Geological observations, seismic data as well as laboratory experiments have shown that faults lithify and recover their strength (heal) during interseismic periods. The mechanical-chemical process of fault healing is a key in understanding many aspects of fault behavior, such as earthquake recurrence and rupture dynamics. Such processes do not only play an important role in understanding unconventional seismicity, such as ‘slow and low frequency earthquakes’ as observed at active plate boundaries, but are also pivotal for the application of deep geothermal energy, CO₂ sequestration and the underground storage of radioactive waste. In this study we investigate the mechano-chemical recovery of fractures in carbonates at upper crustal conditions. In the upper crust, fractures are dominantly sealed through mineral precipitation from supersaturated fluids that are chemically out of equilibrium with the host rock. In order to simulate the healing process, we performed fluid percolation experiments on intact as well as pre-fractured carbonates with varying timescales representing different healing rates. In order to quantitatively document the healing process, the selected rock samples are analyzed by X-ray microtomography before and after the experiments. In addition, optical as well as scanning electron microscopy is applied to document the mechanical-chemical processes of healing. The role of the initial (micro)fracture network, the effect of the initial chemistry of the injected fluid and the effect of temperature on the healing process will be investigated. The experiments on both intact and pre-fractured rock are carried out with a percolation cell that allows the fluid-rock interaction to be reproduced at confining pressures up to 100 MPa, pore pressures up to 100 MPa and temperatures up to 250°C. This work will advance knowledge about the damage-recovery cycle in fractured carbonates through the investigation of healing processes active at different timescales using a unique experimental approach.

How to cite: Akker, I. V. and Fondriest, M.: Fracture healing processes in upper crustal carbonates – insights from fluid percolation experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-140, https://doi.org/10.5194/egusphere-egu25-140, 2025.

During the interseismic phase, faults regain frictional strength through a process commonly referred to as fault healing. Key mechanisms include contact welding by dissolution-precipitation creep and cementation by mineral precipitation in fluid-rich environments. While much research has focused on experimental investigations of silicate systems, e.g. in slide-hold-slide experiments, the complex interaction between mechanical and chemical processes, as well as recurring fault healing over multiple earthquake cycles remain understudied. Particularly in the case of natural fault systems, the database is scarce as processes of interest occur at depth and show a low preservation potential during exhumation.

Here, we present a combination of microstructural and microchemical observations from a carbonate-hosted fault zone located within the Helvetic nappe stack of the south-western Swiss Alps which was recently exposed due to glacial retreat, creating excellent outcrop conditions. The microstructural record allows us to distinguish three major healing episodes within the principal slip zone. These episodes follow brittle deformation at sub-seismic to seismic rates, forming veins along sets of discrete fault-parallel fractures. Due to continuous brittle deformation, individual veins experienced subsequent mechanical overprinting which led to the modification of the vein texture, an increase in the local porosity and the formation of new fluid-rock interaction faces. Additionally, we use the unique geochemical fingerprint of each set of veins, documented and analysed by high-resolution X-ray fluorescence mapping of trace elements, to differentiate and characterize individual fluid pulses and dynamic changes in the physio-chemical conditions of the fluid-rock system over time. While we interpret the principal slip zone to represent the youngest deformation event in our study, adjacent vein-derived domains that are deformed by aseismic viscous processes represent relatively older structures. Comparison of the isotopic composition of newly formed calcite crystals with relict grains and the country rock provides insight into possible isotope fluid-rock equilibria during tectonic processes and therefore fluid sources. Measured stable oxygen isotopes (δ¹⁸O) show a significant influence of meteoric water while clumped isotope thermometry indicates temperatures of 65-120°C, which are at least 100°C lower than in the country rock and literature values of T_max in the area.

Our results suggest that the observed microstructural record is representative of seismic deformation and associated fault healing caused by low-magnitude earthquakes at shallow crustal levels near the upper limit of the seismogenic zone. This interpretation is consistent with the depth distribution of current hypocenters within a seismically active structure that is located in the vicinity of our study area, the so-called Rawil Fault Zone. We, therefore, conclude that the processes identified in the exhumed tectonite samples can serve as proxies for active deformation and fluid flow at depth. In a wider context, this may offer valuable insights for geothermal exploration in southwest Switzerland.

