Deception Island, the most active volcanic system in the South Shetland Islands (Antarctica), has recorded over 20 explosive monogenetic eruptions in the past two centuries. The island’s most recent eruption in 1970 was one of its most violent, with a Volcanic Explosivity Index (VEI) of 3. This event generated a column height of up to 10 km and produced an estimated bulk eruptive volume exceeding 0.1 km³, with tephra fallout recorded over 150 km away on King George Island. To investigate the magmatic processes leading up to this significant eruption, we conducted detailed geochemical and textural analyses of near-vent pyroclastic deposits and distal tephra fall-out layers preserved in Livingston Island’s glaciers. Near-vent deposits include dilute pyroclastic density currents (PDCs) and lithic-rich breccias. Olivine crystals in these deposits exhibit two distinct populations: low-forsterite (Fo_65–70 mol.%) and high-forsterite (Fo_80–85 mol.%), with similar CaO contents (0.1–0.5 wt.%) but varying NiO concentrations (0–0.4 wt.% in low Fo; 0.02–0.10 wt.% in high Fo). Pyroxene microanalyses also reveal two distinct populations: i) augite-diopside (En_45–50, Fs_5–25, Wo_38–50) and ii) enstatite (En₉₀, Fs₁₀, Wo₀). Augite-diopside crystals can be further subdivided based on their Mg# (Mg# = Mg/(Mg+Fe) x 100) and TiO₂ contents. The first group shows Mg# values between 80–85 mol.% and TiO₂ ranging from 0.5 to 3.0 wt.%, while the second group displays Mg# values of 55–70 mol.% and narrower TiO₂ concentrations (0.5–1.25 wt.%). Notably, the enstatite population was not found in distal tephra layers. Plagioclase crystals range in composition from Bytownite to Andesine (An_85–40 mol.%). Comparative analyses with distal tephra layers confirm the presence of both olivine populations and overlapping augite-diopside compositions but lack enstatite. Plagioclase compositions show consistency between near-vent and distal deposits. These findings align the 1970 eruption deposits with compositional trends observed in other post-caldera collapse eruptions, shedding light on the island's eruptive history and magmatic evolution.

This work has been partially financed by the grant PID2023-151693NA-I00 funded by MCIN/AEI/10.13039/501100011033.This work is part of the CSIC Interdisciplinary Thematic Platform (PTI) Polar zone Observatory (PTIPOLARCSIC) activities. This research was partially funded by the MINECO VOLCLIMA (CGL2015-72629-EXP) and HYDROCAL (PID2020-114876GB-I00) MICIU/AEI/10.13039/501100011033 research project. Sampling was founded by CICYT (ANT91-1270, ANT93-0852 and ANT96-0734) and MICINN grant CTM2011-13578-E.

How to cite: Albert, H., Ruiz, J. L., Hopfenblatt, J., Pedrazzi, D., Geyer, A., Aulinas, M., Polo-Sánchez, A., Álvarez-Valero, A. M., and Vilanova, O.: Magmatic processes driving the 1970 eruption on Deception Island, (Antarctica), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20055, https://doi.org/10.5194/egusphere-egu25-20055, 2025.

A mineralogical study of early Cretaceous lamproite sill intrusions from the Raniganj Gondwana sedimentary basin in eastern India shows that apatite occurs as both phenocrystic and groundmass phase. Based on texture and compositional zoning patterns of apatite in lamproites from the Rajpura and Ramnagore collieries, three paragenetic stages of apatite are identified. Early-magmatic apatite (Ap-I), which forms the core of zoned grains, is Sr-rich–LREE-poor fluorapatite. This apatite underwent resorption prior to the growth of a second generation of magmatic fluorapatite (Ap-II). In Rajpura, Ap-II overgrowth rim is richer in Sr and LREE compared to Ap-I core. The increase in LREE is explained by the substitutions: (Na,K)⁺ + ∑LREE³⁺ = 2Ca²⁺, and [2∑LREE³⁺ + ₶ = 3Ca²⁺]. Ramnagore Ap-II overgrowth rim is oscillatory-zoned with fluctuations in Sr and LREE, which likely resulted from slow rate of diffusion of these elements relative to fast growth of crystals. Apatite of the third generation (Ap-III) forms the outermost rim of zoned grains and is marked by enrichment in Na, K and Ba. The substitutional schemes which explain the increase in Na and K from Ap-II to Ap-III are: (Na,K)⁺ + CO₃^2– = Sr²⁺ + PO₄^3– and [(Na,K)⁺ + (F,OH)^– = ₶ + ₶]. The role of carbonate in the former substitution is supported by high content of stoichiometrically calculated carbon (0.21–0.30 apfu) in Ap-III. The formation of Ap-III is attributed to metasomatic alteration of Ap-II by CO₂-bearing hydrothermal fluid and is associated with sodic metasomatism. Microporous texture has developed in Rajpura Ap-III which suggests a dissolution–reprecipitation mechanism for its development. This study demonstrates that compositional variations among different generations of apatite provide a meaningful record of melt evolution from early magmatic to magmatic-hydrothermal stages.

How to cite: Saini, J., Patel, S. C., and Kaur, G.: Apatite compositional constraints on the magmatic to hydrothermal evolution of lamproites from Raniganj Basin, eastern India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1988, https://doi.org/10.5194/egusphere-egu25-1988, 2025.

Four multicomponent metaluminous glasses were designed to investigate the evolution of residual glass-ceramics comprising glass and crystals. Samples were obtained from melting of quartz-feldspars mixes (with varying Na/K ratio and silica content) further fast sintered at temperatures of 1200-1260°C. Using an integrated approach combining high- and low-frequency Raman spectroscopy and Differential Scanning Calorimetry (DSC), we characterized the viscous and elastic response of the residual glass and its role in the mechanical properties of the corresponding ceramic products.

High-frequency Raman spectroscopy allows for the analysis of Qn species, which represent the polymerization state of the glass network. Q⁰, Q¹, Q², Q³, and Q⁴ correspond to isolated tetrahedra, short chains, branched structures, and fully polymerized networks, respectively. This provides insights into how chemical composition affects the microscopic structure of the residual glass. Simultaneously, low-frequency Raman spectroscopy probes the boson peak, a signature of collective vibrational modes in the glass, which is directly linked to its elastic properties. By coupling the boson peak analysis with the elastic medium scaling law, we determine the vibrational density of states and shear modulus, key parameters for understanding the mechanical behavior of the system.

DSC measurements further enable the determination of critical thermal transitions of the glass, including the glass transition temperature, crystallization, and relaxation processes, which are essential for characterizing the viscous behavior of the residual glass. The integration of these techniques provides a comprehensive understanding of the role of residual glass in stress transfer and mechanical properties control within multicomponent ceramics.

