Aqueous salt solutions are the simplest systems in which to study multicomponent solidification with the mushy-layer growth [1]. The reactive melting/dissolution often leads to the formation of so-called chimneys, narrow channels devoid of solid through which the buoyant fluid escapes the mush. In sea ice, the channels provide the flux of saltier water into the ocean [2]. Tabular dunite bodies are believed to provide the evidence for channel formation due to the reactive dissolution of the partially molten mantle [3]. The channelized transport of volatiles is relevant for magma chamber evolution [4].

Modelling coupled with experiments play a crucial role in the investigation of mushy layers. Of importance is the relationship between the initial conditions, the cooling history and the evolution of the mush. The full model of transient evolution of a mushy layer with chimneys is too complicated even for numerical treatment ([5], [6]). To date, most of the theoretical studies focused on the steady-state mushy layers with constant growth rate. We aim at understanding some aspects of the evolution of the channelized mushy-layer convection related to the more realistic situations, namely finite extent of the domain and time-dependent cooling.

We report on a combined experimental and theoretical study directed to investigate the interaction of chimney convection and solidification in a binary fluid cooled from below. The experiments with aqueous ammonium chloride are conducted in a tank where temperature, concentration, and mush thickness have been monitored.  We quantify a solute flux between the mush and the liquid, and determine a relationship between the time-dependent cooling rate, the released potential energy, the porosity and the mush height, describing the temporal evolution of the system towards a steady state. To understand the behavior of the system, we develop a model of the evolution of the gross characteristics of the mush/liquid system, where the velocity of the fluid leaving the chimney is a function of the difference between the concentration in the liquid and the vertically averaged  concentration in the mush.

This research was funded by the Mobility Plus Project supported by the Czech Academy of Sciences (SAV-23-06) and the Slovak Academy of Sciences (CAS-SAS-2022-01). We thank J. Šimkanin for technical assistance with the experiments.

[1] Kumar, V., Sakalkale, K., Karagadde, S., Convection-induced bridging during alloy solidification. Phys. Fluids 34, 053605, 2022

[2] Anderson, D. M. and Guba P., Convective phenomena in mushy layers. Annu. Rev. Fluid Mech. 52, 93-119, 2020

[3] Rees Jones, D. W. and Katz, R. F., Reaction-infiltration instability in a compacting porous medium. J. Fluid Mech. 852, 5-36, 2018

[4] Annen, C. and Burgisser, A., Modeling water exsolution from a growing and solidifying felsic magma body. Lithos 402-403, 105799, 2021

[5] Wells, A. J., Hitchen, J. R. and Parkinson, J. R. G., Mushy-layer growth and convection, with application to sea ice. Phil. Trans. R. Soc. A 377, 20180165, 2019

[6] Katz, R. F. and Worster, M. G., Simulation of directional solidification, thermochemical convection, and chimney formation in a Hele-Shaw cell. J. Comput. Phys. 227, 9823-9840, 2008

How to cite: Kyselica, J. and Guba, P.: Channelized convection and solidification of a binary melt cooled from below: an experimental and theoretical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1928, https://doi.org/10.5194/egusphere-egu23-1928, 2023.

The Rhenish Massif in Central Europe, which includes the Eifel Volcanic Fields, has shown ongoing ground deformation and signs of possible magmatic activity. A buoyant plume with distributed partial melts exerting uplift forces at the bottom of the lithosphere has been proposed to explain the current deformation; the hypothesis that melt is accumulating in the crust or lithospheric mantle has not been explored yet. Here, we test deformation models in an elastic half space considering sources of varying aspect ratio, size and depth. We explore the effects of data coverage, noise and uncertainty on the inferred source parameters. We find that melt accumulation within the lithosphere cannot be ruled out if this emplacement occurs in sub-horizontal structures expanding at the rate of 0.045 km^3/yr. We discuss our results in the context of plume and underplating models worldwide and elaborate on what further observations may be needed to better constrain the structure of the Eifel magmatic system.

