GMPV5.4 | Volcanic hydrothermal alteration and fluid-rock interactions
EDI
Volcanic hydrothermal alteration and fluid-rock interactions
Convener: Claire Harnett | Co-conveners: Michael Heap, Alexandra Kushnir, Thomas R. Walter, Marlene Villeneuve
Orals
| Tue, 25 Apr, 16:15–18:00 (CEST)
 
Room -2.33
Posters on site
| Attendance Tue, 25 Apr, 10:45–12:30 (CEST)
 
Hall X2
Orals |
Tue, 16:15
Tue, 10:45
Hydrothermal systems exert crucial influence on volcanic hazards. For example, hydrothermal alteration can reduce the strength of edifice- and dome-forming rocks, increasing the likelihood of volcano spreading and flank collapse, and high pore pressures that develop within hydrothermal systems can promote phreatic/phreatomagmatic explosions and further increase volcano instability. On the other hand, hydrothermal systems also offer the opportunity to exploit minerals of economic interest, and their heat can be harnessed to produce energy. A detailed understanding of hydrothermal systems, fluid-rock interactions in hydrothermal systems, and the resulting effects of alteration, using multidisciplinary studies, is required to better anticipate the hazards posed, to exploit the economic opportunities they provide, and to execute engineering design. We invite diverse contributions dedicated to the characterisation, imaging, monitoring, and hazard/economic assessment of volcanic hydrothermal systems and associated fluid-rock interactions. Contributions can be based on fieldwork, laboratory work, modelling, or a combination of these approaches. Because understanding hydrothermal systems requires multidisciplinary, collaborative teamwork, we welcome contributions based on any subdiscipline (e.g., geology, geophysics, geochemistry, engineering) and using any technique or method (e.g., geological mapping, magnetic, gravity, and spectroscopic methods, laboratory experiments, gas monitoring, numerical modelling). It goes without saying that we hope to have a diverse session in terms of both speakers and audience.

Orals: Tue, 25 Apr | Room -2.33

Chairpersons: Claire Harnett, Alexandra Kushnir, Marlene Villeneuve
16:15–16:20
16:20–16:40
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EGU23-12564
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solicited
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Virtual presentation
Corentin Caudron, Thomas Lecocq, Alexander Yates, David Dempsey, Alberto Ardid, Thomas Hermans, Lore Vanhooren, Olivier Fontaine, Tom Bultreys, and Társilo Girona

Most volcanoes on Earth host a volcano-hydrothermal system. Lying between the surface and magma reservoirs, they exert a dramatic influence on volcano dynamics. Understanding their behavior is however challenging because of the complex interplay between gas, liquid, and rocks. Volcanic gas can, for example, be completely scrubbed through interactions with groundwater whereas the kinetics of these reactions are controlled by thermodynamic conditions that are poorly constrained. While fluid circulation gives rise to a range of geophysical signals such as ground vibrations, self-potential, or variable resistivity observable at the surface, their complex dynamics complicate the isolation of pre-eruptive signals and the interpretation of the observed volcanic activity. Indeed, some volcanoes remain on alert for months or years without experiencing any eruption. Such situations severely affect the credibility of the agencies in charge of monitoring volcano activities.

In this contribution, we will focus on multi-disciplinary efforts to better characterise the time evolution of these complicated systems. Our ultimate goal is to deconvolve the contribution of dynamic processes occurring in such systems (temperature, gas saturation, alteration, precipitation) to possibly facilitate real-time monitoring efforts. Our examples come from different parts of the world, in both hemispheres.

How to cite: Caudron, C., Lecocq, T., Yates, A., Dempsey, D., Ardid, A., Hermans, T., Vanhooren, L., Fontaine, O., Bultreys, T., and Girona, T.: Towards monitoring volcanic hydrothermal alteration using geophysical approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12564, https://doi.org/10.5194/egusphere-egu23-12564, 2023.

16:40–16:50
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EGU23-12873
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ECS
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On-site presentation
Lore Vanhooren, Olivier Fontaine, Corentin Caudron, Elien Vrancken, Warre Dekoninck, Hanne De Lathauwer, and Thomas Hermans

Volcanic Hydrothermal systems (VHS) are three-phase reservoirs between the magma chamber and the earth’s surface, they are present in most volcanoes on Earth but the dynamical behavior is currently poorly known. As fluid circulation gives rise to a range of geophysical and hydrothermal signals, it complicates the detection of pre-eruptive signals, hence certain volcanoes remain on alert for significant amounts of time without erupting. Moreover, VHS lie at the basis of phreatic or hydrothermal eruptions, which can cause significant casualties. Given these safety concerns it is thus paramount that we gain a better understanding of the dynamics of VHS.

