This session will bring together new observations, models, and ideas to help understand the complex factors influencing extensional reactivation, rifting, and drifting during the Wilson Cycle. Works investigating time-dependence, inheritance, plate kinematics, strain localisation, magmatism, obliquity, interior plate deformation, driving forces, sedimentation, surface processes, lithospheric/crustal structure, and the interaction/feedback between processes controlling the Wilson Cycle are therefore welcomed to this session.
Contributions from any geoscience discipline, including but not limited to geophysics, marine geosciences, seismology, ocean drilling, geochemistry, petrology, plate kinematics, tectonics, sedimentology, field and structural geology, numerical and analogue modelling, or thermo/geochronology etc., are sought. We particularly encourage cross-disciplinarity, innovative studies, spanning different spatio-temporal scales, and thought-provoking ideas that challenge conventions from any and all researchers, especially including students.
Orals: Wed, 6 May, 10:45–12:30 | Room K2
The theory of plate tectonics describes how continents are separated from each other by lateral movement that is accommodated by transform faults connecting mid-ocean ridge sections, which leaves inactive fracture zones on the ocean floor. The occurrence of continental crustal slivers in these fracture zones at distances of hundreds of kilometres to 1,000 kilometres from continents has been documented worldwide, yet their occurrence is not expected from classical plate tectonic theory. Here we use three-dimensional magmatic-thermomechanical numerical simulations to investigate the transition from continental rifting to the birth of oceanic transform fault zones and their relationship to mantle melting and crustal tectonics (1). These simulations show that continental slivers are entrapped within shear zones in the oceans inherited from preceding continental rifting stage. They also show three distinct stages of transform fault zone formation—continental rift linkage, proto-transform, oceanic transform—resulting from progressive strain localization into a narrowing extension-parallel strike-slip shear zone. Additionally, continental sliver emplacement into oceanic lithosphere is shown to be associated with specific stages of subsidence and uplift linked to the changing transtensional and transpressional stress field. Short-lived transpression and transform uplift episodes are driven by transient stages of overlapping ridge geometries even in the absence of large-scale plate velocity reorganization. These processes modify the ocean floor morphology, mid-ocean ridge melting conditions and transform fault seismicity.
(1) Balazs A., Gerya T., Tari G. 2025. Presence of continental slivers in oceanic transform faults determined by rift inheritance. Nature Geoscience, 18, 1303–1310.
How to cite: Balázs, A., Gerya, T., and Tari, G.: Presence of continental slivers in oceanic transform faults determined by rift inheritance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5352, https://doi.org/10.5194/egusphere-egu26-5352, 2026.
Plate-tectonic reorganizations are characterized by rapid shifts in plate motions, boundary forces, and margin tectonics, yet the role of mid-ocean ridge extinctions (MOREs) during these events remains poorly constrained. We address this gap by systematically examining a suite of MOREs occurring within plate reorganizations and by comparing them with strength-profile analyses of thermally evolving oceanic lithosphere beneath spreading axes following spreading shutdown. Thermal models and strength-envelope calculations show that extinct ridges undergo rapid lithospheric strengthening, developing sufficient mechanical resistance to transmit slab-pull stresses within ~2–10 Myr after spreading cessation. This rapid welding transforms formerly weak ridge–transform networks into coherent lithospheric blocks capable of mediating far-field stress transfer. We illustrate this process using three well-constrained Cenozoic MOREs. Extinction of the Wharton Ridge promoted Indo–Australian plate welding and enhanced slab pull along the Sunda–Java trench, accelerating plate motion and sustaining post-collisional India–Asia convergence. Progressive shutdown of Pacific–Farallon ridge fragments enabled coupling between the Pacific and North American plates and facilitated subsequent Pacific stress transmission, driving deformation in the Gulf of California rift and the San Andreas system. In the western Pacific, cessation of the Shikoku Ridge strengthened the Philippine Sea Plate, enabling efficient transmission of slab pull in the Ryukyu–Nankai/Izu–Bonin–Mariana double subduction system and triggering trench advance and regional compressional tectonics in northeast Japan. Our results indicate that MOREs act as active amplifiers of plate reorganizations by enhancing lithospheric coupling and facilitating far-field stress propagation. These findings support a cascading, plate-to-plate mode of tectonic reorganization (rather than mantle-driven) and highlight extinct ridges as critical nodes in the episodic reorganization of the global plate network. Building on these insights, we extend the discussion to the Paleozoic–Mesozoic Tethyan system, where successive terrane collisions and episodes of subduction initiation may likewise have involved MOREs acting as stress transmitters across ridge–transform networks.