How to cite: Silverii, F., Mantiloni, L., Rivalta, E., and Dahm, T.: Lithospheric sill intrusions and present-day ground deformation at Rhenish Massif, Central Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6119, https://doi.org/10.5194/egusphere-egu23-6119, 2023.

The Campi Flegrei caldera is in an unrest phase, manifested by increasing ground uplift, seismicity and hydrothermal activity since 2005. The seismicity mainly involves the first 3 km below the main hydrothermal site of Solfatara-Pisciarelli, where an intensifying heating and pressurization phase is inferred by gas geothermobarometers. Geodetic data inversions generally localize the deformation source around this depth in the central sector of the caldera. Two driving mechanisms of magmatic and non-magmatic unrest have been proposed. Recent studies have demonstrated that the main magma storage area is localized at a depth of ~8 km and is periodically recharged by a mafic deeper source. Magmatic fluid transfer from these reservoirs toward the surface can occur through small-volume shallow intrusions, and can occasionally culminate in an eruption. In this frame, investigating the physical properties of subsurface rocks can be valuable to define the source of the current and past unrest. In fact, they can largely affect local stress and strength, controlling volcano dynamics. We explored subsurface rocks of the Campi Flegrei caldera, extracted from 3-km-deep exploratory geothermal wells. X-ray microtomography investigations were combined with in-situ mechanical experiments (4D imaging at room temperature and dry conditions) to characterize rock properties and link them with 3D microstructural changes. The cores were collected according to the most representative stratigraphic levels and are dominated by tuffs alternating with minor lavas. The mineralogical assemblage reflects different depth-dependent T-P conditions ranging from argillic alteration (150 °C) to thermometamorphism (350 °C). Their tensile strength varies between 2 and 15 MPa and shows a general increase with depth, suggesting that a similar excess pressure is required within a potential shallow chamber to drive magma transfer. Combining this preliminary data with correspondent elastic properties, it can be inferred that a volume change between 0.001 and 1 km³ is sufficient to cause rupture conditions in a sill with radius between 0.5 and 5 km, respectively. These results are in agreement with magma volumes erupted during past eruptions at Campi Flegrei caldera, and particularly consistent with volcanological and petrological data of products from small-scale events.

How to cite: Buono, G., Caliro, S., Chiodini, G., Giudicepietro, F., Maccaferri, F., Macedonio, G., Pappalardo, L., Pozzi, G., Spagnuolo, E., and Tramelli, A.: The influence of physical properties of crustal rocks on volcanic unrest at Campi Flegrei caldera, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11866, https://doi.org/10.5194/egusphere-egu23-11866, 2023.

The knowledge of the dynamic of the Campi Flegrei calderic system is a primary goal to mitigate the volcanic risk in one of the most densely populated volcanic areas in the world. From 1950 to 1990 Campi Flegrei suffered three bradyseismic crises with a total uplift of 4.3 m. After 20 years of subsidence, the uplift started again in 2005 accompanied by a low increment of the seismicity rate. In 2012 an increment in the seismic energy release and a variation in the gas composition of the fumaroles of Solfatara/Pisciarelli (in the central area of the caldera) were recorded. Since then, a slow and progressive increase in phenomena continued until today. We analyzed the Campi Flegrei seismic catalogue from 2000 and the main seismic swarms in order to look for any variation in the seismic parameters and compare them with other geophysical information. A remarkable correlation between earthquake cumulative number, CO/CO2 values and vertical ground deformation is evidenced. Moreover, the focal mechanisms show an agreement with the tensional stress induced by the caldera uplift. Most of the swarms and remaining seismicity delineate a highly fractured volume extending vertically below the Solfatara/Pisciarelli vents, where gases find preferential paths to the surface triggering earthquakes. The main swarms are located below this volume where the presence of a rigid caprock is still debated.