Traditionally seismometers are used to monitor VHS but the high level of background noise complicates the application of standard processing techniques. Here we apply geo-electric methods for characterization and monitoring. Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) provide a relatively high resolution image of the subsurface electrical properties. The main dynamic processes occurring in VHS are temperature changes, variations in saturation and mineral precipitation, all of which influence the electrical signal making ERT/IP a suitable method to monitor this system. Similarly, the spontaneous potential signal (SP) is influenced by fluid flow and diffusion/conduction processes and should therefore bring complementary information to ERT/IP.  

In this project the Gunnuhver geothermal area in Iceland is monitored on a daily basis since October 2022. Prior to the monitoring campaign a field characterization was executed where 5 profiles were measured using ERT/IP and SP. Due to the proximity to the ocean, the groundwater in this area is saline which complicates the IP data acquisition, as saline environments have a low ability to store electrical charge. Hence, in the characterization phase we attempted to find the most suitable method for acquiring an IP signal in this high-temperature, saline setting. The static ERT profiles show a high spatial variability in the area, where the alteration zone, characterized by very low resistivity, is clearly distinguishable from the more resistive basalt. Adjacent to the geo-electrical methods the characterization and monitoring also include seismicity, fiber-grating, CO2 measurements and shallow soil-moisture and -temperature measurements.

By developing a novel time-lapse inversion approach, where the auxiliary data helps to constrain the interpretation of the ERT/IP profiles, we are able to get new insights into the inner workings of Volcanic Hydrothermal Systems.

How to cite: Vanhooren, L., Fontaine, O., Caudron, C., Vrancken, E., Dekoninck, W., De Lathauwer, H., and Hermans, T.: Characterization and Monitoring of the Gunnuhver geothermal site using electrical methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12873, https://doi.org/10.5194/egusphere-egu23-12873, 2023.

16:50–17:00
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EGU23-11501
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On-site presentation
Gabor Kereszturi, Antonio M. Álvarez-Valero, Nessa D'Mello, Craig Miller, and Daniel A. Coulthard Jr

Composite volcanoes can progressively weaken through hydrothermal alteration, which may lead to volcano collapse, forming far-reaching debris avalanches. Hydrothermal minerals can also contribute to flank instability as they play a critical role in moderating volcanic degassing by changing the porosity and permeability of the rock and thereby changing the local pore-pressure distribution. Therefore, a robust model and understanding of hydrothermal alteration within a volcanic edifice is important to improve hazard assessment efforts. This study investigates the type and extent of hydrothermal alteration on Mt Ruapehu, New Zealand, using a combination of mineralogical, hyperspectral imaging, and aero-magnetic studies.

Mt Ruapehu shows a diverse suite of surface weathering and hydrothermal alteration minerals, which are distributed heterogeneously on the surface. The surface weathering has abundant goethite, hematite and phyllosilicate mineral associations, while the hydrothermal alteration is characterised by phyllosilicates, Fe-oxides, pyrite, jarosite, alunite, gypsum anhydrite, and native sulphur minerals. Although surficial evidence of alteration on Mt Ruapehu is limited, aero-magnetic data and inversion modelling indicate deep-seated (≤500 m) alteration of demagnetized rocks. The decrease of magnetic susceptibility can be linked to the dissolution of (Ti-) magnetite phases, as well as the deposition of brecciated horizons between lava flows and intercalated glacial till and volcaniclastics. Surface outcrops mapped by airborne hyperspectral imaging combined with Scanning Electron Microscopy (SEM-EDS), Short wavelength Infrared (SWIR) Spectroscopy, X-Ray Diffraction and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) data of ground samples reveal a complex alteration history developed around older vent/crater systems of Mt. Ruapehu in last 250 ky. This study provides a simplified geological model to capture the hydrothermal processes on Mt Ruapehu, aiding future studies on delineating areas prone to mass movements.

How to cite: Kereszturi, G., Álvarez-Valero, A. M., D'Mello, N., Miller, C., and Coulthard Jr, D. A.: A multidisciplinary approach to constrain hydrothermal alteration history on Mt Ruapehu (New Zealand), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11501, https://doi.org/10.5194/egusphere-egu23-11501, 2023.

17:00–17:10
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EGU23-12942
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ECS
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On-site presentation
Daniel Müller, Thomas R. Walter, Valentin Troll, Jessica A. Stammeier, Andreas Karlsson, Erica De Paolo, and Antonino Fabio Pisciotta

