We collected samples from the lava flows from the Cumbre Vieja 2021 eruption, the 1677 San Antonio eruption and picrites from the 3 Ma old Taburiente calderaand in La Palma (Canary Islands) with the aim to investigate the geochemistry of the lavas and their He and CO2 isotopic composition in fluid inclusions. The above information is crucial to better understand the evolution in time of the volcanic system and the nature of the local mantle source.

Our results suggest that during the Cumbre Vieja eruption there was a systematic increase in the volatile concentrations (particularly He and CO₂) between late September and early October. The above is accompanied by an increase of the whole rock Mg#, CaO/Al₂O₃ and the Nb/La ratios from 50.5 to 58.7, from 0.78 to 0.87, and from 0.88 to 1.01, respectively (we also observed that these variations coincide with the occurrence of deeper earthquakes; 30-40 km; D’Auria et al., 2022), which likely indicate the intrusion of a more primitive less-degassed magma rising from the asthenosphere at the end of September. Regarding the mineral chemistry, the composition of olivine and pyroxene do not show any noticeable heterogeneity in all analyzed samples. The ³He/⁴He ratios are homogeneous over time and exhibit MORB-like signatures between 7 and 7.5 Ra. In comparison the whole rock composition and the ³He/⁴He ratios of the San Antonio lavas are very similar to the lavas erupted in late October-early November 2021, whereas the picritic lavas from the Taburiente caldera show higher ³He/⁴He ratios equal to 9.4±0.1 Ra that are comparable with the signatures measured in the Dos Aguas cold spring (Pérez et al., 1994; Padrón et al., 2022) indicating plume origin.

In conclusion, the He isotopic differences between lavas form northern and southern La Palma could be advocated to the small-scale heterogeneities in the mantle, and/or a plumbing system responsible for the lower ³He/⁴He of the 2021 Cubre Vieja magmas.  Moreover, considering the more radiogenic helium ratios reported in mantle xenoliths from La Palma (6.5 - 7.2Ra; Sandoval Velasquez et al., 2022) we propose that the isotopic signatures observed at Cumbre Vieja and San Antonio are likely the result of a mixing between a plume component (highlighted by the ³He/⁴He in the picrites and the Dos Aguas Spring of the Taburiente caldera) and a more radiogenic reservoir located in the shallower lithospheric mantle.

How to cite: Sandoval-Velasquez, A., Rizzo, A. L., Casetta, F., Ntaflos, T., Aiuppa, A., Alonso, M., Padron, E., Pankhurst, M., Mundl-Petermeier, A., and Perez, N. M.: The 2021 Cumbre Vieja eruption (La Palma, Canary Islands): new perspectives on the geochemistry of lavas and noble gases isotopes trapped in fluid inclusions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14572, https://doi.org/10.5194/egusphere-egu23-14572, 2023.

The Southalpine tectonic domain hosts numerous magmatic manifestations related to the trachybasaltic to trachyandesitic magmatic event that shaped the area during the Ladinian age (Middle Triassic). The identification of systematic compositional zoning patterns in the clinopyroxene population among volcanic products allowed us to unravel the architecture and dynamics of the feeding systems of the main magmatic centres from the Dolomites (Southern Alps; Italy) that remained unknown until now.

The recurrent zonation consists of different step zoning patterns between lower Mg# and Cr2O3 contents (Mg# 67-77; Cr₂O₃<0.1 wt%) augitic composition and high-Mg# and Cr2O3-rich diopsidic parts (Mg# 78-91; Cr₂O₃ up to 1.2 wt%). The diopsidic domain appears to a lesser extent and is more frequently present as a variable thick single or multiple bands between augitic cores and rims. It could be documented in cores as resorbed or mottled. Oscillatory zoning and sector-zoned crystals are also present in minor numbers.

Thermometric calculations reveal that the diopsidic domain delivers an equilibrium temperature that ranges from 1143 to 1204°C, remarkably higher than the temperature calculated from the augitic domain which ranges from 966 to 1150°C. Since the barometric computation show the same range of pressure for both compositional domains (120-400 MPa), our proposed model involves periodic mafic recharge pulses of primitive and hot basaltic magma into a crystal mush in the shallower portion of the plumbing system (4-14 km) that led to the formation of the high-Mg# domain within the already formed augitic crystals. These new results support the model proposed for the Cima Pape volcano-plutonic complex (Nardini et al., 2022) and extend it also to the other Dolomitic centres.

Diffusion chronometry computations based on Fe–Mg diffusion in clinopyroxene have been applied to evaluate the residence times for the crystals in each compositional zone with the NIDIS model (Petrone et al., 2016). Computations have revealed a time span from injection to eruption from short timescales (less than a year) to decades with variation between the different systems considered. Further studies are requested to better constrain the timing of each feeding system in the Dolomites, and this will enable an extremely detailed description of the dynamics that fueled the Middle Triassic magmatism in the Southalpine domain. Our final aim is to discuss this ancient magmatism as a proxy for active volcanic complexes thanks to the forthcoming analysis of the outcropping plutonic counterparts, impossible to do in an active system, making this part of the Alps a volcanological laboratory for testing the approaches/models currently adopted for active volcanoes.

References

Nardini, N., Casetta, F., Ickert, R. B., Mark, D. F., Ntaflos, T., Zanetti, A., & Coltorti, M. (2022). From the Middle Triassic Cima Pape complex (Dolomites; Southern Alps) to the feeding systems beneath active volcanoes: Clues from clinopyroxene textural and compositional zoning. Journal of Volcanology and Geothermal Research, 422, 107459.