The correlation between the seismological, geochemical and geodetic observables can be interpreted in terms of injection of magmatic fluids into the hydrothermal system or its pressurization. The comparison between the geophysical information and the seismicity leads us to interpreted the current unrest in term of a gradual increment in the activity of the wide hydrothermal system whose most evident manifestation is the enlargement of the fumarolic field of Pisciarelli.

This contribution was funded by the MIUR project PRIN-2017 WZFT2p “Stochastic forecasting in complex systems” and by the INGV Project LOVE-CF.

How to cite: Tramelli, A., Giudicepietro, F., Godano, C., Ricciolino, P., Orazi, M., Caliro, S., De Martino, P., and Chiodini, G.: The seismicity of Campi Flegrei in the contest of the current unrest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12800, https://doi.org/10.5194/egusphere-egu23-12800, 2023.

The Campi Flegrei caldera (Italy) is one of the most dangerous volcanoes in Europe and is in a new phase of an unrest that has persisted intermittently for several decades. The geophysical and geochemical changes accompanying the unrest stimulated a number of scientific investigations that resulted in a remarkable production of articles over the last decade. However, large uncertainties still persist on the architecture of the caldera plumbing system and on the nature of the subsurface processes driving the current (and previous) unrest. LOVE-CF is a 4-years project started in October 2020 and funded by INGV, with the aim of improving our ability to forecast the behaviour of the restless Campi Flegrei caldera, through a multi-disciplinary approach based on a combination of volcanological, petrological, geochemical, seismological and geodetic observations, as well as experiments and numerical models. We aim at reconstructing a comprehensive view of the architecture and the dynamics of the plumbing system, through the investigation of representative past events, as a framework to interpret geochemical and geophysical changes observed during past and current unrests. This will allow us to better evaluate the source of the current volcanic unrest (magmatic or not magmatic) and to forecast its possible evolution towards an eruption. Merged petrological and geochemical results show the existence of a multi-depth magmatic system constituted by a shallow (150–200 MPa, corresponding to 6–8 km) felsic (trachyte-phonolite) storage area, recharged by a mafic (trachybasalt-shoshonite) deeper (>200 MPa, > 8 km) source. Model simulations of magma degassing show that the measured (N₂-He-CO₂) geochemical changes at the fumaroles of Solfatara hydrothermal site in the last decades are the result of massive (about 3 km³) magma degassing in the deep portion (≥200 MPa, >8 km of depth) of the plumbing system. This degassing mechanism would be able to flood the overlying hydrothermal system with hot magmatic fluids, thus heating and fracturing the upper crust inducing the shallow seismicity and deformation measured at the caldera.  Moreover, numerical simulations have been applied to model the actual deformation time series as well as those obtained by archeological data regarding quote variation since 35 BC until the last 1538 AD Monte Nuovo eruption. Results show that the combined activity of the magmatic fluids sources recognized at different depths can justify the ground deformation observed during the whole caldera history. 

How to cite: Pappalardo, L., Caliro, S., Tramelli, A., and Trasatti, E.: Linking surface Observables to sub-Volcanic plumbing-system:a multidisciplinary approach for Eruption forecasting at Campi Flegrei caldera (Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13708, https://doi.org/10.5194/egusphere-egu23-13708, 2023.

The structure of magma plumbing systems controls the distribution of volcanism and influences tectonic processes. Yet determining the structure of such plumbing systems is difficult because: (1) active intrusion networks cannot be directly accessed; (2) field outcrops are commonly limited; and (3) geophysical data imaging the subsurface are restricted in areal extent and resolution. Our current view is thus that plumbing systems are dominated by the vertical transfer of magma via dykes and/or some form transcrustal networks of conduits and reservoirs, extending from a melt source to overlying reservoirs and eruption sites. Whilst there is a wealth of evidence to support the occurrence of vertically dominated systems, field- and seismic reflection–based observations highlight that extensive lateral magma transport (over 10’s to 1000’s kilometres) may occur within mafic sill-complexes. Most mafic sill-complexes occur within sedimentary basins, but some intrude crystalline continental crust and volcanoes, and consist of interconnected sills and inclined sheets. Yet the extent to which active volcanic systems and rifted margins are underlain by sill-complexes remains poorly constrained, despite important implications to elucidating magmatic processes, melt volumes, and melt sources. Furthermore, questions remain as to how magma can travel through sill-complexes, across vast areas, without erupting or freezing. Here, we demonstrate how we can use geophysical data (particularly seismic reflection), tempered with geological structural, petrological, and chemical data, to map sill-complexes and understand their construction.

