TS1.7 | Stress, strain, deformation mechanisms and fluids in folded and faulted rocks
Stress, strain, deformation mechanisms and fluids in folded and faulted rocks
Including Arne Richter Award for Outstanding Early Career Scientists Lecture
Convener: Olivier Lacombe | Co-conveners: Nicolas Beaudoin, Stefano Tavani
Orals
| Mon, 24 Apr, 14:00–18:00 (CEST)
 
Room D1
Posters on site
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
Hall X2
Posters virtual
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
vHall TS/EMRP
Orals |
Mon, 14:00
Tue, 16:15
Tue, 16:15
The session aims at making the point on our understanding of the relationships between the development of folds and fault zones, the mechanisms and history of rock strain acquisition from the macroscopic to the microscopic scales, the orientations and magnitudes of stresses and the fluids that flowed within the rocks and interacted with them. We invite contributions covering these aspects, from field-based case studies to modeling.

Orals: Mon, 24 Apr | Room D1

Chairpersons: Olivier Lacombe, Stefano Tavani
14:00–14:05
14:05–14:35
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EGU23-1798
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solicited
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Arne Richter Award for Outstanding Early Career Scientists Lecture
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On-site presentation
Jessica McBeck, Francois Renard, and Yehuda Ben-Zion

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.

Fracture pattern and mechanical stratigraphy
14:35–14:55
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EGU23-8776
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solicited
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On-site presentation
Stephen Laubach and Stephanie Forstner

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.

14:55–15:05
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EGU23-4374
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ECS
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On-site presentation
Paul Joseph Fimbiyaha Namongo Soro, Juliette Lamarche, Sophie Viseur, Fateh Messaadi, and Pascal Richard

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.

15:05–15:15
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EGU23-5630
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ECS
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On-site presentation
Canio Manniello, Simona Todaro, Ian Abdallah, Giacomo Prosser, and Fabrizio Agosta

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.

Fault growth
15:15–15:25
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EGU23-6717
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On-site presentation
Roger Soliva, Sylvain Mayolle, Stéphane Dominguez, and Christopher Wibberley

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.

15:25–15:35
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EGU23-6753
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ECS
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On-site presentation
Sylvain Mayolle, Roger Soliva, Stéphane Dominguez, and Christopher Wibberley

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.

15:35–15:45
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EGU23-14635
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ECS
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On-site presentation
Lucas Eskens, Nevena Andrić Tomašević, Matthias Müller, and Rolf Herrman

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.

Coffee break
Chairpersons: Olivier Lacombe, Nicolas Beaudoin
Deformation mechanisms
16:15–16:25
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EGU23-8940
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On-site presentation
Daniel Koehn, Daniel Hafermaas, Saskia Köhler, Jürgen Lang, Bakul Mathur, Rahul Prabhakaran, and Ruaridh Smith

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.

16:25–16:35
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EGU23-9301
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ECS
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On-site presentation
Maria Eleni Taxopoulou, Marine Lartigau, Charles Aubourg, Nicolas Beaudoin, Elli-Maria Charalampidou, and Jean-Paul Callot

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.

16:35–16:45
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EGU23-5184
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On-site presentation
Francesca Remitti, Andrea Festa, Giuseppe Nirta, Edoardo Barbero, and Silvia Mittempergher

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.

16:45–16:55
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EGU23-16523
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On-site presentation
Yang Chu, Zhentian Feng, Wei Lin, Lingtong Meng, and Guangyao Xin

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.

16:55–17:02
Fluids and fluid flow in folded and faulted rocks
17:02–17:22
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EGU23-6476
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ECS
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solicited
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On-site presentation
Manuel Curzi, Luca Aldega, Andrea Billi, Chiara Boschi, Eugenio Carminati, Gianluca Vignaroli, Giulio Viola, and Stefano Bernasconi

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.

17:22–17:32
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EGU23-1686
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ECS
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On-site presentation
Giulia Schirripa Spagnolo, Fabrizio Agosta, Luca Aldega, Andrea Billi, Stefano Bernasconi, Giacomo Prosser, Luca Smeraglia, and Eugenio Carminati

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.

17:32–17:42
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EGU23-12282
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On-site presentation
Giulio Viola, Manuel Curzi, Francesco Giuntoli, and Gianluca Vignaroli

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.

17:42–17:52
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EGU23-16602
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On-site presentation
Anne Battani, Domokos Gyore, Benjamin Brigaud, Alexis Bernard, Philippe Sarda, and Finlay Stuart

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.

