Session TS1.10

[Programme]

TS1.10 | A truly multiscale understanding of salt tectonics and structural geology - a session in memory of Janos Urai

A truly multiscale understanding of salt tectonics and structural geology - a session in memory of Janos Urai

Convener: Manuel MenzelECSECS | Co-conveners: Dan Mircea TamasECSECS, Prokop Závada, Susanne Buiter, Pablo Granado, Florian Fusseis, Christoph von Hagke

Orals

| Tue, 16 Apr, 16:15–18:00 (CEST)

Room K1

Posters on site

| Attendance Wed, 17 Apr, 10:45–12:30 (CEST) | Display Wed, 17 Apr, 08:30–12:30

Hall X2

Posters virtual

| Attendance Wed, 17 Apr, 14:00–15:45 (CEST) | Display Wed, 17 Apr, 08:30–18:00

vHall X2

Deformation mechanisms, salt deformation and salt tectonics, the microporous structure and deformation of clays and claystones, open fracture networks, and the regional tectonics of Naxos and Oman: Janos Urai advanced our understanding in all these topics, and many more, using a wide range of techniques and building on a never-ending flow of ideas and enthusiasm. In this session, we would like to honour Janos’ comprehensive contribution to modern structural geology and tectonics, and map his legacy. With his multidisciplinary approach, combining field geology, microstructure images, analogue experiments, and analytical and numerical solutions, Janos truly has advanced our understanding of rock deformation ranging from nano- and microscale deformation processes to tectonic processes at the scale of mountain ranges. He also was an outstanding teacher of structural geology at all levels, and an immensely creative and productive out-of-the-box thinker and innovator. Beyond his retirement, Janos remained deeply invested in science and his many collaborations.

Here, we invite contributions on all topics that have their roots in Janos’ work and build on it, including work that was inspired by his research, ideas and collaborations with others. Janos was a 'salt giant', so a particular focus of this session will be salt-related deformation from microtectonic to regional scales.

Session assets

Session summary

Orals: Tue, 16 Apr | Room K1

Chairpersons: Dan Mircea Tamas, Manuel Menzel, Prokop Závada

16:15–16:25

EGU24-19007

ECS

solicited

On-site presentation

The microstructure of naturally deformed gneissic Zechstein 2 rock salt (Kristallbrockensalz) from the northern Netherlands – a review

Jessica Barabasch, Joyce Schmatz, Jop Klaver, Alexander Schwedt, and Janos L. Urai

Janos Urai's contributions have significantly enhanced our understanding of salt deformation, particularly in predicting the long-term evolution of solution-mined caverns and radioactive-waste repositories in salt formations. His work delved into phenomena such as the weakening of rock salt by water during long-term creep at low differential stresses. Unlike most laboratory measurements, which are at higher differential stress, Urai's research considers dislocation creep and pressure solution (dissolution-precipitation creep), processes not commonly included in current engineering predictions.

Microstructural observations on Zechstein 2 (Z2) rock salt cores in the northern Netherlands reveal substantial grain-size-dependent differences in rock salt rheology. The study compares undeformed salt layers with strongly deformed diapiric ones, showcasing variations in megacrystals and fine-grained halite microstructures that point to different microphysical processes. The microstructural analysis, including optical microscopy of gamma-irradiated thin sections, recrystallized grain-size measurements, electron microscopy, and subgrain-size piezometry, indicates differential stresses between 0.5 and 2 MPa during deformation.

The findings highlight the importance of pressure solution creep at low differential stresses, demonstrating its significant impact on strain rate in rock salt. Integrating these results into constitutive flow laws reveals a four-order-of-magnitude difference in strain rates between halite types, emphasizing the role of different dominant deformation mechanisms. The study suggests that incorporating pressure solution creep and microstructural analysis can substantially enhance engineering and tectonic models of rock salt deformation in low-stress conditions.

How to cite: Barabasch, J., Schmatz, J., Klaver, J., Schwedt, A., and Urai, J. L.: The microstructure of naturally deformed gneissic Zechstein 2 rock salt (Kristallbrockensalz) from the northern Netherlands – a review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19007, https://doi.org/10.5194/egusphere-egu24-19007, 2024.

16:25–16:35

EGU24-3225

ECS

On-site presentation

Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration

Baoqin Hao, Maria-Gema Llorens, Albert Griera, Paul D. Bons, Ricardo A. Lebensohn, Yuanchao Yu, and Enrique Gomez-Rivas

Full-field numerical modelling is a useful method to gain understanding of rock salt deformation at multiple scales, but it is quite challenging due to the anisotropy and complex plastic behavior of halite and other evaporite minerals at the single crystal level, together with dynamic recrystallization processes. We overcome these challenges and present novel results of full-field numerical simulation of dynamic recrystallization of halite polycrystalline aggregates during simple shear deformation, including subgrain rotation and grain boundary migration recrystallization processes. The results illustrate that the approach successfully reproduces the evolution of pure halite microstructures from laboratory torsion deformation experiments at 100-300℃ up to shear strain of four. Temperature determines the competition between (i) grain size reduction controlled by dislocation glide and subgrain rotation recrystallization (at low temperature) and (ii) grain growth associated with grain boundary migration (at higher temperature), while the resulting crystallographic preferred orientations are similar for all cases. The analysis of the misorientation reveals that the relationship between subgrain misorientation and strain follows a power law relationship with a general exponent of 2/3. However, with progressive deformation, dynamic recrystallization leads to a gradual deviation from this relationship. Therefore, predicting strain or temperature from microstructures necessitates careful calibration.

How to cite: Hao, B., Llorens, M.-G., Griera, A., Bons, P. D., Lebensohn, R. A., Yu, Y., and Gomez-Rivas, E.: Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3225, https://doi.org/10.5194/egusphere-egu24-3225, 2024.

16:35–16:45

EGU24-10987

On-site presentation

Using crystal-lattice distortion data for geological investigations: the weighted Burgers vector method

John Wheeler, Piazolo Sandra, David Prior, Patrick Trimby, and Jacob Tielke

Janos Urai made major contributions to our understanding of rock deformation and the microstructural fingerprints that can be used to investigate it.

One such fingerprint is intracrystalline distortion. Crystals can be distorted due to deformation or growth but the distortion gives insights into processes in either case. Distortion is generally due to the presence of dislocations which give information on slip systems, stress levels, growth mechanisms etc. Electron backscatter diffraction (EBSD) allows detailed quantification of distorted crystals, and we summarise here a method for extracting information on dislocations from such data. The weighted Burgers vector (WBV) method calculates a vector at each point on an EBSD map, or an average over a region. The vector is a weighted average of the Burgers vectors of dislocation lines intersecting the map surface. It is weighted towards dislocation lines at a high angle to the map but that can be accounted for in interpretation. The method is fast and does not involve specific assumptions about dislocation types; it assumes only that elastic strains have little effect on the calculation. It can be used, with care, to analyse subgrain walls (sharp orientation changes) as well as gradational orientation changes within individual grains. It can complement established methods for subgrain wall analysis and frees us from some assumptions made in other methods.

We give examples of its use applied to olivine and plagioclase. The magnitude of the vector relates to dislocation density but, as a vector, we find its directional information particularly informative. Code to implement this approach is available from the first author (“Crystalscape”), from Oxford Instruments (a commercial version) and aspects are implemented in MTEX.