How to cite: Magee, C., Jackson, C., and Kopping, J.: Lateral magma flow in sill-complexes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13263, https://doi.org/10.5194/egusphere-egu23-13263, 2023.

Buoyant hydraulic fractures (HF) are a viable approach to model propagating magmatic intrusions in the lithosphere. Solutions for fully planar three-dimensional (3D) HF suggest the existence of a family of solutions as a function of fluid and solid properties [1]. Theoretically, such buoyant fractures ascent in a self-sustained manner if no heterogeneities exist.

We investigate the presence of a neutral buoyancy line (NBL) as a possible arrest mechanism of such buoyant self-sustained fractures. The NBL stems from a change in solid density and leads to a reversed buoyancy. In other words, the rock density in the upper layer is smaller than the density of the fluid, whereas the inverse is true in the lower layer (see figure 1). When a vertically propagating dike encounters this kind of heterogeneity, three outcomes are possible: The fracture can laterally spread along the NBL, arrest without lateral propagation and possibly initiate an intermediate magma chamber, or “burst” through the upper layer and become a feeder dike.

We focus on the first two possible outcomes and exclude the emergence of feeder dikes. Using numerical simulations, we delimit the conditions distinguishing the arrest from lateral spreading and characterize the transition from vertical to lateral dike propagation under various conditions.

Our simulations emphasize the dependence of lateral diking on the ratio between the total volume release and a limiting, minimal volume required for the emergence of self-sustained vertical dikes [2, 3, 4]. If the release volume is sufficient, the dike spreads laterally along the NBL. In the resulting horizontal intrusion, two-dimensional (2D) solutions of horizontal cross-sections in the viscosity- [5] and the toughness-dominated regime emerge. The emergence of the respective limits strongly correlates with the depth of the source magma chamber, a problem parameter we vary to compare simulation results with observations from lateral dike rifting intrusions. In particular, we discuss if these rifting sequences require a shallow, proximal to the NBL magma chamber or can originate from a deeper source as vertical dikes and then transition to lateral propagation.

Figure 1: Buoyant hydraulic fracture encountering a neutral buoyancy line.

References

[1] A. Möri and B. Lecampion. Three-dimensional buoyant hydraulic fractures: constant release from a point source. J. Fluid Mech., 950, A12, 2022.

[2] D. I. Garagash and L. N. Germanovich. Gravity driven hydraulic fracture with finite breadth. In Proceedings of the Society of Engineering Science 51st Annual Technical Meeting, 2014.

[3] D. I. Garagash and L. N. Germanovich. Notes on propagation of 3D buoyant fluid-driven cracks. arXiv:2208.14629, 2022.

[4] T. Davis, E. Rivalta, and T. Dahm. Critical fluid injection volumes for uncontrolled fracture ascent. Geophys. Res. Lett., 47, 14, 2020.

[5] J. R. Lister. Buoyancy-driven fluid fracture: similarity solutions for the horizontal and vertical propagation of fluid-filled cracks. J. Fluid Mech., 217:213–239, 1990.

How to cite: Möri, A., Garagash, D., and Lecampion, B.: Transition from Vertical to Lateral Diking at the Neutral Buoyancy Line, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15623, https://doi.org/10.5194/egusphere-egu23-15623, 2023.