Petrone, C. M., Bugatti, G., Braschi, E., & Tommasini, S. (2016). Pre-eruptive magmatic processes re-timed using a non-isothermal approach to magma chamber dynamics. Nature communications, 7(1), 1-11.

How to cite: Nardini, N., Casetta, F., Petrone, C. M., Coltorti, M., and Ntaflos, T. N.: Magma recharge dynamics in Middle Triassic volcanoes: features and timing of Ladinian feeding systems in the Dolomites (Southern Alps; Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14606, https://doi.org/10.5194/egusphere-egu23-14606, 2023.

Homogeneous and heterogeneous nucleation are two important mechanisms of mineral formation. Heterogeneous nucleation is theoretically more favourable because it requires overcoming a lower energetic barrier, and is thus supposed to be the prevalent nucleation mechanism during magma crystallisation and crystal cluster formation. However, it remains challenging to identify whether a given crystal population is formed by homogeneous or heterogeneous nucleation.

Here we present results that allow us to reconstruct the nucleation mechanism of titanomagnetite (Tmt) crystals formed alongside dendritic clinopyroxene (Cpx) from a synthetic trachybasaltic melt (with 2 wt.% added H₂O) in crystallisation experiments carried out in a piston-cylinder apparatus at a constant pressure of 4 kbar. After 30 minutes of superheating at 1300°C, the samples were cooled at a rate of 80°C / min to the final resting temperatures of 1150°C and 1100°C. These temperatures correspond to a respective undercooling (∆T expressed as T liquidus – T experiment) of 30° and 80°. The dwell times at these temperatures were 30 minutes and 8 hours, respectively.

High-resolution synchrotron X-ray computed microtomography (µCT) and subsequent 3D image processing and analysis allow to discriminate three main Tmt populations: a) Tmt grains > 100 µm in size, skeletal in shape, and mostly isolated in the melt (population 1); b) Tmt grains between 2 and 100 µm in size, anhedral in shape, and always decorating Cpx grain surfaces (population 2); c) Acicular Tmt grains almost completely enclosed within Cpx grains (population 3).

The 3D spatial distribution of the centroids of the Tmt grains was employed to understand if the grains of the different populations are randomly distributed, ordered, or clustered, using the pair correlation function g(x). Tmt grains of population 1 have g(x) near 1, a sign of an ordered point pattern. We attribute this to a homogeneous nucleation origin. Populations 2 and 3 have peak g(x) values up to 1.5 at interpoint distances between 10 and 30 µm, denoting strong clustering at these distances. We attribute this to heterogeneous nucleation of Tmt on Cpx, which is corroborated by 3D microstructure and the relationship between Tmt grains and compositional zoning of Cpx.

Electron backscatter diffraction analysis enables us to clarify the crystallographic relationships between Cpx and nearby Tmt crystals. More than 85% of the Cpx-Tmt boundary length in Tmt populations 2 and 3 follow a crystallographic orientation relationship (COR). This strongly points to formation by heterogeneous nucleation of Tmt on top of Cpx grains for these populations. Single grains in Tmt population 1 which touch Cpx crystals show a COR with Cpx less frequently (cpx-tmt boundaries sharing a COR are <60%, confirming that at least some proportion are the result of homogeneous nucleation. Population 1 Tmt with CORs may represent large heterogeneously nucleated grains or potentially reflect Tmt-Cpx interaction after nucleation.

In conclusion, multiple, potentially simultaneous Tmt nucleation events led to observable differences in microstructure, clustering, and CORs that enable the crystallisation process to be reconstructed.  

Funded by the Austrian Science Fund (FWF): P 33227-N

How to cite: Peres, S., Griffiths, T., Colle, F., Iannini Lelarge, S., Masotta, M., Pontesilli, A., and Mancini, L.: Homogeneous and heterogeneous nucleation in synthetic trachybasalts: microstructural evidence from Titanomagnetite crystals of different populations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15129, https://doi.org/10.5194/egusphere-egu23-15129, 2023.

The formation of bubbles in magma in response to changes in pressure and temperature exerts a fundamental control on magma properties (Coumans et al., 2020). As contemporary models of magma chambers have moved away from the ‘liquid tank’ towards a model of a mush zone comprising a mix of solids and melt, it is important to understand better how magma cam be mobilized from a mostly crystalline matrix (Maguire et al., 2022). Here we propose that in-situ bubble formation may be a key driver.

Deformation of a packed, congested magma slurry with melt fraction below around 20% can result in Reynolds dilation of the granular skeleton. Where this happens, the coordination number (Z), defining the minimum number of grain contacts, drops as intergranular space is created. The corresponding pressure drop in the interstitial melt phase for a mush of thickness H with a position-dependent permeability can be estimated as a function of variable strain rate (Petford et al., 2020). For expediency, previous work in dilating magmas regarded the melt phase as incompressible, with the caveat that compressibility could be added as an important refinement to modified Biot’s equations for poro-elasticity. 

We present here initial results combining estimates of melt pressure drop in dilating mafic and silicic magmas with estimates for bubble nucleation and growth derived from experiments and numerical modelling. Using appropriate elastic constants (shear and bulk moduli) and particle diameters (1-5 mm) for mixtures of olivine, plagioclase and quartz, order-of-magnitude comparisons suggest that in-situ deformation of congested granular magma can result in pressure drops in the range 5-10 MPa, consistent with bubble formation (Coumans et al., 2020; Hamling & Kilgour, 2020), provided the local shear strain rate exceeds 10^-10 s^-1.