This is a first insight on the characteristics of technologically relevant glasses for the production of porcelain and vitrified ceramic tiles. The approach here followed actually allows appreciating the effect of variations in the Na/K ratio and silica content that mirror what can occur in the industrial production. This paves the way for application in more complex materials and real industrial conditions.

Contribution of PNRR M4C2 - PRIN 2022PXHTXM - STONE project, funded from EU within the Next generation EU program. CUP: D53D23004840006

How to cite: Giordano, D., Cassetta, M., Conte, S., Zanelli, C., Molinari, C., Dondi, M., and La Felice, S.: Characterization of Residual Glass Evolution from Vitrified  Ceramics: Insights from Raman Spectroscopy and DSC into Viscous and Elastic Properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8978, https://doi.org/10.5194/egusphere-egu25-8978, 2025.

Vulcano Island in Aeolian Archipelago last erupted in 1888-1890 and since then it is affected by an intense fumarolic activity from both the summit crater area of La Fossa volcano and by the hydrothermal system of Baia di Levante located very near to the main settlement of Vulcano Porto.  Ordinary solfataric activity is periodically interrupted by unrest crisis at La Fossa crater associated with increase in fumarole temperature and output, anomalous seismicity, ground deformation and accompanied by an increase in diffuse soil CO₂ degassing at Vulcano Porto. In Autumn 2021 a new major unrest crisis began exposing to a high gas hazard Vulcano Porto settlement due to contemporary dispersion of crater fumarolic plume and diffuse soil CO₂ degassing; Starting from February 2022, with apex in May, a huge increase in gas output of the geothermal system of Levante Bay was observed. The Baia di Levante area is characterized by the presence of a low-temperature fumarolic field (<100°C) either onshore and offshore and fed by a shallow hydrothermal aquifer heated by magmatic gases. A wide diffuse soil CO₂ degassing area extends all over the main beach. The chemical composition of bubbling gases is CO₂-dominant, associated with a 1-3 vol.% of H₂S and minor CH₄ and H₂. The Bay is one of the main sites of attraction for the thousands of tourists who visit the island and given the increased risk for gas emissions and possible phreatic eruptions (due to overpressuration of the geothermal aquifer) we carried out some extraordinary geochemical surveys. These consisted of (i) estimation of diffuse soil CO₂ flux over a target area (154 points over 16,750 m²) established since 2004; (ii) estimation of the convective CO₂ and H₂S flux (the main hazardous gases) from the onshore (50 points in the Mud Pool and surrounding areas) and offshore gas vents (2 main large vents and 60 small vents); (iii) Repeated measurements of the chemico-physical parameters (temperature, pH, Eh, conductivity and dissolved O₂) in the Baia di Levante sea water (107 profiles; water depth from 50cm to 12m). In particular we investigated the areas characterized by the presence of whitish waters, trains of gas bubbles, emissive vents. Results shown significantly increased values ​​compared to the past of the total CO₂ and H₂S output (diffuse and convective) measured on land and at sea surface. The sea water shows the presence of a wide anomalous pH in the near-shore sector between Faraglione and Vent 1 and to a lesser extent to the N of the bay. A wide anomaly of negative Eh values ​​persist at all depths in almost all of the bay. A huge emissions of acid gases from the increased submarine fumaroles alter the chemical-physical parameters of the sea water along the bay. Considering the increased gas hazard the adoption of risk prevention measures was suggested to authorities.

How to cite: Ranaldi, M., Carapezza, M. L., Tarchini, L., Pagliuca, N. M., Pruiti, L., and Sortino, F.: Gas hazard assessment at the hydrothermal system of Baia di Levante at Vulcano Island during the 2021-23 unrest of La Fossa crater (Aeolian Islands, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20387, https://doi.org/10.5194/egusphere-egu25-20387, 2025.

In the last decades, the volcanically active Aeolian Islands have been the focus of numerous geochemical investigations and monitoring activities, primarily focused on the islands of Vulcano, Stromboli and Panarea. However, relatively few studies have explored the geochemical characteristics of other islands, despite evidence of hydrothermal activity. Salina, for instance, hosts a shallow, cold, low-salinity aquifer that overlies a deeper warmer aquifer, with highly saline water. Additional noteworthy features include hydrothermal deposits on the seafloor and offshore submarine gas emissions. Similarly, Lipari hosts a thermal aquifer (e.g. Terme di San Calogero) and exhibits significant hydrothermal emissions along its western coast, particularly in areas of Valle del Fuardo and Caolino quarry. In this study we conducted detailed geochemical surveys on Lipari and Salina to investigate the origins of the fluids and their relationship with the geodynamic framework. The research is part of the Project CAVEAT (Central-southern Aeolian islands: Volcanism and tEArIng in the Tyrrhenian subduction system), which aims to provide a comprehensive understanding of the current geodynamics in the southern Tyrrhenian region, focusing on the interaction between volcanism and tectonic activity within the Tyrrhenian subduction system.

On Salina and Lipari islands, soil CO₂ flux measurement campaigns were conducted to examine the spatial distribution of soil CO₂ emissions. Thermal surveys using an Unmanned Aircraft System were conducted over fumarolic areas to detect thermal anomalies associated with zones of preferential fluid emissions. These measurements helped define preferential pathways for fluid migration and identify active tectonic structures associated with areas of elevated soil CO₂ emissions. At selected sites, isotopic composition of gas was analyzed to infer the gas origins. On Lipari, soil CO₂ emission anomalies revealed a NNW-SSE alignment consistent with the area’s primary tectonic structures. Isotopic analysis confirmed a contribution of deep-origin fluids to these emissions. Thermal (up to 45.8 °C) and cold waters from Salina and Lipari were sampled and analyzed for their chemical and isotopic composition, as well as for dissolved gases. The isotopic composition of the water clearly indicates that the sampled groundwater originates from a mix of meteoric water and seawater, with varying degrees of mixing at each site. Gases dissolved in water exhibit an atmospheric component with a high content of CO₂ in the most brackish samples. At Salina, the isotopic composition of dissolved helium reflects a mantle contribution. Collectively, the findings emphasize the significant influence of mantle and deep-origin origin fluids in shaping the geochemistry of both islands. They further highlight the critical role of geodynamic and tectonic processes in governing fluid emissions across the two islands.

How to cite: Camarda, M., De Gregorio, S., Liotta, M., Di Martino, R. M. R., Oliveri, Y., Palano, M., Pisciotta, A., Riolo, G. M., and Romano, P.: Unveiling the geochemistry of fluids in the Central Aeolian Islands (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10890, https://doi.org/10.5194/egusphere-egu25-10890, 2025.