The Ditrău Alkaline Massif (DAM; Eastern Carpathians, Romania) is a unique pluton with a presently tilted vertical cross-section of a pre-existing alkaline magma storage system, which consists of various rock types from ultramafic cumulates to granitoid rocks, crosscut by lamprophyre, syenite, ijolite and tinguaite dykes. The igneous event took place in an intra-plate, rift-related tectonic environment during the Middle–Late-Triassic.

During the roughly 190 years of scientific exploration of the DAM, felsic rocks were considered as homogeneous, uniform units of the massif. However, recently identified structural, textural and geochemical features revealed open-system magmatic processes that operated during the crystallization of the DAM (e.g., Batki et al., 2018). The heterogeneity of the felsic rocks can only be revealed on micro-scale and is mostly determined by the presence of mafic mineral aggregates. However, felsic minerals are also characterised by disparate microtextural traits. The felsic rocks in the northern part of the DAM were classified into two groups based on their field occurrence and microtextural features: (1) felsic rocks (lacking or containing scant mafic phases) spatially related to mafic rocks and (2) felsic rocks (with mafic minerals and clusters) spatially unrelated to mafic rocks (Kiri et al., 2022).

Distinct attributes (e.g., idiomorphic–hypidiomorphic feldspars aligned parallel to their crystal faces, contact melting and embayment, feldspar aggregates) of Group 1 suggest the settling and accumulation of the rock-forming minerals. Such textural features can also be observed in Group 2. Isolated mafic phases are scant in rocks of the latter group; however, different variants of clusters containing identical or different mafic minerals are prevalent. There are other particular textural properties: feldspar megacrysts, adjacent feldspars with contrasting zoning sequences and biotite clusters in the metamorphic country rock and xenoliths.

The formation of mafic clusters could be associated with: (1) mineral accumulation, (2) magma mixing–mingling and (3) entrainment of exotic (crustal or restitic) materials. Petrologic and geochemical evidences of such processes have already been reported from the DAM (e.g., Batki et al., 2018). Some of the clots are polycrystalline pseudomorphs after antecrysts and/or xenocrysts (e.g., clinopyroxene, green amphibole, garnet) that were entrained by the interplay between different magma batches or by country rock contamination. All cluster varieties revealed a transition from fresh aggregated crystals through imperfect to complete replacement. Hence, disparate clots could imply different phases of hybridisation of the incorporated materials.

Micro-scale characteristics of felsic crystal accumulation, mafic clusters and flow fabrics as well as metamorphic wall rock xenoliths indicate that the studied rocks were formed under dynamic magmatic circumstances. Crystal settling, shear flow, convection, along with numerous open-system igneous processes (e.g., magma mixing and mingling, magma recharge, crystal/mush transfer and recycling, wall rock assimilation) played an important role in the petrogenesis of the felsic suite of the DAM.

References

Batki, A., Pál-Molnár, E., Jankovics, M.É., Kerr, A.C., Kiss, B., Markl, G., Heincz, A., Harangi, Sz. (2018). Lithos, 300–301, 51–71.

Kiri, L., Szemerédi, M., Pál-Molnár, E. (2022). Central European Geology, 65, 1, 49–76.

How to cite: Kiri, L., Szemerédi, M., and Pál-Molnár, E.: Petrographic traces of open-system magmatic processes in the felsic suite of the Ditrău Alkaline Massif (Eastern Carpathians, Romania), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1158, https://doi.org/10.5194/egusphere-egu23-1158, 2023.

Rate of magma transfer and differentiation processes can be estimated from radioactive disequilibria between radionuclides in the ²³⁸U-chain if the mechanism that fractionate the nuclides can be constrained. Once constrained, the variable half-lives of the radionuclides allow to restrict the time elapsed from the fractionation. Over the last centuries, eruptions from Mt. Hekla have terminated with emission of phenocryst-poor Fe-rich basaltic andesite (or icelandite) of uniform composition, produced by approximately 50% fractional crystallisation from basalt. The crystallising mineral assemblage is composed of 8-13% olivine, 34-40% clinopyroxene, 32-41% plagioclase (An_50-65) og 15-17% Fe-Ti oxides (Sigmarsson et al., 1992; Chekol et al., 2011).