In-situ pressure drops of this magnitude are equivalent to instantaneous transport of the melt phase several hundreds of metres upwards from their resting level and is enough to trigger bubble formation and growth if certain conditions are met. This solid-fluid coupling offers a novel way to explore how bubble nucleation and growth mechanisms change over time in response to shear-induced (local) variations in melt pressure and should be considered an additional mechanism for promoting instability in crustal mush zones.

References

Coumans, JP, Llewellin, EW, Wadsworth, FB, Humphreys, MCS, Mathias, SA, Yelverton, BM, Gardner, JE, (2020). An experimentally validated numerical model for bubble growth in magma. J. Volc. Geothermal. Res. 402. 107002.

Hamling, IJ, Kilgour, G, (2020). Goldilocks conditions required for earthquakes to trigger basaltic eruptions: Evidence from the 2015 Ambrym eruption. Science 6, doi: 10.1126/sciadv.aaz5261.

Maguire, R, Schmandt, B, Li, J, Chengxin, J, Guoliang, Li, Justin, W, Chen, M, (2022).  Magma accumulation at depths of prior rhyolite storage beneath Yellowstone Caldera, Science, 1001-1004 doi:10.1126/science.ade0347.

Petford, N, Koenders, MA, Clemens, JD, (2020). Igneous differentiation by deformation. Contrib. Min. Pet. 5, 1-21.

How to cite: Petford, N. and Llewellin, E.: Dilatancy and in-situ bubble formation in poro-elastic granular magma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2081, https://doi.org/10.5194/egusphere-egu23-2081, 2023.

The climate-controlled variations of the glacio-lithostatic load in glaciated terrains can potentially affect the tempo of volcanic eruptions, by modifying the pressure conditions acting on the underlying plumbing system. During glacial periods, increasing ice load hinders magma eruption, thus leading to prolonged residence time in the crust. This allows the magma to crystallise, differentiate and accumulate volatiles over a longer time span with respect to non-glacial periods.

In Antarctica, volcanism in glaciated regions has been acting since the Miocene. In detail, in northern Victoria Land, volcanoes are located either in attenuated or thick cratonic lithosphere. Among the volcanic edifices built on thick crust, the quaternary Pleiades Volcanic Complex (PVC) is made up of some 20 monogenetic, partly overlapping scoria and spatter cones, that erupted over the last 900 ka. The erupted products range in composition from hawaiite to trachyte, defining a complete mildly Na-alkaline differentiation trend, which is quite unusual among alkaline monogenetic volcanic fields.

Six samples from the PVC, representative of the whole differentiation trend, have been investigated by means of electron microscopy, electron microprobe and laser ablation ICP-MS. The parageneses of the rocks includes dominant feldspar and clinopyroxene with minor olivine. The mafic phenocrysts are characterised by significant resorption textures: specifically, the olivine presents deep embayments with absence of compositional zoning, while clinopyroxene frequently shows spongy texture and compositionally zoned mantle and rims, often with patchy and convoluted patterns.

Petrography, textures and mineral chemistry suggest that the magma experienced first a rapid decompression, followed by a prolonged residence time, likely supported by increased ice load. During this time interval, resorption of the early formed mineral phases occurred, probably also enhanced by crustal assimilation processes, coupled with re-crystallization under isobaric conditions. Moreover, the prolonged residence time, coupled with the occurrence of (multiple) magma recharge(s) caused the mixing of a basaltic magma with other differentiated magmas stalling in the plumbing system, yielding to the formation of intermediate magma compositions. Finally, magma refilling of the plumbing system during an ice loss period, favoured the eruption. Machine-learning based thermo-barometric estimates consistently indicate crystallization of clinopyroxene at transcrustal pressures, ranging from the crust-mantle interface (early crystallization) to shallow crust (late crystallization in a shallow plumbing system under glacial load).

How to cite: Rocchi, I., Tomassini, A., Masotta, M., Petrelli, M., Ágreda López, M., and Rocchi, S.: Evolution of a plumbing system under the influence of variable ice load - The Pleiades volcanic complex, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12546, https://doi.org/10.5194/egusphere-egu23-12546, 2023.

The crustal feeding systems under volcanoes like Toba caldera in Sumatra remain largely unknown due to the lack of existing seismic arrays and consistent effort to apply advanced imaging techniques. Even if they were obtained, the interpretation of seismic anomalies in terms of melt content and geochemical differentiation would remain largely speculative without a framework that allows the connection between seismic attributes and petrophysical properties.

We collected data from existing seismic arrays across Sumatra and applied ambient noise and earthquake tomography techniques. We used thousands of dispersion curves spanning both the shallow crust and the upper mantle using SeisLib¹, the first open-access Python package for surface-wave tomography. We inverted the dispersion curves for phase-velocity maps at different periods, using a linearized-inversion algorithm based on the ray theory with a roughness damping constraint and an adaptive parameterization. Our results show low-velocity and high-attenuation sill-like structures under most of the northern and central portions of Toba calderas. We used the shear-wave velocity model as data and additional volcanological and geophysical data as constraints for a Bayesian inversion of magmatic composition and melt content under Toba. The forward model is provided by the MAGEMin³ code, which uses a Gibbs energy-minimization solver coupled with geological, geophysical, and volcanological information to identify portions of the crust where mafic sills are located. The Bayesian inversion quantifies from the melt content within the sill-like structures to the characteristics of the caprock overlaying them. It confirms the existence of a deep extended mafic sill reaching depths up to 12 km, currently disconnected from similar pockets of melt underneath the Toba lake stalling at a similar depth.

By coupling seismic and thermodynamical modeling, we invert for (petro)physically-constrained quantitative images of the current state of a volcano. These images provide a cornerstone for a temporal description of volcanological responses based on physical modeling.

