The Achankovil Shear zone (AKSZ), juxtaposing the Trivandrum Granulite Block (TB) and the Madurai Granulite Block (MB) of the Southern Granulite Terrane (SGT), represents a paleo-suture zone related to the late Neoproterozoic to early Cambrian Gondwana assembly (Rajesh et al., 1998; Praharaj et al., 2021). The polyphase deformational history of the Achankovil Shear Zone (AKSZ) reveals progressive transition from a ductile to brittle deformation regime concomitant with high-grade granulite facies metamorphism and subsequent cooling–exhumation of the granulites. Progressive evolution of the state of stress and the variation of crustal dynamics during the ductile to brittle deformation regime transition, and the genetic link between these two contrasting episodes, if any, have been evaluated from statistical analysis of solid-state fabric and kinematic analysis of brittle fractures.

Three ductile deformation phases, D₁, D₂, and D₃, and associated solid-state fabrics, i.e., S₁, S₂, and S₃, are discernible at the mesoscopic scale. S₁ fabric is gneissic in character and is only preserved in strain shadow regions. Elsewhere, S₁ is transposed along the later S₂ fabric, which is axial planar to fold on S₁. Prevalence of high-temperature deformation conditions during D₂ and D₃ deformation stages is manifested by the presence of S₂-parallel stromatic leucosomes and diatexite leucosome along dilatant S₃ fabric, developed parallel to the axial planes of fold on S₂. Significant simple shear component during D₃ deformation is evidenced from the asymmetric nature of S₂ folds, asymmetric porphyroclast tail and other shear sense markers. Eigen vector analysis reveals a change of maximum eigen vector, i.e., pole to the mean foliation, from NW-SE (D₁: 311⁰/62⁰ NE) to N-S (D₃: 187⁰/80⁰ W). The maximum eigen vector of D₂ (125⁰/53⁰ SW), though similar in trend with D1, shows a reversal of dip direction. Fabric shape analysis reveals a progressive change from girdle to a strong clustered distribution of solid-state fabric from D₁ to D₃ deformation regime, suitably accounting for intense ductile shearing and transposition of earlier fabric during the D₃ deformation stage.

Minor conjugate faults are ubiquitous at different locations along the AKSZ. Dihedral angle of ~60 or less for these faults suggests a shear or hybrid fracture origin, diagnostic of a compressive stress regime. Also, the observed slip of striations on slickensides suggests a consistent oblique reverse kinematics. Fault kinematic and paleo-stress analysis further reveals two distinct stress regimes with NW-SE and NE-SW directed maximum compressive stress (s₁). Stress ratios for these faults imply a compressional to transpressional tectonic regime. Superposition of the slip tendency of NW–SE directed stress tensor over NE–SW directed stress tensor and vice-versa suggests that the NW-SE stress tensor precedes the NE-SW stress tensor during a progressive brittle deformation regime. Summarily, the cooling and exhumation and the switch over from ductile to brittle deformation regimes of the granulites took place under a compressive stress field developed during terrane accretion along the AKSZ. The brittle faults seemingly result from the relaxation of the orogenic far-field stress.

How to cite: Manilal Girija, A. and Bhadra, S.: Ductile to brittle tectonic evolution of the Achankovil Shear Zone, Southern Granulite Terrane – Constraints from statistical analysis of fabric and paleostress inversion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20066, https://doi.org/10.5194/egusphere-egu26-20066, 2026.

The Kadavur Anorthosite Complex represents a distinctive structural domain within a folded high-grade crystalline terrain, where a massif-type anorthosite body occupies the core of a regional-scale fold and is surrounded by folded quartzite ridges. This study examines the relationship between lineament development and the pre-existing ductile fold architecture through integrated DEM–SRTM data analysis and quantitative lineament network characterisation using FracPaQ. The objective is to assess how fold geometry and lithological contrasts influence the spatial distribution and mechanical behaviour of brittle structures. DEM analysis reveals a coherent folded morpho-structural architecture characterised by a well-defined core, axial-plane domains, and limbs expressed as quartzite ridges. FracPaQ-derived results show that lineaments are non-randomly distributed and define multiple dominant orientation sets, reflecting systematic structural control rather than random patterns. Spatial variations in lineament density and lineament intensity show pronounced localisation within and adjacent to the fold core, whereas lineament attributes vary systematically between the anorthosite-dominated core and the surrounding folded quartzite limbs.