17:52–18:00

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall X2

Chairperson: Stefano Tavani
X2.235
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EGU23-4909
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ECS
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Marco Mercuri, Stefano Tavani, Luca Aldega, Fabio Trippetta, Sabina Bigi, and Eugenio Carminati

The characterisation of the fracture network is a fundamental step for modelling the circulation of different types of geofluids at multiple scales, including at the reservoir scale. Due to the difficulty of sampling the fracture network with a spatial continuity, fracture networks are often derived from a stochastic approach applied to ground truth parametrized datasets. Classical field methods for collecting and analysing fracture data sets (i.e., scan-lines or scan-areas) have limited sample area and the results might be affected by local factors (e.g., facies variations and faults). In poorly- to non-vegetated regions, field-derived data can be integrated with satellite and aerial images providing a “big-picture” of the study area. The availability of open-source, high-resolution aerial and satellite images (e.g., Google Maps, Bing Maps) coupled with the development of specific software and tools (e.g., NetworkGT; FracPaQ) allow to digitize and analyse very large and spatially continuous data sets of fractures at multiple scales for a single case study.

In this work, we test the use of Bing Maps imagery for the analysis of the fracture network affecting the Kuh-e-Asmari anticline, in the Zagros fold-and-thrust belt. The Kuh-e-Asmari anticline is considered as an outcropping analogue of fractured reservoirs and is in a scarcely vegetated area, covered by high resolution open-source aerial images (~2.6 m/pixel). We obtained three different image-derived fracture data sets by manually digitizing the fracture network at three different scales (1:50000, 1:5000, and 1:500) in QGIS. Each data set has been analysed using the NetworkGT plugin within QGIS. In detail, we analysed the orientation, length distribution, abundance, and topology of each fracture network data set, and we have compared the results with structural data from scan-lines performed in the field on the same anticline.

Results proved to be scale-dependent, with each scale having its pros and cons, as follows. The 1:50000 data set is the only spatially continuous data set, allows to rapidly map the main tectonic features (e.g., major faults and fracture corridors) but it is not accurate enough in terms of the definition of orientation sets and length analyses. The 1:5000 data set is potentially spatially continuous and allows to analyse fracture and connectivity distributions with high detail, by highlighting strongly fractured/connected elongated zones, possibly representing damage zones of known, previously mapped, fault strands. The 1:500 scale cannot guarantee the spatial continuity of the data set but, if applied to a small area, provide reliable results.

Results obtained in this work suggest that the manual interpretation of open-source aerial images is a viable way for the characterization of fracture networks in poorly vegetated areas only if the right scale is chosen. For the case study presented here we suggest interpreting the fracture network at 1:5000 or similar scales. A successful testing of semi-automatic or automatic algorithms for lineament detection is required to perform a spatially continuous interpretation and analysis at the highest possible resolution, and/or to analyse the fracture dataset at multiple scales (more than the 3 investigated here).

How to cite: Mercuri, M., Tavani, S., Aldega, L., Trippetta, F., Bigi, S., and Carminati, E.: The usage of open-source aerial images for the characterisation of a fracture network. Insights from a multi-scale approach in the Zagros Mts., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4909, https://doi.org/10.5194/egusphere-egu23-4909, 2023.

X2.236
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EGU23-7033
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ECS
Santu Biswas and Manish A. Mamtani

Hydrothermal veins can form when pre-existing anisotropy gets dilated by increase in fluid pressure (Pf). In addition fluctuation in Pf can result in the deposition of economically important deposits, such as gold in veins. Therefore, statistical analysis of dilational quartz veins can help to identify the mineralization potential of an area. This present study is focused on this aspect. The metavolcanic rocks of Dharwar Craton (Southern India) are replete with quartz veins, but mineralization is restricted to certain domains in the vicinity of Gadag, Hutti, and Kolar. To study the topological importance in mineral exploration, an experiment is carried out in different parts (e.g., Gadag, Hutti, Raichur, Gadwal) of Dharwar Craton. Orientation of dilational quartz veins, thickness, and spacing data are collected from different transects of the above-mentioned areas. Variations in driving pressure ratio (ΔRʹ), fractal dimension (Dc), Weibull modulus (α), vein intensity (Vi), and coefficient of vein spacing (Cv(S)) are calculated from vein data of each transect. These parameters are integrated to plot a three-axes “mineralization potential plot”, also known as P-D-F plot (Lahiri et al., 2020). The distance between the origin (0,0,0) and the point representing the transect in the P-D-F plot gives the “mineralization potential parameter” (Md). It is established that a transect in mineralized zone is represented by a point that lies closer to origin than non-mineralized zone. However, it is our observation that the points representing mineralized zone show more clustering on the P-D-F plot, whereas the points representing non-mineralized zone are dispersed.  We infer that in order to identify a zone as having high mineralization potential, the Md value should not only be lower but also the clustering should be higher.