How to cite: Gianni, G., Gianni, C., Gallo, L., Sippl, C., and Ramos, V.: Mid-ocean ridge extinctions as amplifiers of plate-tectonic reorganizations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4005, https://doi.org/10.5194/egusphere-egu26-4005, 2026.
A persistent limitation in reconstructions of East Gondwana is the absence of a margin-scale numerical plate model. Existing reconstructions are largely regional or schematic, commonly rely on limited datasets, and in many cases conflict across adjacent sectors of the margin. To address this gap, a new numerical tectonic reconstruction of the East Gondwanan margin is presented, spanning 780–0 Ma and focusing on the coupled evolution of eastern Australia, the East Antarctic margin, and New Zealand during 780–250 Ma. The reconstruction is embedded within a globally consistent plate framework and links seamlessly to established Mesozoic–Cenozoic reconstructions, providing continuity across the full evolution of the Panthalassa-facing margin.
The model synthesises ~113,000 datapoints across ~12,000 geological samples, including igneous, detrital, and metamorphic geochronology, igneous isotopic geochemistry, potential-field datasets, paleogeographic constraints, and extensive literature synthesis. Implemented in GPlates, the reconstruction enforces plate-like behaviour and enables inherited geological features, such as rift systems and suture zones, to be tracked through time.
At the scale of the full margin, the reconstruction captures a series of first-order tectonic events and behaviours. Neoproterozoic–Cambrian rifting marks the initial development of Panthalassa as an Atlantic-type ocean, followed by a transition to a Pacific-type system with the initiation of continent-dipping subduction between ~555 and 525 Ma. Convergence is punctuated by major collisional events, including accretion of the VanDieland Superterrane at ~495 Ma and collision of the Hikurangi Plateau at ~100 Ma; in both cases, subduction jump promotes trench rollback and back-arc spreading that matures into rifting. In contrast, episodes of highly oblique plate motion drive inboard oblique subduction and transform systems, displacing the East Lachlan (430–395 Ma) and New England (430–395, 360–330, and 285–260 Ma) superterranes along strike and generating substantial vertical-axis rotation and oroclinal curvature. These processes illustrate how obliquity and lithospheric inheritance complicate simple opening–closing cycles along long-lived convergent margins.
By resolving these processes within a single, internally consistent reconstruction, this work provides a framework for identifying emergent tectonic cycles along the East Gondwanan margin. Interpreted within a modern Wilson Cycle context, the results highlight how inherited lithospheric architecture and subduction dynamics condition whether convergence leads to rollback, rifting, or continued accretion along long-lived supercontinent margins.
How to cite: Tu, A., Zahirovic, S., Boone, S., Glen, R., Mahoney, L., Salles, T., and Rodriguez Corcho, A.: Emergent tectonic cycles along the Panthalassan margin of East Gondwana from numerical plate reconstruction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15528, https://doi.org/10.5194/egusphere-egu26-15528, 2026.
Late Cretaceous convergence between the Afro-Arabian and Eurasian plates triggered a short-lived yet complex subduction–obduction cycle along the Arabian margin, culminating in the Campanian obduction of Neo-Tethyan oceanic lithosphere onto the Arabian continent. Although the Oman Mountains preserve an exceptional record of this evolution, the timing and tectonic significance of deformation and metamorphism along the Arabian margin remain poorly constrained. This is particularly true for the Jabal Akhdar Window (JAW), a tectonic feature traditionally regarded as exposing the most external, non-metamorphic and little deformed portions of the margin.
We present new geochronological constraints integrated with structural and metamorphic data that call for a revision of the tectonic history of the Cryogenian–Cretaceous JAW succession. Raman spectroscopy of carbonaceous material (RSCM) and chlorite–white mica–quartz–water multiequilibrium thermobarometry constrain synkinematic temperatures and pressures for two distinct regional contractional deformation phases (D1 and D2), while U–Pb dating of structurally constrained calc-mylonites provides much-needed absolute age control on deformation.