Natural CO₂ emissions play a crucial role in understanding global CO₂ budget estimates. Consequently, numerous studies have focused on CO₂ emissions across various regions worldwide. However, the majority of these investigations have concentrated on terrestrial CO₂ emissions, with relatively fewer studies exploring submarine CO₂ emissions. Moreover, almost all the studies have focused on areas with significant hydrothermal activity, particularly those along Mid-Oceanic Ridges, while shallow-water hydrothermal vents have received comparatively little attention. Furthermore, diffuse submarine gas emissions, lacking or with little visible surface evidence, remain largely unexplored. This study investigates the CO₂ emissions in the shallow submarine environment around the coast of the Island of Vulcano (Aeolian Islands, Italy) by measuring dissolved CO₂ concentrations. Vulcano, has been characterized by an intense hydrothermal activity since its last eruption from La Fossa cone (1888-­1890). Vulcano features several fumarole fields, including one on the northern crater rim of La Fossa cone and another near the sea in the northeastern sector. Additionally, significant soil CO₂ degassing occurs across the volcanic edifice. In the Vulcano Porto area, numerous thermal wells discharge fluids with temperatures reaching up to 80 °C. Submarine emission areas are visible, at shallow depths, close to the beaches in the southern and northeastern sectors. Measurements of dissolved CO₂ concentrations were conducted along seashores and rocky coastlines and in sites encompassing both visible and non-visible emissions. In the northeastern sector, measurements focused on the area between the Vulcanello peninsula and the northern slopes of the volcanic cone. The northernmost section of this area, extending to the Faraglione cone, is widely recognized in the literature as Baia di Levante (BL), a well-documented site of significant CO₂-dominant hydrothermal fluids discharge, trough submarine vents placed on the seafloor, at shallow depth, near the shoreline. In this area, we performed measurements along the beach at depth of about 50 cm below sea surface. The measured values remain elevated throughout the entire profile, consistently surpassing those of seawater in equilibrium with the atmosphere (ASSW). Concentrations peaked near visible bubbling zones, with concentration values ​​that exceeded the 20%. Moving southward, between the port dock and the crater slopes, measurements were conducted both close to the coastline and approximately 30 meters off the coast. In this area, sporadic bubble emissions from the seafloor were observed and the concentration of dissolved CO₂ decreases significantly compared to the BL area. However, the dissolved CO₂ concentration remain elevated, above those expected for ASSW. Along the eastern coast, measurements were performed in two selected sites along the rocky coastlines. Anomalous dissolved CO₂ concentrations, reaching up to 1400 ppm, were recorded also in these areas. In the southern sector, measurements were taken along Gelso beach. CO₂ concentrations were consistently high along the entire beach profile. The results indicate that submarine CO₂ emissions are not confined to areas with visible surface evidence, but also occur in areas with minimal or no-visible hydrothermal activity.

How to cite: De Gregorio, S., Camarda, M., Cappuzzo, S., Francofonte, V., and Pisciotta, A.: Investigations on the shallow submarine CO2 emissions around the Island of Vulcano (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11968, https://doi.org/10.5194/egusphere-egu25-11968, 2025.

The Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Etneo (INGV-OE) is in charge to monitor Mt. Etna (Catania, Italy), one of the most active volcanoes in Europe. Its activity is characterised by mild strombolian to powerful lava fountains. Monitoring active volcanoes is fundamental to reduce the volcanic hazard, in particular in dense populated areas as it is the case for the Mt. Etna [1]. The combination of different remote sensing systems can improve the analysis of Etna volcanic activity and give a more reliable quantification of volcanic source parameters as the Cloud Height, Mass Eruption Rate, Fine ash Mass and Particle Size. Volcanic source parameters are used as input parameters by volcanic ash transport and dispersal model. A more accurate estimate of these parameters reduces the uncertainty of numerical dispersal model simulations. The data used for this study come from different sources: The VIVOTEK IP8172P is a visible camera located in Catania. The second is a Thermal-Infrared camera located in Nicolosi that collects images (320 x 240 pixels) at few meters resolution [2] [3]. The third instrument is a X-band (9.6 GHz) polarimetric weather radar located nearby the International Airport Vincenzo Bellini (Catania). The fourth is the Spinning Enhanced Visible and Infrared Imager onboard the Meteosat Second Generation Geostationary Satellite [4]. Through the use of complementary remote sensing systems, we aim at improving our understating of explosive phenomena at Etna volcano.

[1] Bonadonna, C., Folch, A., Loughlin, S., & Puempel, H. (2012). Future developments in modelling and monitoring of volcanic ash clouds: outcomes from the first iavcei-wmo workshop on ash dispersal forecast and civil aviation. Bulletin of volcanology, 74 , 1–10.

[2] S. Scollo, M. Prestifilippo, E. Pecora, S. Corradini, L. Merucci, G. Spata, et al., "Eruption column height estimation of the 2011–2013 Etna lava fountains", Ann. Geophys., pp. 57, 2014.

 [3] S. Calvari, G.G. Salerno, L. Spampinato, M. Gouhier, A. La Spina, E. Pecora, et al., "An unloading foam model to constrain Etna’s 11–13 January 2011 lava fountaining episode", J. Geophys. Res. Solid Earth, vol. 116, pp. B11207, 2011.

[4] S. Scollo, M. Prestifilippo, C. Bonadonna, R. Cioni, S. Corradini, W. Degruyter, et al., "Near-Real-Time Tephra Fallout Assessment at Mt. Etna Italy", Remote Sens., vol. 11, pp. 2987, 2019.

How to cite: Romeo, F., Mereu, L., Prestifilippo, M., and Scollo, S.: Etna volcano monitoring by remote sensing systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20022, https://doi.org/10.5194/egusphere-egu25-20022, 2025.

Correlating surface hotspot volcanism with sharply defined edges of Large Low Shear Velocity Provinces (LLSVPs) is a common yet potentially oversimplified approach in mantle geodynamics. Such direct radial projections ignore the lateral displacement of plume conduits observed in seismic tomographic imaging, which suggests that purely vertical transport through the mantle is not guaranteed. Furthermore, many studies merge the African and Pacific LLSVPs, despite evidence that their correlation with hotspots differs significantly. These oversimplifications can lead to misinterpretations of plume-lithosphere interactions, the interaction between mantle plumes and the ambient ”mantle wind”, and mantle flow dynamics in general. Here, we systematically investigate how varied criteria can alter the inferred hotspot– LLSVP edge relationship. We separately analyze African and Pacific LLSVPs using: multiple tomography models, horizontal-gradient based definitions of edges, different vote-map methodologies, and distinct plume geometry assumptions–from perfectly vertical “spokes” to randomly deflected trajectories. We also apply the Back-and-Forth Nudging (BFN) method applied to time-reversed thermal convection, initialized with a present-day seismic–geodynamic–mineral physics model (Glisovic & Forte, 2016), to provide a geodynamically consistent assessment of the relationship between present-day hotspot locations and their source regions in the deep lower mantle. This independent geodynamic assessment clarifies how arbitrary choices concerning the interpretation of hotspots and LLSVP edges may lead to biased or skewed deep-plume reconstructions. Our results reveal that adjustments in hotspot catalogs, or the decision to combine the two main LLSVPs rather than regard each as dynamically distinct, can yield important differences in the significance attributed to sharply defined LLSVP edges. These findings underscore that commonly cited correlations between hotspot locations and LLSVP boundaries hinge on assumptions that vary considerably across the literature. Recognizing and rigorously defining input parameters–particularly the separate treatment of the African and Pacific LLSVPs and the inclusion of realistic lateral plume deflection–proves essential for robust interpretations of deep Earth structure. This highlights the need for standardized methodologies and careful parameter choices to avoid overstating the importance of LLSVP edges in shaping plume pathways.