Slip tendency analysis indicates that brittle deformation is predominantly shear-controlled across the study area, while dilation tendency values are generally low to moderate, suggesting a subordinate role for opening-mode fracturing. Lineaments within the anorthosite core are comparatively longer, less densely spaced, and display lower orientation dispersion, reflecting brittle stress accommodation within a mechanically competent lithology. In contrast, lineaments developed in the folded quartzite ridges are shorter, more closely spaced, and strongly influenced by lithological layering and fold-related bending stresses.

Although comparable lineament orientation patterns occur across the fold core, axial planes, and limbs, their geometric characteristics, spatial distribution, and inferred mechanical roles differ significantly, indicating that brittle deformation was modulated by local fold geometry and lithological contrasts. The results indicate a structural association between ductile folding and later brittle deformation; however, the tectonic conditions responsible for anorthosite exhumation cannot be uniquely constrained from the present dataset. This study highlights the importance of domain-specific lineament analysis in folded crystalline terrains and emphasizes the role of inherited ductile architecture in controlling later brittle deformation.

How to cite: Prathapachandran, A., Manilal Girija, A., and Kumar, R. S.: Quantitative lineament network analysis of a folded crystalline terrain using FracPaQ: The Kadavur Anorthosite Complex, Southern Granulite Terrane, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16222, https://doi.org/10.5194/egusphere-egu26-16222, 2026.

With the continuous advancement of geological research, quantitative analysis of fracture networks has become a crucial research direction in geological exploration and resource development. To overcome the limitations of traditional methods in quantitatively analyzing fault data under complex geological conditions, we adopt a quantitative fracture characterization method based on geometric and topological theories. This study focuses on the overlay analysis of multi-period and multi-layer faults in a typical area of the western Junggar Basin, aiming to reveal their significant role in hydrocarbon exploration. By means of this method, we achieve multi-dimensional automatic quantification of geometric features (including fracture network length, orientation, and Pxy system), as well as node/branch types and topological parameters. Through the construction of a fracture topological network, we can quantitatively analyze the connectivity characteristics of each period and the vertically favorable conduction zones across multiple periods, thereby providing valuable guidance for hydrocarbon migration path prediction.

How to cite: Tao, Y., Cui, L., Niu, Y., Huang, Y., Bai, S., Zhao, G., Piluolan, P., and liu, Y.: Quantitative Characterization of Fracture Networks Based on Geometric-Topological Integration and Its Application in Hydrocarbon Migration Prediction in the Western Junggar Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18367, https://doi.org/10.5194/egusphere-egu26-18367, 2026.

This study investigates the deep structure of the Ouarzazate Basin, located between the Central High Atlas and the Anti-Atlas, using gravity data analysis. Gravimetric methods were applied to map subsurface structural lineaments beneath the sedimentary cover. The resulting structural map reveals that the basin is mainly controlled by ENE-WSW oriented faults, with subordinate E-W and NE-SW trends related to Variscan deformation, Triassic-Jurassic rifting, and Atlas tectonic inversion. Positive gravity anomalies show preferential NE-SW and E-W orientations and are linked to the structural configuration of the Central High Atlas, which acted as a major source area for the basin. The identified fault systems and compressional structures in the Central High Atlas and Anti-Atlas are consistent with the regional geodynamic evolution. These results highlight the strong tectonic connection between the Ouarzazate Basin and adjacent Atlas basins, particularly the Central High Atlas, and provide new insights into the basin’s geodynamic development.

How to cite: Bouali, B., Tabayaoui, F.-Z., Sahbi, H., Manar, A., Nouayti, A., Boujamaoui, M., and Berkat, N. E.: Subsurface structural mapping using high-resolution gravity data and advanced processing techniques in the Ouarzazate Basin, Southern Morocco., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3508, https://doi.org/10.5194/egusphere-egu26-3508, 2026.