How to cite: Schwichtenberg, B., Berger, A., Herwegh, M., Schrank, C., Jones, M. W., Bernasconi, S. M., Fleitmann, D., Kewish, C. M., and Neuenschwander, T.: Unravelling cyclic fault healing in carbonates: A natural example for the interaction of mechanical and fluid-mediated processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15657, https://doi.org/10.5194/egusphere-egu25-15657, 2025.

Rock petrophysical properties, including porosity and permeability, are fundamental factors in regulating fluid ingress, flow and fluid-rock interaction across various length scales and tectonic settings. The composition of fluids, and their modes of ingress into- and reaction with host rocks, in turn influence bulk rock properties. Therefore, fluids can significantly alter rock rheology, potentially modifying their density, long-term viscosity, porosity and permeability. Mineralizing fluids may also change the rock composition, heal fractures, and promote strain hardening within active fault systems, potentially impacting the seismic cycle.

To better understand these processes and the governing background conditions, it is particularly useful to investigate the pathways for fluid flow, especially in rocks with low primary porosity and permeability, which would normally hinder significant fluid circulation. In micritic, horizontally-bedded carbonates, for example, vertical fluid flow is generally limited far away from tectonic fractures, whereas lateral, bed-parallel circulation is favoured exploiting laterally continuous planar anisotropies (e.g., bed-bed interfaces), to progressively permeate the succession. Secondary anisotropies, such as pressure-solution seams (e.g., stylolites), may represent other interesting features for fluid flow, being at times very abundant in limestone. However, they are typically considered to reduce the permeability and porosity of host rocks due to (i) the cementation and precipitation of dissolved materials in pores within the immediately surrounding rock and (ii) the accumulation of insoluble, fine-grained and low-permeability material on their surfaces. Recent studies in carbonates challenged this assumption, demonstrating that burial stylolites can be preferential pathways for karst dissolution.

We present here new data on the petrophysical properties of Cretaceous micritic limestone from the Lessini Mountains, Veneto, Italian Southern Alps, where much of the exposed, generally sub-horizontal Mesozoic carbonate succession underwent pervasive dolomitization during Eocene extensional tectonics and the onset of the Venetian Volcanic Province magmatism. Petrographic analyses, Hg-porosimetry, and He-pycnometry were applied to assess the effects of Mg-rich fluids, probably connected with the volcanic environment, on micritic limestone. Preliminary results indicate that burial stylolites developed in low porosity limestone are selectively dolomitized, with dolomitization seams 1-10 mm thick, suggesting pervasive bedding-parallel fluid flow. Dolomitization occurred also along vertical fractures and in fracture meshes of mosaic breccias, suggesting across-bedding Mg-rich fluid circulation associated with normal faults accommodating.

Dolomitization significantly increased rock density from ~2.65 g/cm³ in the pristine micritic limestone to ~2.9 g/cm³ in the fully dolomitized rock. Additionally, pore size, porosity, and the capillary threshold pressure of Hg injection change gradually but substantially from the limestone to the dolomite, with median pore sizes increasing from ~0.012 μm to ~0.33 μm, porosity from ~3.2% to 21.8%, and capillary threshold values decreasing from ~5140 to ~35 PSI.

These results demonstrate that, under specific conditions, stylolites can actually serve as effective pathways for fluid ingress/migration and thus promote fluid-rock interaction in rocks characterized by overall low porosity and permeability (e.g., micritic limestone). Furthermore, we show that dolomitization significantly modified the petrophysical rock properties, further enhancing fluid ingress and likely promoting fracturing and brecciation by changing rheology, with consequences for deformation localization and partitioning during later tectonic activity.

How to cite: Zuccari, C., Vignaroli, G., Balsamo, F., Berio, L., and Viola, G.: Burial stylolites favouring Mg-rich fluid ingress and fluid-rock interaction: petrophysical variations during regional dolomitization in the Lessini Mountains (Southern Alps, Italy) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7082, https://doi.org/10.5194/egusphere-egu25-7082, 2025.