How to cite: Biswas, S. and Mamtani, M. A.: Mineralization potential from vein statistics at regional scale – an example from the Dharwar Craton (Southern India), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7033, https://doi.org/10.5194/egusphere-egu23-7033, 2023.

X2.237
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EGU23-9789
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ECS
Stephen Brown, Yves Missenard, Philippe Robion, Laurent Beccaletto, Cécile Allanic, and Frédéric Haurine

Deformation of intraplate sedimentary basins essentially results from tectonic stresses that propagate from plate boundaries. Yet, the detailed characteristics of this far field propagation are often poorly constrained, especially in age. Recent developments of U/Pb dating of calcite precipitations in fault planes and veins hopefully greatly help to frame the schedule of deformation. This is the case for the Meso-Cenozoic Paris basin, liable to have recorded several Cenozoic events due to its location in the western Eurasian plate, like Pyrenean and Alpine collisions and Oligocene extension (ECRIS).

Our study focusses on the southern Paris basin area, north of the Morvan massif, where Alpine deformations are expected. Field data reveal almost exclusively strike-slip deformations with variable σ1 direction. These results are about to be confirmed at the microscopic scale using Anisotropy of Magnetic Susceptibility and of P-Wave Velocity methods. Associated U-Pb dating of synkinematic calcites from Jurassic strata indicates distributed Eocene deformation and an absence of Oligocene or Miocene ages. Such ages suggest the record of Pyrenean and possibly ECRIS tectonic events. Strikingly, Alpine deformation and especially stress propagation leading to the growth of the Jura fold-and-thrust belt during Miocene does not imprint the studied area although the Alpine orogen is located closer than the Pyrenean belt.

How to cite: Brown, S., Missenard, Y., Robion, P., Beccaletto, L., Allanic, C., and Haurine, F.: Structural investigations and U/Pb dating in the southern Paris basin do not record any Alpine deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9789, https://doi.org/10.5194/egusphere-egu23-9789, 2023.

X2.238
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EGU23-7298
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ECS
Pablo Granado, Jonas B. Ruh, Marcel Guillong, and Luis Rodríguez-Terente

The Permian–Mesozoic Asturian (NW Spain) hosts a series of world-class fluorspar deposits - a critical raw material for the EU - with more than 15 Mt. extracted to date. Asturian fluorspar deposits are hosted in silicified Paleozoic and Triassic carbonate rocks, spatially associated with the fault-bound margins of the basin. The Asturian fluorspar deposits show an important structural and lithological control, being hosted in fault-fill veins, jogs and breccias associated with steeply-dipping extensional faults and related folds, and strata-bound bodies replacing carbonate rocks. The general paragenesis comprises fluorite, calcite, quartz, (±) barite, and minor sulfides including pyrite, sphalerite, chalcopyrite, (±) galena. Formation of these fluorspar deposits has been assigned to the Permian volcanic activity during the extensional event following the Variscan orogeny, or the Mesozoic opening of the Atlantic realm.

For this study, we have sampled and measured the orientation of the main ore body at La Collada underground works. The ore body is hosted in a fault-fill vein moderately dipping to the SSW (mean plane is 214/47; n=41), ranging in thickness from a few meters to 15m. Observed sub-vertical veins of calcite are kinematically compatible with the main SSW-dipping fault-fill vein, and suggest concomitant ore deposition and extensional faulting. Laminated textures and localized high-dilation breccias in the main fault-fill vein suggests multi episodic fault activity associated with fluid overpressures (fault-valving?). S/C structures and fault slickensides (n=6) indicate oblique right lateral reactivation. Three representative samples from the main fault-fill vein were taken for U–Pb dating by LA-ICP-MS. Calcite spot analysis yielded two age populations (155Ma, 131Ma.) thus suggesting multiepisodic precipitation of calcite, and a potential open system. Obtained radiometric ages are consistent with rift initiation in the Asturian basin, and opening of the Bay of Biscay since Upper Jurassic times. Coupled with structural geology and textural analysis, LA-ICP-MS U-Pb dating of hydrothermal calcite aids in constraining the timing of fluid-flow events and fault activity responsible for ore deposit formation and re-mobilization, and refines the regional context of the Asturian fluorspar deposits.