Urai, J. L., Means, W. D. & Lister, G. S. 1986. Dynamic recrystallisation of minerals. In: Mineral and Rock Deformation: Laboratory Studies (edited by Hobbs, B. E. & Heard, H. C.). Geophysical Monograph 36. AGU, Washington, D.C., 161-199.

Urai, J. L. & Spiers, C. J. 2007. The effect of grain boundary water on deformation mechanisms and rheology of rocksalt during long-term deformation. In: 6th Conference on the Mechanical Behavior of Salt. Proceedings and Monographs in Engineering Water and Earth Sciences, Fed Inst Geosci & Nat Resources, Hannover, 149-+.

Wheeler, J., Piazolo, S., Prior, D. J., Trimby, P. W. & Tielke, J. A. 2024. Using crystal lattice distortion data for geological investigations: the Weighted Burgers Vector method. Journal of Structural Geology 179, 105040.

How to cite: Wheeler, J., Sandra, P., Prior, D., Trimby, P., and Tielke, J.: Using crystal-lattice distortion data for geological investigations: the weighted Burgers vector method , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10987, https://doi.org/10.5194/egusphere-egu24-10987, 2024.

16:45–16:55

EGU24-6560

ECS

On-site presentation

Strain partitioning during 3D general shear in a heterogeneous low-angle shear zone: some hold strong, while the schists fall flat

Taylor Ducharme, David Schneider, Bernhard Grasemann, Alfredo Camacho, Kyle Larson, and Victoria Scoging

General shear, wherein deformation incorporates elements of both coaxial and non-coaxial strain, is a prevalent strain regime in natural high-strain zones. In extensional tectonic settings, three-dimensional forms of general shear may enhance exhumation via additional crustal thinning (i.e., via pure shear or flattening strain components) or counteract it by inducing crustal thickening (i.e., via a constrictive strain component), without necessarily producing a conspicuous crustal-scale shear zone or fault. Schists and phyllonites demarcating a major tectonic boundary between thrust sheets on Evia in the NW Cyclades record structural evidence for general shear with a NE-directed non-coaxial component and contemporaneous flattening. The package of rock accommodating this strain is lithologically heterogeneous, comprising intercalations of carbonate-, quartz-, and phyllosilicate-dominated schist, as well as dispersed m- to hm-scale olistoliths and blocks of marble and metabasite. Flattening in these rocks is exemplified by foliation-oblique quartz ± calcite veins exhibiting pinch-and-swell or boudinage structure alongside dominant bidirectional dips perpendicular to the regional NE-SW stretching lineation. We combine in-situ ⁴⁰Ar/³⁹Ar and ⁸⁷Rb/⁸⁷Sr dating of white mica with quartz c-axis petrofabric analysis of the deformed quartz veins to elucidate the timing and styles of deformation recorded by these rocks. White mica provides mainly late Oligocene ⁴⁰Ar/³⁹Ar dates in samples with a single dominant foliation, whereas mica defining composite or crenulated foliations records late Eocene-early Oligocene dates, or age populations spanning the Oligocene. Some samples record dispersed Paleocene-Eocene dates older than the earliest proposed timing of metamorphism, although white mica from these rocks provides more geologically plausible early Oligocene ⁸⁷Rb/⁸⁷Sr dates. Vein quartz c-axis fabrics consist primarily of c-axis maxima or small-circle girdles centered about the Z-axis, with subordinate fabrics defining top-to-NE asymmetric type-I cross girdles or Y-axis maxima. Considered together with vein macro- and micro-structure, our data indicate that the deformed schists accommodated top-to-NE general shear at temperatures only slightly above 300°C, resulting in an oblate finite strain ellipsoid. Deformation over this interval produced differential transposition of earlier tectonic fabrics and structures into a sub-horizontal penetrative cleavage in the rheologically weak mica schists, whereas sections dominated by more quartzose- and carbonate-rich lithotypes display comparatively well-preserved older foliations and structures and a spaced secondary cleavage. The prevalence of late Oligocene ⁴⁰Ar/³⁹Ar dates in samples exhibiting a single, shallowly-dipping micaceous foliation implies that flattening general shear coincided with, and likely helped facilitate, exhumation. Our data indicate that unroofing may be partly facilitated by inconspicuous zones accommodating distributed inhomogeneous strain, a potentially important observation for exhumed subduction zones featuring prevalent block-in-matrix mélanges.

How to cite: Ducharme, T., Schneider, D., Grasemann, B., Camacho, A., Larson, K., and Scoging, V.: Strain partitioning during 3D general shear in a heterogeneous low-angle shear zone: some hold strong, while the schists fall flat, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6560, https://doi.org/10.5194/egusphere-egu24-6560, 2024.

16:55–17:05

EGU24-10801

On-site presentation

Salt tectonics and gliding in the Tyrrhenian Sea: a centripetal salt deformation system in a back-arc basin

Fabiano Gamberi and Valentina Ferrante

The Tyrrhenian Sea salt is part of the Messinian Mediterranean salt giant. Its regional distribution was mapped during the early exploration of the Tyrrhenian back-arc basin. More recently, detailed studies have focused on the reconstruction of the salt setting in the Sardinian offshore. A regional overview of salt tectonics character in the Tyrrhenian Sea is thus missing. With this in mind, we present the first basin-scale interpretation of a combined data set of multibeam bathymetry and seismic lines. In the relatively flat, proximal areas of the Cornalia and the Campania Terraces, vertical rise of diapirs is the dominant style of salt movement. Whereas most of the diapirs are buried, some of them emerge at the seafloor and their circular form of salt stocks is apparent. Widespread extensional faulting of the overburden is indicative of reactive diapiric rise and control the location and evolution of local depocentres. However, large parts of the Tyrrhenian Sea consist of areas dipping seaward, towards the centre of the Tyrrhenian Sea. Here, salt gliding is the prevalent style of salt deformation. In the Sardinian margin a belt characterized by salt gliding spans a length of 230 km and is up to 130 km wide, reaching the Vavilov Basin in the centre of the back-arc system. In the Campanian margin a more equant salt gliding area has a length of 106 km and a width of 80 km. Smaller areas with evidence of salt gliding are located at the foot of the base-of-slope escarpment in the northern Sicilian margin to the south of the Vavilov Basin. Salt gliding results in discrete lobes with complex pattern of deformation. Deformation in the overburden often originates polygonal networks of grabens, scalloped scarps, circular or elongate minibasins, growth anticlines and synclines. When the halokinetic structures are present at the seafloor, their relative importance in the different sectors of the main lobes is apparent. Discrete zones of deformation, and a highly 3-D style of salt gliding and overburden deformation are thus recognized. Belts dominated by strike-slip deformation separate the different sectors of the main lobes and are often associated with salt stocks or faults. They are indicative of the linkage between discrete salt gliding systems with different movement direction. A complex deformation style and movement is thus evident in the Tyrrhenian Sea and the deformation of the overburden indicate the recent or active character of salt flow. Our analysis illustrate the processes and elements that characterize salt tectonics in irregular continental slope, with divergent gliding, and where different system interact. At the basin-scale, salt deformation style does not comply with the simple patterns often observed in passive margins, consisting, moving seaward, of three domains: extensional, translational and contractional. In the Tryrrhenian Sea a more complex pattern is evident and can be related to the complex trend of the peripheral zone of the gliding salt masses inherited from the rifting stage. The crustal evolution and magmatic history of the basin also influences the discrete, but kinematically linked, slat gliding domains.