• 1) Magrini, Fabrizio, et al. "Surface-wave tomography using SeisLib: a Python package for multi-scale seismic imaging" Geophysical Journal International (2022). ggac236, https://doi.org/10.1093/gji/ggac236.
• 2) Riel, Nicolas, et al. "MAGEMin, an efficient Gibbs energy minimizer: Application to igneous systems" Geochemistry, Geophysics, Geosystems (2022).

How to cite: De Siena, L., Magrini, F., Riel, N., Diaferia, G., Forni, F., and Kaus, B. J. P.: Petrophysical Inversions from Seismic Images detect and characterize Melt under Toba Caldera (Indonesia)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4328, https://doi.org/10.5194/egusphere-egu23-4328, 2023.

Basaltic volcanoes can remain active for tens to thousands of years with the continual presence of magma, requiring storage and transport conditions that can sustain persistently eruptible melt. Magma storage conditions beneath these volcanoes may significantly change with time, leading to sudden and dramatic changes in explosivity. Determining the rates and causes of these changes and how they modulate eruptive style over societally relevant timescales is of paramount importance for evaluating potential hazards. In June-August 2019, one major explosion and two paroxysms occurred at Stromboli volcano (Southern Italy) within only 64 days offering a unique opportunity to study the short-term variations in a basaltic plumbing system that can lead to paroxysmal events.

Stromboli is an active open conduit basaltic volcano well-known for its persistent mild (normal) Strombolian activity occasionally interrupted by sudden, short-lived events ranging in size and intensity from major (violent Strombolian) to paroxysmal explosions. Strombolian activity, effusive eruptions and major explosions, all involve a degassed, highly porphyritic (hp) magma from a shallow reservoir. Deep-seated more mafic and, volatile-rich low-porphyritic (lp) magma is erupted, alongside hp-magma, during paroxysms, and in smaller quantities during some of the major explosions. Both lp- and hp-magmas were erupted during the 3 July and 28 August 2019 paroxysms, whereas only hp-magma was erupted during the major explosion on 25 June 2019.

Via a multifaceted approach using clinopyroxene from the summer 2019 paroxysms, we reveal a key role for batches of volatile-rich lp-magma recharge arriving in the shallow reservoir up to a few days before these events. Our data indicate a rejuvenated Stromboli plumbing system where the extant crystal mush is efficiently permeated by recharge lp-magma with minimum remobilisation promoting a direct linkage between the deeper (lp) and shallow (hp) reservoirs. This sustains the current variability of eruptive styles with near immediate eruptive response to mafic magma recharge. The remarkable agreement between our calculated recharge timescales and the observed variation in time of various monitoring signals strongly supports such a model.

Our approach provides vital insights into magma dynamics and their effects on monitoring signals demonstrating that detailed petrological studies integrated with volcano monitoring signals are fundamental for a fast response during a volcanic unrest phase or crisis.

This work has been published in Nature Communication: Petrone, C.M., Mollo, S., Gertisser, R. et al. Magma recharge and mush rejuvenation drive paroxysmal activity at Stromboli volcano. Nat Commun 13, 7717 (2022). https://doi.org/10.1038/s41467-022-35405-z.

How to cite: Petrone, C. M., Mollo, S., Gertisser, R., Buret, Y., Scarlato, P., Del Bello, E., Andronico, D., Ellis, B., Pontesilli, A., De Astis, G., Giacomoni, P. P., Coltorti, M., and Reagan, M.: Evolution of Stromboli basaltic plumbing system via magma recharges and mush rejuvenation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6218, https://doi.org/10.5194/egusphere-egu23-6218, 2023.

Magma production, storage, and migration beneath volcanic ocean islands has been a matter of controversy and a multitude of methods are currently used to unravel magma evolution,  storage and migration processes. Here we report on a temporal sequence of lava samples^{1, 2} spanning the entirety of the 2021 La Palma eruption (19/09 to 13/12) for which time-series seismic information is also available. Based on the seismic data, initial tephrite lavas were likely drawn from a storage level at or just above the Moho (10-15 km depth), with increasing contributions from a deeper reservoir (>20 km depth) that delivered more primitive basanite lava as the eruption progressed. Early tephrite lava compositions changed rapidly during the first few weeks of the eruption and show significant oxygen isotopic variability (δ18O = +4.9 to 5.8‰), with some samples requiring a low-δ18O component. Later basanite lavas are compositionally less variable after day 20 of the eruption and show a narrower range in oxygen isotopes (δ18O = +5.3 to 5.7‰), close to Atlantic MORB values and similar to values from other historical eruptions and to earlier values recorded from the Cumbre Vieja volcanic system. The larger variability in δ18O in the early lavas is associated with significantly more radiogenic 187Os/188Os and the presence of amphibole and frequent gabbroic micro-xenoliths. Interaction with high-T altered Jurassic oceanic crustal gabbros and basalts with high-time-integrated Re/Os and variable δ18O could be an explanation for the initially wider variations in oxygen isotopes. This is in line with the seismic evidence that indicates the early lavas had been stored at (sub-)Moho levels within the Jurassic oceanic crust at ca. 8-15 km below the island prior to eruption. Later erupted magmas derive from a deeper, upper mantle storage level (>20 km depth) and have had little to no interaction with the igneous and sedimentary portions of the Mesozoic ocean crust, thus providing a useful estimate of primitive mantle δ18O values for the Western Canary Islands.

¹Carracedo J.C., Troll V.R., Day J.M.D., Geiger H., Aulinas Junca, M., Soler V., Deegan F.M., Perez-Torrado F.J., Gisbert G., Gazel E., Rodríguez-González, A., and Albert H. (2022) The 2021 eruption of the Cumbre Vieja Volcanic Ridge on La Palma, Canary Islands. Geology Today 38: 94-107. 