Shallow crustal fault zones, particularly those within carbonate successions, are deformation zones that influence subsurface fluid migration, localization, and interaction. These zones, characterized by fault-controlled fracturing and brecciation, can act as important conduits for fluid flow in the Earth's crust. The interaction between fluids and the fractured carbonates rock matrix can induce significant changes in the mineralogical and mechanical properties of fault zones. Therefore, studying fluid-rock interactions in such environments is crucial not only for understanding the natural processes governing subsurface fluid dynamics, deformation, and metamorphism but also for addressing significant challenges in energy and mineral exploration as well as in underground engineering.

This study presents, for the first time in the southern Apennines (southern Italy), evidence of fault-driven hydrothermal dolomitization during the late Triassic rifting event in the western Adria plate. We investigated the fault-controlled saddle dolomite formation in Norian dolomites exposed in the western sector of the Matese Massif. The study focused on dolomite breccias associated with N-S and NNW-SSE striking normal faults. These structures include layers of mature cataclasites made of clasts with angular boundaries within a highly porous matrix, crossed by veins, mosaic and chaotic breccias. The breccias are composed of angular clasts of host rock dolomite, formed by early marine replacive dolomitization of shallow-water carbonates, surrounded by coarse saddle dolomite cement. The saddle dolomite cement is characterized by two distinct phases. The first phase (SD1) is yellow, inclusion-rich, and forms a rim around the clasts, while the second phase (SD2) is euhedral, exhibiting well-defined zoning with a transition from cloudy to limpid crystals. The saddle dolomite cement texture, coupled with decreasing δ¹⁸O and ⁸⁷Sr/⁸⁶Sr values, suggests that it precipitated at temperatures of 100-120°C from fluids that likely interacted with magmatic sources.

U-Pb dating of the dolomite cement provides late Triassic crystallization ages of approximately 206 ± 13 Ma and 217.0 ± 6.6 Ma. Additionally, the ferroan dolomite cement contains quartz and hydrothermal minerals, including fluorite and apatite, in minor quantities. These findings suggest that the brecciation and hydrothermal saddle dolomite precipitation were linked to normal fault activity during the breakup of Pangea, contributing to the separation of the SW sector of Eurasia from the western margin of the Adria Plate.

How to cite: Awais, M., Diamanti, R., Camanni, G., D'antonio, M., Della porta, G., Di renzo, V., Graziano, S. F., Iannace, A., and Kylander-clark, A.: Fault-induced saddle dolomitization during the Late Triassic rifting of Pangea in the southern Adria region (Southern Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19182, https://doi.org/10.5194/egusphere-egu25-19182, 2025.

The mechanical and hydraulic behavior of faults in geothermal systems is strongly impacted by fluid-induced alteration. For instance, hydrolytic alteration of felsic volcanic rocks deeply affects the frictional and permeability properties of fault rocks, controlling the hydraulic behavior of faults. We investigated fault rocks from the caprock of a fossil hydrothermal system in the Northern Apennines, by combining field structural observations with mineralogical and microstructural analyses, friction experiments and permeability tests on fault rocks. Hydrolytic alteration promoted general weakening of fault rocks by enrichment of kaolinite-alunite-group minerals in the fault core, favoring strain localization. Enrichment of kaolinite along major faults induces a local decrease in permeability of three orders of magnitude (1.62x10^-19 m²) with respect to the unaltered protolith rocks (1.96x10^-16 m²) transforming faults from fluid conduits into barriers.

Alunite-kaolinite-rich rocks shows a velocity-strengthening frictional behavior, suggesting that hydrolytic alteration favors stable slip of faults at low temperatures (160-270°C). 

How to cite: Marchesini, B., Pozzi, G., Collettini, C., Carminati, E., and Tesei, T.: Structurally controlled genesis of caprock in volcanic hydrothermal systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11033, https://doi.org/10.5194/egusphere-egu25-11033, 2025.

Reconstructing the tectonic and geomorphological history of geological terranes poses significant challenges, particularly when interpreting deeply buried and exhumed settings. The Rolvsnes granodiorite terrane exposed in the Bømlo archipelago on Norway’s southwestern coast, provide invaluable insights into these processes. This granodioritic to granitic intrusive body serves as an onshore counterpart to offshore basement reservoirs, such as those on the Utsira basement high, where altered basement rocks are overlain by Permian to Cretaceous sediments. These analogs enable researchers to link surface observations to subsurface conditions, offering a rare opportunity to understand complex fracture and alteration histories.