Fumarole fields and hydrothermal alteration are prominent signs of volcanic degassing at many volcanoes, and their monitoring is an essential part of the assessment of volcanic unrest. Yet, our knowledge about the detailed structure of fumarole fields and the spatiotemporal processes in their complexity is still poor, owing to limited accessibility. By using modern drone and sensor technologies we now are able to provide high-resolution data that allows us to analyze fumarole fields at cm-scales. From 2018 to 2022, we conducted repeated drone surveys at the fumaroles of La Fossa volcano on Vulcano Island (Italy). Drones equipped with a 20 MP camera and a radiometric thermal infrared sensor allowed the close-range acquisition of optical and thermal infrared images. By means of Structure from Motion (SfM) processing, the generation of high-resolution ortho- and infrared mosaic data was achieved. Applying Principal Component Analysis and image classification to the orthomosaic data, we detected and classified areas affected by degassing and hydrothermal alteration covering more than 60.000 sqm. By analyzing their spectral characteristics, we defined 4 surface types, of which type 1 and 2 are largely coincident with the thermally active surface. Type 3 is an altered low-temperature surface and type 4 is an unaltered surface. To evaluate these surface types, samples were analyzed in the lab for their mineralogical and geochemical composition by X-ray diffraction and fluorescence analysis, showing significant variability in composition. Further, we analyzed the spatial variability of the surface degassing activity using a portable multi-gas device. The combination of these methods allows us to constrain factors that are controlling the observed surface pattern of the degassing system, and to better understand the structural setup of the fumarole field and broader field of activity. We find that the actual high-temperature fumarole sites only account for <10% of the active surface. Besides, large thermally active areas, thermal aureoles for instance, display a rather diffuse activity. During the 2021 volcanic crisis, next to the high-temperature fumaroles, especially those diffuse features showed a response to the increased gas flux, emphasizing their structural importance. We summarize spatiotemporal variations during the crisis, and indicate possible widespread effects of the long-term gas-rock interaction like surface sealing, and forced lateral gas migration, affecting large parts of the fumarole field. The results suggest that detailed structural studies of fumarole fields by means of drone-based remote sensing in combination with in-situ measurements can contribute to a better understanding of degassing and alteration effects, with relevance for degassing sites elsewhere and during volcanic crises. 

How to cite: Müller, D., Walter, T. R., Troll, V., Stammeier, J. A., Karlsson, A., De Paolo, E., and Pisciotta, A. F.: Drone and field-based monitoring of the degassing and alteration structures of the La Fossa fumarole field (Vulcano Island), before and during the 2021 volcanic crisis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12942, https://doi.org/10.5194/egusphere-egu23-12942, 2023.

17:10–17:20
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EGU23-12320
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On-site presentation
János Szepesi, Alessandro Vona, István János Kovács, Krisztián Fintor, Kata Molnár, Alex Scarani, Guido Giordano, and Réka Lukács

The silicic flows and domes can impose mechanical and thermal stress on the underlying substrate causing mineralization and lithification of granular bodies. In addition, the released water from the permeable substrate as dominant volatile species can contribute to the glass hydration of the flow. This fluid-lava interaction can be directly studied in ancient successions with exposed contacts. The Lebuj flow (Tokaj Mountains, Hungary) developed in a Miocene caldera setting, where the erosion revealed its basal zone including lava-substrate interaction textures. The main textural units comprise (1) a rhyolitic lava flow (F1: perlitic glass with obsidian marekanite, F2: microcrystalline-glass transition and F3: a basal breccia layer) and (2) the underlying mixed substrate unit (S1: massive rhyolite and breccia S2: enclosed partially sintered rhyolite tuff). The thin section textural analyses were completed by BSE imaging, Raman mapping (SiO2 polymorphs) and FTIR spot measurement (perlite H2O, clays). Glass transition temperature (Tg) was estimated using the chemical based GRD model.

The flow margin contacted with underlying volcanoclastic deposits along a steeply inclined (50-75°) plane with subordinate fragmentation. The substrate suffered re-heating by the flow where porosity loss and welding (solid-state sintering) occurred. The silica polymorphs are observed growing into open pore spaces and fractures and interpreted as precipitates from vapor phase fluids passing through the permeable lithologies. The smectite group minerals typically record acidic type alteration, where the water-rock interaction commonly produces glass replacement minerals. The FTIR-identified clays (mixed layer kaolinite/montmorillonite or beidellite) indicate low-to medium alteration degree (estimated temperature between 50-100 °C).

The lithophysae, spherulites and microcrystalline bands in the flow unit are textural evidence for prolonged groundmass crystallization above Tg. The relict obsidian grains in the glass are proofs of an incomplete hydration process. The FTIR and BSE investigations demonstrate the presence of sharp transitions from the hydrated ~3 wt.% perlitic rims to non-hydrated obsidian cores.

Textural and mineralogical evidence suggest that the following series of events occurred as the consequences of the lava-substrate interaction: a) a viscous rhyolite flow advanced on an irregular topography; b) shear and brittle fracturing occurred at the contact; c) groundmass crystallization (above Tg, ~ 690-715 °C) and hydration (below Tg) acted in the flow; d) low temperature mineralization and variable scale sintering occurred in the substrate (below Tg). According to the fluid exchange model beneath silicic lava domes (Ball et al. 2015), the water – rock interaction resulted in weak hydrothermal alteration of the substrate and water flux to the quenched glass (flow). As an interaction of the two processes, the increased sintering and mineralization reduced the porosity of the substrate which probably restricted further water uptake for hydration. Thus the obsidian results from a ‘quenched’ hydration front (Bindeman and Lowenstern 2016).

