at low pressures, through clinopyroxene and amphibole at intermediate pressures, to garnet above 14 kbar. Experimentally produced mineral assemblages correspond well to plutonic xenolith found in Lesser Antilles and change from dunnite, and olivine and hornblende gabbro dominated lithology at pressure ≤ 10 kbar to hornblende pyroxenite, hornblendite and eclogite at pressures ≥ 10kbar.

Melt compositions describe liquid lines of descent that resemble those of many magmatic arc sequences; only alumina shows any strong correlation with pressure. Water saturation (as determined by the difference method) is lower than predicted by most solubility models. The evolved melts generated at low crustal conditions from these experimental series do not resemble silicic melts associated with porphyry copper deposits.

I also address the long-debated origin of high-An plagioclase (An > 90), which occurs in many volcanic and plutonic rocks associated with arc magmatism. Additional experiments on HAB at water-undersaturated and fluid-saturated experiments with 2M CaCl2 solution and CaCO3 have been carried out at 7 kbar to evaluate fluid composition and aH2O on An content of plagioclase. These experiments, combined with existing experiments on broadly basaltic compositions, demonstrate that high-An plagioclase (An ≥ 90) crystallises readily from fluid-saturated high-alumina basaltic melts at pressures of 1 to 10 kbars and temperatures 850 – 1100 ºC. However, the limit of An content produced by experiments is An96. Addition of CaCl2 to the fluid and CaCO3 to the system does not have a significant effect on An content. To produce plagioclase with An content more than 96 mol% a secondary process such as re-melting/re-crystallisation must be involved (Melekhova et al 2022).

Melekhova E., et al. (2022) Journal of Petrology 63.5 (2022): egac033.

How to cite: Melekhova, E.: An experimental study of high-alumina basalt differentiation and the effect of H2O and pressure on plagioclase – melt equilibria , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18369, https://doi.org/10.5194/egusphere-egu24-18369, 2024.

Posters on site: Tue, 16 Apr, 16:15–18:00 | Hall X2

Display time: Tue, 16 Apr 14:00–Tue, 16 Apr 18:00
Chairpersons: Pascal Aellig, Charline Lormand, Catherine Booth
X2.39
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EGU24-4328
Takashi Hoshide and Keita Kondo

Petrographic studies of the multi-textured layered gabbro series of the lower crustal section recovered from U1415P were conducted to determine the mechanism of orthopyroxene formation in lower crustal gabbros drilled in the Hess Deep rift near the East Pacific Rise. In a particular horizon of the series (U1415P 6R-1 to 6R-2), homogeneous medium-grained troctolite and fine-grained spinel-bearing heterogeneous olivine gabbro occur in proximity.

The samples from the Hole1415P 6R are divided into homogeneous troctolite parts with medium-grained equigranular textures and spinel-bearing heterogeneous olivine gabbro parts with poikilitic textures (irregularly shaped fine-grained plagioclase characrysts enclosed in Ol-oikocrysts and Cpx-oikocrysts). The wide variation in TiO2 content against nearly constant Mg# and Cr2O3 of clinopyroxene in these rocks is quite different from the compositional trend of clinopyroxene in layered mafic intrusions explained by the fractional crystallization of magma.

Recently, Yang et al. (2019) conducted a reaction experiment between MORB melts and troctolite and reported microtextures and mineral chemical compositions of the experimental products. In the experiment, fine-grained plagioclase was found to be poikilitically enclosed in olivine and clinopyroxene in the melt infiltration zone within troctolite near the boundary between troctolite and melt. The poikilitic textures and the oikocristic clinopyroxene compositional variations in the Hess Deep spinel-bearing olivine gabbro are very similar to those in the reaction experiment by Yang et al. (2019). These indicate that the heterogeneous olivine gabbro of the Hess Deep was formed by a melt-rock (or crystal mush) reaction.

              In addition, the multiphase solid inclusions of Cpx-Pl assemblage with basaltic magma composition and Opx-bearing multiphase solid inclusions with composition of high-Mg basaltic-andesite to andesite are enclosed in Cr-spinel from the spinel-bearing heterogeneous olivine gabbro. The presence of Opx-bearing multiphase solid inclusions indicate that the injection of SiO2-rich melt different in composition from the troctolite-forming magma has occurred. The SiO2-rich melt reacted with the troctolite to form spinel-bearing heterogeneous olivine gabbro. Our results may suggest that the sheeted sills model, in which magma of various compositions intrudes into the crust, is a more appropriate mechanism for the formation of the lower oceanic crust.

