The progressive localization of deformation has long been recognized as a fundamental phenomenon of the macroscopic failure of rocks. Our recent analyses using X-ray tomography during triaxial compression indicate that fractures and higher magnitudes of shear and dilative strain spatially localize as rocks are driven closer to macroscopic failure. Similarly, geophysical observations of low magnitude seismicity in southern and Baja California show that deformation localizes toward the future rupture plane of M>7 earthquakes. These sets of observations indicate that deformation can increase in localization toward failure, and that deformation can temporarily decrease in localization (delocalize) during this overall increase. These observations indicate that the spatial organization of deformation may be used to recognize the acceleration of the precursory phase leading to large earthquakes and the macroscopic, system-scale failure of heterogeneous materials. However, such efforts will require identifying the conditions that promote phases of delocalization, and how these perturbations in the overall trend of increasing localization influence the timing of macroscopic failure. In this presentation, I will describe these analyses, and new work that aims to identify which characteristics of the fracture networks determine the localization at a particular level of stress, and the change in localization from one stress step to the next in triaxial compression experiments at the confining stress conditions of the upper crust.

How to cite: McBeck, J., Renard, F., and Ben-Zion, Y.: Episodic delocalization in the upper crust: Implications for earthquake forecasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1798, https://doi.org/10.5194/egusphere-egu23-1798, 2023.

Under diagenetic conditions between ca. 50 ℃ to 250 ℃ the systematics of cement precipitation and differential infill makes network porosity, and thus permeability and strength, scale and thermal history dependent. Using examples of regional opening-mode fractures in sandstones from the Cambrian Flathead Formation, Wyoming, a low-enthalpy geothermal outcrop analog, we show that quartz deposits preferentially fill fractures up to ca. 0.05 mm wide with a transition from mostly sealed to mostly open fractures over a narrow size range of opening displacements from 0.05 to 0.1 mm. Scale- and diagenesis- dependent connectivity can be described using use rule-based node descriptions to rapidly measure diagenesis sensitive connections within the context of current field practice.  In our example, although networks have trace connectivity, effective connectivity for fluid flow is greatly reduced by quartz cement. Near some faults, trace connectivity increases as initially wide porous fractures preferentially shear and wing cracks form, increasing fracture intersections (Y-nodes). However, pore space is lost due to the development of quartz-cemented microbreccia. Macro-scale trace connectivity increases, but porous connectivity diminishes and thus potential for fluid flow is markedly lower. We illustrate how diagenesis-sensitive contingent nodes can be used to extrapolate permeability estimates to locations having different thermal histories.

How to cite: Laubach, S. and Forstner, S.: Scale-dependent fracture patterns and flow in low-enthalpy geothermal targets: the role of diagenesis and contingent nodes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8776, https://doi.org/10.5194/egusphere-egu23-8776, 2023.

Modelling Discrete Fracture Networks (DFN) in naturally fractured reservoir (NFR) implies identifying and understanding the fracture spatial distribution and relationships to stratigraphic interfaces (crosscutting or abutment) in 3D. However, capturing fracture geometric parameters in the subsurface has always been a challenging task. To palliate the lack of data, and to better constrain modelling inputs, outcrop analogs are often used. While Simonson (1978) showed that mechanical contrasts at bed interfaces are essential to control fracture abutment, Cooke (2006) showed that bed/inter-bed thickness ratio is also an important parameter to account for.

Our goal is to predict fracture network geometry in stratified sedimentary rocks. To this purpose, we present a new original python toolbox. We performed an integrated approach that quantifies and automatically computes the bed interface’s compliance to let fractures go through (or not). Accounting for abutment, cross-cutting relations and bed thickness data, a compliance value is calculated for each interface using 1D scanline or 2D outcrop photograph. The process comprises (1) a field survey data or a digitized image (stratigraphy and fracture pattern) and (2) the processing of the data. First, we applied the method to existing classification and quantification from other authors as case study to check the feasibility of the code. Second, we applied the method to naturally fractured and stratified carbonates located in SE France and Centre Albania.

How to cite: Namongo Soro, P. J. F., Lamarche, J., Viseur, S., Messaadi, F., and Richard, P.: Python toolbox for fracture stratigraphy quantification and mechanical interface characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4374, https://doi.org/10.5194/egusphere-egu23-4374, 2023.