How to cite: Granado, P., Ruh, J. B., Guillong, M., and Rodríguez-Terente, L.: New constraints from structural data and U-Pb calcite geochronology on La Collada fluorspar ore body (Asturian basin, NW Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7298, https://doi.org/10.5194/egusphere-egu23-7298, 2023.

X2.239
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EGU23-5306
Alessio Lucca, Silvia Mittempergher, Andrea Succo, Andrea Bistacchi, Marco Meda, and Fabrizio Storti

The NW-SE striking Pag anticline, in the External Dinarides fold and thrust belt, provides an appropriate field site for studying fold- and fault-related deformation patterns at different scales in a transpressional setting due to outstanding exposures. We performed a multiscale structural analysis together with petrographic and isotopic characterization of syntectonic calcite cements. Results indicate that the Pag anticline, is a box fold developed mainly by detachment folding in response to NE-SW oriented compression. Depth-to-detachment calculation indicates that the basal thrust of the anticline is located in the Upper Jurassic evaporitic complex, at a depth of about 2.5 km. The geometry of the fold is strongly controlled by the interaction and overstepping of a major thrust-backthrust fault pair. In the northern sector, backthrust activity produced a northeastern facing, steeply dipping to near vertical backlimb. Moving southward, the forelimb gradually becomes vertical to overturned and fold asymmetry switches to a southwestward facing. Late- to post-folding tightening resulted in non-cylindrical and compartmentalized deformation by near vertical N-S right-lateral, and E-W, left-lateral, strike-slip faults trending oblique to the fold axis. These fault sets make a wider angle than expected for transversal conjugate strike-slip faults commonly associated with folding, possibly due to lateral propagation from inherited, folded soft-sediment extensional faults. Paleostress analysis indicates that the evolution of the Pag anticline occurred in a stress field that switched from contractional to transpressional configuration, maintaining a N40-50° oriented major stress axis. Petrographic and isotopic data support infiltration of meteoric fluids into exposed carbonates in the pre-folding stage, followed by mixing with marine fluids during folding at shallow burial conditions and, eventually, meteoric fluid circulation along strike-slip faults in the late to post-folding stage. Stable isotope ratios suggest that fluid flow evolved from a bedset confined system to an open one in the late to post-folding stage. As such, a major role to control paleofluid flow is played by the transversal sets of low-displacement near orthogonal strike-slip faults. This suggests that, in reservoir structural characterization, particular attention should be paid to the presence of low-displacement strike-slip faults because of their role to enhance fluid flow mixing and channeling. The presence and, particularly, the abundance of such deformation features are difficult to constrain in buried fractured reservoirs by seismic reflection imaging because of low displacement values. We, consequently, stress the importance of studying field analogues by multidisciplinary approaches for better understanding the relationships between folding, faulting, the associated incremental deformation patterns, and the impact on fluid flow.

How to cite: Lucca, A., Mittempergher, S., Succo, A., Bistacchi, A., Meda, M., and Storti, F.: Deformation pattern, paleostress, and paleofluid evolution in the Pag anticline, External Dinarides of Croatia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5306, https://doi.org/10.5194/egusphere-egu23-5306, 2023.

X2.240
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EGU23-16265
Nicolas Beaudoin, Anne Battani, Irène Aubert, Antoine Léon, Charles Aubourg, Laurent Emmanuel, and Finlay Stuart

The evolution of deformation structures and associated past fluid flow is a key to better appraise both the reservoir properties of a rock and the regional evolution of an area. Indeed, the meso-scale fracture network often develops over a long period of time, granting access to a long term evolution of a past fluid system (i.e. the temperature, origin and migration pathways of the fluids) on the one hand. On the other hand, major thrusts are believed to enable episodic fluid migrations on larger spatial scales, in relation to their activity calendar, whether this activity is over or ongoing. It is seldom however to reconstruct both the past fluid flow and the present-day fluid flow on the same structure, yet it can be very enlightening about the evolution of the thrust connectivity at depth since before a fold developed over it.