How to cite: Gamberi, F. and Ferrante, V.: Salt tectonics and gliding in the Tyrrhenian Sea: a centripetal salt deformation system in a back-arc basin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10801, https://doi.org/10.5194/egusphere-egu24-10801, 2024.

17:05–17:15

EGU24-3623

ECS

On-site presentation

The role of post-salt carbonates on salt tectonic minibasin formation

Leonardo Muniz Pichel, Ritske Huismans, Rob Gawthorpe, and Jan Inge Faleide

17:15–17:25

EGU24-8722

ECS

On-site presentation

Evolution of a prograding shelf complex affected by salt tectonics, the case of the SW Valencia Trough

Adrià Ramos, Menno J. de Ruig, Antonio Pedrera, Pedro Alfaro, and Iván Martin-Rojas

The Valencia Trough is a NE-SW trending sector of attenuated crust located between the Iberian Peninsula and the Balearic Islands in the western Mediterranean, bordered by the Catalan Coastal Ranges to the northwest, the Iberian Chain to the west, and the Balearic fold and thrust belt to the south. It includes several kilometers of Jurassic-Cretaceous rocks deposited over Upper Triassic salt associated with rifting in the western Tethyan margin. The Mesozoic deposits are deeply eroded as a result of basin inversion and uplift in Oligocene time, followed by extension in latest Oligocene-Early Miocene time. Overlying Middle-Late Miocene foreland basin sediments are associated with the subduction and rollback of the Tethyan oceanic lithosphere. During the Pliocene and Quaternary, a prograding shelf complex was established on the eastern margin of Iberia reaching 3000m in thickness and affected by extensional faulting.

The inspection of the available surface (geological maps and structural data) and subsurface data (2D seismic profiles and exploratory wells) allowed us to document the major role of the Triassic evaporitic sequence on the tectonic style and the configuration of the Pliocene to present-day sedimentary infilling in the Valencia Trough. Our results indicate that large N-S trending extensional faults, which control the depocentres of the Plio-Quaternary prograding shelf complex and offset underlying Mesozoic-Cenozoic sequence, detach into the salt layer. Supra-salt extensional deformation appears to be decoupled from extension in the sub-salt basement.

Sequential backstripping restorations also illustrate the evolution of the deformation and depositional space associated with the flexing down of diapiric structures, which are nucleated over inherited basement faults, parallel to the supra-salt ones. These diapirs were developed in the basin margin during the Mesozoic and Miocene times. The salt expulsion is mainly triggered by the overburden deposition of the prograding clinoforms wedges sourced from the rivers located to the west (e.g., Júcar, Túria and Serpis). Salt diapirs recording a Plio-Quaternary activity can be encountered in the surroundings of the basin, synchronously to the development of the withdrawal salt depocenters.

Moreover, the determination of the two extensional faults systems, salt-detached versus basement-involved, has significant implications on evaluating the structures responsible for the instrumental and historical seismicity in the area.

How to cite: Ramos, A., de Ruig, M. J., Pedrera, A., Alfaro, P., and Martin-Rojas, I.: Evolution of a prograding shelf complex affected by salt tectonics, the case of the SW Valencia Trough, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8722, https://doi.org/10.5194/egusphere-egu24-8722, 2024.

17:25–17:35

EGU24-4104

On-site presentation

Using salt diapirs and minibasins to constrain interpretations of crustal rifting and inversion in the Basque Pyrenees, Spain

Mark G Rowan, Josep Anton Muñoz, Eduard Roca, Oriol Ferrer, Eloi Carola, and Iñaki Garcia

Published interpretations across the Basque Pyrenees vary significantly in their depictions of rifting and subsequent inversion. Major points of disagreement relate to: (i) the asymmetry of the margin, i.e., whether the major extensional and contractional detachment dipped toward the north or south; and (ii) the degree of decoupling between supra- and subsalt deformation and thus the amount of thin-skinned translation of the cover relative to basement. Here we use outcrop and subsurface data to analyze the salt structures along a regional transect in order to resolve this ongoing debate.

Several aspects of the salt-related geometries are diagnostic of thin-skinned deformation. First, Villasana de Mena diapir has significantly thicker synrift strata on its basinward (northern) flank, contains stringers of Paleozoic rocks, and was growing passively during crustal extension. Its origin was consequently related to an underlying basement fault, yet it is situated today above an unfaulted detachment, suggesting that the diapir was translated above the salt during rifting and/or shortening. Second, Salinas de Rosio diapir is located at the southern termination of landward-shifting synrift depocenters and developed as a postrift to synorogenic salt pillow and then diapir. Thus, thin-skinned translation over a fault-related ramp in the base salt created synrift ramp-syncline basins, with the basement fault subsequently localizing salt inflation due to differential loading and then contractional buttressing. Third, Poza de la Sal diapir is at the basinward end of another set of synrift ramp-syncline basins and along a thin-skinned fold and thrust structure that was active during the synrift. Fourth, the large-scale geometry from the Bilbao Anticlinorium to the south documents contractional translation above a continuous salt detachment with a ramp-flat geometry.

In summary, the salt and suprasalt geometries in a large part of the Basque Pyrenees demonstrate two phases of thin-skinned translation above a north-dipping salt detachment: (i) decoupled, basinward (northward) translation during rifting; and (ii) thin-skinned, southward-directed thrusting during inversion. The geometries are incompatible with thick-skinned inversion on a major south-dipping crustal detachment and smaller, basement-rooted faults that cut through the salt and its overburden.

How to cite: Rowan, M. G., Muñoz, J. A., Roca, E., Ferrer, O., Carola, E., and Garcia, I.: Using salt diapirs and minibasins to constrain interpretations of crustal rifting and inversion in the Basque Pyrenees, Spain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4104, https://doi.org/10.5194/egusphere-egu24-4104, 2024.

17:35–17:45

EGU24-603

ECS

Virtual presentation

New insight into salt-related structure in the Onshore Zagros foreland basin, a prospect into the deep gas reservoirs

(withdrawn)

Aref Shamszadeh, Masoud Lotfpour, Oriol Ferrer, Artabaz Adhamian, and Ali Asaadi

17:45–17:55

EGU24-17484

solicited

On-site presentation

Folds in evaporites. What can we learn about the rock-salt rheology?

Marta Adamuszek, Jessica Barabasch, Janos L. Urai, and Marcin Dabrowski

Due to the presence of low-viscosity rock-salt, evaporite sequences show a remarkable susceptibility to deformation across diverse geological settings. These sequences often exhibit intercalations of rock-salt with siliciclastic rocks, anhydrite, and sometimes various bittern salts like carnallite and bischofite. Their distinct layering serves as invaluable markers, facilitating a comprehensive analysis of internal salt deformation. The extensive deformation of the evaporites often gives rise to complex internal architectures within the salt body, characterized by commonly observed fold structures. The geometries of these structures are highly sensitive to the mechanical properties of the layers, thus offering profound insights into rock-salt rheology. Unravelling the rheological behaviour of rock-salt holds significant implications, particularly in salt mining, salt cavern operation, and advancing our understanding of salt tectonics.