 

Ball J.L., Stauffer P.H., Calder E.S., Valentine G.A. (2015). Bull Volcanol 77:1–16.

Bindeman I.N., Lowenstern J.B.  (2016).  Contrib to Mineral Petrol 171:89

 

Aknowledgements

This research has been funded by the Hungarian–Italian MTA-CNR bilateral research project 2019–2022. The research was also supported by Development and Innovation Office–NKFIH No. 131869 OTKA project. RL was supported by the Bolyai János Research Fellowship.

How to cite: Szepesi, J., Vona, A., Kovács, I. J., Fintor, K., Molnár, K., Scarani, A., Giordano, G., and Lukács, R.: Lava – substrate interaction: constraints on perlitic hydration and low temperature mineralization, Lebuj rhyolitic flow, Tokaj Mountains, Carpathian-Pannonian region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12320, https://doi.org/10.5194/egusphere-egu23-12320, 2023.

17:20–17:30
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EGU23-7059
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On-site presentation
Jens Niclaes, Marie Detienne, Michael Heap, Pierre Delmelle, and Hadrien Rattez

The growing structure of active volcanoes due to material addition can lead to oversteepening and overloading (McGuire, 2003). This situation can be worsened by seismic activity as most volcanoes are in seismically active areas. Moreover, the materials forming volcanic edifices are subjected to extreme conditions in terms of temperature, pore pressure (consequence of several combined factors) and chemically aggressive fluids (very low pH for example) which can all destabilize volcanoes’ flanks. Among these factors, hydrothermal activity is of particular interest as it enhances rock dissolution (and thus, increases rock porosity), promotes high pore pressures and leads to the creation of mechanically weaker materials (like clay-rich rocks) and promote the instability (Rattez and Veveakis, 2020). However, the effects that these processes have on volcano stability have been barely quantified (Heap and Violay, 2021).

To better understand the influence of different types of hydrothermal alteration on the hydraulic and mechanical properties of volcanic rocks, permeameter and triaxial experiments have been performed on samples retrieved by Detienne et al. (2016) from the Tutupaca volcano (17° 01′ S, 70° 21′ W). This volcano is a dacitic dome complex located at the southern end of the Peruvian arc. The study focuses on a remarkably well-preserved debris avalanche deposit emplaced to the northeast of the volcano. The debris avalanche is sourced to Eastern Tutupaca; it left a horseshoe-shaped crater open to the northeast and was accompanied by a pyroclastic flow (volume: 6.5-7.5 x 107 m3) (Samaniego et al., 2015). The mineralogy and the microstructure of the samples have been investigated using X-ray diffraction and micro-computed tomography respectively. Preliminary results exhibit a high variability of mineralogy, microstructures, and mechanical properties. It appears that the alteration degree may have more influence on the mechanical behavior of volcanic rocks than the porosity. This dataset could be further used in numerical models of flank collapses to better constrain the role of hydrothermal alteration on the nucleation of those events. 

References

Detienne M. (2016) “Unravelling the role of hydrothermal alteration in volcanic flank and sector collapses using combined mineralogical, experimental, and numerical modelling studies”. PhD thesis, UCLouvain.

Heap M. and Violay M. (2021) “The mechanical behaviour and failure modes of volcanic rocks: a review”, Bulletin of Volcanology, 83:33. 

Lipman PW, Mullineaux DR (eds) (1981) “The 1980 eruptions of Mount St Helens, Washington.” U.S. Geological Survey, Professional Paper 1250, 844 pp.

McGuire WJ (2003) Volcano instability and lateral collapse. Revista 1:33–45.

Rattez H, Veveakis M (2020). “Weak phases production and heat generation control fault friction during seismic slip”, Nature Communications, doi: 10.31223/osf.io/xupr8

Samaniego, P., Valderrama, P., Mariño, J., De Vries, B. V. W., Roche, O., Manrique, N., Chédeville, C., Liorzou, C., Fidel, L. & Malnati, J. (2015). “The historical (218±14 aBP) explosive eruption of Tutupaca volcano (Southern Peru) ». Bulletin of Volcanology, 77, 1-18.

 

How to cite: Niclaes, J., Detienne, M., Heap, M., Delmelle, P., and Rattez, H.: Experimental insight into the role of hydrothermal alteration on the mechanical and microstructural properties of the volcanic rocks: The case of Tutupaca, Peru, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7059, https://doi.org/10.5194/egusphere-egu23-7059, 2023.

