Posters virtual: Wed, 6 May, 14:00–18:00 | vPoster spot 1a
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.
We investigate the heterogeneity of the Indian subcontinent using seismic recordings from the Mw 7.7 Myanmar earthquake that occurred on 28 March 2025. This event was recorded by broadband stations across India. These variations in waveforms at different stations highlight the influence of radiation pattern, crustal structure, wave-propagation paths, and local site conditions. Sedimentary basins, characterized by relatively soft sediments, are known to amplify seismic energy and modify ground motion characteristics, often resulting in enhanced shaking. Understanding these effects is essential for assessing seismic hazard.
We use time-series data from approximately 88 seismic broadband stations provided by the National Centre for Seismology (NCS), India. We apply frequency spectrum analysis, horizontal-to-vertical spectral ratio (HVSR) analysis, and surface wave dispersion analysis. The frequency spectrum helps identify frequency bands where seismic energy is amplified while HVSR analysis is used to estimate the site’s fundamental resonance frequency and the corresponding amplification factor. Surface wave dispersion analysis provides shear-wave velocity information, which is crucial for characterizing near-surface geological conditions.
Together, these analyses help us to understand the influence of local geological conditions at the receiver sites and contributes to a better analysis of regional seismic wave propagation and site-specific ground motion characteristics across the Indian subcontinent.
How to cite: Gupta, S., Silwal, V., and Bora, S. S.: Dynamic Triggering and Effects of Crust Heterogeneities on Propagating Waves due to the 2025 Mw 7.7 Myanmar Earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21372, https://doi.org/10.5194/egusphere-egu26-21372, 2026.
Unravelling the tectonic evolution of collisional orogens and the forces driving the exhumation of high-grade metamorphic rocks requires constraining the kinematics and timing of major fault systems. The Main Mantle Thrust (MMT) in the Swat Valley (northern Pakistan) marks the Eocene suture between the Indian Plate and the Kohistan–Ladakh Island Arc. Its later reactivation is critical yet debated, with models ranging from dominantly dextral strike-slip faulting with minor normal offset (typically less than a few meters) to significant normal faulting facilitating regional exhumation of high-grade metamorphic rocks. This research integrates structural geology with a new, multi-method low-temperature thermochronology dataset—including zircon and apatite (U–Th)/He and apatite fission-track ages—to contribute to this debate. Structural analysis of over 150 kinematic indicators collected along the MMT and its footwall shows that the MMT experienced semi-ductile to brittle reactivation dominated by top-to-the-north normal faulting. Structures formed under greenschist- to sub-greenschist facies conditions (e.g., C′ shear bands) in the footwall record progressive exhumation, with purely brittle cataclastic deformation marking the final stages. Our new thermochronometer dateset includes zircon (U–Th)/He (ZHe) single-grain ages (14.9 ± 1.2 to 24.4 ± 2.0 Ma), apatite (U–Th)/He (AHe) single-grain ages (7.6 ± 0.4 to 15.9 ± 1.0 Ma), and apatite fission-track (AFT) central ages (15.3 ± 2.4 to 16.4 ± 3.2 Ma). This dataset, alongside its thermal history modelling, reveals a consistent cooling signal across the Swat Valley. Following the Eocene collision and peak metamorphism, a major tectonic shift occurred in the Early Miocene. Our data indicate the onset of rapid cooling at ~20 Ma, with a slightly later initiation at ~18 Ma in the eastern Loe Sar Dome. This distinct phase of rapid cooling records the top-to-the-north normal reactivation of the MMT, which lasted until ~15–14 Ma. Collectively, our results provide structural and timing constraints supporting a model of protracted, normal-sense reactivation of the MMT between ~20 and 15 Ma. This event facilitated the final unroofing of high-grade metamorphic rocks in the Swat Valley.
How to cite: Hernández Chaparro, D. R., Faccena, C., Olivetti, V., Fellin, G., and Ghani, H.: Constraining Early Miocene Reactivation of the Main Mantle Thrust (Swat Valley, Pakistan) through Integrated Structural and Thermochronologic Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12696, https://doi.org/10.5194/egusphere-egu26-12696, 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.
Charnockite is generally regarded as a product of high-temperature melting; however, its specific origin, generation, and preservation mechanisms, as well as its relationship to high-grade metamorphism or deep crustal reworking, remain poorly constrained. During the early Paleozoic, the South China Block underwent intense orogeny that resulted in significant crustal shortening and thickening, subsequently inducing widespread anatexis and extensive S-type granites. This study identifies ~431 Ma charnockites containing granulitic enclaves that were exposed in the Yunkai massif, providing key insights into the early Paleozoic crustal reworking and deep crustal melting behaviors in South China. The body displays A-type characteristics with crustal reworking zircon isotopic features (δ18O = 8.0–9.8 ‰; εHf(t) = - 11.5 to - 3.4). The charnockite and its enclaves show identical mineral assemblages and comparable orthopyroxene chemical compositions. The two anhydrous minerals of orthopyroxene and garnet are identified as of peritectic and magmatic origins given their textural features and geochemical compositions. Moreover, petrographic observations and bulk geochemical data argue that the peritectic minerals were derived from the entrainment of their granulitic sources. Crystallization phase modeling indicates orthopyroxene would have been completely hydrated and formed biotite when water contents exceed ∼0.3 wt.% near the solidus. Water-in-zircon analysis and thermodynamic modeling indicate low magma water contents (∼0.15 wt.%; 135 ppm, zircon water medians) for the Gaozhou charnockite from early crystallization to final solidification. CO2‐rich fluids flushed the charnockite reservoir further contributing to the stabilization of the orthopyroxene. Accordingly, the Yunkai charnockite reveals deep crustal melting processes involving anhydrous minerals entrained in a low-water environment. This low-water environment correlates with high-temperature melting of granulite-facies rocks in the lower crust and the presence of CO₂-rich fluids within the system. Regional magmatic-metamorphic-tectonic data indicate that the formation of the Yunkai A-type charnockite occurred within a post-orogenic extension regime, representing the peak of intracrustal reworking in South China.
How to cite: yang, H. and Yao, J.: Formation of A-type charnockite and constraints on deep crustal anatexis in early Paleozoic orogen, South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8520, https://doi.org/10.5194/egusphere-egu26-8520, 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.