In this project, we focus on specific outcrops within salt mines located in Romania, Austria, and Poland, where prominently exposed fold structures offer unique field laboratories. These sites hold significant potential for deciphering the mechanical behaviour of rocks during their long-term deformation. In our study, we combined field observations, detailed mapping and microstructural analysis of various single and multilayer folds complemented by numerical models of fold evolution. In our numerical simulations, we use the Carreau model for rock-salt, which captures two primary deformation mechanisms: pressure solution and dislocation creep. The mechanisms correspondingly result in the linear (Newtonian) and non-linear (power-law) rheological regimes, influenced by rock grain size and differential stress. Varying the rock-salt grain size enabled us to analyse fold evolution in both regimes as well as in the transitional domain. By systematically comparing our numerical analysis with field observations, we refine our understanding of the mechanical properties of evaporites, contributing to advancements in the study of rock deformation.

How to cite: Adamuszek, M., Barabasch, J., Urai, J. L., and Dabrowski, M.: Folds in evaporites. What can we learn about the rock-salt rheology?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17484, https://doi.org/10.5194/egusphere-egu24-17484, 2024.

17:55–18:00

Discussion

Posters on site: Wed, 17 Apr, 10:45–12:30 | Hall X2

Display time: Wed, 17 Apr 08:30–Wed, 17 Apr 12:30

Chairpersons: Susanne Buiter, Pablo Granado, Christoph von Hagke

X2.1

EGU24-13072

ECS

Poseidon’s seismic breadcrumbs: ultracataclasite vein evolution within a granodiorite along the Naxos Detachment System

Olivia Rolfe, Renelle Dubosq, David Schneider, and Bernhard Grasemann

Ultracataclasites and pseudotachylytes often reflect localized deformation due to coseismic slip and the temporal evolution of seismogenic fault zones. Interaction of these structures and their mechanisms of nucleation and propagation into crustal rocks remain poorly constrained. Herein we conducted a microstructural analysis on a series of ultracataclasitic veins within a deformed granodiorite on Naxos, Greece. The island is a classical Miocene Cycladic metamorphic core complex, with migmatites and the granodiorite at its core. The Naxos detachment dissects the granodiorite, producing a strong N-S stretching lineation and SCC’ fabric indicating top-to-N kinematics. The granitoid cooled rapidly from crystallization (650-680°C) at c. 12 Ma to <60°C by c. 9 Ma. The investigated ultracataclastic veins are slightly anastomosing and oblique to the main foliation fabric in the granodiorite. Petrographic analysis of the granodiorite shows a coarse-grained (50 μm–2 mm) host rock matrix primarily composed of quartz, albite, orthoclase, hornblende and biotite, intersected by the fine-grained (5–60 μm) ultracataclasitic veins of the same composition. Quartz grains within the host rock occur as inequigranular, interlobate to amoeboid shaped grains exhibiting a shape preferred orientation that defines the foliation and appears to flow around larger feldspar porphyroclasts. Bulging and subgrains within the quartz grains are indicative of dynamic recrystallization. Albite occurs as subhedral porphyroclasts displaying undulose extinction, subgrains with fuzzy boundaries, tapered deformation twins, and bookshelf microfracturing. Orthoclase porphyroclasts within the host rock are subhedral to sigma-shaped, exhibiting undulose extinction with small subgrains (<50 μm) near the clast rims and vein margins. All feldspar porphyroclasts in the host rock are heavily fractured with increasing density proximal to the veins. Electron backscatter diffraction (EBSD) mapping of quartz, albite and orthoclase directly crosscut by the ultracataclastic veins reveals variations in relative phase deformation. Larger host rock quartz grains (50–300 μm) reveal internal lattice distortions (max. misorientations of ~20° relative to the grain average orientation) and low angle grain boundary (LAGB) development, with LAGB density and misorientation degree increasing towards grain edges. Smaller quartz grains (5–25 μm) display a moderate crystallographic preferred orientation and minimal misorientation (max. 8°). EBSD mapping of albite and orthoclase porphyroclasts (100 μm–1 mm) evinces crystal-plasticity in the form of a linear to heterogeneous misorientation pattern, with a maximum misorientations of ~38° and ~27°, respectively. Smaller grains of albite and orthoclase (<50 μm) with scattered orientations occur at clast rims and vein tips, and display a maximum misorientations of ~10° and ~15°, respectively. The localized subgrain structures observed in the feldspar are suggestive of dynamic recrystallization. The veins crosscut these recrystallized zones, suggesting propagation occurred after recrystallization of the feldspar. LAGB development is also observed in the feldspar clasts with increasing density towards the clast rims. The co-occurrence of fractures from dislocation and crystal-plastic microstructures in the feldspar porphyroclasts is indicative of fracture propagation in the brittle-ductile regime of feldspar (450–600°C). It remains equivocal whether the ultracataclastic material was injected into pre-existing fractures or the injection of the material induced fracturing within the host rock.

How to cite: Rolfe, O., Dubosq, R., Schneider, D., and Grasemann, B.: Poseidon’s seismic breadcrumbs: ultracataclasite vein evolution within a granodiorite along the Naxos Detachment System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13072, https://doi.org/10.5194/egusphere-egu24-13072, 2024.

Discussion Post a comment

X2.2

EGU24-4777

ECS

Structural architecture of brittle-ductile mineralized veins in a Cenozoic orogenic gold deposit along the North Cycladic Detachment System, Greece

Laurence Hamel, Taylor Ducharme, David Schneider, and Bernhard Grasemann

The Kallianos Au-Ag-Te deposit, located on southern Evia island in the NW Aegean Sea, is a Cenozoic orogenic gold deposit hosted in carbonate-epidote-phlogopite schists and phlogopite marbles of the Cycladic Blueschist Unit (CBU). Fluids that generated the deposit were channelized by a crustal scale post-orogenic extensional structure, the North Cycladic Detachment System (NCDS), which facilitated Miocene exhumation of the CBU into the brittle crust. Whereas ore deposits in the Cyclades have been broadly related to late Miocene granitic intrusions, magmatism of this age is notably undocumented on Evia. Field observations illustrate the connection between the structural architecture that host mineralization and deformation associated with the post-orogenic structures, refining the paragenetic model for Cenozoic gold deposits in the Cyclades. Mineralized veins, alongside unmineralized tension gashes, faults, conjugate faults, and joints, occur in parallel sets that locally define en-echelon arrays. Younger sub-vertical tension gashes cross-cut older boudinage mineralized veins. The vein orientations of the Kallianos deposit strike NW-SE and NNW-SSE, which is generally orthogonal to the sub-horizontal ~NE stretching lineations related to crustal extension and thinning accommodated by the NCDS. Brittle-ductile kinematic indicators such as shear bands exhibit top-NE displacement, consistent with footwall deformation related to the NCDS documented elsewhere along strike of the detachment. The two populations of vein orientations are not evident based on structural data alone, but field observations show clear cross-cutting of the earlier NW-striking vein set by later NNW-striking veins. The mineralization is hosted in subvertical mm- to m-scale veins composed of quartz, calcite, albite, with minor titanite and epidote and notable sulfide mineralization including pyrite, galena, chalcopyrite, bornite and hematite concentrated in cm-scale veins. Obvious native Au and Ag are not observed in the veins. The NNW-striking vein sets contain significantly more albite and mineralization than the NW-striking veins and generally exhibit greater evidence of strain, with an abundance of sutured and bulging grain boundaries preserved in the quartz. Vein arrays developed within the cataclastic deformation zone below the exposed NCDS detachment plane are parallel to those observed deeper in its footwall. Our structural data strongly imply a connection between mineralized veins of the Kallianos Au-Ag-Te deposit and the regional strain field imposed by displacement along the NCDS. Despite structural evidence linking the architecture of this Cenozoic gold deposit to the crustal scale NCDS, an origin for the mineralizing fluids remains equivocal due to the local absence of magmatism, and the distribution of brittle-ductile strain to significant depths in the footwall may implicate devolatilization reactions coinciding with exhumation through the brittle-ductile transition as an important fluid source.