17:30–17:40
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EGU23-14028
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ECS
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Virtual presentation
Vijay Saini, Piyush Sriwastava, and George Mathew

The global dominance of basaltic rock in the crust plays a dominant role in the global elemental geochemical cycle. Smectite clay is a ubiquitous alteration product of basalt. Despite having a complex silicate structure, a phyllosilicate dominance of smectite raises a question on the kinetics aspect of its formation and underlying nucleation and growth mechanism during basalt alteration. In the experimental formation of smectite, Zhang et el., 2019 have shown that coherent scattering domain size (CSDS) remains constant for starting few days during the growth of the sheet, and then stacking of fundamental particles takes place, resulting in the growth along C*. A later study by Kuliviesz et al., 2018 has shown variation in the layer charge with clay size. This implies chemical changes in the clay with its growth, which complicates the problem. The current study aims to investigate the mechanism and pathway of smectite crystallization. We have studied the role of magnesium in the growth of smectite clay and its mechanism.

Experimental alteration of basaltic glass has been performed at 150 degree Celsius in two different fluid compositions. One is containing 0.3M MgCl2 and the other pure water. Products have been investigated under XRD, FTIR, TEM, and SEM; solution has been investigated under ICP AES.

We found that both the experimental setup resulted globular flower-like feature along with a honeycomb structure on the glass surface. There is no XRD-detectable crystalline product, but electron microscopy has confirmed smectite, the globular flower-like structure (similar to Fiore et al. 2001). There is a discernible difference in the size of globules. Mg bearing condition has leather size flakes and globule than without Mg. Magnesium bearing experiment has shown higher Si concentration in the solution than without Mg, similar to Al's behaviour.

Smectite formed in the Mg bearing experiment has twice the amount of Mg in clay structure than smectite formed in an experiment without Mg. Based on 11 oxygen, the chemical composition of smectite has been used to calculate the abundance of cation pairs in the octahedral sheet if there is a random distribution of all cations. At the same time, observation based on FTIR spectra has shown a dominance of Mg-Mg pairs. This has been observed in both experiments. Our study confirms a preferential ordering of Mg-Mg cation pairs in the octahedral sheet and better growth in the presence of Mg.

Further TEM investigation is being performed to observe the fundamental particle size and chemical relation.

How to cite: Saini, V., Sriwastava, P., and Mathew, G.: Experimental Study of Basalt Alteration At 150 °C: An Approach To Understand Smectite Nucleation And Crystallization Pathways, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14028, https://doi.org/10.5194/egusphere-egu23-14028, 2023.

17:40–17:50
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EGU23-9333
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On-site presentation
Peter LaFemina, Emilie Saucier, Maureen Feineman, and Armando Saballos

Telica volcano is a persistently restless volcano with activity expressed as long-lived high-temperature fumaroles and magmatic degassing, high rates of background seismicity and frequent (sub-decadal) explosive, phreatic to phreatomagmatic eruptive activity. We are studying this system through the combination of geophysical, geochemical, and geologic observations and analyses. To date our observations and analyses indicate: 1) long-lived fumaroles and subsequent hydrothermal alteration of the crater walls lead to regions of preferential crater wall collapse into the active the crater; and 2) hydrothermal alteration and mineralization within the shallow hydrothermal system leads to sealing of the conduit, a build-up of pressure and explosions. The partial to complete sealing of the top of the volcanic conduit is thought to occur through the deposition of salts and silicate minerals from hydrothermal fluids, moving the volcano from an open to a closed system. The formation of a seal is observed indirectly by the eruption of hydrothermal mineral species and altered rock, decreases in measured gas flux, thermal anomalies, and LF seismicity that indicates a decrease in gas flow, and deformation of the volcanic edifice due to the increase in pressure from gas accumulation. Additionally, the eruption of a small volume lava dome in 2017 indicates the presence of highly viscous basaltic andesite magma in the conduit, which may also contribute to sealing of the conduit and the observed deformation. Here, we model cGPS displacement time series based on our conceptual model for the transition from an open to a closed system, utilizing our disparate, but complimentary data sets, including gas flux, terrestrial and remotely sensed thermal, web camera and cGPS displacement time series. Our numerical model incorporates changes in permeability of the conduit due to mineralization and the subsequent accumulation of gas beneath the seal. The increase of pressure due to sealing of the system and rising magma eventually leads to failure of the seal and phreatic explosions. Improving our knowledge of this transition from an open to closed system is important for understanding Telica’s eruptive processes and hazards, as well as gaining a better understanding of how this transition could manifest at other volcanic systems.

How to cite: LaFemina, P., Saucier, E., Feineman, M., and Saballos, A.: Persistent Activity and Crater Formation at Telica Volcano Driven by the Shallow Hydrothermal System, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9333, https://doi.org/10.5194/egusphere-egu23-9333, 2023.