The study carbonates are exposed in the axial zone of the southern Apennines ftb, Italy. These rocks form a natural laboratory to investigate the time-dependent variation of primary heterogeneities and both dimensional properties and distribution of high-angle joints, veins, and shear fractures. We integrate field-based stratigraphic and structural analyses of the platform carbonates with both petrographic and microstructural investigations of selected specimens to unravel their depositional setting and diagenetic evolution. Furthermore, we focused on the modalities of pressure solution-assisted deformation of bed interfaces and single beds to investigate their possible control on the geometry, distribution, and relative timing of the high-angle fractures. The platform carbonate succession includes a Pliensbachian in age, well-layered, lagoonal carbonate unit including both mud-and grain-supported limestone beds, and a Toarcian in age oolithic carbonate unit. Our results showed that pressure solution mainly localized within bed-parallel interfaces and within the grain-supported limestone beds. During early-to-burial diagenesis, precipitation of calcite rims and blocky calcite cements predominantly occurred in the latter beds, in which ghosts of meniscus cements associated to the earliest diagenetic stages are documented. The fracture intensity (P10) computed for the earliest high-angle fracture set shows the highest values in correspondence of the grain-supported beds. During the Oligo-Miocene Apennine orogeny, the mechanical layering of the carbonates evolved due to flexural slip of the layered carbonates, and formation of intra-carbonates thrust faults with flat-ramp-flat geometries were documented. Specifically, there formed s-c-c’ tectonites along the primary interfaces juxtaposing the single bed packages, and oblique-to-bedding reverse faults offsetting the single beds developed due to pressure-solution assisted deformation.The Plio-Quaternary transtension dissected the platform carbonates, and caused both their uplift and exhumation from shallow crustal depths. By computing the fracture density (P20) and intensity (P21) associated to transtension, the highest values were calculated within the coarser grained carbonate beds. Independently from their thickness, these carbonate beds are the most fractured ones in the study succession. These results hence showed that the platform carbonates acquired the mechanical properties during early-to-burial diagenesis, that later permitted strain clustering within the stiffer, grains-supported beds. We invoke that chemical/physical compaction and diffuse cementation of these carbonate beds were responsible for the Plio-Quaternary fracture distribution throughout the platform carbonates. Moreover, we also documented similar P20 and P21 variations, which are consistent with the profound control exerted by primary mechanical interfaces on vertical growth of transtensional fractures. Indeed, we interpreted the similar P20 and P21 variations as a result of shear stress localization along per-existing, stratabound fractures, which ruptured these interfaces forming small-scale process zones (high P20 values) at their extensional quadrants (high P21 values). Ongoing petrophysical analysis will shed lights on the dimension, distribution, and overall connectivity of the pore system aiming at assessing the overall control exerted by bed-parallel stylolites and pressure solution seams on the efficiency of the mechanical interfaces abutting the stratabound transional fractures.

How to cite: Manniello, C., Todaro, S., Abdallah, I., Prosser, G., and Agosta, F.: The role of pressure solution in the evolving fracture stratigraphy properties of Mesozoic platform carbonates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5630, https://doi.org/10.5194/egusphere-egu23-5630, 2023.

The study of faults in the upper crust has generated interests in modelling their impact on fluid flow and the mechanical behavior of the earth's crust. Fault damage zones are important structures with multiple implications for resource management and earthquake studies. This work aims to characterize the distribution and growth of damage around faults, and to study its impact on the Displacement - Damage thickness (D-T) scaling law. Two complementary approaches of field analyses and analog modelling of normal faults are developed to answer this question. We presents new results of fault damage mapping, D-T scaling in carbonate rocks and the first analog modelling experiments of fault damage zones inspected in-plane. The results show a heterogeneous and asymmetric distribution of damage around faults, mainly influenced by fault interactions during their growth (segmentation, conjugate faults). A D-T law specific to wall damage is established and shows a normal correlation between D and T for less than c. 100 m of fault displacement, and also confirms the existence of a damage thickness threshold after c. 100 m of displacement. To explain this law, we propose a damage zone growth model controlled by the interaction and coalescence of fault segments. Analogue modelling shows a failure mode transition during fault growth, from a segmented dilatational-shear mode to a localized compactional-shear mode. They also demonstrate that initiation of segmentation, segment activity selection, interaction and coalescence processes control the development of fault damage zones and the D-T law. Furthermore, the thickness of the faulted brittle layer is a main controlling parameter of segmentation, strain localization and the fault damage thickness threshold observed.