²Day J.M.D., Troll V.R., Aulinas M., Deegan F.M., Geiger H., Carracedo J.C., Pinto G.G., and Perez-Torrado F.J. (2022) Mantle source characteristics and magmatic processes during the 2021 La Palma eruption. Earth and Planetary Science Letters 597: 117793.

How to cite: Troll, V., Deegan, F., Bindeman, I., Harris, C., Day, J., Aulinas, M., Geiger, H., Perez Torrado, F., Carracedo, J. C., Soler, V., Pinto, G., and Albert, H.: Oxygen isotopes in 2021 La Palma lavas reveal pre-eruptive magma storage and primitive mantle values, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6518, https://doi.org/10.5194/egusphere-egu23-6518, 2023.

Deciphering the architecture of the plumbing system beneath active volcanoes and the pre-eruptive magma dynamic is of key importance to discuss about the eruptive style and petrological warning signal. Here Dominica in the Lesser Antilles arc is chosen as a key case study to illustrate the scientific approach. The first step is a field study in order to well identify the characteristics of the deposits to well constrain in particular the style, number and age of eruptions, and to well sample them for petrological studies. On Dominica, we proposed a new chronostratigraphy of the explosive eruptions along the island in the last 50 kyrs, based on stratigraphic correlations, lithology, 14C dating and glass chemistry. To reconstruct the magma plumbing architecture, melt inclusions composition entrapped in minerals from the key eruptions were investigated. Their volatile content highlights that two magma ponding zones may be identified: a deepest one located at ~ 4 kbars, giving birth to the large pumiceous eruptions, formely recognized as the ignimbritic eruptions, and a shallowest, at 1.5-2 kbars, one leading to Plinian-type eruptions. These results are similar to those obtained by experimental petrology. Such data allows us to conclude that the magma plumbing system is organized as a transcrustal magma system, with the magma ponding zones linked to the structure of the crust (lower and middle crust), as derived from geophysical studies. Melt inclusions also help us to constrain magma source at depth, and the influence of slab-derived fluid respect to sediment melting in a subduction zone. To go further, the petrological processes occuring within the magma reservoirs may be investigated. Tracking the pre-eruptive history of magma storage and ascent is a key challenge of modern volcanology, in particular to gain insight into the timescale of pre-eruptive processes at active volcanoes. By focusing now on crystal composition, the pre-eruptive magma dynamics may be identified adopting the « Crystal System Analysis » approach, and their timescales estimated using the diffusion chronometry (Fe-Mg interdiffusion in orthopyroxens). On active and monitored volcanoes, the correlation between the petrological clock and the pre-eruptive warnings given by the monitoring network (seismic but not only) is now established on different volcanoes, using various petrological clock. In Dominica, we showed that a mixing processes between different magma batches systematically occures a decade prior the eruption within the deepest reservoir giving birth to the oldest ignimbritic eruptions. For the recent Plinian eruptions, similar mixing process begins ~ 10–30 years prior eruption, with more sustained mixing in the last decade, accelerated in the last 2 years. On active and monitored volcanoes, the correlation between the petrological clock and the pre-eruptive warnings given by the monitoring network (seismic but not only) is now established on different volcanoes, using various petrological clock. Thus, on Dominica, that has no monitored eruption, time constrain may help authorities in volcanic risk mitigation in case of volcanic reactivation. Such integrated study may be conducted on any volcanic target and lead to a more comprehensive understanding on the behaviour of the magma plumbing system, with strong implications in volcanic risks.

How to cite: Balcone-Boissard, H.: Petrological and geochemical tools for unravelling the architecture and dynamic of a magma plumbing system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9186, https://doi.org/10.5194/egusphere-egu23-9186, 2023.

Following an unprecedented seismic activity that started in May 2018, a new volcanic edifice, Fani Maoré, was constructed on the ocean floor 50 km east of the island of Mayotte (Indian Ocean). This volcano is the latest addition to a submarine volcanic chain characterized by an alkaline basanite-to-phonolite magmatic differentiation trend. Here, we performed viscosity measurements on five silicate melts representative of the East-Mayotte Volcanic Chain compositional trend: two basanites from Fani Maoré, one tephri-phonolite and two phonolites from different parts of the volcanic chain. A concentric cylinder viscometer was employed at super-liquidus conditions between 1500 K and 1855 K, and a creep apparatus was used for measuring the viscosity of the undercooled melts close to the glass transition temperature in the air. At super-liquidus temperatures, basanites have the lowest viscosity (0.11 to 0.99 log₁₀ Pa⸱s), phonolites the highest (1.75 to 3.10 log₁₀ Pa⸱s), while the viscosity of the tephri-phonolite falls in between (0.89 - 1.97 log₁₀ Pa⸱s). Viscosity measurements at undercooled temperatures have only been performed for one phonolite melt because Raman spectroscopy showed nanolites within the basanite and tephri-phonolite glass samples. The phonolite has a viscosity of 10.19 to 12.30 log₁₀ Pa⸱s at 1058 to 986 K. Comparison with existing empirical models revealed discrepancies up to 2.0 log units with our experimental measurements. This emphasizes (i) the lack of data falling along the alkaline basanite-to-phonolite magmatic differentiation trend to calibrate empirical models, and (ii) the complexity of modeling the variations in viscosity as a function of temperature and chemical composition for alkaline magmas. The presented new measurements indicate that, at eruptive temperatures between 1050 °C and 1150 °C, the anhydrous, crystal- and bubble-free basanite melt is very fluid with a viscosity around 2.6 log₁₀ Pa⸱s whereas the anhydrous phonolite crystal- and bubble-free melt at eruptive temperatures ranging from 800 to 1000 °C has a viscosity around 6 - 10 log₁₀ Pa⸱s. These new viscosity measurements are essential to define eruptive models and to better understand the storage, transport and ascent dynamics of Comoros Archipelago magmas, and of alkaline magmas in general, from the source to the surface.