17:50–18:00

Posters on site: Tue, 25 Apr, 10:45–12:30 | Hall X2

Chairpersons: Claire Harnett, Michael Heap, Thomas R. Walter
X2.161
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EGU23-2401
Claire Nichols, Stephanie Halwa, and Stuart Robinson

Eoarchean (3.7 Ga) banded iron formations (BIFs) from the Isua Supracrustal Belt, Southwest Greenland have been variably metamorphosed and deformed.  At the top of the northeastern extent of the belt, the lowest degree of metamorphism is observed with a maximum pressure and temperature of 1.5 – 4 kbar and 360 – 400 °C, respectively.  Previously, the banding in these BIFs has been interpreted as entirely tectono-metamorphic in origin3.  However, in the best preserved regions in the northeastern part of the belt the BIFs are exceptionally well preserved, and exhibit potentially sedimentary features including possible way-up indicators.

 

A particularly striking features of the BIFs in the northernmost region are repetitive bands of brecciated material which are approximately 30 cm wide and occur every 1 – 2 m.  Similar brecciation textures are observed in dolomites in the area which have previously been interpreted as tempestites (storm-wave breccias) and evidence for a shallow marine environment.  The occurrence of similar breccias in the BIFs is at odds with the interpretation that these deposits formed in relatively deep water.  The aim of this study is to interrogate the origin of the brecciated layers in the BIF, and whether these layers represent primary depositional ‘beds’ or were formed by later metamorphism and fluid alteration.

 

Petrographic observations show that the brecciated layers contain extensive carbonates, while the surrounding BIF is dominated by alternating layers of magnetite and chert. This is consistent with the contrast in weathering between the brecciated layers and banded layers from field observations.  The origin of the carbonates is investigated by examining their δ13C and δ18O isotope and rare-earth element compositions.  Preliminary results indicate that the breccias are hydrothermal in origin.  We use these observations, in combination with paleomagnetic field tests to argue for some degree of preservation of primary depositional features in the Isua BIF.

How to cite: Nichols, C., Halwa, S., and Robinson, S.: Hydrothermal breccias in banded iron formations from the Isua Supracrustal Belt, Southwest Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2401, https://doi.org/10.5194/egusphere-egu23-2401, 2023.

X2.162
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EGU23-5968
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ECS
Angela Mormone, Teresa Caputo, Ermanno Marino, Giuseppina Balassone, and Monica Piochi

The combined use of minero-petrological analyses and drone photogrammetry may represent a powerful way to better understand the dynamics of hazardous geological environments. This can help to map, investigate and monitor volcanic structures that are modifying by actual processes, particularly through the creation of a time series of spatial data able to evidence the geomorphological evolution and mechanical features variation of landscapes.

In this study we investigate the relationships between acid sulfate weathering, geostructural framework and geomorphological changes that can be observed at active volcanic hydrothermal systems. The investigated area is Montagnone-Monte Cito, site of high temperature geothermal activity, flank instability and disastrous seismicity in historical and recent times. The target area, in fact, is the one closest to the city of Casamicciola, remembered as the epicenter of the destructive volcanic-tectonic event (approx. magnitude 4.0) which took place on August 21, 2017 and was unfortunately destroyed by a powerful landslide on November 26, 2022.

Photogrammetry of proximity survey, geological field campaign, mineralogical and geochemical analysis with Optical Microscopy (OM), X Ray Diffraction (XRD), Electron Microscopy and Energy Dispersive microanalysis (SEM-EDS), and handheld X-Ray Fluorescence (XRF) to characterize altered outcropping deposits, were repeatedly carried out in the area. We present multitemporal analysis based on the comparison of 3D data obtained by UAV photogrammetry techniques. We comparison two dataset acquired in 2022 for each of which we obtained a 3d point cloud, that has provided the setting of the area at the different times and its evolution through their comparison evaluating volumetric changes.

Modifying sites have been examined in the field and characterized for mineralogical and geochemical features. Our methodological approach appears promising to evaluate evolution and rock fall susceptibility of solfataric terrains subjected to hydrothermal dynamics.

How to cite: Mormone, A., Caputo, T., Marino, E., Balassone, G., and Piochi, M.: Combining minero-petrological and geomorphological analyses at active volcano-tectonic and hydrologically hazardous areas: a case study on Montagnone-Monte Cito at Ischia (southern Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5968, https://doi.org/10.5194/egusphere-egu23-5968, 2023.