How to cite: Hoshide, T. and Kondo, K.: Formation of spinel-bearing layered gabbros by the reaction between the basaltic crystal mush and high-Mg andesitic melts in the lower oceanic crust, East Pacific Rise (IODP Exp. 345 U1415P) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4328, https://doi.org/10.5194/egusphere-egu24-4328, 2024.

X2.40
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EGU24-5290
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ECS
Pascal Aellig, Albert de Montserrat, and Boris Kaus

In order to understand the cause of a caldera-forming eruption, it is crucial to study the pre-eruptive processes, from build-up to the collapse. In recent years, the cyclicity of large-scale magmatic systems and their corresponding caldera collapses has been described through various geochemical and petrological studies. Numerical modelling studies have investigated the collapse stage using a pressurised cavity or gas-filled chamber, studying the evolution of the surrounding lithosphere by inflating and deflating the chamber. Another modelling approach involves investigating the displacement effects of moving a piston-shaped object.

In this study, we use a multi-physical numerical modelling approach to investigate different aspects of the caldera cycle, including the accumulation of magma, the evolution of stress, the strain rate and the dynamics within the forming magmatic system. To achieve this, we couple an open-source thermal evolution magma intrusion code with a Stokes solver. The coupling allows for the evaluation of thermal and volumetric changes in the magmatic system, taking into account the complex interaction between magma dynamics and the surrounding host rock. The use of nonlinear visco-elasto-plastic rheology enables the assessment of fracturing and thermal effects on the lithosphere, which create downward propagating weak zones that are later utilised as eruption channels. These faults not only provide pathways but are also associated with the caldera collapse stage of the eruption cycle, which leads to geomorphological transformations of the surface.

Our approach is also applicable for assessing the evolution of current magmatic systems taking into account their topography. The model is applied to the well-studied area of the Toba caldera in Sumatra. The magma is injected into areas where seismic inversion studies have identified a melt phase. This allows for an assessment of the system's evolution and provides insights into an active magmatic system. Additionally, it serves as a reference for correlating and referencing our model with observational data.

How to cite: Aellig, P., de Montserrat, A., and Kaus, B.: From build-up to caldera collapse: High resolution modelling of large scale magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5290, https://doi.org/10.5194/egusphere-egu24-5290, 2024.

X2.41
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EGU24-11344
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ECS
Catherine Booth, Matthew Jackson, Steve Sparks, and Alison Rust

Geophysical, geochemical, and petrological studies indicate that magma storage and chemical differentiation can occur at various depths in the continental crust. Examination of exposed ancient magmatic systems reveal a continuum from a refractory lower crust to a silica-rich upper crust, prompting a debate on the mechanisms governing magma storage and differentiation in vertically extensive magmatic systems.

Conceptual models for magma storage and chemical differentiation within the crust range from (i) a low crystallinity magma body, where differentiation occurs primarily by fractional crystallisation and partial melting of the crust, to (ii) a trans-crustal high crystallinity ‘mush’ reservoir consisting of a porous crystal matrix with melt in the pore space. Chemical differentiation in these mush reservoirs is driven by the compaction of the crystal matrix, buoyant upward reactive flow of melt, and partial melting of the surrounding crust.

We use a numerical model to investigate magma storage and chemical differentiation in the continental crust. The model assumes a magmatic system sustained by the intrusion of mantle-derived basalt into the lower crust.  We find that intrusion of basalt creates a high crystallinity reservoir in the lower crust. Reactive flow and compaction cause melt to accumulate at the top of the reservoir, creating a layer of low crystallinity, chemically differentiated magma.  Buoyancy overpressure causes this magma to  evacuate via dikes and we assume the magma intrudes the mid-crust to form a second high crystallinity mush reservoir. Reactive flow and compaction once again lead to the accumulation of low-crystallinity, evolved magma at the top of the reservoir that can evacuate and intrude the upper crust, driving volcanic eruptions or forming shallow plutons.

The compositional evolution of magma as it ascends through the system is influenced by the flux of the parental basalt and the fertility of the crust. A higher basalt flux leads to warmer reservoirs that evacuate less evolved magma. Reservoirs in infertile crust that cannot melt are formed only of hot, parental magma, and also evacuate less evolved magma. Partial melting of fertile crust allows melt to percolate upwards and accumulate in cooler crust, leading to the evacuation of evolved (silicic) magma.