D1 records pervasive brittle–ductile to ductile deformation affecting both the pre-Permian basement and the overlying Permian passive-margin carbonates, with an overall top-to-the-NE transport direction. U–Pb geochronology of top-to-the-NE calc-mylonites yields an age of 106 ± 13 Ma, consistent with field-based constraints and regional correlations. Synkinematic RSCM and thermobarometric data indicate upper greenschist- to lower blueschist-facies conditions (~370 °C, minimum ~0.7 GPa), consistent with an Albian HP–LT accretionary event related to early convergence along the Arabian margin. D1 is interpreted as due to progressive nappe stacking within a NE-verging accretionary prism formed above an immature and short-lived intracontinental SW-directed subduction zone.
D2 represents a younger, lower-grade, top-to-the-S/SW-verging deformation event localized within Upper Cretaceous carbonates, mainly in the northern JAW. RSCM analyses from top-to-the S/SW calc-mylonites constrain synkinematic temperatures to ~330 °C, while U–Pb carbonate ages from the same rocks cluster between ~80 and 75 Ma. These data link D2 deformation to southwestward obduction, coeval with the emplacement of the Semail Ophiolite and Hawasina nappes.
We propose a two-stage evolution for the northeastern Oman Mountains, involving a transient, SW-directed Albian subduction associated with HP–LT accretion followed by Late Cretaceous obduction driven by a newly established NE-dipping intraoceanic subduction zone.
These results demonstrate that HP–LT metamorphism in the JAW is regionally developed and temporally resolved, highlighting the critical role of geochronology of structurally well-constrained fabrics in deciphering transient subduction–obduction processes during the Late Cretaceous Wilson Cycle evolution of the Arabian margin.
How to cite: Viola, G., Degl'Innocenti, S., Zuccari, C., Giuntoli, F., Callegari, I., Kylander-Clark, A., and Vignaroli, G.: When obduction meets accretion: new geochronological and metamorphic constraints on an Albian-Campanian transient subduction-obduction system in NE Oman , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4262, https://doi.org/10.5194/egusphere-egu26-4262, 2026.
Rifted margins form when continents rift apart and are commonly characterized by a thinned transition zone between the continental crust and the oceanic crust. This transition zone can display a wide range of characteristics, which primarily depend on the regional tectonic evolution. The velocity and duration of the rifting process as well as the geodynamic setting influence the properties and geometry of the margins, which are often grouped into two main categories: magma-poor and magma-rich.
Magma-rich margins are characterized by large input of mafic melt, while magma-poor margins are characterized by much less magma production during the rifting process, resulting in variations in geometry and rheology of rifted margins worldwide.
Using the finite elements code Citcom, we show how different types of rifted margins can influence the dynamics of continental collision, focusing on the time and depth of slab break-off after collision and the fate of margin material. We compared these models as a function of various parameters (e.g., margin length, density, and viscosity), in order to understand how the architecture of a passive margin affects the dynamics of continental collision.
We find that rifted margins have a noticeable impact on subduction dynamics, as we observe large variability in slab break-off times and depths. In particular, the presence of a rifted margin can delay slab break-off to up to 60 Myr after the onset of collision.
Our results show that a large portion of the weak crust of magma-poor margins is likely to detach from the subducting plate and accrete to the upper plate, while the dense and strong mafic and ultramafic component of magma-rich margins causes most of the margin to subduct and be lost into the mantle, leaving only a small fraction of transitional and oceanic crust at the surface. Therefore, the volume of accreted material is much larger when the margin is magma-poor than magma-rich, which is consistent with geological observations that fossil magma-poor rifted margins are preserved in many mountain ranges, whereas remnants of magma-rich rifted margins are scarce.
Importantly, our results show that rifted margin type controls the architecture of the subsequent collisional phase of the Wilson cycle.
How to cite: Turino, V., Magni, V., Kjøll, H. J., and Jakob, J.: The effect of magma poor and magma rich rifted margins on continental collision dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13121, https://doi.org/10.5194/egusphere-egu26-13121, 2026.