Both ²³⁸U-²³⁰Th disequilibria and Th isotope ratios are identical in the basaltic andesite and basalt erupted around the volcano consistent with magma differentiation by fractional crystallisation. Modest radioactive disequilibrium is observed between thorium and radium that decreases from the basalt to the basaltic andesite with (²²⁶Ra/²³⁰Th) from 1.16 to 1.01. Such a decrease may represent decay of ²²⁶Ra (T_1/2: 1600 yrs) if the fractional crystallisation took longer than 200 years, which is the minimum time for measurable effect of ²²⁶Ra disintegration. On the other hand, if Ra enters the extracted mineral phases, the time of fractionation would be much shorter.

Radium is an incompatible element which concentration increases with magma differentiation. Its bulk partition coefficient (D_Ra; min-melt)) between the minerals fractionating and the derived melt can be estimated from the variations of Ra and Th concentrations as 0.12 ± 0.03. Since Ra only enters plagioclase of the fractionating mineral assemblage, the plagioclase D_Ra (plag-melt) is 0.12/0.4 = 0.3. Melting experiments result in partiioning of Ra between plagioclase and melt close to 0.3 for An₅₀ plagioclase (Fabbrizio et al., 2009), consistent with measured Ra and Th variations in Hekla lavas. Consequently, the lower (²²⁶Ra/²³⁰Th) in the basaltic andesite is fully explained by plagioclase fractionations on a timescale significantly shorter than 200 years.

Radium disintegrates to ²²²Rn, which in turn decays with a half-life of only 3.8 days to ²¹⁰Pb. The volatile behaviour of the inert gas Radon is thus the main fractionation process generating ²²⁶Ra-²¹⁰Pb disequlibrium, whereas the D (min-melt) for Pb and Ra is comparable. Hence, outgassing or accumulation of gas containing Radon is an effective fractionation mechanism on a short timescale causing Ra-Pb disequilibria that can be studied for approximately a century. Indeed, the first emitted tephra of the last Hekla eruptions display excess ²¹⁰Pb over ²²⁶Ra suggesting volatile accumulation in a hermetic magma chamber explaining the initial explosive character of Hekla eruptions (Garance and Sigmarsson, 2023). Taken together, U-series disequilibria suggests that magma residence and transfer to surface occurs on a decadal timescale beneath Hekla volcano with important role for gas accumulation in the basaltic andesite affecting the repose time between eruptions.

References

Chekol et al. 2011

Fabbrizio et al. 2009

Hervé and Sigmarsson 2023

Sigmarsson et al. 1992

How to cite: Sigmarsson, O.: Magma residence and transfer rate from U-series disequilibria: the case of Hekla volcano, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9046, https://doi.org/10.5194/egusphere-egu23-9046, 2023.

All magmas form crystals upon cooling and volatile loss, following shifts in the melt liquidus during both decompressive ascent and eruption. Crystallisation modifies the melt chemistry and adds solid particles (crystals) in suspension in a magma. Both changes increase the bulk viscosity of the magma, potentially affecting the final eruptive style. Hence, it is crucial to understand the complete evolution of viscosity in a magmatic system in order to properly constrain its role in the evolution of a magma from depth to surface.