In most of our simulation cases, the reservoirs remain as discrete bodies in the lower- and mid-crust, with magma transfer occurring via dikes; a trans-crustal reservoir does not form. The lower-crust reservoir evacuates mafic to intermediate magma, whilst the cooler mid-crust reservoir primarily evacuates evolved, silicic magma, consistent with vertical compositional trends in exposed, ancient magmatic systems. Both reservoirs comprise primarily low-melt fraction mush, consistent with geophysical imaging of contemporary systems.  Layers of accumulated low-crystallinity magma are transient and likely too thin to resolve in geophysical data. The predicted volume, composition, and frequency of episodic magma intrusions into the upper crust are consistent with observed data from large volcanic eruptions. Our results suggest that reactive flow in multiple mush reservoirs controls magma storage and differentiation.

How to cite: Booth, C., Jackson, M., Sparks, S., and Rust, A.: Magma Storage, Differentiation and Transfer in Vertically Extensive Magmatic Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11344, https://doi.org/10.5194/egusphere-egu24-11344, 2024.

X2.42
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EGU24-11411
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ECS
Gabriele Amato, Vittorio Minio, Mariangela Sciotto, Laura Spina, Leighton M. Watson, and Andrea Cannata

The maim objective of this work is to investigate the structure of the superficial portion of the plumbing system at Mt. Etna in terms of interconnection among the conduits and internal variations linked to eruptive activity. For this purpose, the lava fountains that occurred in the years from 2011 to 2015 were taken into consideration, for a total of 51 events, and the infrasonic signals recorded by two stations were analysed. We extracted the infrasonic events, and analysed the evolution in time of the spectral content by using normalized and non-normalized pseudospectrograms, peak and mean frequency values. In addition, the sources of the events were located. We noted how, although the eruptions took place at South-East and Voragine craters, the infrasonic events recorded before and after the lava fountains are mostly generated by the North-East Crater. Most of the energy of these events is comprised in the frequency range 0.1 – 2 Hz. Furthermore, in most of the lava fountain episodes, we observed a decrease in the frequency peaks of the infrasonic events after the eruptions. To interpret the variations of the plumbing system responsible for these spectral changes, as well as the interconnection among the conduits feeding the main craters, we model the infrasonic events from the North-East Crater as an acoustic resonance of the crater and conduit, whose length changes with time as magma ascends or descends in the conduit.

How to cite: Amato, G., Minio, V., Sciotto, M., Spina, L., Watson, L. M., and Cannata, A.: Study of the variations of the feeding system at Mt. Etna during the paroxysmal activities by using infrasonic data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11411, https://doi.org/10.5194/egusphere-egu24-11411, 2024.

X2.43
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EGU24-13201
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ECS
Louis-Maxime Gautreau, Thor Hansteen, Maxim Portnyagin, and Philipp Brandl

Conical Seamount is an active submarine volcano of the Tabar-Lihir-Tanga-Feni island chain (TLTF) in north-eastern Papua New Guinea. This island chain is located within the New Ireland Basin and the related alkaline to shoshonitic magmas are ascending through a thick sedimentary sequence. The TLTF hosts several Cu-Au mineralized volcanic centers. Conical Seamount is a rare example of a submarine epithermal-style mineralization and is considered to be a juvenile analogue of the Ladolam world-class gold deposit located on the nearby island of Lihir.

Recent research assessed important crustal magmatic processes as precursors for the mineralization at Conical Seamount. More specifically, the presence of a degassing crustal magma chamber has been found to be critical for the metal concentration and transfer into the epithermal system. This may explain why other seamounts in the TLTF island chain remain barren (unmineralized).

Here we present new volatile (H2O, CO2, F, Cl, S) as well as major and trace element data of clinopyroxene-hosted melt inclusions. These data along with fluid inclusion data allow us to further constrain the volcanic plumbing system, more specifically the pressure (i.e., depth) of the crustal magma chamber, the degassing stage and sulfide saturation processes. Chalcophile elements and Au in particular are scavenged within sulfides concomitant with the magmatic fluid exsolution, leading to ideal conditions for the transfer of metals into the ore-forming system.

 

How to cite: Gautreau, L.-M., Hansteen, T., Portnyagin, M., and Brandl, P.: The importance of magmatic degassing at a mineralized, submarine volcano: The case of Conical Seamount, Papua New Guinea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13201, https://doi.org/10.5194/egusphere-egu24-13201, 2024.