How to cite: Chevrel, O., Verdurme, P., Le Losq, C., Pannefieu, S., Médard, E., Berthod, C., Komorowski, J.-C., Bachèlery, P., Neuville, D. R., and Gurioli, L.: Viscosity of crystal-free silicate melts from the active submarine volcanic chain of Mayotte, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7520, https://doi.org/10.5194/egusphere-egu23-7520, 2023.

Cotopaxi is a glacier-clad volcano located in the Andes of Ecuador (South America). Since its last big eruption, occurred in June 1877, alluvial fans have developed in the lower flanks of the volcanic edifice due to water-related erosional-depositional processes. Two of those fans can be identified in the adjacent Pucarumi and Jatabamba drainages, whose source zones are closely located in the upper north-east flank of Cotopaxi volcano. Geological, ground-penetrating radar and sediment-componentry and granulometry data show that both fans have been deposited after the 1877 eruption and are similar in size, thickness and composition. These measurements thus suggest that the medium- to long-term development of the adjacent fans was controlled by similar processes affecting both drainages. However, when the current deposition in both drainages was surveyed during a one-year period using drone ortho-photogrammetry, the Jatabamba drainage proved to be much more active than the Pucarumi drainage. Although the observed depositional activity at Jatabamba can be broadly correlated to the year-round rain-pattern, the contrasting behavior observed at the adjacent Pucarumi drainage strongly suggest that rainfall alone is unable to entirely explain the erosional processes occurring at Cotopaxi volcano. Instead, recent satellite imagery shows that the source zone of the strongly active Jatabamba drainage currently displays a glacier tongue, which is absent in the case of the weakly active Pucarumi drainage. It is thus concluded that erosional processes occurring at Cotopaxi volcano are mostly driven by water originated by an interaction between rainfall and ice at the glacier border. The precise nature of such interaction remains to be determined.

How to cite: Andrade, S. D., Povea, M. J., Saltos, E., and Vásconez, F. J.: Ice-rain interaction determining the erosional-depositional behavior of adjacent drainages at Cotopaxi volcano (Ecuador), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16635, https://doi.org/10.5194/egusphere-egu23-16635, 2023.

How to cite: Toth, N. and Maclennan, J.: A Deep Learning Enabled Approach for Igneous Textural Timescales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9289, https://doi.org/10.5194/egusphere-egu23-9289, 2023.

The eruptive style of a volcanic system and the energy of the eruption depend on a complex interplay among several internal and external factors, as temperature, pressure, volatile composition and content, and geometry of the volcanic system, all of which concur to affect the rheology of the magma and thus the eruptive strength of a volcano.

The comprehension of the rheological behavior of the mixtures of melt, crystals, and bubbles is necessary to understand the migration of magma within the volcanic system and the modality of eruptions. To date, crystal-bearing magmas and their behavior have been the focus of the majority of investigations by the scientific community.

The paucity of studies on bubble-bearing magmas may have been partly due to the greater challenges posed by the experimental procedure, mostly related to the outgassing of the gas phase during the experiments. So, while the influence of crystals in magma rheology has been parameterized in detail, a comprehensive model for the rheology of the bubble-bearing magmas has yet to be formulated.

The aim of this work is to understand the complex dependence of the viscosity on the bubble content and strain rate, by performing suites of in situ degassing experiments on rhyolitic magma at an experimental temperature of 850 °C, followed by uniaxial deformational experiments (constant strain rates of 5 x 10^-5, 10^-4 and 10^-3 s^-1) through a vertical uniaxial press at experimental temperatures varying between 720 and 800 °C. Experimental parameters are selected to investigate the rheology under unsteady flow conditions (i.e., prior to equilibrium deformation of bubbles). Such conditions may be very common during explosive volcanic eruptions, where bubbles are not able to relax in the fast-ascending magmas.

For constant strain rates, results show trends of apparent viscosity as a function of bubble content, consisting of an initial increase of viscosity for low amounts of bubbles (0-20%), followed, above the 20% threshold porosity, by a general viscosity decrease. At fixed porosity, a strain rate dependence of viscosity is also observed, with viscosity decreasing as the strain rate increases. Overall, the sample's apparent viscosity appears to be non-linearly controlled by both ambient conditions (Temperature T_def and Strain rate ) and sample texture (Porosity and Vesicle Number Density VND), whose interplay concurs to define the degree of flow unsteadiness. We, therefore, discuss the weight of each parameter in determining the apparent viscosity of the magmatic mixture.

How to cite: Frontoni, A., Vona, A., and Romano, C.: Rheology of bubble-bearing magma suspensions under unsteady flow conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11815, https://doi.org/10.5194/egusphere-egu23-11815, 2023.

Approximately 17% of the Earth’s 1,413 Holocene volcanoes are glacier covered or possess at least one glacier within a radius of 5 km. Glacier-volcano interactions are therefore relatively common, yet our understanding of these interactions is hindered by a sparsity of observations and a lack of quantitative data. Furthermore, glaciovolcanicanism has been implicated in a number of particularly deadly and costly volcanic eruptions in recent decades. Documenting and quantifying the impacts of glacier-volcano interactions is therefore increasingly needed to both accurately forecast the future dynamics of volcanic glaciers and mitigate associated glaciovolcanic hazards.