In this study we reconstructed the deformation pattern and associated past fluid system related to the development of the Sierra de Orba Anticline (Spain), and we compare it to the current-day fluids resurging in the vicinity of the fault. The Sierra de Orba anticline is part of a fault-propagation fold system that developed in the northern part of the Jaca Basin, Southern Pyrenean foreland, Spain. This fold affects the sedimentary succession including the Triassic decollement level, the Upper Cretaceous to Paleocene carbonate strata and the Middle Eocene marls. The N110 striking major thrust, where the Upper Cretaceous Marboré Fm. lies unconformably onto the Eocene marls, was sampled, along with the fracture network in the hangingwall and the footwall of the thrust. The fracture network includes a sequence of prefolding sets of joints and veins, striking E-W and N060 and flexural-slip related reverse faults. Then, the network encompasses the orogeny history since likely the forebulge development until the strata tilting during folding. Syn-kinematic calcite cements were characterized petrographically in both joints and faults, then studied by means of oxygen and carbon isotopic measurements coupled with fluid inclusion microthermometry. Results highlight that the fluid system recorded an alternation between meteoric fluids (δ18O signature of the fluid: -5‰ SMOW) heated up at 70-80°C, and evolved seawater (δ18O signature of the fluid: +5 to +10‰SMOW) heated up at 70-100°C. That past fluid system around the main thrust did not record any deep-sourced fluids, unlike similar structures in the southern Pyrenean foreland. The major gas content of current day fluids was analysed from a resurgence in the footwall of the thrust. This gas is especially nitrogen-rich (>86%), and is characterized by an heavy δ13C signature of the methane content (4‰PDB). Both these features could relate to deep processes, such as an oxidation of a potential abiotic carbon that can be related to a serpentinization process. This hypothesis needs to be further evaluated by means of a study of noble gas content. Beyond regional implications, this case study illustrate how a combination of geochemical proxies can help to unravel the evolution of a fluid system at a fold-thrust scale, from its onset to today.

How to cite: Beaudoin, N., Battani, A., Aubert, I., Léon, A., Aubourg, C., Emmanuel, L., and Stuart, F.: Depicting the fluid system evolution in a major thrust and associated fracture network, from layer parallel shortening to today: the Sierra de Orba anticline, Jaca basin, Spain., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16265, https://doi.org/10.5194/egusphere-egu23-16265, 2023.

X2.241
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EGU23-8991
Bakul Mathur, Daniel Koehn, and Ruaridh Smith

Fragmentation in deformation bands and faults is relatively complex with multiple fracture sets breaking single grains into anisotropic splinters. An understanding of the development of deformation bands and faults and the associated mechanical and permeability evolution is important for many applications including treatment of faults in reservoir models, flow properties of faults in geothermal systems and CCS (Carbon Capture and Storage), and seismic hazards. Various mathematical models have been developed to capture rock fragmentation process at single and multi-grain scale as well as to study the hydraulics in large scale geological discontinuities. However a multi-scale approach is needed to understand the implications of the changes in mechanical properties and permeability due to small scale rock fragmentation on the large scale bands, faults and fractures. This study aims to employ an extended Discrete Element Method (DEM) approach with multi-scale aggregates to model the evolution of deformation bands in porous sandstones.

Grain failure in rocks can be caused by different loading conditions, such as compressive loading, shear displacement, thermal, hydraulic or chemical effects. In this study, simulation of the comminution  process of the polyhedral shaped grains is achieved under compressive and shear loading. Single grain fragmentation is realised with the Mohr-Coulomb approach, which is a classical failure criterion for brittle particle systems. The failure criterion is combined with the Weibull statistical distribution that captures the grain size effect. A multiple grain model is simulated with DEM combined with the Mohr-Coulomb-Weibull concept. The computations are carried out with an open-source discrete numerical modelling framework YADE. The study sheds light on the influence of initial rock properties (porosity, grain size and shape) and deformation mechanism (compaction, shearing and combinations) on the development of deformation bands and faults.

How to cite: Mathur, B., Koehn, D., and Smith, R.: Modelling of Fragmentation Process in Deformation Bands and Faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8991, https://doi.org/10.5194/egusphere-egu23-8991, 2023.