How to cite: Soliva, R., Mayolle, S., Dominguez, S., and Wibberley, C.: The growth of fault damage zones; field data and analogue modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6717, https://doi.org/10.5194/egusphere-egu23-6717, 2023.

A better understanding of stress perturbation around faults, strain propagation, and fluid flow in the upper crust require characterization of the evolution of fault damage zones. Numerous studies provide significant amounts of data and description from a broad variety of faults, however, fault damage evolution is not clearly understood.

In this study, we investigate experimentally damage zones dynamic evolution during normal faults population growth. With this aim, we used a sandbox type device and multilayered analog model, monitored by high-resolution cameras. Several types of damage zones are evidenced and we performed an accurate description of their growth from initiation to mature damage. New damage types including conjugate link damage and graben damage are described for the first time and show similarities with observations in nature. We highlight the new concept of “fault system damage” as the increase of deformation and secondary fault density by the interaction of major faults. We also show that fault damage zones grow by segment linkage into corridors of fault segments formed in the first stages of model deformation. Based on these observations, we propose and discuss the new concept of “segment selection in corridors” as the process of the onset of fault maturation and their damage zone development.

How to cite: Mayolle, S., Soliva, R., Dominguez, S., and Wibberley, C.: Fault damage zone growth in analog models: typology and segment selection process into fault corridors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6753, https://doi.org/10.5194/egusphere-egu23-6753, 2023.

The nucleation and subsequent vertical and lateral growth of normal faults have been the focus of many studies in extensional settings as these are important conduits for heat or fluid transfer. However, little attention has been attributed to normal fault growth in flexural foreland basins. The flexural downbending of the foreland plate generates extensional stresses, leading to the formation of normal faults in flexural foreland basins. Therefore, besides having an important role for subsurface fluid flow, normal faults in foreland basins are a fingerprint of the tectonic events associated with the downbending of the lower plate during collisional tectonics. In this study, we quantify the Oligocene to Early Miocene spatial and temporal evolution of the normal faults and their growth styles in the Northern Alpine Foreland Basin (NAFB). For this approach we use two 3D seismic volumes in the depth domain, located in the German part of the NAFB, to interpret both normal faults and prominent seismic horizons. This allows us to construct throw-depth and throw-length profiles to quantify changes in fault-parallel and down-dip throw patterns. This analysis allows us to reconstruct how the normal faults in our study area grew in 3D over time. Throw-depth profiles of the faults generally record throw maxima for either the foreland unconformity reflector or Oligocene aged reflectors, subsequently decreasing both up-and downward. This implies that following nucleation, the faults grew both upward into the syn-flexural fill of the basin and downward into the pre-flexural basement. Furthermore, comparing throw-depth and throw-length profiles of the faults in both seismic volumes shows that lateral fault growth is coupled with the fault tip moving towards younger stratigraphy. This is highlighted in the eastern German NAFB, where the vertical linkage between a lower segment that nucleated in the Eocene-Rupelian and an upper segment that nucleated in the Late Chattian is observed. To summarize, the observations imply that normal faults in the German NAFB were newly formed during flexural downbending of the European plate, preferably nucleating at the top of the plate before growing downward. This is different from fault growth observed in purely extensional settings, where faults typically grow upward instead of downward. Finally, the variable normal fault activity in the different seismic volumes in the German NAFB point out basin-parallel variations in flexural subsidence, possibly driven by spatiotemporal variations in Alpine frontal thrusting and/or slab pull.

How to cite: Eskens, L., Andrić Tomašević, N., Müller, M., and Herrman, R.: Growth of normal faults in flexural foreland basins: a case study of the Northern Alpine Foreland Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14635, https://doi.org/10.5194/egusphere-egu23-14635, 2023.