Encouragingly, recent research has shown that optical satellite imagery can be used to detect volcanic impacts on glacier surface morphology, such as the development of ice cauldrons and widespread crevassing. However, to date the capacity of volcanic activity to influence glacier velocities and wider glacier geometry remains relatively unexplored. Here, we present a comparative study of volcanic and non-volcanic glacier velocities and geometries. We apply descriptive and multivariate statistical analyses to a broad range of glacial, volcanic and climate records in order to: i) compare volcanic and non-volcanic glacier parameters globally for the year 2017/18, and ii) investigate relationships between volcano properties and volcanic glacier characteristics.

Our final dataset comprises ~2,700 volcanic glaciers and ~210,000 non-volcanic glaciers. We reveal that volcanic glaciers typically exhibit greater and more variable velocities than their non-volcanic counterparts, with an average median velocity of 18.09 ma^‑1 versus 7.94 ma^-1 for non-volcanic glaciers. We also find that volcanic glaciers are typically larger, longer and thicker than non-volcanic glaciers, and are more likely to be situated at lower elevations, on more gentle slopes in warmer, wetter climates than their non-volcanic counterparts. However, when controlling for these differences in glacier geometry, situation and climate, we find that the greater velocities observed for volcanic glaciers remain statistically significant. Relationships between volcano properties and volcanic glacier characteristics tentatively indicate that volcano type and tectonic setting may also act as controls on volcanic glacier velocities, and that the greatest volcanic glacier velocities are typically found in glaciers situated closest to volcanoes.

The enhanced velocities documented here, particularly for glaciers most proximal to volcanoes, are hypothesised to be a consequence of locally increased geothermal heat inputs. Consequently, we contend that the velocities of volcanic glaciers may be a valuable proxy for volcanic activity and, with further investigation, may provide considerable potential for monitoring and forecasting volcanic activity, and for improving the mitigation of glaciovolcanic hazards.

How to cite: Mallalieu, J., Barr, I., Martin, M., Symeonakis, E., Edwards, B., Spagnolo, M., and Mullen, D.: An exploration of volcanic controls on glacier velocity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6186, https://doi.org/10.5194/egusphere-egu23-6186, 2023.

  With more than 30 million people living within 10 km of active or dormant volcanoes, eruptions are a natural socio-economic hazard that can have devastating consequences for society. Hence, the timely forecasting of volcanic unrest has real-world, and potentially, life and death implications. A major challenge is the identification and monitoring of precursors to forthcoming volcanic eruptions. The observation and measurement of thermal anomalies is one of the answer to this challenge, with some volcanoes exhibiting signs of thermal unrest over extensive areas of their edifice for several years prior to an eruptive event. Glaciers that sits on volcanoes are likely to respond to the increased heat and could therefore be used as complementary volcano thermometers but a large scale study is missing. 

Our study, which covers 600 Andean glaciers and 37 ice-clad volcanoes, demonstrate glacier mass balance sensitivity to volcanic heat. We distinguish between ‘volcanic-glaciers’ (located ≤1 km from volcanic centres), and ‘proximal glaciers’ (1-15 km) and calculate their equilibrium line altitude (ELA). In most instances, proximal glacier ELAs are lower than those of nearby volcanic-glaciers. In some cases, the ELA decrease proportionally with increasing glacier distance from the volcanic edifice, and a quantitative relationship between ΔELA_mean (i.e., the difference in mean ELA between the proximal and volcanic-glaciers) and ASTER-based measurements of volcanic thermal anomalies could be established. These results highlight the impact of volcanic heat on glacier mass balance; emphasise the need to exclude volcanic-glaciers from glacier-climate investigations; and demonstrate the first-order potential of glaciers as ‘volcanic thermometers’, with the ΔELA_mean representing a proxy for volcanic heat.

How to cite: Spagnolo, M., Howcutt, S., Rea, B., Jaszewski, J., Barr, I., Coppola, D., de Siena, L., Girona, T., Gomez-Patron, A., Mullan, D., and Pritchard, M.: Icy thermometers: how volcanic heat affects glacier mass balance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13282, https://doi.org/10.5194/egusphere-egu23-13282, 2023.

A number of Late Ediacaran post-collisional volcanic sequences are exposed in southern Sinai, which represents the extreme northern tip of the Arabian-Nubian Shield (ANS). To clarify the age and geochemical characteristics of such volcanism, two localities were selected for the present study: the Meknas and Iqna Shar’a volcanics. These undeformed and unmetamorphosed sequences include intermediate to felsic subaerial lava flows, tuffs and ignimbrites accompanied by deposition of immature clastic sediments. New SIMS U-Pb dating of zircons from two samples of the Meknas lava flows yielded ages of 593 ± 12 and 616 ± 1 Ma, while zircons from three samples of the Iqna Shar’a volcanics yielded ages of 600 ± 6, 616 ± 4, and 617 ± 6 Ma. Combined with field evidence, the zircon ages enable us to recognize two phases of post-collisional volcanic activity in southern Sinai, at 592-600 Ma and 616-617 Ma. Geochemically, the volcanic rocks of the two successions display large silica variations and are mostly medium- to high-K calc-alkaline rocks. The lower units of the earlier phase consist of andesite and dacite, whereas the upper units of the later phase are more evolved, rhyodacite to rhyolite. The evolved rhyolites of the second phase have characteristics that are transitional to alkaline A-type magmas, but this is attributed to extensive fractionation and does not require a change in the tectonic regime. Geochemically, the Meknas and Iqna Shar’a volcanics are enriched in most LILE and depleted in most HFSE. Moreover, they are generally enriched in LREE relative to HREE and characterized by moderate degrees of REE fractionation [(La/Yb)_N = 7.0-12.8)]. They evolved from high-K calc-alkaline magmas that were generated in a post-collisional regime. Despite the temporal gap, it appears that all lavas in each locality are cogenetic and formed via fractional crystallization from a common parental melt. Although they erupted in a post-collisional setting, both volcanic suites display geochemical fingerprints of subduction influence, interpreted to reflect remelting of previously formed arc material ca. 750-650 Ma in age. These magmas were derived from the mafic lower crust, which likely melted due to lithospheric delamination. This is consistent with the Hf isotope ratios of their zircons, which consistently yield positive _Hf(t) values (+3.2 ±1.5 and +4.3 ± 1.7, from Iqna Shar’a; +2.6 ± 2.3 and +5.3 ± 1.7 from Meknas). The 50-150 Ma time span between emplacement of this lower crust and its remelting was insufficient for its Hf isotope ratio to evolve to negative values considered representative of an ancient crustal source. Contamination by upper continental crust and fractional crystallization were responsible for the variation observed within the studied volcanic suites.