How to cite: Johnston, G., Liu, S., Forte, A., and Glisovic, P.: Playing with Edges: The Influence of Arbitrary Definitions on Hotspot–LLSVP Correlations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14815, https://doi.org/10.5194/egusphere-egu25-14815, 2025.

A petrological and geochemical study was performed on 5 selected samples of peridotites from two different sites (Finero and Balmuccia) outcropping in the Ivrea Verbano Zone, with the aim to investigate the processes occurring in the deep lithosphere and the possible interaction with the lower crust.

The peridotites from Finero area fall in the harzuburgite (FIN1, FIN3, FIN4) field whereas those from Balmuccia are lherzolithes (BALM1) and werlhites (BALM4), highlighting respectively the presence of a more fertile and primordial mantle for two sites.

The rocks from Finero are featured by higher MgO (42-45.7 wt%) and lower Al₂O₃ (0.6-2.4 wt%), CaO (0.42-2.09 wt%) content with respect to Balmuccia (MgO: 39.6 wt%, Al₂O₃: 2.9 wt%; CaO: 2.8 wt%) as a consequence of their harzburgitic nature. They display an enrichment in large-ion lithophile elements (LILE), light rare earth elements (LREE, La_N/Yb_N:13.6) and depletion in high field strength elements (HFSE) differently from the Balmuccia peridotites, which are featured by a light depletion in LREE (La_N/Yb_N:0.4-0.8) and nearly flat HREE pattern. The LILE and LREE enrichment measured in the Finero peridotites could suggest that a portion of the mantle below Ivrea Verbano area was influenced by metasomatic fluids/melts. The BALM4 sample is characterized by anomalously low values of MgO (16.05 wt%) and high values of Al₂O₃ (16.3 wt%) and CaO (14.5 wt%), reflecting the high modal proportion of spinel.

Even the higher Sr (⁸⁶Sr/⁸⁷Sr= 0.70736-0.72571) and lower Nd (¹⁴³Nd/¹⁴⁴Nd=0.51236) isotopic values measured in selected mineral phases from Finero with respect to Balmuccia (⁸⁶Sr/⁸⁷Sr= 0.70268-0.70644; ¹⁴³Nd/¹⁴⁴Nd=0.51334) allow to speculate a relation with crustal fluids in the Finero mantle.

The composition of fluid inclusions entrapped in olivine and pyroxene crystals from Finero peridotites evidenced CH₄ and CH₄-N₂ associated with antigorite and magnesite whereas prevalent CH₄ associated with antigorite, magnesite and graphite was measured in the rocks from Balmuccia area. The origin of CH₄ could be related to synthesis via reduction of CO₂ by H₂ from internal/external serpentine to minerals or re-speciation of initial CO₂-H₂O fluids associated to graphite precipitation during cooling by obduction after orogeny; differently, the CH₄-N₂ fluids could be introduced by past subduction-related processes.

The isotopic helium (³He/⁴He ratio) varies between 0.08 and 0.17 Ra in the Finero peridotites and among 0.18 and 0.48 Ra in the Balmuccia ones, evidencing an isotopic difference between the two sites that cannot be explained by ⁴He radiogenic production. Differently, the Finero-Balmuccia variability could reflect the helium signature recorded in deep by subduction events and confirm the previous petrologic and geochemical evidences in favour of a metasomatised mantle by crustal fluids in the Finero area with respect to a more primordial in the Balmuccia one.

How to cite: Correale, A., Romano, P., Arienzo, I., Caracausi, A., Carnevale, G., Fazio, E., Mormone, A., Paonita, A., Piochi, M., Rotolo, S. G., and Zucali, M.: Two different mantle types as evidenced from a geochemical and petrological study of peridotites from the Ivrea-Verbano Zone , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8654, https://doi.org/10.5194/egusphere-egu25-8654, 2025.

This study focuses on characterizing seismogenic zones by establishing a interrelationship between electrical and elastic properties using Effective Medium Theories (EMTs). The seismogenic zones exhibit complex geological and geophysical signatures that can be explored through joint analysis of electrical resistivity and elastic moduli. The research applies EMTs such as Self-Consistent Approximation (SCA), Generalized Effective Medium (GEM), and Differential Effective Medium (DEM) to model the physical properties of rocks under varying conditions of pressure, porosity, and fluid saturation.

The study compares theoretical predictions with observed data to understand how resistivity, influenced by fluid connectivity and composition, correlates with elastic properties, which are sensitive to stress and fracture networks. The study can reveal critical insights into the mechanical and fluid characteristics of seismogenic zones. By integrating theoretical models with available geophysical data, this work provides a framework for analyzing the interdependence of electrical and elastic properties in seismogenic regions. The findings contribute to advancing the understanding of fluid dynamics, and rock deformation in seismogenic zones, offering a valuable tool for seismic hazard assessment and monitoring.

How to cite: Raju, K. and Siniscalchi, A.: Interrelationship between the electrical and elastic properties using effective medium theories, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17921, https://doi.org/10.5194/egusphere-egu25-17921, 2025.