X2.163
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EGU23-7382
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ECS
Ali Erdem Bakkalbaşı, Zeynep Döner, Hatice Nur Bayram, Ali Tuğcan Ünlüer, and Mustafa Kumral

The Biga peninsula (NW, Turkey) hosts numerous polymetallic mineral deposits including skarns, porphyry Cu-Mo, vein type Pb-Zn, and epithermal Au–Ag. These mineralizations are mainly associated with widespread high-K magmatism in the Oligo-Miocene period. Of these the epithermal veins which have economic grade Au-Ag concentrations are generally found in volcanic rocks such as dacites, andesites, and pyroclastic rocks. The hydrothermal aureoles' interaction with highly permeable volcanic rocks caused voluminous alteration zones with potential precious metal enrichments. The Kısacık (Biga Metallogenic Province of NW, Turkey) area can be considered as a promising precious metal mineralization zone due to the high-intensity alterations observed in Miocene volcanic rocks (dacites and pyroclastic rocks). In the study area, the hydrothermal activity can also be seen in basement metamorphic (calcschists) and ophiolitic (basalts - dolerites) rocks. The identified hydrothermal alterations in the field are sericitic and argillic alterations with intense silicifications. The silicifications are mostly observed in cracks and joint fractures of volcanic rocks in the form of veinlets and cavity fills. Major oxide-Trace Element and ICP-MS Ag-Au-PGE’s analysis was performed on the samples taken from the field. The calculated alteration indexes (AI) are ranging between %82-99.2 and Chlorite-Carbonate-Pyrite Indexes (CCPI) values are between %73-97 according to major oxide values of altered volcanics. The Au content varies between 0.03 – 21.34 ppm. When the hydrothermal trend is examined in the AI-CCPI diagram, the altered high grade volcanics shows a chlorite-sericite-pyrite alteration trend. These implications are parallel with field observations. The less altered volcanics are located within the andesite/basalt field. Highly altered volcanics are located in the "ore center" area of the diagram. The calculated alteration index (AI&CCPI) values of the volcanic rocks are high, mainly caused by the removal of mobile cations such and a significant enrichment in immobile cations such as Al and Fe. In addition, a silica-carbonate alteration zone around ophiolitic rocks was observed and gold content of up to 0.16 ppm was detected in samples from this area which indicates a listwanite-type Au deposit.

Keywords: Alteration indexes, Miocene Volcanics, Hydrothermal Deposits, Biga Peninsula, Turkey

How to cite: Bakkalbaşı, A. E., Döner, Z., Bayram, H. N., Ünlüer, A. T., and Kumral, M.: The Alteration Chemistry of a Multi-Stage Volcanic Hosted Epithermal Gold Mineralization; Kısacık Case (Biga Metallogenic Province of NW, Turkey), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7382, https://doi.org/10.5194/egusphere-egu23-7382, 2023.

X2.164
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EGU23-7918
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ECS
Hatice Nur Bayram, Mustafa Kumral, Ali Erdem Bakkalbasi, Mustafa Kaya, and Amr Abdelnasser

Fluid inclusion analyses were performed on the gold-bearing quartz carbonate veins in order to pinpoint the source of the gold-bearing fluids and the temperature of the mineralizing systems to better comprehend the genesis of the gold mineralization at the Şirindere area (Aydın, Western Turkiye). The Şirindere area is geologically a part of the Menderes Massif metamorphic complex. It is made up of Neoproterozoic-Paleozoic mica schists of Selimiye Formation and metagranite/gneiss which are is overlain by Permo-Carboniferous phyllite, marble, and quartzite of Göktepe Formation and Mesozoic marbles of Milas Marble. The gold-bearing quartz carbonate veins are hosted in the mica schists of Selimiye Formation occurred within the fault and shear zone trended N-S having locally boudinage forms parallel to the direction of foliation of the mica schist. Wall-rock alterations are mainly silicification and sericitization with carbonatization and subordinate amount of the chloritization. The ore minerals in the auriferous quartz veins include pyrite and hematite with free native gold which has Au contents up to 7.4 ppm. According to fluid inclusion data from the gold-bearing quartz carbonate vein, the Şirindere gold mineralization formed from aqueous-carbonic ore fluids having a metamorphic source. These fluids are characterized by low CO2 content having low to medium salinity (0.88-23.89 wt.% NaCl equivalent) formed at temperatures ranging from 178.7 to 322.5°C with an average of 277.3°C. Therefore, the gold-forming processes in the Şirindere area are nearly identical to those in mesozonal orogenic gold deposits.

 

Keywords: Fluid inclusion data, gold-bearing quartz carbonate vein, Menderes Massif, Şirindere(Aydın,Turkiye)

How to cite: Bayram, H. N., Kumral, M., Bakkalbasi, A. E., Kaya, M., and Abdelnasser, A.: Origin and characteristics of the gold-bearing quartz carbonate veins in Şirindere area, Aydın (Western Turkiye): Implication for fluid inclusion data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7918, https://doi.org/10.5194/egusphere-egu23-7918, 2023.