We provide new evidence from multidisciplinary investigations constraining the fracturing and alteration history of the Rolvsnes granodiorite. Multiple chemically altered bedrock outcrops associated with fracture zones were identified across Bømlo, with samples collected for geochemical, mineralogical, and isotopic analyses. We characterize secondary clay assemblages and constrain the timing of alteration processes. Additionally, three bedrock cores drilled through prominent fracture zones were logged and sampled to enhance the dataset with subsurface information.

K-Ar geochronology dates range from the Carboniferous to the Paleogene, suggesting multiple alteration events over extended periods. Geochemical and mineralogical data indicate significant leaching of alkali and alkaline-earth elements, with the formation of kaolinite, smectite, interstratified illite-smectite, illite, and lepidocrocite in the altered material. Scanning electron microscopy reveals small but significant differences between alteration zones. In some zones, K-feldspar is altered into a mixture of kaolinite, smectite, and illite, while plagioclase (particularly Na-rich laminae) and biotite remain relatively unaffected. In other zones, biotite transforms into vermiculite, illite, and iron (hydro-)oxides, while plagioclase alters into smectite and kaolinite, leaving K-feldspar relatively intact. These findings suggest alteration predominantly by low-temperature meteoric water. Many samples did not yield Kübler Index determinations due to poorly defined 10 Å peaks, but acquired illite-crystallinity data indicate fluid temperatures ranging from 120 to 295 °C. Thus, K-Ar ages should be interpreted cautiously, as multiple alteration events may occur along the same fracture zone at different times.

The data suggests that faulting and hydrothermal alteration initiated as early as the Carboniferous, continuing through the Permian. Late Triassic brittle faulting may have coincided with supergene weathering under humid, tropical conditions, resulting in saprolitic weathering of the crystalline basement along pre-existing fractures. During subsequent marine transgressions, most saprolitic material was eroded, leaving remnants buried beneath sedimentary cover, which was in turn largely removed during the Plio-Pleistocene. The Rolvsnes granodiorite appears to have experienced additional fracturing and alteration events beneath this sedimentary cover, as indicated by K-Ar dates extending into the Early Cretaceous and Paleogene. 

This study highlights the inherent difficulties of reconstructing complex tectonic and geomorphological histories in such terranes. The Bømlo archipelago offers a compelling case study for linking onshore observations to offshore settings, but challenges remain in disentangling overlapping alteration processes and correlating them to specific tectonic events.

How to cite: Margreth, A., Drivenes, K., Schönenberger, J., van der Lelij, R., Fredin, O., and Knies, J.: The complex and prolonged fracturing and chemical alteration history of the Rolvsnes granodiorite on the Bømlo archipelago in southwestern Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18686, https://doi.org/10.5194/egusphere-egu25-18686, 2025.

In the last decades many studies focussed on carbon capture and storage (CCS) to find a possible remedy to reduce the large increase of anthropogenic carbon dioxide (CO₂). CCS can potentially sequester billions of tonnes of CO₂ per year using the Earth as the widest laboratory available for long-term storage. In geological reservoirs, CO₂ can be trapped by physical and chemical mechanisms. Among chemical mechanisms, mineral carbonation plays a crucial role in CCS, being almost irreversible, involving the chemical reaction in aqueous environment between CO₂ and Mg- and/or Ca-rich minerals, where CO₂ is converted into solid carbonates.

In nature, listvenite, a rock mainly composed of Mg-Ca-bearing carbonates, quartz and Cr-bearing mica (fuchsite), documents natural CO₂ sequestration. Indeed, listvenites are the result of the extensive alteration of ultramafic rocks by CO₂-bearing fluids, which involved the substitution of olivine, pyroxene and serpentine by Ca- and Mg-carbonates. To date, very little is known about the kinetics and rate of this reaction, spanning from weeks (serpentinites) to thousands of years (peridotites).