Natural microseismicity serves as a potent tool for exploring smaller-scale hydrothermal and tectonic phenomena. Investigating seismic activities within the hydrothermal fields of mid-ocean ridges(MORs) offers profound insights into earth's internal dynamics. However, studies on natural earthquakes at ultra-slow spreading ridges, especially the Southwest Indian Ridge (SWIR), remain relatively scarce. To investigate the microseismic distribution, heat flow pathways, and tectonic characteristics of the Longqi hydrothermal field, a typical representative of SWIR, this paper processed one month of passive source OBS data from the DY43 cruise through microearthquake detection and relocation, obtaining a catalog of over 3000 earthquakes, significantly expanding the earthquake database for the Longqi field and improving the magnitude completeness. And the b-value calculation and imaging of the earthquake catalog were carried out using the maximum likelihood method and grid search method, respectively. The research results indicate that: ① The overall b-value of the SWIR Longqi field is 0.989; ② The b-value at the center of the Longqi hydrothermal vent is approximately 0.8, while the b-value around the vent is around 1.2; ③ High and low b-value areas alternate at a depth of 10km along the ridge axis; ④ There is an anomalously low b-value area of around 0.5 at depths of 12-16 km to the north across the ridge axis. Combining previous research results on b-values at MORs, this paper suggests that the background b-value of less than 1 in the Longqi field is consistent with its tectonic-type hydrothermal origin. The detachment fault beneath the Longqi hydrothermal vent leads to high stress and a low b-value, while the microseismic activity around the vent originates from rock fracturing caused by the combined effects of cold seawater and hydrothermal fluids. The uneven distribution of high and low b-values in the deep part of the hydrothermal field may reflect the uneven distribution of subsurface magma. The low b-value area in the north is speculated to be due to high stress resulting from torsional compression at the bottom of the detachment fault. In summary, it can be anticipated that the spatial distribution of b-values will serve as an indicator and reference factor for stress, fault structure, and magmatic-hydrothermal activity in MOR hydrothermal field in the future.

How to cite: wang, K.: Spatial distribution of b-values for microseismicity in the SWIR Longqi hydrothermal field and magmatic-tectonic interpretation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20441, https://doi.org/10.5194/egusphere-egu25-20441, 2025.

During active-source 2D marine ocean bottom seismic exploration, significant deviations of shot lines from the designed survey lines can introduce errors in 2D structural models, particularly in areas with rough bathymetry, such as mid-ocean ridges. By employing 3D tomography, it is possible to construct a three-dimensional model of the survey area that incorporates the actual shot locations and Ocean Bottom Seismometer (OBS) positions, leading to more accurate velocity structure models.

In 2021, the Joint Arctic Scientific Mid-Ocean Ridge Insight Expedition (JASMInE) acquired high-quality OBS data from the Gakkel Ridge in the Arctic Ocean. However, due to the presence of dense floating ice, significant offsets occurred between the shot lines and the OBS station profiles. Consequently, applying a 3D tomography-based modeling approach is essential for imaging the velocity structure in this region.

This study utilized the JIVE3D software to develop a 3D P-wave velocity model along a profile perpendicular to the 85°E spreading axis of the Gakkel Ridge, based on high-resolution multibeam bathymetry data. Compared to the velocity structure derived from 2D modeling, the P-wave velocities beneath the spreading axis are found to be lower in the 3D model, while lateral velocity variations in the upper oceanic crust are more pronounced away from the spreading axis. Despite these differences, the overall velocity structure and crustal thickness trends are consistent, indirectly validating the reliability of the 2D structural model.

Based on this 2D P-wave model, with data of 1257 S-wave arrival times picked from 9 OBS stations along the profile perpendicular to the mid-ocean ridge, using a forward modeling trial-and-error approach, a preliminary Poisson’s ratio structure beneath the profile was obtained. The Poisson’s ratio in Layer 2 of the oceanic crust ranges from 0.36 to 0.40, with relatively lower values beneath the spreading axis. In Layer 3, the Poisson’s ratio varies from 0.28 to 0.38. The relatively higher Poisson’s ratio values may indicate the presence of abundant fractures or fluids within the oceanic crust in this region.

How to cite: Niu, X., Li, J., Yang, W., Yu, J., Ding, W., and Zhang, T.: Poisson’s ratio structure and three-dimensional P wave velocity structure beneath the profile across the Gakkel ridge 85°E axis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11736, https://doi.org/10.5194/egusphere-egu25-11736, 2025.

Investigating the main geochemical characteristics of the lower continental crust is essential to understand its formation and evolution, identifying crustal differentiation processes and possible crust-mantle interactions. We performed bulk rock (major and trace elements), noble gases isotopes (He, Ne, Ar), and fluid inclusions (Raman spectroscopy) analyses on metamorphic rocks from Ivrea-Verbano Zone (Southern Italian Alps). Specifically, we studied various lithologies (metapelite, metagabbro, mafic and felsic granulite, amphibolite, and gneiss) to analyse the continuous metamorphic gradient from amphibolite- to granulite-facies.

Bulk rock analyses confirm the mafic nature of the protoliths for metagabbros (MgO = 5.36-10.25 wt.%), mafic granulites (MgO = 8.32-25.80 wt.%) and amphibolite (MgO = 7.98 wt.%) plotting in the metabasite field of the ACF chemographic diagram. Felsic granulite and sillimanite-gneiss fall within metamorphosed quartz-feldspar rocks, except for metapelite, which approaches the metacarbonate field, due to the presence of secondary carbonates. Metagabbros, mafic granulites and amphibolite show low REE concentrations (∑REE between 3 and 25 ppm) and high Cr and Ni contents (up to 1865 and 265 ppm respectively in mafic granulite), reflecting the mafic/ultramafic nature of the protoliths, whereas felsic granulite, sillimanite-gneiss and metapelite show higher REE contents (∑REE between 48 and 197 ppm).

³He/⁴He isotope ratios in metamorphosed quartz-feldspar rocks (0.06-0.30 Ra) and metabasites (0.15 and 0.45 Ra) are significantly radiogenic, although the metabasites show slightly higher values, corroborating a more primitive component in their source. Most samples plot near the air component in the ²⁰Ne/²²Ne vs ²¹Ne/²²Ne diagram, except for mafic granulites which show a crustal-air mixing trend. As regards the Ar isotope ratios, all samples appear rich in radiogenic component (⁴⁰Ar/³⁶Ar up to 2645 in metagabbros).

Raman spectroscopy analyses on fluid inclusions in orthopyroxene from mafic granulites show the coexistence of talc, graphite and magnesite with methane, providing direct evidence of a complex history in terms of post-metamorphic reactions and P-T-fO₂ conditions.

Our preliminary results show the compositional diversity and evolution of the lower continental crust, highlighting the interplay between mafic and sedimentary sources and the importance of fluid interactions and post-metamorphic processes.

How to cite: Carnevale, G., Caracausi, A., Correale, A., Fazio, E., Paonita, A., Romano, P., and Zucali, M.: Geochemical characterisation of Permian lower continental crust: case study from Ivrea-Verbano Zone (NW Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9306, https://doi.org/10.5194/egusphere-egu25-9306, 2025.