X2.44
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EGU24-13454
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ECS
Yong-Un Chae, Youn-Joong Jeong, Jong-Sun Kim, Sujin Ha, Young Ji Joo, Seungwon Shin, and Hyoun Soo Lim

On the Korean Peninsula, located in the eastern region of East Asia, the Gyeongsang Basin, a representative sedimentary basin formed during the Cretaceous Period, occupies about a fourth of South Korea. In the Gyeongsang Basin, the Kusandong Tuff (ca. 103 Ma; Kim et al., 2013), a representative marker bed, is distributed across approximately 200 km from north to south. About 2.5 m-thick tuff layer also develops in Sinsu and Changseon islands, located in the southern part of the basin. There is controversy as to whether it is the southernmost extension of the Kusandong Tuff or a separate tuff body. To resolve this, a total of 4 samples were collected from two islands, and LA-MC-ICP-MS zircon U-Pb dating was performed. As a result, all samples were slightly contaminated with common lead, and lower intercept ages of ca. 99 Ma were calculated, indicating a systematically younger than the reported ages of Kusandong Tuff (ca. 103 Ma). And zircons used in age calculations are largely divided into two domains accoring to the significant differences in brightness in cathodoluminescence (CL) images. Based on the combination of these domains, zircons show: 1) dark overall, 2) dark in the core with bright rims (known as reverse zoning), and 3) only bright oscillatory zoning with/without some inherited cores. In general, dark domains have a uranium content of ca. 3000-7000 ppm, while bright ones range from 34-541 ppm. And in the CL image, some boundary of the dark domains in the cores had melted and infiltrated by bright ones. To understand the evolutionary history of the magma that formed these zircons, trace and rare earth elements were analyzed using LA-ICP-MS. The results indicate that the dark domains of zircons were formed in relatively highly evolved and cooler magma, while the bright domains of zircons were formed in less evolved and hotter magma. To summarize the magma evolution model, crystallization of dark domains occurred first in relatively highly evolved magma, and then domains showing bright and distinct oscillatory zoning were formed with the injection of less evolved magma from deeper sources. At the same time, bright domains grew on the rims of existing dark zircons due to the injected magma. It is thought that the new magma injected into the existing magma chamber caused an increase in internal pressure, which ultimately led to the volcanic eruption. Considering the dating results, it is believed that all of these processes occurred over a short period of time, roughly limited to about 99 Ma on the geological time scale.

How to cite: Chae, Y.-U., Jeong, Y.-J., Kim, J.-S., Ha, S., Joo, Y. J., Shin, S., and Lim, H. S.: Eruption age and magma evolution history of the Sinsudo Tuff in the Cretaceous Gyeongsang Basin, Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13454, https://doi.org/10.5194/egusphere-egu24-13454, 2024.

X2.45
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EGU24-14492
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ECS
María P. Marroquín-Gómez, Mauricio Ibañez-Mejía, and Aleisha C. Johnson

The North Volcanic Zone of the Andes is the result of an overall uniform subduction of the Nazca Plate beneath the South American Plate in Ecuador and Colombia; however, age, composition, and thickness of the continental crust and the distance between the trench and arc, among other components of this subduction system, vary significantly along this segment of the Andes (Stern, 2004). Those changes are most likely responsible for differences in the geochemical characteristics of volcanic products in different parts of the Colombian arc as discussed in Monsalve (2020). Although several works related to the isotopic geochemistry of the volcanic products have been carried out in Ecuador (Bryan et al., 2006; Chiaradia et al., 2009, references therein), there are few records of the same type of data for Colombia and those available focus on the SW part of the arc (Marín-Cerón, 2007). This study seeks to fill the gap and use this new data to elucidate processes of magma generation and differentiation currently occurring under the northern Andes. Whole rock major elements, trace elements, and 176Hf/177Hf analyses from main volcanic centers along the Colombian arc are used to track lithospheric and crustal processes of mixing, assimilation, and fractional crystallization as well as the main source materials and contributions in magma generation in the subduction zone. From a broader view, this new data helps to discuss regional comparisons of the geochemical expressions in the Andean arcs caused by different tectono-magmatic processes.

 

Bryant, J.A., Yogodzinski, G.M., Hall, M.L., Lewicki, J.L. & Bailey, D.G. (2006). Geochemical constraints on the origin of volcanic rocks from the Andean Northern Volcanic Zone, Ecuador. Journal of Petrology, 47(6): 1147–1175.

Chiaradia, M., Müntener, O., Beate, B., & Fontignie, D. (2009). Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling. Contributions to Mineralogy and Petrology, 158, 563-588.

Marín–Cerón, M.I. (2007). Major, trace element and multi–isotopic systematics of SW Colombian volcanic arc, northern Andes: Implication for the stability of carbonate–rich sediment at subduction zone and the genesis of andesite magma. Doctoral thesis, Okayama University, 140 p. Okayama, Japan.

Monsalve–Bustamante, M.L. (2020). The volcanic front in Colombia: Segmentation and recent and historical activity. In: Gómez, J. & Pinilla–Pachon, A.O. (editors), The Geology of Colombia, 97–159.