X2.242
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EGU23-4874
Christoph von Hagke, Armin Dielforder, Johannes Glodny, and Chris K. Morley

Modern concepts of fault strength account for compositional and hence rheological heterogeneity of natural fault zones. An important implication of heterogeneity is strain partitioning between stronger and weaker phases and a gradual transition from brittle to ductile deformation. While a broader brittle-ductile transition zone is consistent with deformation fabrics in fault zones, it remains uncertain how broad the transition zone is and whether deformation fabrics record truly simultaneous brittle-ductile deformation or successions of brittle and ductile deformation driven by temporal changes in temperature, strain rate, and/or pore fluid pressure. Here we present data from a major fault zone of the Permo-Triassic Khao-Khwang fold-and-thrust belt, Thailand. The fault zone is located in marine calcareous shales with Permian limestones in the foot- and hanging wall. Thrusting occurred at peak temperatures of ~200°C. Deformation fabrics document frictional sliding, cataclasis, mineral veining, and pressure solution in the main fault zone and local mylonitization at the base of the hanging wall limestone. Thus, the fault zone records competing brittle and ductile deformation and incipient strain partitioning between the shales and limestones, consistent with a broad brittle-ductile transition zones due to rheological heterogeneity. Radiogenic strontium isotope ratios (87Sr/86Sr) of syntectonic vein carbonates and calc-mylonites, tell, however, a slightly different story. Vein carbonates from the fault zone all have Permian seawater-like 87Sr/86Sr ratios documenting a rock-buffered pore fluid during brittle deformation. By comparison, the calc-mylonites record less radiogenic 87Sr/86Sr ratios hinting at a mantle source. The Sr ratios are similar to those of syntectonic mafic dykes that intruded Khao-Khwang fold-and-thrust belt. We interpret the distinct Sr ratios of the calc-mylonite to document that mylonitization was triggered by migration of hot magmatic fluids. In this case, strain partitioning between the shales and limestone were likely insignificant without the impact of the hot fluids, although the limestones were already close to the brittle-ductile transition at ambient temperatures of ~200°C. Taken together, our findings suggest that the transition from frictional deformation and pressure solution in shales to ductile shearing in limestones might be rather abrupt than gradual.

How to cite: von Hagke, C., Dielforder, A., Glodny, J., and Morley, C. K.: Is mixed brittle-ductile deformation simultaneous or successive? Insights from the strontium isotope systematics of deformation structures in a heterogenous fault zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4874, https://doi.org/10.5194/egusphere-egu23-4874, 2023.

X2.243
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EGU23-9680
Martin Schöpfer, Bernhard Grasemann, and Ralph Hinsch

Although the origin of outer-arc extension fractures in folded sequences is well-understood and documented in many natural examples, geometric and geomechanical factors controlling their spacing are hitherto unexplored. This study investigates the formation of bending-induced tensile fractures during constant-curvature forced folding using two-dimensional Distinct Element Method (DEM) numerical modelling. The DEM model comprises a central brittle layer embedded within elastic layers; the layer interfaces are cohesionless. Folding of this three-layer system is enforced by a velocity boundary condition at the model base, while a constant overburden pressure is maintained at the model top.

The models illustrate several key stages of fracture array development: (i) Prior to the onset of fracture, the neutral surface is located midway between the layer boundaries, consistent with pure bending; (ii) Once the outer-fibre stress equals the tensile strength of the layer, fractures nucleate and propagate through the brittle layer; (iii) The rate of fracture formation as a function of curvature decreases nonlinearly, with new fractures developing approximately midway between two existing fractures; (iv) Eventually no new fractures form, irrespective of any further increase in fold curvature, a state referred to as fracture saturation.

On the basis of these numerical model results, an approximate analytical solution for fracture spacing based on classic beam theory is developed. The predicted range of fracture spacing as a function of fold curvature is in good agreement with the numerical model results. Importantly, the analytical solution reveals which geometric and geomechanical factors control fracture spacing, namely layer thickness, radius of curvature, Young’s modulus, tensile strength and confining pressure. The fracture spacing to layer thickness ratio at saturation however depends only (nonlinearly) on the ratio of tensile strength to overburden pressure.

The numerical model results are qualitatively compared with field observations at outcrops located in the Montpellier Fold region. The folded lithologies are of Jurassic age and comprise (brittle) limestones, with (ductile) marl intercalations. Fracture-bound limestone blocks located within the fold hinges and observed on the fold-profile plane are laterally bound by V-shaped veins that thin towards the fold core. In the inner-arc of each vein-bound limestone block, the marl interbed thickens towards the veins, whereas in the outer-arc it thins towards the veins. Clearly, the thickness distribution of the marl interbeds reflects non-uniform loading, which is consistent with the loading conditions hypothesised on the basis of the theoretical models.