The northeastern margin of the Iberian Peninsula, extending from the Vallès-Penedès Graben to the Valencia Depression, constitutes a passive margin related to the opening of the Valencia Trough during the Neogene. It comprises a series of extensive basins bounded by several mountain ranges, where numerous NNE–SSW-oriented normal faults are present, commonly associated with mountain fronts. Previous studies show that some of these faults, such as the El Camp fault, remain active, although at very low slip rates, as low as 0.02 m/kyr for Late Pleistocene.
Recent analyses of high-resolution Digital Elevation Models (DEMs) have revealed several additional morphological escarpments crosscutting different Quaternary alluvial fan systems across the region. These scarps, found from the Sant Jordi Plain to the La Salzadella Basin, share the same orientation as the Neogene faults, suggesting a common tectonic origin. They are discontinuous, arranged in a right-stepped pattern, and locally display vertical offsets of up to 8 m. Furthermore, several geomorphic features indicate recent tectonic activity, including aligned fissures within the fans and entrenched channels developed on the upthrown block that fade out after crossing the escarpments. Each family of escarpments exceeds 10 km in length, with important implications for the seismic hazard of the region.
Geophysical surveys (ERT, GPR, SRT, HVSR, and MT), validated with borehole data, confirm the presence of faults beneath each analysed escarpment system. At the Vinaixarop escarpment, for instance, ERT profiles revealed a steeply dipping discontinuity plane with a vertical offset of approximately 40 m affecting upper Pliocene sediments.
The faulted alluvial fans are interpreted as Lower to Middle Pleistocene in age and are mainly composed of carbonate gravels. Paleoseismological trenches excavated at four sites (L’Ampolla, Vinaixarop, and two at Sant Rafael del Riu) on different scarps revealed consistent evidence of late Quaternary faulting, such as ruptured strata. Additionally, ground-based hyperspectral cameras (400–1700 nm) were deployed on trench walls as an ancillary tool to map faulted
stratigraphic layers and to detect subtle coseismic deformation. As sedimentation on the fans ceased by the Middle Pleistocene, subsequent activity has been primarily recorded through the deformation of pedogenic features (calcretes), commonly found in the study area. To constrain the timing of this activity, U–Th dating was performed on fault-related carbonates and deformed calcretes. Preliminary results indicate that tectonic activity along these faults persisted at least until the Late Pleistocene. However, a deformed colluvial wedge and the presence of open fissures observed on trench walls suggest Holocene activity.
Additionally, three cosmonuclide depth-profiles were sampled to date displaced geomorphic surfaces, and hence estimating the long-term slip rates of the faults. Ongoing analyses aim to demonstrate Holocene seismic activity and to further characterize paleoearthquakes and their seismic parameters.
In summary, studies of active tectonics in regions of very low strain are inherently challenging, especially when recent sedimentation is scarce and pedogenic processes are intense. Nevertheless, this work highlights that integrating multiple complementary techniques is the most effective approach to address such settings.

How to cite: Ollé-López, M., García-Mayordomo, J., Gallego-Montoya, J., Molins-Vigatà, J., Bellmunt, F., Gabàs, A., Andrés, J., Macau, A., Hasözbek, A., Martí, A., Figueiredo, P., Rodés, Á., García, D., Ortuño, M., and Masana, E.: Constraining Late Pleistocene to Holocene seismic fault activity in NE Iberia: The value of integrating complementary techniques in a low-strain region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21385, https://doi.org/10.5194/egusphere-egu26-21385, 2026.

The Zahedan fault zone in Iran constitutes an active tectonic zone characterised by a complex network of strike-slip faults that dominate the local deformation pattern. This area is located within a large-scale transpressional shear zone accommodating relative motion between the Central East Iranian block and the Afghan Helmand block. The region provides a natural laboratory for investigating the relationship between strike-slip faulting and tectonic blocks rotated around vertical axes.

We present herein, based on high-resolution 2025 Airbus satellite imagery and cartographic and geophysical data, a new strike-slip fault pattern that facilitated the development of the rotated tectonic blocks.

Our observations show that the major strike-slip fault zones are accompanied by dense networks of second-order faults, including single sets of antithetic and synthetic strike-slip faults, conjugate strike-slip fault sets, restraining and releasing stepovers, and thrust faults. In several sectors along the major faults occur the zones of deformation consisting of the rotated tectonic blocks. The scale, orientation, and spatial organisation of the mapped structures indicate that block rotation is controlled by the interaction between major strike-slip faults and subsidiary fault networks.

The individual second-order antithetic faults display that these faults commonly accommodate small displacements, but the faults play a critical role in allowing internal deformation within blocks and facilitate the progressive block rotation. The sense of movements along the major fault and the antithetic strike-slip faults bounding the tectonic blocks allows us to consider the structures as the blocks rotated around vertical axes in a domino-like orientation. Recognised examples of structures show that some rotating blocks are rigid, with no evidence of significant internal deformation, while other rotating blocks exhibit strong internal deformation.