Here we measured the viscosity of magma feeding five events of lava fountaining at Etna volcano, Italy, during a period of seven months in 2021. All measurements were performed using remelted lapilli samples of trachybasalt composition (47-48 wt.% SiO₂, 5.37-5.78 wt.% Na₂O+K₂O), originally collected during or immediately after each explosive event. Rheology analyses were performed at superliquidus conditions between 1198-1490°C in a concentric cylinder rheometer. The results show low viscosity variations - up to 0.14 log units at 1198°C - in time among the explosive events. These results are consistent with calorimetric analyses performed in both the remelted and natural samples. Additionally, pre-eruptive crystal contents vary between 21-53% of mainly clinopyroxene, plagioclase, olivine and orthopyroxene, as well as some oxide minerals, while interstitial melt compositions show an enrichment of up to 7 wt.% in SiO₂ and more than 2 wt.% in Na₂O+K₂O after microlite crystallisation, which affects the magma bulk viscosity. Further analyses will help constrain such evolution of magma bulk viscosity. These results help to better constrain the minimum viscosity for the pre-eruptive magmas, as well as the shifts in bulk viscosity that the magmas experienced during ascent and eruption before quenching in air, potentially affecting the eruptive behaviour.

How to cite: Cáceres, F., Taddeucci, J., Colombier, M., Terán, J., Flores, J., Hess, K.-U., Vossen, C. E. J., and Dingwell, D. B.: The rheology of magma feeding the February-September 2021 lava fountains at Etna volcano (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17320, https://doi.org/10.5194/egusphere-egu23-17320, 2023.

The Garrotxa Volcanic Field (GVF) is one of the monogenetic Quaternary volcanic fields associated with the intraplate European Cenozoic Rift System. The GVF is located between the cities of Olot and Girona, NE Spain, and it covers an area of about 600 km². This volcanic field ranges in age from 0.7 Ma to early Holocene and is considered active since the last eruption dated 11,000-13,000 years ago.

The volcanic activity, mainly controlled by regional normal faults generated during the Neogene extension, was highly variable with over 50 scattered eruptive vents that were produced during short-lived monogenetic eruptions. Scoria cones represent the most common landforms of the GVF with subordinate maars and tuff rings/cones. Most of the volcanoes are located in the northern sector between the towns of Olot and Santa Pau and they stand on a folded Eocene basement. Volcanoes located in southern area of the field, close to the city of Girona, stand mainly on a fractured Paleozoic basement.

The objective of this work is to identify eruptive processes and the geomorphic evolution of volcanic edifices and related them to environmental influencing factors. The best volcanic structures in the GVF have been selected due to their well-preserved morphologies. Cones (W_co) and craters (W_cr) mean diameters, as well as cones maximum height (H_max), maximum crater depth (D_crmax) and external slope of the cones (S_median) have been measured.

This study shows that it is possible to create a catalogue of likely eruption sequences based on field evidences and morphological/morphometric data. In this way, a more realistic eruption scenarios can be developed for different parts of the volcanic field. Morphometry can also provide rough relative age constraints on edifices. These methodologies can improve our understanding for a better evaluation of volcanic hazards in urbanized volcanic fields as the GVF.

How to cite: Pedrazzi, D., Cerda, D., Granell, J., Kerestzuri, G., Geyer, A., Planagumà, L., Martí, J., and Bolós, X.: Eruptive processes and landforms recognition in the Garrotxa Volcanic Field, Iberian Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8444, https://doi.org/10.5194/egusphere-egu23-8444, 2023.