How to cite: Schöpfer, M., Grasemann, B., and Hinsch, R.: Numerical and analytical modelling of bending-induced tensile fractures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9680, https://doi.org/10.5194/egusphere-egu23-9680, 2023.

Posters virtual: Tue, 25 Apr, 16:15–18:00 | vHall TS/EMRP

Chairperson: Stefano Tavani
vTE.1
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EGU23-1023
lu xiulin and jiang youlu

Junggar Basin, located in the northern Xinjiang, is one of the most important oil and gas bearing sedimentary basins in China. Zhong-4 Block, located in Fukang Sag at the southern edge of the basin, is rich in oil and gas resources but low in exploration. Strike slip faults in the study area play an important role in controlling the distribution of oil and gas. Based on seismic and logging data, the static characteristics of strike slip faults are determined, the formation mechanism of strike slip faults is clarified, and the relationship between strike slip faults and oil and gas distribution is clarified. The results show that: (1) North east trending R-type shear fault, northwest trending P-type shear fault and north-south trending T-type extension fracture fault are developed in Zhong-4 block. The cross section of the strike slip fault is steep, with flower like structure, and obvious dolphin effect and ribbon effect can be seen; On the plane, it is characterized by segmented development, consisting of oblique overlapping segment, linear segment and braided structure segment; (2) The faults in Zhong4 Block are generally strike slip faults formed under the single shear mechanism consisting of NWW, NE and NS directions. According to the comprehensive geometric and kinematic characteristics, the fault zone in the work area mainly follows the rightward Riedel single shear mode. The included angle between R shear fault, P shear fault and main fault is mostly 15 °~25 °, which is widely developed in the work area. There are two stages of strike slip activities in the study area. The first stage is left strike slip in the west of Dong 6 well area in the early Jurassic, and the second stage is right strike slip in the whole study area in the late Jurassic; (3) The fault block traps developed in the strike slip fault oblique overlap zone are the main places for oil and gas enrichment in the study area, while the vertical sealing of the fault controls the oil and gas enrichment horizon. When the normal stress of the section is large and the vertical sealing of the fault is strong, oil and gas are enriched in the deep Sangonghe Formation; When the vertical sealing of the fault is poor, oil and gas are distributed in deep Sangonghe Formation and shallow Toutunhe Formation.

How to cite: xiulin, L. and youlu, J.: Characteristics of Jurassic Strike-slip Faults in Block 4 in Junggar Basin and Their Relationship with Hydrocarbon Distribution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1023, https://doi.org/10.5194/egusphere-egu23-1023, 2023.

vTE.2
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EGU23-14859
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ECS
Aniès Zeboudj, Olivier Lacombe, Nicolas Beaudoin, Jean-Paul Callot, Juliette Lamarche, and Abel Guihou

Folded sedimentary layers usually exhibit brittle mesostructures such as faults, joints, veins, and stylolites which accommodate the internal strain of strata during folding but also before strata started to be tilted, i.e. during Layer Parallel Shortening (LPS), and after tilting, i.e. during late stage fold tightening (LSFT) when shortening can no longer be accommodated by fold growth. We have established a fracture sequence in the Mirabeau anticline (SE France) using orientation data and relative chronology with respect to bedding attitude, which comprises the early-, syn- and late-folding fractures related to the folding event (1). This field-based approach is compared to 12 ages out of 32 samples analyzed by LA-ICP-MS U-Pb geochronology of selected syn-kinematic calcite, in order to provide an absolute time frame for the fracture development, along with a potential validation of the sequence of deformation. Along a section across the fold strike axis, the deformation related to the contraction lasted at least 12 Ma (or 26 Ma with uncertainties), bracketed between 52 Ma (± 8 Ma) and 40 Ma (± 6 Ma), indicating that the fold developed in response to the so-called Pyrenean-Provençal phase. In depth however, the sequence of deformation as inferred from the structural study of the fracture network is challenged by the absolute age of the syn-kinematic calcite: syn-folding flexural-slip surfaces are dated from 52 Ma (± 8 Ma), i.e. older than early-folding reverse faults associated to LPS (46 ± 4 Ma).  