Stylolite, fracture and fault networks are important fluid pathways, especially in low permeable rocks such as limestone and therefore important for subsurface applications including geothermal energy production. These systems grow in both time and space and have a given correlation length. Below the correlation length the system becomes saturated and shows a given scaling, for example in roughness for stylolites. Whereas above the correlation length the roughness or width of the growing system becomes constant. The position of this length varies with time and space whilst also being influenced by the system size. This becomes important when the systems connect, for example fractures that grow and merge together such that they have a given size. In this contribution we show with numerical simulations and natural examples how stylolite, fracture and fault networks scale in time and space, how their correlation length is evolving and how they become connected. We discuss the implications for scaling of larger networks as well as implications for deformation and fluid flow.

How to cite: Koehn, D., Hafermaas, D., Köhler, S., Lang, J., Mathur, B., Prabhakaran, R., and Smith, R.: Scaling, connectivity and correlation length of stylolite, fracture and fault networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8940, https://doi.org/10.5194/egusphere-egu23-8940, 2023.

Reservoir rocks, such as carbonates, are rapidly becoming key elements for the energy transition. The damage of these reservoir rocks when placed under a stress field must be characterized, to better predict storage capacity distribution. In the shallow subsurface, carbonate rocks accommodate the stress by developing structures at the mesoscale, such as fractures, deformation bands or stylolites, depending on porosity or fluid content. Those are localized, showing a finite damaged area, outside which the relative host rock can accommodate the applied stress in a different way, usually overlooked in low temperature and pressure conditions.

In this study, we highlight a new marker of accommodation of shortening, characterized by heterogeneous quartz grain rotation in non-porous carbonate matrix. The studied rock is an upper Cretaceous bioclastic calcarenite from the Cotiella Massif (Spain). This rock is composed of 85% carbonate (micrite and recrystallized microsparite), 10% quartz, and <5% of nanometric porosity. It hosts a fracture pattern including fractures, stylolites and deformation bands that correspond to different tectonic stages. However, we focus on investigating the quartz grain orientation in the grains outside the deformation bands, in both the far-field and near-field host rock. We investigated the fabric (typology, distribution and orientation) of thousands of quartz grains using X-ray microtomography on cylindrical cores of 8-26 mm diameter. Each segmented quartz grain is approximated with a best-fit ellipsoid whose major axis (L1) and minor axis (L3) give us information about the average orientation of the quartz grain. We show that the typology of the quartz grains, namely the size and average shape is similar in all our samples.

The average orientation of all quartz grains at the core scale reveals subtle preferences, without clear correlation to the orientation of neither the stylolites nor the deformation bands. We observe that in half of the samples studied, the quartz grain fabric is not controlled by the bedding. Instead, there are two distinct patterns of grain orientation, with the quartz grain fabric either reflecting the early burial stage or revealing a later reorientation perpendicular to one of the major shortening directions. These directions are either striking parallel to the local shortening flow (NE-SW) or to the regional orogenic flow (N-S), that is attributed to the Pyrenean orogeny. Evidence of dissolution-recrystallization are observed in quartz, but the diagenetic conditions constrainthis mechanism from being a robust hypothesis to explain the change of quartz fabric, but rather favour the rigid rotation of quartz in a micritic matrix. The examination of both the quartz grains and the carbonate matrix with EBSD suggests a local strain accumulation within the carbonates in the vicinity of quartz grains. Although the mechanisms causing this rotation need to be better understood, measuring the grain typology and orientation on a considerable number of grains with the aid of X-ray microtomography could result in a new method of deformation quantification in carbonate rocks.

How to cite: Taxopoulou, M. E., Lartigau, M., Aubourg, C., Beaudoin, N., Charalampidou, E.-M., and Callot, J.-P.: Rigid rotation of quartz grains in a low-porosity calcarenite: an indicator of early deformation? , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9301, https://doi.org/10.5194/egusphere-egu23-9301, 2023.

Studies of the shallow part (Tmax< 150°C) of ancient and active prisms documents that ductile (e.g., folds), brittle and localized (e.g., faults) deformation, and diffuse deformation (e.g. scaly fabric), likely contemporaneous at the scale of geological time, may occur in the same outcrop. Moreover, the source areas of precisely located shallow slow earthquakes (downdip locating the transition from brittle to ductile deformation) span a range of depths from <1 to ~15 km below the seafloor, overlapping the temperature range of megathrust earthquake rupture in some convergent margins (e.g. Nankai and Japan Trench), and propagating up to the seafloor in other ones (e.g. Costa Rica). This implies that the shallow part of the accretionary prisms cannot be uniquely defined as characterized by ductile/brittle behavior or as prone to localization or de-localization of deformation.