How to cite: Hamel, L., Ducharme, T., Schneider, D., and Grasemann, B.: Structural architecture of brittle-ductile mineralized veins in a Cenozoic orogenic gold deposit along the North Cycladic Detachment System, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4777, https://doi.org/10.5194/egusphere-egu24-4777, 2024.

Discussion Post a comment

X2.3

EGU24-709

ECS

Resisting the unknown: Enhancing resistivity imaging of the crust through a multidisciplinary approach from µ- to km-scale at the DIVE DT-1B drill site

Sören Tholen, Virginia Toy, Friedrich Hawemann, and Hadis Mansouri

Geophysical methods based on the conductivity of electrical currents through the subsurface (IP, ERT, magnetotellurics) are commonly used to identify mineral deposits or aquifers, for which large conductivity contrasts exist between host rock and target. These methods may also provide insights about tectonic processes, such as when rock masses contain partial melt, or are affected by active deformation. However, further advances in electrical imaging of rocks at depth are hindered by the lack of understanding of the relative contributions of paragenesis, fabric, and active processes to electrical conductivity. The ICDP project DIVE (Drilling the Ivrea-Verbano ZonE) provides a unique opportunity to evaluate these parameters by combining samples and measurements from up to ~580 m depth with a wide range of geophysical surface surveys.

The DT‑1B drill core comprises lower crustal rocks consisting mostly of metapelite and amphibolite with embedded pegmatitic lenses. We took 25 samples from these main lithologies that cover the major variations in fabric (e.g., foliation strength, continuity and style, grain size), as well as intervals rich in micro fractures, hydrous alteration, or highly conductive phases (graphite, sulfide). We focus on two main research questions: (1) How do aspects of rock fabrics such as style and strength of foliation or mineral content and the connectivity of conductive phases affect the electrical properties, and (2) can these micro-scale, fabric-induced electrical properties be extrapolated to larger scales?

Fabric analysis and quantification of mineralogy are carried out at thin-section scale by optical and electron microscopy (EDX, EBSD). Computed tomography (CT) performed on small cylinders drilled from the same samples allows the microstructural data to be extended into the third dimension. The CT ably reveals the elongation and alignment of sulfides, the style, and continuity of the foliation which is defined by biotite, and in places graphite- or sulfide-decorated fracture systems. Measurement of electrical properties of the same cylinders under various fluid saturation conditions and a wide frequency range completes the comprehensive database, enabling us to detect and model electrical pathways in the lower crust.

To scale from the micro to the macro scale, these results will be compared to the data from electrical surveys carried out around the DT-1B drill hole. Results will expand the applicability of resistivity imaging for a wide range of future, structural applications.

How to cite: Tholen, S., Toy, V., Hawemann, F., and Mansouri, H.: Resisting the unknown: Enhancing resistivity imaging of the crust through a multidisciplinary approach from µ- to km-scale at the DIVE DT-1B drill site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-709, https://doi.org/10.5194/egusphere-egu24-709, 2024.

X2.4

EGU24-18140

ECS

Evolution of fracture intensity and topology in granitic rocks: insight from Mt. Capanne Pluton, Elba Island, Italy

Filippo Porta, Luigi Riccardo Berio, Cristian Cavozzi, Niccolò Menegoni, and Fabrizio Balsamo

Field analogue studies of fractured crystalline rocks are important for the clean energy transition and or better understanding the subsurface geothermal systems. In this contribution we present a workflow for multiscale quantitative analysis of fracture network and their connectivity in the monzogranitic pluton of Monte Capanne (Elba Island, Italy). Field structural analysis was integrated with Digital Outcrop Model (DOM) of a 1.5km-long outcrop and with microfracture analysis performed in thin section. The DOM was obtained from images acquired with UAV flights. Field analysis indicate the presence of three main fracture sets with different attributes and showing systematic crusscutting relationships. The quantitative analysis of the DOM was performed with QGIS software and allowed us to characterize the fracture length distributions, density (P20), intensity (P21), and topology (and their parameters). Data derived from field survey and DOM and analysis has been used to create a three-dimensional Discrete Fracture Network (DFN) using a DICE^® (https:// github.com/nicmenegoni/DICE) algorithm in MatLab^® to calculate the 3-dimensional fracture intensity (P32). In addition, we extended the two-dimensional topology concept in the third dimension. Thus, assuming circular fractures, new topology parameters have been calculated such as number of fracture intersection in volume and intersection fracture length in a volume, i.e., I30 and I31 respectively. Finally, based on the relative fracture chronology, we simulated the step-by-step evolution of 2- and 3-three-dimensional fracture density, fracture intensity and topology, describing the relationship between different fracture sets over time. The preliminary results show how fractures connectivity evolve over time. The ultimate goal of this work is to constrain the evolution of fracture porosity to enhance our ability for modelling fluid flow in crystalline rocks.

How to cite: Porta, F., Berio, L. R., Cavozzi, C., Menegoni, N., and Balsamo, F.: Evolution of fracture intensity and topology in granitic rocks: insight from Mt. Capanne Pluton, Elba Island, Italy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18140, https://doi.org/10.5194/egusphere-egu24-18140, 2024.

X2.5

EGU24-593

Fracture attribute and their scaling in the Cenozoic formations, Sylhet Trough, Bengal Basin: Obtaining insight from the Dauki Fault Zone

(withdrawn)

Md. Sakawat Hossain, Md. Sharif Hossain Khan, and Tridib Kumar Mondal

X2.6

EGU24-1059

ECS

Competing development of S and C foliations in mylonites

Pramit Chatterjee, Arnab Roy, and Nibir Mandal

Mylonites are characteristic rocks in ductile shear zones, and they contain two primary fabrics: i) C-fabrics, which are usually aligned parallel to the principal shear planes in the shear zones, ii) S-Foliations, which are oriented at angles to the shear plane, showing their vergence in the shear direction. Despite extensive studies of mylonite structures over several decades, the factors controlling the formation of S and C fabrics and their relative abundance in ductile shear zones are yet to be fully explored. This article investigates the competing development of S and C fabrics in ductile shear zones from two geological terrains of Eastern India. The shear zones offer macroscopic observations of various mylonitic rocks: i) C mylonites ii) S mylonites, and and iii) S-C mylonites. Numerical simulations were performed to replicate them in model shear zones, considering a combination of transient visco-plastic rheology. The model study suggests that the growth of C- versus S- fabrics in mylonites depend on two fundamental non-dimensional parameters: imposed strain rate and bulk viscosity. It is observed that low bulk viscosity and strain rate conditions promoted the formation of S fabrics. With increase in bulk viscosity and strain rate, formation of C bands in the shear zones is facilitated leading to the localisation of strain in the form of narrow zones.