Stern, C.R. (2004). Active Andean volcanism: its geologic and tectonic setting. Revista geológica de Chile, 31(2), 161-206.

How to cite: Marroquín-Gómez, M. P., Ibañez-Mejía, M., and Johnson, A. C.: Geochemistry of the Northern Andean Volcanic Zone, Colombia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14492, https://doi.org/10.5194/egusphere-egu24-14492, 2024.

X2.46
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EGU24-14593
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ECS
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Wiebke Schäfer, Manuel Keith, Marcel Regelous, Reiner Klemd, and Martin Kutzschbach

Valuable understanding regarding the behaviour of chalcophile elements in magmatic systems can be gained by examining magmatic sulphide droplets, which are the solidified remnants of previously immiscible sulphide liquids [1-2]. We analysed the trace element composition of sulphide droplets by LA-ICP-MS, creating a comprehensive data set for volcanic and plutonic rocks from intra-oceanic arcs.

We observed a significant enrichment of elements like Zn, Cd, Sn, Te, and Bi in sulphide droplets from lava samples compared to those hosted by gabbro xenoliths, which cannot be attributed to the fractionation of olivine, spinel, or magnetite [3-5]. These compositional differences are likely the result of changing sulphide droplet composition during cooling and solidification of the silicate melt. This process involves continuous sulphide segregation or re-equilibration with the silicate melt. A key aspect of our suggested model is sulphide droplets' resorption or partial remelting, particularly of the Cu-Fe-rich intermediate solid solution proportion. This process is driven by pressure decrease during magma ascent, leading to an increase in sulphur solubility in the silicate melt [6], which potentially liberates elements like Cu, Au, Zn, Bi, Te, and Ag from the sulphide droplet to the silicate melt. Our findings further suggest that subsequent magma stagnation and fractional crystallisation lead to a second stage of sulphide saturation, likely dominated by the elements previously liberated from the intermediate solid solution.

The complex crystallisation history indicates that sulphide droplet formation during silicate melt evolution in subduction-related settings is a non-equilibrium process. We further propose that volatile saturation preceding the second stage of sulphide segregation from a silicate melt enriched in chalcophile elements liberated from intermediate solid solution could result in particularly metal-rich fluids (e.g., Cu, Au, Bi, Te) with a high ore-forming potential in magmatic-hydrothermal environments.

 

[1] Wood, B. J. and Kiseeva, E. S. (2015), Earth and Planetary Science Letters, 424, 280-294. [2] Patten, C. et al. (2013), Chemical Geology, 358, 170–188. [3] Distler, V. V. et al., (1983), Initial Reports of the Deep Sea Drilling Project, 69, 607-617. [4] Keith, M. et al. (2017), Chemical Geology, 451, 67–77. [5] Schäfer, W. et al., in prep. [6] Peach et al. (1990), Geochimica et Cosmochimica Acta, 12, 3379-3389.

How to cite: Schäfer, W., Keith, M., Regelous, M., Klemd, R., and Kutzschbach, M.: Crystallisation history of magmatic sulphide droplets in intra-oceanic arcs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14593, https://doi.org/10.5194/egusphere-egu24-14593, 2024.

X2.47
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EGU24-16936
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ECS
Lorenzo G. Candioti, Chetan L. Nathwani, and Cyril Chelle-Michou

The modern view of magmatic systems includes transport and storage of melt at depths within the solid crust. Parameters that control the depths and duration of magma storage include the rheology (especially the depth of the brittle-ductile transition) and chemistry of the melt and solid, the crustal heat budget, and the tectonic setting. Understanding the large spatio-temporal variation in the magmatic output of volcanic arcs, therefore, requires consideration of solid deformation, melt transport, and chemical differentiation in transcrustal magmatic systems.

 

We present preliminary reactive transport models of transcrustal magmatic systems in the ductile limit. The model couples deformation of a compressible solid and Darcy-flow of melt through the solid matrix to phase equilibria calculations. The thermomechanical solver is self-developed in the Julia language and employs a matrix-free pseudo transient solution technique (e.g., Raess et al. 2022). Julia solves the two-language problem and allows for rapid transition from the development stage to massively parallelized production simulations. The thermomechanical two-phase flow equations are numerically discretized on 1D and 2D cartesian finite difference grids. Two different approaches of thermodynamic-thermomechanical coupling are implemented: (i) On-the-fly calculation of stable mineral phases using the Gibbs energy minimization software MAGEMin (Riel et al. 2022) and (ii) interpolation from a precompiled phase diagram.