To better understand how deformation affects the frontal part of accretionary prisms, the general architecture and internal structure of the frontal part of accretionary prisms need to be considered.  Field evidence of the deformational structures occurring in the frontal part of active and ancient accretionary prisms from the mesoscale to the regional scale suggests that recumbent and isoclinal folding are frequent in the shallow part of accretionary prisms, developing in pre-lithification to poorly metamorphosed rocks. In this framework, diffuse scaly fabric and pervasive boudinage, traditionally considered as evidence of shear delocalization, could be alternatively seen as the result of the progressive deformation envisioned in literature for the formation of recumbent folds i.e.: buckling with the development of an overturned fold limb and subsequent kinematic amplification by coaxial strain components with vertical maximum shortening. However, the plethora of brittle structures accommodating the change in shape on the hinge and limbs of the folds, have a different distribution in space and accommodate a different strain than brittle fracture associated with faults and/or thick shear zone. Therefore, this interpretation has implications in terms of the distribution in space of brittle structures and in the distribution of shear strain in the frontal part of subduction zones.

How to cite: Remitti, F., Festa, A., Nirta, G., Barbero, E., and Mittempergher, S.: Internal architecture of the frontal part of subduction accretionary prism: the role of folding in brittle diffuse deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5184, https://doi.org/10.5194/egusphere-egu23-5184, 2023.

Mid-to-lower crustal rock exhumation is common in orogenic belts, but the deformation process exposing these rocks remains debated. Distributed deformation in low viscous crust extruding mid-to-lower crustal rocks as channel flow and localized deformation along shear zones imbricating rigid blocks are two end-members that account for crustal thickening and unroofing. At the northwest of the Early Paleozoic orogenic belt in the South China Block, the Jiuling Massif includes orogenic root rocks exhumed from deep crustal level. Their structural pattern and exhumation history can improve our understanding on how continental mid-to-lower crust is deformed, thickened, and finally transported to the surface. Structural analysis reveals that two major mid-crustal ductile shear zones and their splays are developed at temperatures of ∼350°C–550°C. Anisotropy of magnetic susceptibility (AMS) shows that the Southern Jiuling Batholith has a modified AMS pattern by syn-orogenic compression, suggesting a gradually deformed rigid block. Combining surface geological evidence and deep structures by gravity modeling, we find shear zones rooted in basal décollement incrementally stacked the rigid granitic blocks. Along strike, the major shear zones evolved differently with more splays at their eastern portions. Thus, tectonic imbrication gradually evolve to pervasive flow-like deformation as shear zones continue to splay and form an anastomosed shear zone system. The complexed structures by splayed shear zones segmenting and imbricating small rigid blocks may correspond to the geophysically low-velocity zone in the crust, so shear zone splaying is a linking mechanism between tectonic imbrication and viscous flow deformation of the crust, and reconcile these two end-members.

How to cite: Chu, Y., Feng, Z., Lin, W., Meng, L., and Xin, G.: Basal Décollement Splaying characterizes Mid-Crustal Deformation and Exhumation of orogenic cores in an intracontinental orogen, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16523, https://doi.org/10.5194/egusphere-egu23-16523, 2023.