 

In order to better constrain the onset of Layer-Parallel Shortening (LPS), we further analyzed the bedding parallel sedimentary stylolites through the inversion of their roughness to better define the burial depth range during which the Jurassic and Upper Cretaceous formations of interest were submitted to a vertical stress σ1. Once projected on the burial-time model of the investigated strata, the depth range, going up to 3 km, constrains the time at which σ1 presumably switched from vertical to horizontal in response to the onset of tectonic loading. Altogether, this work questions the limits of absolute dating in understanding fold-fracture relationships, and forewarn of potentially misleading interpretation of absolute ages when associated with deformation features. The example of the Mirabeau Anticline enables a discussion about the compatibility and complementarity of different approaches to date mesoscale and macroscale deformation features in fold-and-thrust belts where the sedimentary record is not well preserved.

 

Keywords : Absolute dating, fracturation, fold, carbonates

 

(1) Lacombe O., Beaudoin N., Hoareau G., Labeur A., Pecheyran C. & Callot J.P., 2021. Dating folding beyond folding, from layer-parallel shortening to fold tightening, using mesostructures : Lessons from the Apennines, Pyrenees and Rocky Mountains.  Solid Earth, 12, 10, 2145-2157

How to cite: Zeboudj, A., Lacombe, O., Beaudoin, N., Callot, J.-P., Lamarche, J., and Guihou, A.: To what extent does U-Pb geochronology of calcite cements help to constrain the sequence of fracture development in folded strata? The Mirabeau Anticline (SE France) as a case study., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14859, https://doi.org/10.5194/egusphere-egu23-14859, 2023.

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EGU23-15471
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ECS
David Cruset, Daniel Muñoz-López, Jaume Vergés, and Anna Travé

Structural analyses of vein and faults related with the growth of the South Pyrenean fold and thrust belt are coupled with the U-Pb ages of fracture-filling calcites compiled in Cruset et al. (2020) and Muñoz-López et al. (2022). Fractures include conjugated vein systems and reverse, strike-slip and normal faults cemented by calcite. The results reveal the orientation of tectonic stresses during the Pyrenean compression and their spatial and temporal evolution since the Late Cretaceous.

 Late Cretaceous to late Palaeocene U-Pb dates between 70.6 and 55.3 Ma registered compressional deformation in the inverted Mesozoic salt-related extensional basins corresponding to the Bóixols and Upper Pedraforca thrust sheets. Calculated paleostresses show a predominant N-S direction of tectonic transport, with more pronounced NW-SE directions in the western termination of the Bóixols and in the northern sector of the Upper Pedraforca.

Fracture data and U-Pb ages between 47.9 and 42.3 Ma measured in the Lower Pedraforca thrust sheet reveal N-S and NW-SE directions of tectonic transport during the middle Eocene, similar to those in the Bóixols and Upper Pedraforca thrust units. Contrarily, younger late Eocene to Oligocene U-Pb ages between 36.2 and 28.4 Ma measured in the lowermost Cadí thrust sheet reveal an homogeneous N-S trend during the emplacement of this unit.

Fractures cutting the Bóixols and Upper Pedraforca thrust sheets, and filled with cements yielding U-Pb ages from 48.8 to 25.68 Ma, show the same directions of tectonic transport than those measured for the Late Cretaceous-Paleocene. These Eocene and Oligocene ages also register the post-emplacement deformation of upper tectonic units on top of the Lower Pedraforca, Cadí, Montsec and Serres Marginals lower thrust sheets.

This research was funded by the project ALORBE (PIE-CSIC-202030E310), DGICYT Spanish Projects PID2021-122467NB-C22 and PGC2018-093903-B-C22 Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, Unión Europea. David Cruset acknowledges the Spanish Ministry of Science and Innovation for the "Juan de la Cierva Formación” contract FJC2020-043488-I AEI/10.13039/501100011033.

References

Cruset, D. et al., 2020. Quantifying deformation processes in the SE Pyrenees using U-Pb dating of fracture-filling calcites. Journal of the Geological Society, 177: 1186-1196.

Muñoz-López, D., et al. 2022. Spatio-temporal variation of fluid flow behavior along a fold: The Bóixols-Sant Corneli anticline (Southern Pyrenees) from U–Pb dating and structural, petrographic and geochemical constraints. Marine and Petroleum Geology, 143: 105788.

How to cite: Cruset, D., Muñoz-López, D., Vergés, J., and Travé, A.: Paleostress evolution in the South Pyrenean fold and thrust belt based on the structural analysis of fractures and U-Pb dating of carbonates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15471, https://doi.org/10.5194/egusphere-egu23-15471, 2023.