The Neoproterozoic western margin of the Yangtze Block in South China records significant continental crust-forming and modification processes through two distinct magmatic episodes. Using integrated geochemical and petrological approaches, we demonstrate that the 811-802 Ma Yuanmou Complex comprises alkaline high-Nb mafic rocks characterized by high Nb (15.7-41.9 ppm), TiO₂ (2.13-3.39 wt%) contents and positive ε_Nd(t) (+4.8 to +6.9), coupled with adakitic granodiorites showing high Sr/Y (17.4-49.0), (La/Yb)_N (16.3-52.6) and consistent bulk rock ε_Nd(t) (-0.5 to -1.5) and zircon ε_Hf(t) (0.0 to +2.3). The younger 750 Ma Jinping I-type granites exhibit high SiO₂ (71.2-73.5 wt%) and alkalis contents, enriched LREE patterns and depleted isotopic signatures (ε_Nd(t): -0.4 to +1.3; zircon ε_Hf(t): +4.83 to +8.37). Thermodynamic modeling reveals how crustal water content-controlled magma generation at different depths - low water-fluxed melting (2.0-3.5 wt% H₂O) produced I-type granites at medium pressure (6-9 kbar), while deeper settings with higher water content generated adakitic melts. The high-Nb mafic rocks in the Yuanmou Complex, derived from metasomatized mantle wedge, provide evidence for crustal-mantle interaction during back-arc extension. These coupled magmatic processes demonstrate how water content variations with depth influenced continental crust formation and evolution in arc settings.

How to cite: Huang, B., Wang, W., Zhao, J., Khattak, N. U., Li, R., Huang, S.-F., Lu, G.-M., Sun, L., Xue, E.-K., Zhang, Y., and Cai, X.-Y.: Water-fluxed melting and back-arc extension in the continental arc: Evidence from I-type granites, adakitic rocks and high-Nb mafic rocks at the western margin of the Yangtze Block, South China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7536, https://doi.org/10.5194/egusphere-egu25-7536, 2025.

This study analyses shear wave splitting measurements for core-refracted SKS and SKKS phases using data from nine strategically positioned seismic stations operated between 2023 to 2024 in the Central Indian Tectonic Zone (CITZ). The CITZ was formed during the mesoproterozoic orogeny in central India, resulting from the collision of the northern Bundelkhand Craton with a jumble of South Indian cratons (Dharwar, Bastar and Singhbhum Cratons). Understanding seismic anisotropy in this region is essential for elucidating mantle deformation patterns, which provides vital insights into geodynamic processes, lithospheric interactions, and ongoing tectonic activities shaping the CITZ. We employed both rotation-correlation and transverse energy minimisation techniques to determine the shear wave splitting parameters, namely the fast polarization directions (FPDs) and splitting delay times (δt). A total of 104 high-quality splitting measurements and 37 null measurements were obtained from 85 earthquakes (M ≥ 5.5) within epicentral distances of 84°-145° for SKS phases and 84°-180° for SKKS phases. The averaged δts at each seismic station ranges from 0.8 to 1.3 seconds, demonstrating significant anisotropy and heterogeneity in the upper mantle under the studied region. Our observations predominantly reveal NE-SW FPDs throughout the majority of stations, which correlate with the Absolute Plate Motion (APM) of the Indian plate. The discrepancies between FPDs and APM direction at some stations suggest the presence of fossilised anisotropic fabrics resulting from prior subduction events during mesoproterozoic. The smaller δt (0.8 sec) at the seismic station in the Pachmarhi region may be attributed to the significant magmatism during the cretaceous period. Null measurements, in conjunction with splitting measurements, suggest that the stations may be located in a region characterized by multi-layered or complex anisotropy. Our observations indicate that the mantle flow beneath the CITZ is influenced by the contemporary APM direction of the Indian plate as well as lithospheric frozen anisotropy.

How to cite: Bishoyi, N., Tiwari, A. K., and Dubey, A. K.: Mantle Deformation Pattern Beneath Central Indian Tectonic Zone: A Seismic Anisotropy Study in Satpura Gondwana Basin and Surrounding Areas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-964, https://doi.org/10.5194/egusphere-egu25-964, 2025.

Transform faults are often considered to be geometrically simple, nearly linear, vertical structures that localize crustal deformation within a narrow zone surrounding the fault. The deformation kinematics are typically purely strike-slip, parallel to far-field plate motion, with seismic slip above the brittle-ductile transition, near the 600 °C isotherm, which is well predicted by thermal models. Although deviations from these simplified features have been described, much remains to be learned about the seismogenic behavior of transform faults, for example, why they release much less seismic moment than predicted by plate motion models, or why they so rarely produce earthquakes of magnitudes as large as would be expected given their geometric segmentation (>M7). 

The Oriente Transform Fault (OTF) along the southern margin of eastern Cuba, at the boundary between the Caribbean and North American plates, is a particularly relevant example to inform on the seismogenic behavior of transform faults for at least 5 reasons: (1) the OTF geometry changes from a nearly continuous trace along the Cayman Ridge to a highly segmented one westward along eastern Cuba, (2) the geometrically continuous segment was the location of a magnitude 7.8 supershear earthquake in January 2020, (3) GNSS-derived strain measurements indicate that this segmentation variation corresponds to a transition from very shallow (<5 km) mechanical coupling —perhaps creep— of the fault, to complete coupling across the entire crustal thickness (20 km), (4) earthquake hypocenters offshore eastern Cuba locally reach subcrustal depths, (5) earthquake focal mechanisms and offshore geological observations show fault-normal compressional deformation along this purely strike-slip segment.

Here we revisit the offshore trace and seismotectonics of the OTF in light of recent data. We benefit from several oceanographic campaigns in the northern Caribbean, in particular the recent Haiti-TWIST campaign of the Pourquoi Pas? R/V, during which new high-resolution bathymetric and seismic reflection data were acquired, filling several important gaps. We also benefit from recent deformation results from GNSS measurements in Cuba, as well as a new compilation of earthquake moment tensor solutions.

How to cite: Calais, E., Leroy, S., Poort, J., Lebrun, J.-F., Mercier de Lépinay, B., Gonzalez, O., Moreno, B., Granja-Bruna, J.-L., Roest, W., Marcaillou, B., Aiken, C., and Klingelhoefer, F.: Seismotectonics of the Oriente Transform Fault revisited, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20933, https://doi.org/10.5194/egusphere-egu25-20933, 2025.

The continent-derived nature of the western Philippines (Palawan-Mindoro Microcontinental Block; PCB) contrasts with the island arc-dominated eastern Philippines (Philippine Mobile Belt; PMB). Petrological investigation on the P-T-D history of the metamorphosed rocks in between these two terranes and how they relate to the broader tectonic events are however lacking. In this study, we examined rock units related to the arc-continent collision events in two areas: the Romblon Island Group and the central Zamboanga Peninsula.