Geofluids play an important role to seismic faulting both at hypocentral depth during earthquake nucleation and at shallower crustal levels during seismic rupture propagation. Pre- to co-seismic anomalies of crustal fluid circulation have thus far been identified by hydrogeochemical and seismological (Vp/Vs) monitoring and are generally interpreted as potential precursors, triggers, and/or facilitators of large magnitude earthquakes. Structural and geochemical studies on syn-tectonic mineralizations have highlighted different patterns of fluid ingress, circulation and fluid-rock interaction during the seismic cycle of thrusts and normal faults. Understanding fault rock-fluid relationships in exhumed faults is useful for revealing the role of fluids also in still ongoing seismic cycles from different tectonic settings. We present a review of published studies and original data on the chemical-physical characteristics of syn-tectonic mineralizations formed by fluids that assisted fault-related deformation in the Apennines (Italy). We use our data to build a general model of fluid circulation during thrusting and normal faulting during the seismic cycle, and define a multi-technique workflow to identify tectonic-related physical/chemical equilibria/disequilibria in fluid-rock systems. The proposed workflow relies upon multiscale structural analysis, stable C, O, and clumped isotope analysis, radiometric dating and burial-thermal modeling. The chosen study area is the Central Apennines fold-and-thrust belt, where post-orogenic extensional deformation, characterized by numerous Mw ≥ 6.5 earthquakes, currently overprints Neogene-Quaternary folds and thrusts. We show that thrusting mostly develops in closed fluid systems where fluid and host rock are close to chemical equilibrium. Subsequent normal faulting is characterized by a dominant upward and/or downward open fluid circulation system with an overall range of δ¹⁸O of paleofluids from -10‰ to +13.5‰ (V-SMOW). Isotopic and thermal fluid-rock disequilibria are particularly evident during pre-/ and co-seismic extensional deformation with mineralizations that are up to 30° C warmer and 16° C colder than the host rock and are associated with the ingress of exotic (meteoric or deep crustal) fluids.

How to cite: Curzi, M., Aldega, L., Billi, A., Boschi, C., Carminati, E., Vignaroli, G., Viola, G., and Bernasconi, S.: Fluid-rock chemical-physical equilibrium/disequilibrium inferred from tectonic carbonates in the Apennines (Italy): an advanced approach to track seismic cycles and earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6476, https://doi.org/10.5194/egusphere-egu23-6476, 2023.

Structural analysis coupled with geochemical study of syn-tectonic mineralizations unraveled the role of fluids during the polyphase tectonic evolution of the Val D’Agri, a seismically-active intermontane basin located in the Southern Apennines fold and thrust belt, hosting the largest onshore oil field in western Europe. In this basin, the structural control on present-day fluid circulation is still not well constrained. For this reason, the aim of this work is to reconstruct the Val d’Agri fault system (VAF) architecture and paleo-fluid circulation during the basin tectonic evolution. The VAF evolution was caused by non-coaxial polyphase stress regimes that can be summarized in: 1) Upper Miocene-Lower Pliocene compressional regime; 2) Upper Pliocene-Lower Pleistocene late orogenic strike-slip regime 3) Early Pleistocene-Present post-orogenic extensional regime. Based on new field work, mapping, and structural analysis, we recognized that the VAF is organized in different oriented faults sets. The main sets are N-S-, NE-SW-, and ESE-WNW-striking faults, where the last one has the higher degree of maturity. U-Pb dating of calcite slickenfibres highlighted the long-term tectonic history of these fault sets, with episodes of activation and reactivation of inherited faults. In particular, we recognize: N-S-striking normal faults that reactivated inherited Upper Miocene-Lower Pliocene thrusts; Upper Pleistocene NE-SW-striking normal-lateral faults; one Miocene ESE-WNW-striking normal-lateral fault, with also evidence of reactivation in more recent time. Clumped isotopes analysis together with optical and cathodoluminescence observations of about 50 syn-tectonic calcite mineralizations allowed us to link specific fluid pathways to the different stress regimes. Indeed, bed-parallel veins and mineralizations sampled along transpressive, transtensive, and normal fault sets show that: 1) during the Upper Miocene-Lower Pliocene compressive tectonic phase, fluid circulation occurred in a closed system, characterized by host-rock buffered fluids; 2) during Upper Pliocene-Lower Pleistocene late orogenic phase, fluid circulation occurred in an open system, characterized by meteoric water with low to moderate residence time; 3) during the Lower Pleistocene-Present extensional phase, fluid circulation occurred in an open system, characterized by the mixing of meteoric water and uprising deep high temperature fluids. We highlight that the reconstruction of paleo to present-day fluid circulation is a valid tool for assessing natural and induced seismic hazard in seismically active areas where hydrocarbons are exploited and fluids are injected into the crust, such as in the Val d'Agri basin.

How to cite: Schirripa Spagnolo, G., Agosta, F., Aldega, L., Billi, A., Bernasconi, S., Prosser, G., Smeraglia, L., and Carminati, E.: Upper Miocene to Present fault architecture and fluid pathways in the Val d’Agri basin (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1686, https://doi.org/10.5194/egusphere-egu23-1686, 2023.