 

MAGEMin is parallelized and shipped with a Julia wrapper. These features allow near seamless integration of thermodynamic calculations into the newly-developed geodynamic algorithm. The following workflow is applied: (1) Stable mineral phases are calculated at each numerical grid point as a function of local pressure and temperature values using MAGEMin. A starting bulk rock composition characteristic to arc magmas is used for the first time step. (2) The densities as well as the predicted major-oxide fractions of the solid and melt are used in the two-phase flow algorithm to solve for solid deformation, porosity evolution, and major-oxide transport. (3) The local major-oxide fractions predicted by the thermomechanical solver are used as new starting compositions in MAGEMin for the next time step. 

 

For the second approach, we compiled data from published fractional crystallization experiments at relevant pressure and temperature conditions. The data set contains the major-oxide fractions as well as calculated melt and solid densities. During the thermomechanical solution procedure, the data is interpolated from this phase diagram according to local pressure and temperature conditions at each grid point. A detailed comparison of the two approaches and potential implications for natural systems are presented.

 

 

References:

 

 

Räss, L., Utkin, I., Duretz, T., Omlin, S., & Podladchikov, Y. Y. (2022). Assessing the robustness and scalability of the accelerated pseudo-transient method. Geoscientific Model Development, 15(14), 5757-5786.

 

Riel, N., Kaus, B. J., Green, E. C. R., & Berlie, N. (2022). MAGEMin, an efficient Gibbs energy minimizer: application to igneous systems. Geochemistry, Geophysics, Geosystems, 23(7), e2022GC010427.

How to cite: Candioti, L. G., Nathwani, C. L., and Chelle-Michou, C.: Towards fully-coupled thermodynamic-thermomechanical two-phase flow models of transcrustal magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16936, https://doi.org/10.5194/egusphere-egu24-16936, 2024.

X2.48
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EGU24-133
Geochronology, petrogenesis and tectonic implications of Late Neoproterozoic gabbroic intrusions from the Taba-Nuweiba district, Sinai, Egypt
(withdrawn)
Mokhles Azer, Bassam Abuamarah, Paul Asimow, Jason Price, Mauricio Ibañez-Mejia, and Oliver Wilner
X2.49
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EGU24-3818
Christoph Beier, Simon Turner, Philipp A. Brandl, and Karsten M. Haase

Subduction zones are key regions of mass exchange between the Earth’s crust and mantle, and magmas in the sub-arc mantle form as a result of the release of volatiles from the subducting slab, i.e. fluid-flux melting. Introducing unique geochemical tracers (e.g., Large Ion Lithophile Elements) into the depleted mantle wedge allows tracing of the flow of material underneath the island arcs. Back arc spreading centres form as a result of slab-rollback, and here melts form due to decompression melting similar to those forming at mid-ocean ridges. Back arc systems situated angular to their adjacent island arc encompass a range of slab depths and provide a unique means to assess the compositional changes as a function of distance to the active arc and above the subducting slab. The Valu Fa Ridge (VFR), Eastern Lau (ELSC) and Central Lau (CLSC) spreading centres are situated at an increasing distance from the active Tonga arc from south to north. Here, we present new major, trace and volatile element data along with radiogenic isotope and U-Th-Ra disequilibria along the VFR and ELSC and across the VFR. A systematic change of, e.g., Ba/Nb, Nb/La, H2O contents and Pb isotopes with increasing distance between the back arc and the Tonga arc could be interpreted to reflect the slab-related metamorphic dehydration reactions. However, we do not observe a gradual change in geochemical compositions at a distance <100 km between the arc and the backarc, suggesting that the decompression and fluid-fluxed melting regimes overlap. At distances of >100 km between the arc and back arc, the occurrence of (230Th/238U) excess suggests that melting is due to decompression and that the systematic decrease in subduction influence observed with increasing distance is likely the result of melting of hydrous, ancient slab remnants during rollback. We conclude that the melting regimes between the ELSC and Tonga island arc separate at ~100 km total distance, as evident from the stepwise change in trace element and isotope geochemistry. The decrease in subduction-related signatures along the VFR and ELSC results from an overlap of the melting regimes and melt mixing between the arc and back arc in which the melting of the depleted mantle underneath the back arc becomes more prominent with increasing distance.

How to cite: Beier, C., Turner, S., Brandl, P. A., and Haase, K. M.: Fluid-flux versus decompression melting – the Tonga arc – Lau back arc system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3818, https://doi.org/10.5194/egusphere-egu24-3818, 2024.