Understanding these spectra of behaviours and the determination of the relationships between them will improve our knowledge of fault interaction processes in eastern Iran and related patterns of seismicity, and it also has implications for seismic hazard assessment in active transpressional settings.

How to cite: Paktarmani, Z., Konon, A., and Mikołajczak, M.: Rotation of tectonic blocks controlled by strike-slip component along the Zahedan fault, Iran, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5809, https://doi.org/10.5194/egusphere-egu26-5809, 2026.

As recent hydrocarbon discoveries rekindle exploration activities in the Black Sea Basin (BSB), efforts to understand the geodynamic processes that led to the formation and evolution of the basin have started to play a significant role in understanding the structural trends formed during rifting. The debate on whether the basin rifted open as one east-west oriented basin, or as two separate basins named the Eastern and Western Black Sea Basins, has been discussed in numerous models. Evidence for the two-basin hypothesis focuses on the basin's semi-parallel ridge and depression architecture, which trends NW-SE in the east and W-E in the west. Conversely, the single-basin model is supported by the correspondence between the regional structure and geodynamic rifting models, specifically those involving an asymmetrical rift pivoting on an eastern hinge caused by slab roll-back of the subducting plate located in the south of the basin.
To address existing tectonic uncertainties, we established a new structural framework for the BSB by reinterpreting 24 long-offset 2D seismic lines. These structural constraints enabled the development of two 2D computational models, allowing us to simulate the distinct kinematic evolution of the basin's western and eastern sections. Our 2D sectioned models show that rift velocities vary significantly in the east-west direction. This contradicts previous analog models showing that the formation of the BSB was related to a simple asymmetrical rift with constantly increasing velocities towards the west from a hinge point located at the eastern margin of the basin. The complex velocity changes throughout the rift axis suggest an uneven movement throughout the subduction zone that drives the back-arc rift. Ultimately, proposing a new complex kinematic history during the evolution of the rift and alternating rift velocities throughout the rift axis, provide a better understanding of the timing of all tectonic events and the final ridge depression geometry observed throughout the BSB.

How to cite: Kaykun, A. and Pysklywec, R.: A New Approach to Rift Kinematics During the Formation of the Black Sea Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9303, https://doi.org/10.5194/egusphere-egu26-9303, 2026.

This study presents a paleostress reconstruction of the metavolcanic and granitoid rocks of the Hutti-Maski greentone belt, Eastern Dharwar Craton (EDC), southern India, aimed at evaluating progressive changes in the regional stress field at ca. 2.5 Ga. Paleostress was constrained using quartz vein orientations, Anisotropy of Magnetic Susceptibility (AMS) fabrics, and fault–slip data from metavolcanic and granitoid rocks.

Anisotropy of Magnetic Susceptibility (AMS) data from granitoids reveal a dominant NNW–SSE–striking magnetic fabric developed during earlier D1/D2 deformation. Paleostress analysis using vein orientations of dilational quartz veins in the granitoids yields an apparent NE–SW compressional stress field. However, kinematic analysis demonstrates that these veins in the granitoids were formed by dextral simple shear along the pre-existing NNW–SSE–oriented fabric under a regional N–S–directed D3 compression. From previous studies it is already well established that this regional N–S–directed D3 compression was responsible for D3 folds with E–W–striking axial planes found in different parts of EDC. N-S-oriented dilational quartz veins in the metavolcanic rocks of this greenstone belt were also formed due to this N-S oriented D3 compression. This interpretation is further supported by comparable stress ratio values obtained from three-dimensional Mohr circle analyses of vein populations in both lithologies.

Fault–slip analysis of displaced veins in granitoids reveals a late-stage NNE–SSW compressional stress field, indicating localised brittle deformation during the final stages of D3. This late brittle overprint is interpreted as resulting from late-D3 brittle deformation during the cratonization of the Dharwar Craton at approximately 2.5 Ga.

Therefore, this study demonstrates that there are pitfalls in the direct evaluation of paleostress using only vein orientations and that it is crucial to integrate kinematic constraints with vein orientation data during paleostress analysis of dilational veins.

How to cite: Goswami, S. and Mamtani, M. A.: Progressive evolution of paleostress in the Hutti-Maski Greenstone belt, Eastern Dharwar Craton, southern India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17196, https://doi.org/10.5194/egusphere-egu26-17196, 2026.