We studied carbonated serpentinites from the Zermatt-Saas Zone (Corno del Camoscio, Western Alps, Italy) which underwent fluid-mediated natural carbonation under hydrothermal conditions. Hydrothermal carbonation is spatially associated to Oligo-Miocenic brittle faults of the Aosta-Ranzola system (Bistacchi et al., 2001). Field structural surveys identified two main strike-slip fault sets (N-S and NW-SE striking) controlling fluid flow, with voluminous carbonation observed mainly along the NW-SE-striking set. We collected a series of structurally-controlled samples along a reaction front from serpentinite to listvenite close to a major fault zone, aiming to relate the CO₂-rich fluid/rock interaction with mega and meso-structures, along with detailed microstructural and chemical analyses.

The petrographic study, along with X-ray maps and microprobe chemical analyses, identify the following mineral associations, from serpentinite to listvenite: (i) serpentine + chlorite and minor quartz + fuchsite, talc, calcite and dolomite, (ii) serpentine + brucite + chlorite and minor quartz, talc, calcite and dolomite-siderite, (iii) dolomite, quartz, chlorite, serpentine and minor fuchsite associated with quartz-chlorite layers, (iv) quartz, dolomite and fuchsite with relict brucite. Interestingly, samples collected close to the serpentinite show microfolds where dolomite is stable, subsequently cut by brittle deformation related to the large-scale faults, suggesting a previous stage of fluid-mediated carbonation under a ductile deformation regime.

Qualitative and quantitative X-ray powder diffraction data enabled us to calculate a mass balance to model the rate of reaction and the composition of the original fluids. Preliminary results indicate a structural control on the fluid drainage and the role of brucite to dominate the carbonation reaction, as reported by experimental results of Campione et al. (2024), along with fuchsite.

Bistacchi, A., Dal Piaz, G., Massironi, M., Zattin, M., Balestrieri, M. (2001). The Aosta–Ranzola extensional fault system and Oligocene–Present evolution of the Austroalpine–Penninic wedge in the northwestern Alps. International Journal of Earth Sciences, 90, 654-667

Campione, M., Corti, M., D’Alessio, D., Capitani, G., Lucotti, A. Yivlialin, R., Tommasini. M., Bussetti, G., Malaspina, N. (2024). Microwave-driven carbonation of brucite. Journal of CO₂ Utilization, 80, 102700

How to cite: Pasquinucci, A. M. B., Malaspina, N., Ceccato, A., Giuntoli, F., D'Alessio, D., Campione, M., and Dal Piaz, G. V.: A natural laboratory for carbon capture and storage: listvenites along regional fault zones (Zermatt Saas Unit, Western Alps, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11801, https://doi.org/10.5194/egusphere-egu25-11801, 2025.

How to cite: Cateland, B., E.Beaudoin, N., Battani, A., Mouthereau, F., Caracausi, A., and Pujol, M.: Tracing mantle-crust fluid interactions in a lithospheric extension zone: Insights from the Betic Cordillera, Spain., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5693, https://doi.org/10.5194/egusphere-egu25-5693, 2025.

CO₂ degassing in orogenic settings, derived from either prograde metamorphic decarbonation or deep mantle sources, is commonly linked to deep and shallow seismicity along major deformation zones. However, the scarcity of natural fossil analogues of these deformation zones hosting CO₂-rich fluid flow limits our understanding of the causative mechanisms and hinders validation of proposed explanatory models and inferences from geophysical and geochemical observations.

We describe a set of shear zone-hosted, carbonate-bearing breccias from the basement units of the Gotthard nappe, Aar, and Mont Blanc massifs (Central and Western Alps), interpreted as evidence of regional-scale, fault zone-hosted flow of CO₂-rich metamorphic fluids during Alpine orogenesis. Field observations, microstructures and geochemical data suggest these breccias serve as fossil analogues of fault/shear zone networks controlling CO₂-rich fluid flow in active orogenic settings, providing new insights on crustal-scale transport of carbonic fluids and its relationship with tectonic deformation.