In central Philippines, the Romblon Metamorphic Complex (RMC) represents the PCB-derived materials. The RMC consists of metapelitic and metapsammitic paraschists in Tablas, Romblon, and Sibuyan with minor orthoschists and marbles. Using two-feldspar geothermometery, and Raman Spectrometry of Carbonaceous Material, the temperature variations revealed a low P/TStage 1 metamorphism of all RMC units with peak T and P values of about 450-540°C at <5 kbars. Based on tensional structures (e.g. boudins) and preserved metapelitic-metapsammitic interlayering, we attribute this Stage 1 to the PMB continental rifting and subsequent shallowing of the paleogeothermal gradient. The RMC paraschists which are adjacent to the Sibuyan Ophiolite  Complex (SOC) meanwhile register significantly higher T at the same low P conditions (= 570-630 °C). This suggests a second stage of higher T deformation and metamorphism directly linked with the juxtaposition of the continental RMC and the island arc SOC. This is consistent with the subsolidus shearing and metamorphism of the isotropic gabbro units of the SOC with preserved P-T conditions of about 500-800°C.

The southern extension of the PCB-PMB collision is even less understood although earlier works extend the arc-continent suture zone in Mindanao Island, southern Philippines. The purported boundary of the continent-derived Zamboanga Peninsula and the island arc Eastern Mindanao is the northwest-southeast trending Siayan-Sindangan Suture Zone. Our field mapping in central Zamboanga Peninsula however revealed a distinct northeast-southwest trending suture zone of an apparent arc-continent collision zone. Across this NE-SW suture zone, the lithologies progress from the paraschists of the Gutalac Metamorphic Complex (GMC) in the northeast to the amphibolites of the Dansalan Metamorphic Complex (DMC). Further southeast, the residual peridotites and pillow lavas with intercalated chert, deep marine turbidites and limestones of the Polanco Ophiolite Complex (POC) are exposed. Such progression hints at a NE-SW convergence of an ancient arc (POC) with its metamorphic sole (DMC) against the continent-derived GMC following the consumption of an ancient oceanic basin.

How to cite: Valera, G. T., Badillo, J. K., Tabilog, A. E. S., Balanial, N. M., Alcancia, M. L., and Payot, B. D.: Understanding the arc-continent collision zones in western Philippines: Novel insights from the Romblon Island Group and the Central Zamboanga Peninsula, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21462, https://doi.org/10.5194/egusphere-egu25-21462, 2025.

The Sargur Schist Belt (SSB), the oldest supracrustal greenstone belt, present in the south-eastern part of the Western Dharwar Craton (WDC), is a ~ 320 km long N-S to NNE-SSW trending discontinuous belts that occurs as patches and pockets within the granitic‒gneissic complex. The SSB is mainly composed of metamafic, metaultramafic, metapelite, banded magnetite quartzite, micaceous quartzite, pyroxene granulite, amphibolite, hornblende-biotite schist/gneiss, etc. The schistose belt has undergone at least five deformations in which the last three are very prominent. The N-S trending high strain zones with S₄ mylonitic foliation were produced during the EDC-WDC accretion (D₄ deformation). The D₅ deformation (developed due to the accretion of the WDC to Southern Granulite Terrane (SGT) along the Moyar/Bavali Shear Zone (BSZ)) developed broad open folds/warps in the N-S trend of the SSB (as well as WDC) with E-W trending axial planes. On a regional scale, the D₃ fold axes curve into the WNW-striking BSZ (D₅ deformation), a steeply dipping transpressional shear zone with dextral kinematics.

The estimated metamorphic P-T conditions of 440-585 °C and 6.0-9.5 kbar in metapelites from north to south and 640-770 °C and 7-10 kbar in granulites present in south only. The grade of metamorphism varies from greenschist facies in the north to upper amphibolite to granulite facies in the south. The metapelite and pyroxene granulite shows a loading and slow cooling path. The top to the north movement along the BSZ thrusted the high-grade metapelites, mafic-ultramafic rocks and granulite facies rocks over the WDC lithologies. The higher grade of metamorphism along the southern part as compared to the rest of the WDC is due to its location close to the WDC-SGT accretion zone. The zircons from the metapelitic schist provided older age population ranging between 3.3-3.2, 3.1-3.0 Ga followed by 2.9-2.7 Ga and 2.55-2.4 Ga, whereas the granulites (2.5 and 2.4 Ga) and foliated granites (2.6 Ga) yielded only the younger age populations. However, the monazites in schistose rocks located along the northern part recorded the oldest ages up to 2.7 Ga followed by 2.4 and 2.2-2.1 Ga ages. The monazites from foliated granites, irrespective of their location, provided ages of 2.53, 2.36 and 2.24 Ga. However, the monazites in schists and granulites from the southern part provided younger ages of 0.77, 0.67, 0.53 Ga. The prominent 0.84, 0.76 and 0.62 Ga monazite ages obtained from the metapelites close to the BSZ suggests that the accretion along the BSZ initiated in Mid-Neoproterozoic and continued till Early-Paleozoic. 

How to cite: Swain, M. and Rekha, S.: Structure, metamorphism and geochronology of Archean Sargur Schist Belt, southern India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-941, https://doi.org/10.5194/egusphere-egu25-941, 2025.

Experimental data on rock physical properties obtained through laboratory methods are enhanced by advanced techniques like X-ray microtomography (µCT) and image analysis. Lava rocks are important geological formations worldwide with varying textures, structures, and physical and mechanical behaviour. This research focuses on the heterogeneity analysis of vesicular lava rocks with intermediate composition from the Fogo Volcano (or Água de Pau Volcano, S. Miguel, Azores, Portugal). The effective porosity of six cubic samples is determined using the buoyancy technique. Ultrasonic wave velocities and capillarity absorption coefficient are obtained along three orthogonal directions using the through-transmission method and a European standard, respectively. Unconfined compressive strength (UCS) combined with µCT is determined in three cores from a single cube.

Results demonstrate that pore structure governs water uptake by capillarity and ultrasonic wave velocities. Regardless of the direction, the nonlinear water imbibition reflects a bimodal pore size distribution, confirmed through µCT imaging. The Sharp Front model describes this behaviour as the sum of two separate absorption processes related to larger (28.01-12.96 g/m²·s^0.5) and finer (0.45-1.73 g/m²·s^0.5) pores. Capillary-connected porosity (5.07%) is lower than connected porosity (18.5–20.1%) since gravitational fluid transport dominates for large pores (>1 mm). P-wave velocities (2802–3208 m/s) show minor dependence on pore shape, while Vp/Vs ratios (1.76 ± 0.25), dynamic Young’s modulus (16.78 ± 3.20 GPa), and Poisson’s ratio (0.23 ± 0.11) reflect vesicular textures.

µCT-based image analysis enables porosity quantification, revealing that effective porosity includes vesicles and pore-linking fractures. Permeability (0.7–6.6 mD) depends on tortuosity, which reduces fluid percolation despite higher connected porosity.