Except in migmatite complexes, well-displayed field evidence of the possible physical behaviour of magma-crystal mush-solid rock systems is quite uncommon. Tonalites from Capo Vaticano Promontory, making up the oldest and deepest granitoid unit of the c. 13 km-thick late Variscan Serre Batholith, show outstanding examples of magma-mush interaction, at the transition with both underlying migmatite host rocks and overlying porphyritic granodiorites. Basal tonalites exhibit varying stages of interaction with garnet-bearing or garnet-free granitic magma produced by melting of the metapelitic migmatites after tonalite intrusion. Initial stages are characterized by infiltration of the granitic magma through the mushy tonalite along irregular channels, then forming an interconnected network of cm- to dm-wide channels. In some outcrops with high volumetric proportions of granitic magmas, peculiar hybrid rocks, characterized by pervasive intermingling of granite and tonalite, occur as the result of cm-scale disaggregation of the mushy tonalites.  In other outcrops, evidence of interaction between a crystal-poor tonalitic mush and the granitic magma is only provided by the occurrence of large peritectic garnet in apparently homogeneous tonalite. At the roof of the tonalitic unit, emplacement of the overlying porphyritic granodioritic magma involved displacement of the mushy tonalite, with local disaggregation in rounded blocks up to 1.5 meter in size. Compared to the basal tonalites, such evidence indicates a more rigid state of the roof tonalites at the time of granodiorite emplacement, even though rare occurrence of hybrid rocks testifies for possible mixing processes also between the granodioritic magma and mushy tonalite. Finally, an outstanding field evidence of the physical behaviour of mush systems, with significant implications for the mechanisms of magma differentiation, is given by mechanical accumulation of K-feldspar megacrysts at a place where the granodioritic magma was intruding the mushy tonalite, but only the liquid part of the magma was able to pass through, depicting a clear filter-press mechanism. This preliminary work aims to contribute to the general understanding of the evolution of mushy regions by presenting some outstanding examples of magma-mush interactions taking place during the construction of the deep-intermediate levels of the Serre Batholith (depth of c. 20-17 km depth), as a base for further in-depth multidisciplinary investigations.

How to cite: Fiannacca, P., Russo, D., Fazio, E., Fiducia, D., Merlo, R., and Cirrincione, R.: Magma-mush interaction at the base of a post-collisional batholith: field evidence from Capo Vaticano Promontory granitoids (Calabria, southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9102, https://doi.org/10.5194/egusphere-egu23-9102, 2023.

La Palma is one of the youngest and the most active island of all the Canary archipelago, with a total of seven subaerial eruptions over the last 500 years. This magmatic activity is linked to the undergoing growth and development of the youngest volcanic complex in the island: the Cumbre Vieja edifice, a 20 km long and 1950 m high, north-south trending ridge with aligned volcanic cones and fissures forming its summit and flanks. The youngest of them is the Tajogaite volcanic vent, which is located in the western flank of the Cumbre Vieja ridge, and was built up by a mainly strombolian eruption from 19^th September to 13^th December 2021. The first erupted, clinopyroxene-amphibole-phyric tephrite lavas, are more evolved in composition than the subsequent clinopyroxene-olivine-phyric basanite flows, in a pattern resembling those described from the two former eruptions in Cumbre Vieja: Teneguía (1971) and San Juan (1949). Furthermore, the detailed study of lava samples from the Tajogaite volcano reveals not only a drastic change in mineralogy, from amphibole-rich to olivine-rich lavas, but also the existence of complex textures and chemical zoning patterns including: 1) different olivine crystal populations, with and without disequilibrium textures (reverse zoning trends; reaction rims or coronae); 2) sodium-rich corroded clinopyroxene cores -with occasional titanite inclusions- overgrown by oscillatory zoned euhedral rims in equilibrium with groundmass; 3) a range of oxide mineral compositions from magnetite to chromite and spinel and, 4) the occurrence of early, nickel-bearing sulphides as inclusions in clinopyroxene. All these features record the interaction between ascending primitive mantle magmas and, at least, one shallow reservoir where differentiation had already taken place leading to iron, alkalis and water enrichment. This kind of interaction probably triggered the onset of the eruption, and could also be responsible for episodic phreatomagmatic activity pulses during the whole length of the volcanic process.   

How to cite: de Ignacio, C., Real, E., Martín-Crespo, T., Gómez-Ortiz, D., Martín-Velázquez, S., Arnoso, J., and Montesinos, F.: Equilibrium-disequilibrium textures and mineral chemistry of lavas from the Cumbre Vieja 2021 eruption, La Palma, Canary Islands, Spain: insights into magma plumbing systems under intraplate ocean islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16267, https://doi.org/10.5194/egusphere-egu23-16267, 2023.