X2.50
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EGU24-8392
Alp Ünal, Şafak Altunkaynak, and Daniel Nývlt

South Shetland Islands (western Antarctica) host widespread magmatism through the Meso-Cenozoic as a result of the subduction of the Phoenix plate along the South Shetland trench. With the logistical support of the Czech Antarctic Research Center and in-kind assistance from TÜBİTAK MAM Polar Research Institute, geological fieldwork was conducted on the Fildes Peninsula in order to understand the magma evolution beneath western Antarctica. This study presents preliminary results from field, petrographic and geochemical studies obtained from the volcanic and intrusive rocks in Fildes Peninsula- King George Island.

Fildes Peninsula represents the southwestern parts of King George Island which is located at the northeastern tip of the South Shetland Islands. The dominant lithologies in the study area are Paleocene- Eocene volcanic and intrusive rocks, with a minor presence of sedimentary rocks. The volcanic rocks cropping out on Fildes Peninsula are referred to as the Jasper Hill, Agate Beach, Block Hill and Long Hill formations. They mostly display similar compositions changing from basalt to basaltic andesite lavas and accompanied by pyroclastic rocks (tuffs and volcanic breccias). Intrusive rocks are composed of gabbro-micro gabbro stocks and diabase dykes. Petrographic investigations show that volcanic and intrusive rocks in the area mostly display disequilibrium textures such as sieve textures and embayments in plagioclase and pyroxenes, patchy and oscillatory zoning in different generations of plagioclases. Geochemically, all volcanic rocks show similar characteristics; they are represented by basic rocks that mostly display tholeiitic affinity. Their MgO and SiO2contents range from 3.04 to 6.18 and 44.80 to 48,47wt. %, respectively. The samples are slightly enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) compared to N-MORB and they display depletions in Nb and Ti elements which are the typical indicators of subduction zone magmatism. All volcanic rocks display low Y and high Sr/Y contents which are typical for adakites.  These adakites are specifically represented by “low-silica adakites” due to their low SiO2 (<48 wt. %). They also have low Zr and high Zr/Y abundances suggesting garnet in their source. These major- trace element characteristics and published Sr-Nd-Pb isotope compositions may collectively suggest that the adakites of Fildes Peninsula were originated from the partial melting of the mantle-wedge which was metasomatized by subduction processes along the South Shetland trench.

How to cite: Ünal, A., Altunkaynak, Ş., and Nývlt, D.: Source characteristics of the adakitic lavas and intrusions in Fildes Peninsula, King George Island (South Shetland Islands, Antarctica), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8392, https://doi.org/10.5194/egusphere-egu24-8392, 2024.

X2.51
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EGU24-12434
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Highlight
Olgeir Sigmarsson

The composition of MgO-rich basalt produced during the six-months long 2021 eruption at Fagradalsfjall, Reykjanes Peninsula, varied from those with low K2O/TiO2 and incompatible element contents to basalt enriched in incompatible elements with high K2O/TiO2 over a timespan of a month, explained by binary mixing of different mantle melts (Halldórsson et al., 2022). For the rest of the eruption, the basalt composition varied in a periodic manner as illustrated by long-lived radiogenic isotope ratios. For example, the periodicity of 87Sr/86Sr from early May to middle of September 2021 was 52 days, likely representing the time elapsed from the final melt mixing at depth (the moment of acquiring the measured isotope composition) until eruption at surface. Preliminary results on Th isotope ratios in the 2021 Fagradalshraun yield relatively high Th isotope ratios [(230Th/232Th) = 1.30] in the first lava emitted (the low K2O/TiO2 basalt) relative to basalt erupted at the end of the eruption [(230Th/232Th) = 1.18]. While this observation could be explained by slower mantle melting, excellent correlation between Th and Nd isotope ratios confirms the importance of binary mixing of melts from a depleted mantle source (with high Th and Nd, and low Sr isotope ratios) with melt(s) from enriched mantle lithology (having lower Th and Nd, and higher Sr isotope ratios) before magma ascent and eruption. Consequently, mantle heterogeneity, melt aggregations and mixing dominate the composition of the erupted basalt, rather than the duration of mantle melting. Correlation between Sr isotope ratios and time-averaged discharge rate indicate mantle source fertility control on the discharge rate during the 2021 eruption.  Both the 2022 and the summer 2023 eruptions started with a stronger discharge rate than that of 2021 and produced basalt of similar composition as that emitted in September 2021, interpreted as a result of an establishment of crustal magma accumulation zone since at the end of the 2021 eruption. Moreover, whether the exhaustion of the low K2O/TiO2 and 87Sr/86Sr magma reservoir led to the end of the 2021 eruption remains to be explored.