How to cite: Chatterjee, P., Roy, A., and Mandal, N.: Competing development of S and C foliations in mylonites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1059, https://doi.org/10.5194/egusphere-egu24-1059, 2024.

X2.7

EGU24-5090

Seismic interpretation of the Messinian salt of the Levant basin offshore Lebanon: new insight into the geology and tectonics of the eastern Mediterranean region

(withdrawn)

Tony Nemer, Karam Sarieddine, and Reenal Faysal

X2.8

EGU24-685

ECS

The internal deformation of the Praid salt diapir and implications for potential storage applications

Daria Dohan, Dan Mircea Tamas, Alexandra Tamas, and Ioana Silvia Mihaela Tocariu

The Praid salt diapir is located in the Transylvanian Basin, Romania and it stands out as one of the earliest discordant salt structures to be described. The salt that forms this structure was deposited during the middle Miocene salinity crisis. Under geological conditions, rock salt exhibits plasticity, resembling a fluid, leading to highly intricate folding patterns in its deformation. Understanding the evolution of salt structures holds significant importance for a number of industries such as the hydrocarbon industry or hydrogen storage. To utilize such formations for storage purposes, a comprehensive understanding of the deformation processes, impurity distribution, and mineral composition becomes crucial. These factors wield considerable influence on the overall rock properties.

Certain diapiric salt formations within these areas hold potential as sites for hydrogen storage due to their substantial dimensions, reaching around ~3500m in size, and existing caverns within some of these formations. This investigation centers on analyzing the deformation of the Praid salt diapir. The site features a public-accessible salt mine and numerous surface salt exposures. Our study involves detailed mapping of both surface and subsurface areas, focusing on internal salt deformation, the nature and distribution of impurities, and exploring salt-sediment interaction where exposed.

In our research, we utilized surface and underground mapping within the accessible salt mine, coupled with photogrammetry and LiDAR technology, to construct detailed 3D models capturing complex large-scale deformation patterns. The majority of the salt layers exhibit steep to near-vertical inclinations, with diverse orientations that suggest curtain-fold-like structures. Certain areas notably display signs of refolding. Within the salt, various impurities of differing origins exist, predominantly large-scale blocks composed of siltstone to sandstone slabs that have undergone boudinage. This study is part of an ongoing initiative aimed at evaluating both the potential and associated risks of implementing hydrogen storage projects within these salt formations or similar structures.

Acknowledgements: The work of DD was financed through the Scientific Performance Scholarship, offered by Babes-Bolyai University, Cluj-Napoca.

How to cite: Dohan, D., Tamas, D. M., Tamas, A., and Tocariu, I. S. M.: The internal deformation of the Praid salt diapir and implications for potential storage applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-685, https://doi.org/10.5194/egusphere-egu24-685, 2024.

X2.9

EGU24-5204

ECS

Timing and rates of salt movement in the Romanian Eastern Carpathians: insights from Radiocarbon and OSL dating

Dan Mircea Tamas, Alexandra Tamas, Gabriela Odilia Sava, Anca Avram, and Alida Timar-Gabor

Salt, an age-old resource, holds significance in human history and emerges as a potential solution in transitioning from fossil fuels to sustainable energy, due to its unique properties. Its geological fluidity results in formations like salt diapirs, influencing deformation in the past and present. Understanding the details and timing of such deformation is crucial for certain energy transition projects like hydrogen storage in salt caverns.

Salt tectonics in the Romanian Eastern Carpathians has long been studied. Initially, it was studied for its significance as a natural resource, but its implications for the hydrocarbon industry were later explored. Techniques such as seismic interpretation, well-log analysis, analogue and numerical modelling, and field observations are used to examine salt movement and interaction with sediment. In order to understand the Quaternary uplift rates of salt diapirs and the timing of salt movement in the Eastern Carpathians, we use radiocarbon and optically stimulated luminescence (OSL) dating.

This innovative combination of radiocarbon and OSL dating marks a breakthrough in understanding salt diapir uplift rates in the area of interest, shedding light on the historical dynamics of geological formations and erosion processes.

How to cite: Tamas, D. M., Tamas, A., Sava, G. O., Avram, A., and Timar-Gabor, A.: Timing and rates of salt movement in the Romanian Eastern Carpathians: insights from Radiocarbon and OSL dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5204, https://doi.org/10.5194/egusphere-egu24-5204, 2024.

X2.10

EGU24-15737

Quantification of the surface deformation on salt diapirs using high-resolution Persistent Scatterer Interferometry (PSI) and Multi-Spectral satellite imagery, Zagros mountains, southern Iran

Stefanie Rieger, Prokop Závada, Jiří Bruthans, Mugabo Wilson Dusingizimana, Christina Plattner, Beth Kahle, and Anke Friedrich

Salt diapirs are ubiquitous in the Zagros Mountains, but salt-flow dynamics in their extrusive parts and interaction with their caprocks are complex and poorly understood. For a better understanding of the interaction between salt dynamics and the caprock on the surface of the salt extrusions, knowledge of high-resolution spatiotemporal surface deformation and multispectral satellite imagery analysis is essential. However, the contemporary vertical surface deformation pattern across salt diapirs is difficult to detect and interpret along disciplinary boundaries. With the aid of high-resolution PSI measurements and multispectral imagery analysis we detected high-precision spatiotemporal deformation patterns of the surfaces of salt diapirs and their caprocks. Furthermore, time-series analysis helped to distinguish between salt-supply-driven domal uplift and vertical surface modification induced by precipitation, dissolution, and erosion.

In this study, we analysed Sentinel-1 PSI time-series, processed by the German Aerospace Center (DLR), to obtain the highest available spatiotemporal resolution of the vertical surface-deformation pattern across three diapirs – Karmostaj, Siah Taq, and Champeh – in the Zagros.

Furthermore, the Persistent Scatterers are correlated to their lithological composition based on multispectral analysis of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite images. Preliminary results indicate that the deformation pattern of the salt diapirs does not correlate with seasonal effects, such as precipitation and heat. The vertical surface deformation pattern on these three diapirs implies that these diapirs are active and that caprock influences the salt flow pattern.

Unnderstanding the activity of salt diapirs in general is also important, for example, in the feasibility studies of salt diapirs as strategic storage facilities for hydrocarbons, waste material, and CO₂ storage over longer time-scales worldwide.

How to cite: Rieger, S., Závada, P., Bruthans, J., Dusingizimana, M. W., Plattner, C., Kahle, B., and Friedrich, A.: Quantification of the surface deformation on salt diapirs using high-resolution Persistent Scatterer Interferometry (PSI) and Multi-Spectral satellite imagery, Zagros mountains, southern Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15737, https://doi.org/10.5194/egusphere-egu24-15737, 2024.