X2.165
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EGU23-13904
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ECS
Patricia Fehrentz, Magnús Tumi Guðmundsson, Hannah Iona Reynolds, and Anette Kærgaard Mortensen

Young igneous geothermal systems derive their energy from magma in their roots.  Some of them have been utilized for electricity production and other uses of geothermal energy.  Iceland has several young igneous geothermal systems and has been pioneering the harnessing of geothermal energy derived from such systems.  Iceland is ideally located for the occurrence of young igneous systems, being underlain by a mantle plume and sitting on the Mid-Atlantic Ridge. Although the overall structure and temperature distribution of young igneous systems are well known in some areas, the nature of how they are recharged by magma has been poorly constrained.  The Krafla high-temperature geothermal area in North-East of Iceland is one of the best-known such systems.  Between 1975-1984 the so-called "Krafla Fires" took place, associated with the widening of the Krafla fissure swarm by several meters, during episodes of volcanic activity consisting of 20 extrusive and intrusive events.  The effects of this intrusive and extrusive activity on the geothermal system are a subject of ongoing research. The intrusions, injected into the geothermal system, are estimated to have had a volume of 0.12-0.19 km3 and added 4-8 x 1017 J of heat to the system through the solidification and cooling of these intrusions. This heat is released and transferred within and out of the system as cooling and solidification occur.  After each rifting event, some of which were accompanied with fissure eruptions on the surface, this additional heat input was visible on the surface of the geothermal system as intensive steaming.  This was especially prominent in fissures and fractures along the main axis of rifting.  The intrusive activity may have increased the temperature in parts of the system by several tens of degrees. 

How to cite: Fehrentz, P., Guðmundsson, M. T., Reynolds, H. I., and Mortensen, A. K.: The effect of intrusive activity on the Krafla geothermal system, NE-Iceland: The Krafla fires 1975-84, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13904, https://doi.org/10.5194/egusphere-egu23-13904, 2023.

X2.166
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EGU23-16332
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Gianluca Lazzaro, Manfredi Longo, Cinzia Caruso, Sergio Sciré Scappuzzo, Agostino Semprebello, Paolo Manganello, Domenico Traina, and Francesco Italiano

Passive acoustic may represents a sustainable and safe method for long-term investigation of hydrothermal vents, as direct measures can be challenging due to the extreme environmental conditions (high temperature and acidic fluids) as demonstrated in the recent past [Heinicke, et al. 2009, Longo et al. 2021]. Here we present preliminary results of short-term monitoring of the submarine hot hydrothermal spring located in the hydrothermal field within the islets about 2 nautical miles  E of Panarea island, in the NE sector of Aeolian arc (Aeolian Island, Italy). The so-called “Black Point” spring shows peculiar characteristics with respect to to the surrounding field; it is featured  by extremely high temperatures close to 140 °C, very low pH (with values spanning between 2.8-3.5) and dark/brown fluid emissions from the vent [Italiano and Nuccio, 1991, Müller 2011].

The main scope of the present work is to describe for the first time the spectral signature of the shallow hydrothermal brine using non invasive passive acoustic methods and to provide a useful and long-life tool to track the flow rate evolution along the time. High resolution acoustic records were collected using a dedicated battery powered smart hydrophone installed in the proximity of the thermal emission in different periods, providing a panoramic view of the investigated phenomena. The application of various methods of spectral analysis and metadata extrapolation permitted the identification of different energetic frequency peaks and narrow tones, diverging from the ambient background noise, depicting distinct features in terms of bandwidth and energy levels. The bandwidth extension, comprising both infrasonic and audible bands, suggest the coexistence of different source  mechanisms, as previously highlighted in different deep hydrothermal sites [Little et al. 1990, Crone TJ et al. 2006, Smith and Barclay 2021]. The application  of customised thresholding algorithms allowed the identification of the acoustic source related to bubble nucleation processes induced by the turbulent flowing fluid throughout uneven conduits. Afterwards, the analysis of  the PSDs of each record emphasised the temporal evolution of both the power spectral levels and the frequency peaks during the observing period.
Preliminary results show persistent and  almost constant contributions in well defined frequency range. Frequency shifts testify a behaviour change of the hydrothermal vent turbulence due to natural forces. Furthermore, vibrational induced signals and the presence of narrow tonal components, due to the conversion of seismic energy into acoustic waves along the solid-liquid interface, were identified in the range [50 - 150] Hz, underlying the complexity of mechanisms and the hidden information that can be extracted from the hydrothermal area. In addition, coupling short-time passive acoustic with multidisciplinary data coming from   the pre-existing fixed underwater infrastructure, it was possible to observe the evolution of the hydrothermal field activity over time. The ongoing research demonstrates how a deep understanding  of the acoustic sources could shed light over the behaviour of the hydrothermal reservoir, acting as a powerful proxy to identify fluid flux change induced by magmatic contribution over long-term deployments.

How to cite: Lazzaro, G., Longo, M., Caruso, C., Sciré Scappuzzo, S., Semprebello, A., Manganello, P., Traina, D., and Italiano, F.: The acoustic signature of shallow hydrothermal brine of Panarea: source mechanism recognition and behaviour changes over mid-term observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16332, https://doi.org/10.5194/egusphere-egu23-16332, 2023.