How to cite: Sigmarsson, O.: Basaltic magma dynamics during the 2021-2023 eruptions at Reykjanes Peninsula, Iceland, constrained by Sr, Nd and Th isotope ratios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12434, https://doi.org/10.5194/egusphere-egu24-12434, 2024.

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EGU24-20493
Ba-Mg isotopes in high Ba-Sr granites: implications for mantle mass transfer and crustal growth
(withdrawn)
Renzhi Zhu, Mike Fowler, Emilie Bruand, Fang Huang, Craig Storey, Xiaojun Wang, Lihui Chen, Jiyuan Yin, and Shaocong Lai

Posters virtual: Tue, 16 Apr, 14:00–15:45 | vHall X1

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 18:00
Chairpersons: Pascal Aellig, Adina E. Pusok, Nicolas Riel
vX1.21
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EGU24-15179
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ECS
Pan Hu

The origin and extent of crustal material in arc magmas are critical for tracing the crust-mantle interaction at subduction zones. Arc volcanic rocks often have a characteristic range of trace elements and isotopic compositions that constrain the influx of crustal material, such as hydrous fluids derived from slab dehydration, melts of the subducted plate's veneer sediments, or heterogeneous mélange. Especially, the traditional geochemical proxies struggle to investigate the contribution of tectonic melange into the enriched subarc mantle source. Lithium and molybdenum isotope compositions provide a potential means of tracing the different components to the mantle wedge in subduction zones.

Here, we report Li-Mo isotope compositions of the Fushui mafic complex in the Qinling orogen, central China, to trace their source nature and to constrain metasomatic component(s) transferred during the early Paleozoic subduction event. The Fushui mafic rocks exhibit typical arc-type trace element features and enriched radiogenic isotope compositions, suggesting a mantle source had incorporated subducted compenents. The Fushui rocks also exhibit a light Li isotope composition providing direct evidence for the contribution of dehydrated serpentinites and eclogite. The variable Mo isotope values further suggest the mantle source has been metasomatized by aqueous fluid and hydrous melt. This study, therefore, confirms the transportation of dehydrated oceanic plates from footwall to hanging wall and its critical role in the subarc mantle source. The interpretation provides a new perspective to study the recycling of subducted oceanic lithosphere and associated petrogenesis of arc magmatism.

How to cite: Hu, P.: Lithium and molybdenum isotope systematic for Fushui complex and implications for the recycled oceanic crust in the source of arc magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15179, https://doi.org/10.5194/egusphere-egu24-15179, 2024.

vX1.22
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EGU24-9011
Ömer Kamacı, Alp Ünal, and Şafak Altunkaynak

Tertiary migmatizations are pivotal events in the geologic history of the Menderes Massif, one of the world's most extensively studied core complexes. In northern Menderes Massif (Gördes Submassif) several granitic intrusions were emplaced into the migmatitic core rocks. They are mostly monzogranitic and granodioritic in composition and cut by associated pegmatitic dikes. These granitoids exhibit holocrystalline granular and porphyritic textures, characterized by plagioclase and, occasionally, biotite phenocrysts. The mineral composition of the granodiorites comprises 35–45% plagioclase, 30–35% quartz, 15–25% K-feldspar, and 5–10% biotite, with ± 5–8% muscovite. In contrast, the monzogranites are distinguished by a reduced plagioclase/K-feldspar ratio. Secondary phases include opaque minerals and sericite, with muscovite also observed. Accessory phases are zircon minerals. The granites exhibit an ASI index between 1 and 1.1, classifying them as slightly peraluminous I-type granites. They predominantly display high-K calc-alkaline characteristics and, less frequently, calc-alkaline nature. The Eu/Eu* ratio of these granites varies from 0.8 to 1.4. Trace element patterns suggest a possible derivation from basaltic and greywacke source rocks. Notably, high LaN/YbN ratios (reaching up to 107 ppm) and elevated Sr/Y ratios (up to 108 ppm) imply the presence of garnet or amphibole in the source. DyN/YbN and LaN/YbN ratios and their relationships specifically indicate the presence of garnet, rather than amphibole in the mafic source region. These data imply the crucial role of lower crustal melting in the formation of granitoids and the evolutionary history of the Menderes Core Complex.

How to cite: Kamacı, Ö., Ünal, A., and Altunkaynak, Ş.: Geochemical Implications for Tertiary Lower Crustal Melting in Northern Menderes Massif (Western Anatolia): Preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9011, https://doi.org/10.5194/egusphere-egu24-9011, 2024.