UCS (15.5-36 MPa) variations depend on pore size, orientation relative to the loading direction, and connected porosity, with minor influence from pore shape. µCT imaging reveals failure through tensile splitting, with fractures propagating from pore edges in all cores. The weakest specimen has more plagioclase phenocrysts, whose borders, intragranular cracks, and pores contribute to reduced strength.

These findings underscore the need to consider the heterogeneous pore structure of vesicular lavas when interpreting field measurements or improving volcano stability models. Advanced imaging and computational techniques clarify the role of vesicles and phenocrysts in strength and crack development patterns, providing important insights into the mechanics of lava rocks.

How to cite: Pereira, M. L., Cueto, N., Pappalardo, L., Buono, G., Falasconi, A., Moreira, M., Zanon, V., and Fernandes, I.: Characterisation of the heterogeneity of vesicular lava rocks from Fogo Volcano (Azores, Portugal) combining conventional laboratory methods with X-ray microtomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9505, https://doi.org/10.5194/egusphere-egu25-9505, 2025.

Vailulu’u seamount, located at the eastern extent of the Samoan hotspot chain, is an active deep-sea volcano with strong hydrothermalism and a recent history of eruptive episodes. Since 1999, a cone more than 500 m in diameter and with height greater than 300 m has formed within the caldera, while hydrothermal vent fields are known throughout the basin. These include regions of diffuse venting, substantial microbial mat formation, and chimneys emitting buoyant plumes of gas bubbles that are dominated by carbon dioxide. Measurements of turbidity and chemical enrichment in the caldera, temperature anomalies, and tracer dye studies have all previously been used to estimate and model the hydrothermal exports from this active volcano. Biological observations across the caldera – including the prevalence of carcasses in the so-called “Moat of Death” surrounding the Nafanua cone – have been used to infer the impact and fate of these volcanic emissions. However, it has previously been challenging to acquire high resolution in situ measurements of the discharged carbon dioxide at Vailulu’u, with the gas composition and distribution instead being determined primarily from discrete samples.

We present here a comprehensive spatiotemporal study of the carbon dioxide discharge from across the Vailulu’u seamount, acquired using SAGE, a new in situ carbon dioxide sensor. SAGE – the Sensor for Aqueous Gases in the Environment – was developed at Woods Hole Oceanographic Institution to quantify the concentration of dissolved gases in the deep sea. Dissolved gases are extracted across a gas-permeable membrane and into a hollow core optic fiber, which acts as an absorption cell for infrared absorption spectroscopy. SAGE has both a low detection limit (ca. 10 ppm) and a fast time response time (1-5 minutes). During a cruise on EV Nautilus in September 2024, SAGE was deployed on ROV Hercules and AUV Sentry to acquire high-resolution spatiotemporal maps of the carbon dioxide discharges from Vailulu’u. Comprehensive analysis of the hydrothermal exports from the vent fields on the rim allow estimation of the fate and flux of these discharges. Surveys from the caldera provide chemical context for the so-called “Moat of Death” and evidence for a significant diffuse venting across the Nafanua cone. To the best of our knowledge, this is the first study using in situ sensing of carbon dioxide at Vailulu’u.  

How to cite: Burkitt-Gray, M., Youngs, S., Marquardt, S., Remar, J., German, C., Soule, A., Kapit, J., and Michel, A.: Carbon dioxide emissions and fate from Vailulu’u seamount mapped using SAGE, a new in situ optical sensor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20524, https://doi.org/10.5194/egusphere-egu25-20524, 2025.

Banded Iron Formations (BIFs), generally containing magnetite (Fe₃O₄), hematite (Fe₂O₃), and quartz (SiO₂) in Archean oceans, have important implications for the primitive-life and sea-water condition of the primitive Earth. It is generally agreed that BIFs were deposited within marine sediments on stable continental margins (Superior-type) or associated with volcanic rocks (Algoma-type). The oxidation of Fe with free O₂ is challenging due to the lack of knowledge on the extent and amount of the free oxygen available in oceanic water. Iron can precipitate in two oxidation states, i.e., +2 and +3, in magnetite and hematite, respectively. In addition, the magnetite crystallizes in the isometric crystal system, whereas hematite crystallizes in the trigonal crystal system. Since Electron Probe microanalysis cannot differentiate the oxidation states of Fe, we use X-ray diffraction and δ⁵⁶ Fe values to identify the mineral phases in BIFs and utilize the EH–pH diagram to constrain the pH and redox state of Archean oceans.

The Banded Iron Formation occurs in two east-west trending linear belts in the Bundelkhand Craton. The northern belt, extending from Babina in the west to Mauranipur in the east, is an Algoma-type BIF. In contrast, the least explored southern belt, near Girar, is a Superior-type BIF. Powder X-ray diffraction patterns of the northern BIF belt indicate hematite and quartz without carbonates. On the contrary, the X-ray diffraction pattern of BIFs from Girar suggests the presence of quartz, hematite, and siderite. In addition, the result of Fe-isotope data indicates that the δ⁵⁶ Fe values of Northern BIFs range from 0.205⁰/₀₀ to 0.255⁰/₀₀, while the δ⁵⁶ Fe values from the Southern BIFs range from 1.350⁰/₀₀ to 2.126⁰/₀₀.

The high positive δ⁵⁶ Fe from the Fe-rich bands indicates that Fe (III) delivery was the primary mechanism driving iron enrichment in the Southern BIFs. The Southern BIF's substantial Fe isotope fractionations indicate initial partial Fe (II) oxidation in low-Eh conditions as siderite, the primary mineral for hematite, was deposited between pH and Eh of 7.5 to 10 and -0.3 to -0.2 volts. With an increase in the Eh to -0.2 to -0.1, magnetite becomes the stable phase. Still, with an increase in the Eh (0.1 to 0.3 Volts), hematite becomes stable in phases with the same pH range as the aqueous medium. Since an increasing Eh with a similar pH range indicates oxidation, we suggest that southern Bundelkhand Craton BIFs materials were deposited in more oxidized conditions. This evidence suggests that microbial Fe (III) reduction in Southern BIFs occurred during the Earth's Late Neoarchean – Early Paleoproterozoic transition. The increased oxidation condition, i.e., excess oxygen in the Archean Sea in Bundelkhand Craton, could probably relate to photochemical or microbial oxidation.

How to cite: Bisht, B. P. S., Kk, A., and Nasipuri, P.: X-ray diffraction pattern and Fe-isotope of Banded Iron Formation to constrain the fluctuating redox State of Archean Ocean: A Case Study from Banded Iron Formation from Bundelkhand Craton, North Central India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-123, https://doi.org/10.5194/egusphere-egu25-123, 2025.