The breccias are localized on a pre-Alpine fault network within the crystalline basement rocks and are mainly composed of coarse-grained (mm-to-cm in crystal size) blocky calcite/dolomite forming a matrix that encloses angular host rock clasts. The large volumes of carbonates and the macro- and micro-textures indicates formation during transient, but repetitive (carbo-)hydraulic fracturing in the presence of CO₂-rich fluids, potentially at amphibolite/upper-greenschist facies conditions. C-O stable isotopes (-8.49‰ < d¹³C_VPDB < +0.73‰, +8.07‰ < d¹⁸O_VSMOW < +16.39‰) and the enrichment of (Heavy) REE elements, as well as the characteristic Y/Ho and La_N/Lu_N ratios, suggest the fluids potentially originated from high-grade metamorphic decarbonation during Alpine collision.

These breccias, together with previously reported H₂O-CO₂ flow examples in the Central-Western Alps (e.g., carbonate shear zones along the Glarus thrust; retrograde calcite-bearing Alpine clefts), point to orogen-scale flow of CO₂-rich fluids spanning prograde, peak, to retrograde metamorphism during Alpine collision. Although evidence for seismogenic deformation is limited, field and microscale structures show evidence for transient tectonic deformation, potentially aided by elevated pore fluid pressure. Tectonic stress drops associated with fluid pressure changes in these zones might have promoted (transient) H₂O/CO₂ phase immiscibility, leading to carbonate saturation and voluminous deposition. The resulting large carbonate volumes suggest that the shear zones intermittently acted as both conduits and reservoirs for CO₂ -rich fluids transported from depth toward the surface. This highlights their dual role in controlling orogenic CO₂ degassing and buffering emissions, with implications for understanding fluid-mediated tectonics and carbon cycling in collisional orogens.

How to cite: Ceccato, A., Tavazzani, L., Malaspina, N., Behr, W. M., and Bernasconi, S. M.: Shear zone-mediated transfer and buffering of CO2-rich fluid during orogenic degassing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6533, https://doi.org/10.5194/egusphere-egu25-6533, 2025.

Mylonitic shear zones funnel significant amounts of fluids through the crust. However, the physical mechanisms and pathways for mass transfer remain debated. Grain boundaries, creep cavities, and pores formed by mineral reactions involving volume change and mass transport are considered the most important fluid conduits. So far, the imaging of these pores was either limited to µm-resolution, or in the case of nm-scale resolution, to very small areas (e.g., TEM investigates regions in the µm²-range) with limited statistical power. Moreover, many pores involved in ductile fluid flow only remain open intermittently before they are closed again by mineral growth and plastic deformation. To find traces of closed pores and assess pore production and consumption due to mineral reactions, high-resolution microchemical maps are needed.  

Here, we present a study that addresses these challenges through applying scanning small-angle X-ray scattering (SAXS) and X-ray Fluorescence Microscopy (XFM) to samples of a mylonite transitioning into ultramylonite, derived from a granitic protolith. SAXS delivers maps of nanopores with apertures between 1 and 280 nm while XFM enables spatially resolved mass balance computations, geochemical fluid fingerprinting, and the correlation of nanoporosity with mineral phase and trace-element composition. Importantly, both techniques are applied to an entire thin section, providing a sound observational statistical base from nm- to cm-scale.

Some key observations include:

1) A substantial amount of nanoporosity is discovered, with the same magnitude as microporosity measured previously in granitoid mylonites.

2) The ultramylonite contains twice as much nanoporosity as the mylonite.

3) Nanoporosity is strongly mineral-specific and highly elevated in regions enriched in epidote and mica.

4) Nanoporosity is highly anisotropic and usually aligned with, or at low angle to, the foliation, enabling mass flux along the shear zone.

5) Pore sheets from the mylonite connect with those of the ultramylonite, providing pathways for fluid exchange between high-strain shear zone and host rock.

These results highlight the importance of nanoscale fluid conduits and synkinematic mineral reactions for mass transfer in ductile shear zones. The implications for models of coupled fluid flow in the ductile crust will be discussed.

How to cite: Schrank, C., Bishop, N., Jones, M., Berger, A., Herwegh, M., Paterson, D., Manni, L. S., and Kirby, N.: Nanopores enable fluid flux in mylonites and ultramylonites – novel insights from Scanning Small-angle X-ray Scattering and X-ray Fluorescence Microscopy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7433, https://doi.org/10.5194/egusphere-egu25-7433, 2025.