X2.11

EGU24-6744

Deformation structures in the evaporitic melange. Case study from the Altaussee salt mine

Marta Adamuszek, Marcin Olkowicz, Marcin Dabrowski, Mariusz Fiałkiewicz, Bartłomiej Grochmal, Thomas Leitner, and Oscar Fernandez

We investigated the salt deposits found within the Altaussee salt mine, which represent the Permian to Triassic evaporitic Haselgebirge Formation situated in the Northern Calcerous Alps (Austria). The extensive deformation of the evaporite sequence spanning from the Middle Triassic to Neogene periods led to the formation of a tectonic mélange. The sediments commonly comprise fragments of anhydrite, polyhalite, sandstone and limestone embedded in the halite-rich matrix. The dimensions of these blocks can exceed 10 meters in diameter, while the bulk volume of halite content in these layers is ranging from approximately 30 to 65 volume percent.

Our investigation focuses on the internal structure within the evaporite sequence. In particular, we examine various outcrops in caverns, galleries, and corridors that illustrate the role of block shape and size on the deformation pattern. Particularly noteworthy are findings from a large, well-exposed salt cavern ceiling covering approximately 4000 square meters. Utilizing tailored photogrammetric approach, image post processing techniques and using lidar data as reference, we generated detailed ortophoto map of 1000 square meters of cavern ceiling with resolution of 1 mm/pixel. This reveals intricate patterns around rigid blocks and their interactions at different scales. Fine layering within the rock salt allowed to illustrate spectacular structures that developed around the rigid blocks and also interaction between the blocks. Significantly, observations of layer deflection beneath blocks hint at potential block-sinking dynamics, offering valuable insights into the complex geological processes at play.

How to cite: Adamuszek, M., Olkowicz, M., Dabrowski, M., Fiałkiewicz, M., Grochmal, B., Leitner, T., and Fernandez, O.: Deformation structures in the evaporitic melange. Case study from the Altaussee salt mine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6744, https://doi.org/10.5194/egusphere-egu24-6744, 2024.

X2.12

EGU24-16570

ECS

Fabric and microstructural analyses of fine-grained glacier salt (Kuh-e-Namak, Dashti, southern Iran)

Julia Schmitz, Prokop Závada, and Janos L. Urai

The Kuh-e-Namak diapir consists of a dome and two glaciers and displays flow structures along its profile. Microstructures in salt dome and glaciers are studied for deformation and recrystallization mechanisms in terms of the grain size reduction, grain fabric and its influence on the flow dynamics of the salt system. Using reflected and transmitted light microscopy of gamma-irradiated rock salt thin sections, electron backscatter diffraction and quantitative analysis of digitized microstructures, we show the transition of dislocation creep followed by fluid-assisted recrystallization from the extrusive dome into the glacier where solution-precipitation creep dominates. Along the profile of the glacier, the degree of recrystallization increases, while the porphyroclasts content progressively decreases in favor of the fine-grained matrix. Fabric analysis support the decreasing amount of porphyroclasts and rectangular halite grains. Porphyroclasts in domal salt show the highest misorientation values at the grain boundaries and are consumed by almost misorientation-free, rectangular grains. Further, a development of shape preferred orientation (SPO) in glacier salt is inferred from alignment of the long axes of elongated halite grains visible in the fabric and their rose diagrams. The microstructures are interpreted in terms of combined dislocation creep and solution-precipitation creep. Grain analyses give a mean grain size ranging between 180 and 508 µm and show a moderate aspect ratio around 2, whereas fabric analyses indicate increasing values from dome to glacier salt of up to 4. Subgrain piezometry infers differential stresses of 1.9 to 6.1 MPa, reflecting the high stress in the cold diapir stem, whereas the shear stresses estimated for the glacier are much lower. Estimation for strain rates based on the combination of dislocation creep and solution-precipitation creep are in the orders of magnitude of x10^-10 to x 10^-09. Well-developed SPO is interpreted to support the hypothesis that solution-precipitation creep is the dominant recrystallization mechanism in glacier salt. Since solution-precipitation creep dominates in salt glaciers at low deviatoric stress, the fine-grained salt deforms much faster than predicted by dislocation creep, allowing salt glaciers to flow.

How to cite: Schmitz, J., Závada, P., and Urai, J. L.: Fabric and microstructural analyses of fine-grained glacier salt (Kuh-e-Namak, Dashti, southern Iran), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16570, https://doi.org/10.5194/egusphere-egu24-16570, 2024.

X2.13

EGU24-20283

The role of salt tectonics in the occurrence of the 2021 Central Adriatic seismic sequence

Laura Scognamiglio, Francesca Di Luccio, Mimmo Palano, Alessandro Marchetti, Iva Dasović, Marija Mustać, Federica Magnoni, Pietro Artale Harris, Emanuele Casarotti, Alina Polonia, Luca Gasperini, Anke Dannowski, and Heidrun Kopp

On 27 March 2021 a three-months lasting seismic sequence struck the Central Adriatic Basin, part of Adria that is considered a relatively undeformed plate since recent times. Analyzing the waveform data acquired by the Italian and Croatian seismic networks, we computed the location parameters of 160 earthquakes and the focal mechanisms of the Mw5.2 mainshock and larger aftershocks. Most events align along a WNW-ESE, 30 km long, narrow belt. They form two clusters between 0-3 km and 4-14 km of depth, separated by a 1-2 km thick aseismic zone. Based on literature data, we suggest that such a seismic gap corresponds to a ductile salt layer, which constitutes the primary control factor for the evolution of the 2021 earthquake distribution. Moreover, the presence of a salt layer explains well the relatively high Vp/Vs ratio of 1.83 in the sediment rocks surrounding the salt bodies, as also observed in similar tectonic settings. We suggest that the seismogenic fault likely responsible for the 2021 events is an inherited SW-dipping normal fault, reactivated with prevalent reverse kinematics in response to the regional compressive stress. These results, and the recognition of a specific role of salt deposits in focusing deformation and seismogenesis represent a novel contribution to the long-standing problem of seismic hazard assessment of the Central Adriatic Basin, where moderate to large events could have devastating impacts along the highly populated coasts.

How to cite: Scognamiglio, L., Di Luccio, F., Palano, M., Marchetti, A., Dasović, I., Mustać, M., Magnoni, F., Artale Harris, P., Casarotti, E., Polonia, A., Gasperini, L., Dannowski, A., and Kopp, H.: The role of salt tectonics in the occurrence of the 2021 Central Adriatic seismic sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20283, https://doi.org/10.5194/egusphere-egu24-20283, 2024.

X2.14

EGU24-18516

ECS

Megaflaps flanking salt walls: strain and stress distribution from field observations to numerical modeling.

Marine Lartigau, Jean-Paul Callot, and Claude Gout

The megaflaps are halokinetic objects of multi-kilometer extension corresponding to vertical or overturned strata flanking salt walls or resulting welds. Although their geometry and mechanical behavior can be considered similar to detachment folds, their development mechanism and the consequences regarding strain record remain to be specified.