Long-lived, mature faults can be architecturally complex. The in-depth unravelling of their complexity, including understanding the dynamic and multiscalar evolution of their mechanical properties, requires detailed multidisciplinary studies. Indeed, an integrated approach is the only viable solution to the deconvolution of the at times very complex internal architecture of brittle fault zones, which represents a phenomenal archive of faulting history and conditions through time and in space. Fault zone architectures are commonly characterized by the spatial juxtaposition of “brittle structural facies” (BSFs), which progressively form and continuously evolve during faulting. The mutual spatial and temporal relationships of BSFs impact directly on the bulk static and dynamic permeability structure of fault zones. The permeability structure, in turn, plays a significant role on the distribution of georesources and on seismogenesis in the brittle upper crust, where both natural and induced seismicity are often associated with fluid migration and overpressure. Detailed models of the complexity of fault zones and of their static and dynamic permeability structure are thus necessary to refine our understanding of fluid pathways and of the mechanisms leading to fluid compartmentalization and possible overpressure in the crust. We present a multidisciplinary workflow to decipher exhumed complex fault zones by integrating detailed structural analyses with geochronological dating of the deformation events recorded by the constituent BSFs and systematic in-situ permeability measurements to connect deformation structures to deformation age and hydraulic properties. The absolute dating of BSFs constrains how fault hydraulic properties change not only through space but also in time (during seismic or orogenic cycles, for example) as the fault architecture (and permeability structure) progressively develop. As a case study, we apply this workflow to the Zuccale Fault in the northern Apennines (Italy), a major low-angle fault that formed and was repeatedly reactivated during a time interval spanning at least the last 22 Myr. A stark spatial heterogeneity of its present-day permeability (up to four orders of magnitude) emerges as a key structural and hydraulic feature, even for tightly juxtaposed BSFs. Results show how complex fault architectures steer the 3D hydraulic structure of the brittle upper crust with direct implications on styles and modes of fluid ingress and flow.

How to cite: Viola, G., Curzi, M., Giuntoli, F., and Vignaroli, G.: Structural-, in-situ permeability- and K-Ar geochronological constraints from complex and heterogeneous fault zones: new perspectives on fluid circulation and seismogenesis in the upper crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12282, https://doi.org/10.5194/egusphere-egu23-12282, 2023.

Helium-rich gases (up to 6%) upwell along a fault that bounds the western edge of the granitic Morvan Massif (northeastern part of the French Massif Central) and the sedimentary rocks of the southeastern edge of the Paris Basin. The sampled gas is mainly composed of nitrogen (90 %.). The radiogenic ³He/⁴He (0.02 Ra, where Ra is the atmospheric ratio) and nucleogenic ²¹Ne/²²Ne (0.031) imply that the gas is basement-derived, in good agreement with the presence of granite in the area. The high radiogenic He concentration can be explained by a rock/ water system isolated over geological time scales and might be linked with the presence of a close-by fluorite ore deposit, dated 130 Ma, located above the fault and at the basement/sediment unconformity in Pierre-Perthuis, formed by leaching of granite (Gigoux et al., 2015).

The possible link between the fluorite ore and the He-rich gases should imply that groundwater in which He released from U and Th in granite was trapped for several millions of years in the granite or in the permeable basement/sediment unconformity reservoir, below the sedimentary cover probably reaching 1.5 km in the area at the end of the Cretaceous. Deep groundwaters trapped in the reservoir accumulated helium before tectonic exhumation of the Morvan Massif and remobilization of fluids to the surface through the Bazois fault, whose onset began 40 My ago (Lenoir et al., 2021). Mixing between old deep crystalline-water with superficial water is evidenced by the presence of high amount of atmosphere-derived nitrogen.

The high chloride content of the waters may originate from the marine water trapped in the Early Jurassic clays, and released by faulting, or by water-rock interaction and hydrolysis of minerals, reinforcing the link between chlorine, fluorine, and water from granite.

This geological example shows that in quiescent area, inactive fault can act as a fluid pathway over long time scale.

How to cite: Battani, A., Gyore, D., Brigaud, B., Bernard, A., Sarda, P., and Stuart, F.: Long time degassing of crustal fluids along inactive fault in an intracratonic basin (Morvan, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16602, https://doi.org/10.5194/egusphere-egu23-16602, 2023.