Petrological and geochemical evidence demonstrates that mylonitic ductile shear zones transport significant amounts of fluids through the lithosphere. Because of the lack of percolating pore networks in exhumed mylonitic rocks, it has been hypothesised that most of the fluid pathways in ductile shear zones consist of transient pores with micro- to nanoscale aperture. These transient pores typically include grain boundaries, creep cavities, and pores due to mineral reactions, all of which open and close cyclically during plastic deformation. However, it is not known how much each of these features contributes to crustal fluid flow. Moreover, nano-scale pores are notoriously difficult to map with non-destructive imaging methods. These are the key problems addressed by this research.

We recently used X-ray ptychography to image midcrustal quartzo-feldspathic mylonites at the X-ray Fluorescence Microprobe beamline of the Australian Synchrotron. This transmission small-angle scattering method maps X-ray phase contrast non-destructively with nanometre resolution. In addition, high-resolution trace-element maps are acquired coevally with X-ray Fluorescence Microscopy (XFM). We systematically sampled transects from mylonite to ultramylonite to capture the strain-time evolution of nano- and microvoids and to study how transient porosity and trace-element composition change with deformation intensity, composition, grain size, and deformation mechanism. This dataset will provide novel insights into mass transfer in ductile shear zones.

How to cite: Bishop, N., Schrank, C., Jones, M., Kewish, C., Paterson, D., Berger, A., and Herwegh, M.: Mapping nano- and microporosity in ductile shear zones with X-ray ptychography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7480, https://doi.org/10.5194/egusphere-egu25-7480, 2025.

Collisional orogens are characterized by complex contractional and extensional deformation, which significantly impact fluid migration and mineralization. These processes are crucial for understanding subsurface fluid flow dynamics, with implications for geothermal energy, hydrogen production, and CO2 storage. The Dinarides orogen in southeastern Europe, formed during the closure of the Neotethys Ocean and subsequent Adria-Europe collision, provides an excellent natural laboratory to investigate fluid-flow and fluid-rock interactions driven by orogenic deformation.

The Dinarides have experienced a sequence of tectonic events in their late evolution, including NE-EW Late Cretaceous-Eocene contraction, NE-SW Oligocene contraction, and bimodal NE-SW/NW-SE Miocene extension. These phases created fracture networks, tension gashes, and fault gouges, facilitating fluid migration and mineral precipitation within the orogen. Field investigations across five tectonic units in Montenegro (Dalmatian, Budva, High Karst, Pre Karst, and East Bosnian-Durmitor) documented structural features associated with these deformation phases.

Petrographic and geochemical analyses of vein-filling cements, including optical microscopy, cathodoluminescence, and stable isotope measurements, reveal that vein formation predominantly occurred under burial conditions with episodic transitions to meteoric environments. These results suggest that deformation-controlled fracture network acted as fluid pathways, driving localized dolomitization and calcite precipitation. The structural timing of these features correlates with major orogenic events, providing insights into the relationship between deformation and fluid flow.

Our findings contribute to understanding how fluid migration is driven by tectonic deformation in collisional orogens. By integrating field observations with petrographic and geochemical data, this study offers a framework for linking mineralization processes to tectonic evolution, with broader implications for fluid flow modelling in similar orogenic systems worldwide.

How to cite: Maleš, M., Nader, F. H., Stojadinović, U., Matenco, L., Krstekanić, N., Randjelovic, N., and Divies, R.: Exploring deformation-driven fluid-flow and fluid-rock interactions: insights from the Dinarides orogen, southeastern Europe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12965, https://doi.org/10.5194/egusphere-egu25-12965, 2025.

The emplacement of basic to acid magmas into ultramafic rocks represents a specialized scenario where bimetasomatic exchanges commonly occur. In the Sierra Chica of Córdoba, near the city of Alta Gracia, remmants of the intensely serpentinized upper mantle -tectonically emplaced into the metasedimentary sequence during the Neoproterozoic (pre-Pampean)- are intruded by dykes of tonalitic to granitic compositions. This contribution deals with some of these dykes of trondhjemitic composition that exhibit tabular shapes and relatively small dimensions (< 50 m long and 2 m thick). They develop penetrative reaction zones symmetrically at the contacts between serpentinized ultramafic rocks and trondhjemitic dykes, with regular thicknesses between 0.10 and 1.0 meter. Three distint mineralogical zones were identified, progressing from the dykes towards the serpentinite:

1.- Magnesio-hornblende zone (Mg-Hbl ± Pl ± Ttn ± Chl),

2.- Chlorite zone (Chl ± Mg-Hbl ± Zrn ± Ap)

3.- Anthophyllite zone (Ath ± Tr ± Chr ± Tlc ± Chl).