How to cite: Azer, M., Asimow, P., Price, J., and Ibañez-Mejia, M.: Late Ediacaran crustal thickening in Egypt: Geochemical and isotopic constraints from post-collisional volcanism in southern Sinai, Egypt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1650, https://doi.org/10.5194/egusphere-egu23-1650, 2023.

The Himalayan leucogranites are important for deciphering the role of crustal thickening and anatexis during the tectono-thermal evolution of the Himalayas. The Higher Himalayan Sequences (HHS) in Sikkim are intruded by Miocene leucogranites which comprise two-mica-bearing (2mg) and tourmaline-bearing leucogranites (Tg) both of which are peraluminous in nature, and are characterized by high ⁸⁷Sr/⁸⁶Sr ratios and low ¹⁴³Nd/¹⁴⁴Nd ratios, typical of crustal values. In the case of 2mg, the average (⁸⁷Sr/⁸⁶Sr) ratio is 0.792020, and the average (¹⁴³Nd/¹⁴⁴Nd) ratio is 0.511764 whilst for Tg, the average (⁸⁷Sr/⁸⁶Sr) and (¹⁴³Nd/¹⁴⁴Nd) ratios are 0.772874 and 0.511912 respectively. In comparison to 2mg, Tg has lower average ratios of (⁸⁷Sr/⁸⁶Sr) and slightly elevated average ratios of (¹⁴³Nd/¹⁴⁴Nd). The Sr-Nd isotope compositions for the granitic gneisses from the HHS have an average (⁸⁷Sr/⁸⁶Sr) ratio of 0.764026 and an average (¹⁴³Nd/¹⁴⁴Nd) ratio of 0. 511959. The present day average εNd  values for 2mg, Tg, and granite gneiss are -17.1, -14.2, and -13.2 respectively. The granite gneiss samples all lie within the field defined by the HHS across the Himalayan orogen as do the Tg samples suggesting a source from pelitic rocks within the HHS. The 2mg samples are somewhat evolved towards more radiogenic Sr isotope ratios and slightly lower neodymium ratios suggesting either a source in metagreywacke rocks of the HHC or, alternatively, reflect minor melt contributions from anatexis of the Lesser Himalayan formations.

Keywords: Sr-Nd isotopes, Source magma, Sikkim Himalayas, Leucogranites

How to cite: Srivastava, T., Harris, N., Mottram, C., and Wanjari, N.: Strontium-Neodymium isotopic compositions of Higher Himalayan leucogranites and granitic gneisses from Sikkim Himalayas, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-488, https://doi.org/10.5194/egusphere-egu23-488, 2023.

Complex petrogenetic processes involving multiple sources may account for the presence of silicic rocks (SiO₂ >65 wt%) in Continental Flood Basalts (CFBs). Here, we use a holistic framework involving field observations, petrography, major oxides (n = 56), and trace element chemistry to examine eight scattered but significant silicic rock exposures found within the 65.5-66 Ma old Deccan Traps CFB. Rhyolite and granophyre with subordinate felsite, ignimbrite, trachyte, pitchstone and microgranite coexist with basalt, basaltic andesite, and gabbro. Thermodynamic-based Rhyolite-MELTS modelling suggests that the major oxide composition of associated basalt is a likely candidate for the parental melt composition of the silicic rocks of the Deccan Traps. Two broad REE patterns are noticed in the Deccan Traps silicic rocks; a flat pattern for Barda, Alech, and Chogat-Chamardi silicic rocks, and a steep REE pattern for Osham, Rajula, Pavagadh, Rajpipla, and Bombay silicic rocks. Basalt from Barda (La/Lu_N = 3.57) and Pavagadh (La/Lu_N = 11.0) display similar flat and REE patterns observed in the associated silicate rocks. Trace element modelling reveals that partial melting at different depths (shallow vs. deeper) from lherzolite sources and subsequent extensive fractional crystallization (50-90%) of these two parental mafic melts could generate the trace element composition of the Deccan Traps silicic rocks. The geochemical variability of Deccan Traps silicic rocks reveals an origin mostly from a mantle source with contributions of continental crust at a later stage, which is typical of silicic volcanism in other global CFBs.

How to cite: Halder, M., Paul, D., and Yang, S.: Influence of sources in the generation of silicic rocks of the Deccan Traps Continental Flood Basalt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-341, https://doi.org/10.5194/egusphere-egu23-341, 2023.