Megaflaps record strain before, during, and/or after tilting, and their development involves mechanisms specific to each megaflap (i.e. force folding with limb rotation or kink-band migration, passive folding), to their geological characteristics and the local and regional context. We highlight that the initial carapace, covering the evaporites and forming the future megaflap, constitutes a continuous mechanical unit allowing the transmission of an early homogeneous stress (either local or regional). Folding is then initiated by limb rotation, hinge migration or passive folding. During diapirism, the piercement of the salt structure generally accommodates the stress, that preserves the adjacent sediments from regional deformation. However, due to the evaporites loading, we observe a very localized compressive strain, which is perpendicular to the evaporite wall and results in the development of salt-related meso- and microstructures.

We compared the stress states determined on field analogs are with 2D uncoupled geomechanical models. The stress-strain distribution of two types of megaflaps were studied: a single development step megaflap, presenting a main mechanical unit (e.g. Karayün megaflap, Turkey), and a sequential development megaflap, presenting several mechanical units (e.g. Cotiella megaflap, Spain). Our models are based on well-defined geometries of known field analogs. In each model, the layers constituting the future megaflap record compressive strains, varying in extent and localized near the salt wall. Horizontal compression parallel to the layers, induced by salt push, is consistently observed and matches with field observations. Our models also depict layer folding, which can be accommodated through various mechanisms (extrados and intrados deformation, compressive mechanical guidance). Finally, it seems that the late stage tightening deformation would occur through an intensification of stress magnitude induced by complete welding. Our models show that welding significantly increases the maximum stress magnitude. The ratio between compressive stresses and background stresses is thus four to five after welding, compared to a ratio of two without welding. This matches our observations regarding the formation of new mesostructures during the late stage tightening within the Cotiella megaflap, induced synchronously in all layers (regardless their attitudes, already vertical and overturned, or gently dipping). In contrast, the preservation of salt bodies is correlated with the absence of late micro- and mesostructures perpendicular to the vertical layers as observed in other known field analogs (e.g., Sivas Basin, Paradox Basin, Witchelina diapir). Consequently, some megaflaps may remain unaffected by late-stage tightening even within a regional compressive system undergoing shortening.

How to cite: Lartigau, M., Callot, J.-P., and Gout, C.: Megaflaps flanking salt walls: strain and stress distribution from field observations to numerical modeling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18516, https://doi.org/10.5194/egusphere-egu24-18516, 2024.

X2.15

EGU24-8630

Halokinetic growth wedges in platform carbonates: thoughts on subsidence and carbonate production rates

Oscar Fernandez, Diethard Sanders, Hugo Ortner, Bernhard Grasemann, and Thomas Leitner

The Northern Calcareous Alps (NCA) in the Eastern Alps (Austria) developed during the Triassic as a Tethys-facing salt-rich passive margin. Extensionally-driven salt tectonics, mobilizing evaporites of Late Permian to Early Triassic age on the Tethyan passive margin, started as early as the early Middle Triassic and lasted through to the end of the Triassic. Here we document multiple examples of salt-related growth geometries in the central NCA, with specific emphasis on their dimensions and the implications these have on the balance between subsidence and carbonate production rates. The interaction between these two factors controlled the distribution of facies within the sedimentary growth wedges and the development of the transitions from shallow-water platforms into basinal domains >200 m in depth. The interplay between subsidence, carbonate production, and external factors (ocean currents) appear to have been critical for the persistence of long-lived intra-platform embayments, whose origin and development have long puzzled geologists.
The geometries and sedimentary architectures observed in the central NCA are directly comparable to those documented in other salt-rich basins such as the southern Atlantic passive margin or the (now inverted) Pyrenean rift. Excellent exposure and continuity over a large area render the Triassic of the central NCA an outstanding location for understanding the development of carbonate platforms above salt substrates.

How to cite: Fernandez, O., Sanders, D., Ortner, H., Grasemann, B., and Leitner, T.: Halokinetic growth wedges in platform carbonates: thoughts on subsidence and carbonate production rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8630, https://doi.org/10.5194/egusphere-egu24-8630, 2024.

X2.16

EGU24-21557

Utilising borehole data to characterise geological factors controlling salt cavern shapes: A multi-well case study from NW Switzerland with implications for solution mining and subsurface storage

(withdrawn)

Lukasz Gregorczyk and Johannes Pietsch

Posters virtual: Wed, 17 Apr, 14:00–15:45 | vHall X2

Display time: Wed, 17 Apr 08:30–Wed, 17 Apr 18:00

Chairpersons: Dan Mircea Tamas, Prokop Závada, Pablo Granado

vX2.3

EGU24-2464

Control of salt tectonics on the hydrocarbon traps development: the surrounding structures of the Qom Kuh, Central Iran

Sadaf Nikpoush and Bahman Soleimany

Salt tectonics and salt structures are attractive targets for hydrocarbon exploration since salt-related deformation can form hydrocarbon traps and influence hydrocarbon migration. Salt diapirs are considered a suitable site for reserving natural oil/gas, landfills, and hazardous wastes. Determination of the origin and age of salt diapirs, the diapir formation and evolution model, and their impacts on the surrounding structures are very necessary for hydrocarbon exploration. To characterize the structural and tectono-sedimentary evolution of the salt diapir at the Qom Kuh, located in the Qom basin (Central Iran), this research describes the origin, timing, and evolution history of the salt structure through the tectono-sedimentary analysis and field study. Moreover, the effect of salt diapirism on the surrounding structures is investigated in the study area. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth salt structure indicate that the salt extrusion occurred during two stages in the Qom Kuh. According to the structural evidence (e.g., hook and cusp) and the tectonic-sedimentary analysis, the first stage of salt extrusion happened in the Early Miocene concurrently with the extensional deformation event from the Eocene to the Early Miocene in the study area. The second stage of salt diapirism and its extrusion occurred during multi-stages of the Zagros orogenic compression from the Late Miocene to the present day. The final geometry of the salt diapir at the Qom Kuh formed along a releasing bend that was created by dextral transpressional strike-slip fault activity during the Zagros orogeny. Based on the lower thickness of evaporite units in the Upper Red Formation (Early Miocene) compared to the Lower Red Formation (Early Oligocene) and observing fragments of the Eocene volcanic rocks in the extruded salt on the ground surface, the Lower Red Formation salt along with the Upper Red Formation evaporites considered as the main source of salt diapirism in the Qom Kuh. Salt diapirism affected the surrounding structures of the Qom Kuh such as the Western Kuh-e-Namak and Western Alborz anticlines. The fold geometry and the hydrocarbon trap development in the Western Kuh-e-Namak and Western Alborz fields are controlled by salt tectonics and the occurrence of inversion tectonics. The results of this study could add data to worldwide examples of the impact of salt tectonics on the hydrocarbon trap development in collisional orogenic belts.

Keywords: Salt tectonics; Tectono-sedimentary analysis; Hydrocarbon traps; Qom Kuh; Central Iran

How to cite: Nikpoush, S. and Soleimany, B.: Control of salt tectonics on the hydrocarbon traps development: the surrounding structures of the Qom Kuh, Central Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2464, https://doi.org/10.5194/egusphere-egu24-2464, 2024.

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