According to textural and mineralogical evidence, the following sequence of formation is proposed: 1) Ath zone, 2) Mg-Hbl zone and 3) Chl-zone.

Zircon U-Pb dating of the trondhjemitic dykes yields a concordia age of 528 Ma for the crystallization and emplacement of these rocks. Zircons extracted from the Chl-zone share similar petrographical features and ages, evidencing that they represent xenocrysts derived from the trondhjemitic magmas later affected by chlorite-forming reactions. The age of 528 Ma place the emplacement of the trondhjemitic dykes during the high-grade metamorphism, anatexis and magmatic events of the Pampean orogeny, occurred at 0.65 - 0.85 GPa and 700º- 850ºC. Anthophyllite, typically formed at relatively high temperature (>600 °C), is interpreted to have formed close to the time of trondhjemitic dyke emplacement and crystallization, when the whole enclosing region was undergoing high amphibolite-to-granulite facies at the main events of the Pampean orogeny. The conspicuous presence of chlorite (clinochlore) in all zones crosscutting the formerly crystallized minerals (e.g., Ath and Mg-Hbl), temperature ranges of 273º - 418ºC estimated by Chl geothermometers, along with pervasive low temperature deformation textures (kink folding) evidence that Chl was formed at lower P-T conditions.

Field and petrographic evidence, geochemical and geochronological data obtained in this work indicate that the reaction zones were formed in two different periods. Anthophyllite and Mg-Hbl zones resulted from the bimetasomatic ionic diffusion between the ultramafic rock and trondhjemitic dykes during the Pampean orogeny at high P-T conditions. Conversely, Chl crystallization should have occurred at lower P-T conditions during the Famatinian orogeny that took place from ~500-440 Ma in the Sierras de Córdoba mainly as deformational events. The chlorite zone is therefore proposed to have formed as a result of fluid infiltration in the already altered contact zones between the ultramafic rocks and the trondhjemitic dykes.

How to cite: Muratori, M. E., López Morlhiere, S., Demartis, M., Coniglio, J. E., Boffadossi, M. A., D’Eramo, F. J., Pinotti, L. P., Coniglio, J., and Esteban, J. J.: Bimetasomatic reaction zones between ultramafic rocks and trondhjemitic dykes in the Sierra Chica, Córdoba, Argentina: temporal variations and geochemical features, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10967, https://doi.org/10.5194/egusphere-egu25-10967, 2025.

he interaction between a large, dissolved Mn reservoir in the oxygen minimum zone (OMZ) and the deeper oxygenated water allows for Mn oxidation and precipitation at their interface. The current paradigm posits that the OMZ acts as a Mn²⁺ source necessary for ferromanganese encrustation, while the encrustation itself is not thought to occur within the OMZ, though this remains a subject of ongoing debate. Marine Fe-Mn crusts enrich metals including those with high affinity for Mn oxides (e.g., Ce), which can provide insights into the origin of Mn oxides. In this study, we identify heterogeneous Ce and δ¹⁴²Ce_SW profiles in seawater and Fe-Mn crusts across the OMZ in the Northwest Pacific Ocean, closely linked to the cycle of Mn. Moreover, we quantify a close association of Ce with Mn oxides in Fe-Mn crusts and associated Ce isotope fractionation between the crusts and ambient seawater, bridging the marine Mn and Ce cycles. The outcome reveals that continuous precipitation of Mn oxides could initiate within the OMZ and extend into the deep ocean (5,000–6,000 m seawater depth) in the Northwest Pacific Ocean.

How to cite: Li, W. and the Wenshuai Li: Cerium Stable Isotopes Unveil Ferromanganese Encrustation Across the Oxygen Minimum Zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8324, https://doi.org/10.5194/egusphere-egu25-8324, 2025.