The northern Indian passive margin has witnessed at least two Wilson-cycle-related collisional events since the Proterozoic: the Early Paleozoic Bhimphedian Orogeny and the Cenozoic Himalayan Orogeny. The latter, triggered by the India–Asia collision, produced a series of orogen-scale structures including the Main Frontal Thrust, Main Boundary Thrust, Main Central Thrust (MCT), and South Tibetan Detachment System (STDS), which cut the Himalaya into distinct lithotectonic belts. However, the extent to which vestiges of the Early Paleozoic tectonism persist remains uncertain due to extensive overprinting by Cenozoic deformation. This ambiguity has revived debates on whether the major Himalayan fault systems are exclusively Cenozoic tectonic boundaries or the reactivation of long-lived, inherited Early Paleozoic structures.
This study investigates the tectonic evolution of the MCT, a several-kilometre-thick, foreland-propagating, high-strain shear zone that activated ca. 27–11 Ma. It structurally juxtaposes the Neoproterozoic Greater Himalayan Sequence (GHS) over the Paleoproterozoic Lesser Himalayan Sequence. Integrated structural mapping and U-Pb zircon geochronology were conducted on the GHS rocks from the proximal hanging wall of the MCT in the Dhauliganga (Garhwal) and Pabbar (Himachal) valleys of the NW Himalaya. Ductilely deformed psammitic, ortho- and aplite gneisses, leucogranite, and migmatite display NE-dipping mylonite foliation, NNE-plunging stretching lineation, and persistent top-to-the-SW ductile shearing, consistent with regional MCT kinematics.
Detrital zircon spectra constrain the maximum depositional age of the GHS metasedimentary protoliths to 849 ± 6.7 Ma. These country rocks were syn- to post-tectonically intruded by orthogneiss and leucogranite along a major crustal conduit, the proto-MCT, during the Early Paleozoic Bhimphedian Orogeny. In the Dhauliganga Valley, three distinct tectonothermal pluses are recorded at 554 ± 6.8 Ma, 489 ± 2.8 Ma, and 471 ± 3.2 Ma. In the Pabbar Valley, coeval crustal anatexis along the proto-MCT produced stromatic migmatite at 508 ± 6.7 Ma and 473 ± 3.1 Ma. These ages collectively reflect magmatism, regional metamorphism, and pervasive deformation along the proto-MCT during the Bhimphedian Orogeny. During the Cenozoic Himalayan Orogeny, this dormant proto-MCT was reactivated and subsequently evolved to present-day MCT. This is evident by tectonothermal pulses at 20 ± 3.0 Ma and 16 ± 1.2 Ma, recorded in the leucogranite and aplite gneiss in the Dhauliganga Valley. Notably, a comparable tectonic evolution of the STDS during the Early Paleozoic (a~499–467 Ma) and Cenozoic (~34–25 Ma and 23–13 Ma) has been documented in the upper reaches of the Dhauliganga Valley.
Together, these findings demonstrate that both the MCT and STDS originated as coeval Early Paleozoic proto-tectonic structures and were subsequently reactivated during Late Eocene to Early Miocene Himalayan deformation phases. This dual-stage tectonic evolution underscores that the Himalayan crustal architecture is fundamentally inherited from Early Paleozoic orogenesis, with Cenozoic deformation preferentially exploiting these pre-existing anisotropies. Therefore, comprehensive Himalayan tectonic models must integrate the contributions of Early Paleozoic tectonism, rather than attributing these major shear zones solely to the Cenozoic displacement.
How to cite: Dixit, R., Jain, A., Singh, P., Singhal, S., and Deshmukh, G.: The Main Central Thrust, a Possible Early Paleozoic Structure Reactivated During the Cenozoic: Insights from the NW Himalaya, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-297, https://doi.org/10.5194/egusphere-egu26-297, 2026.
Ophiolites derive from different tectonic settings, including mid-ocean ridges (MOR), supra-subduction zones (SSZ), and ocean–continent transitions (OCT). However, discriminating among these settings and relocating ophiolitic fragments nowadays in orogens to their original paleo-position in space and time remains challenging.
This study aims at constraining the original tectonic setting and paleo-position of three isolated and fragmented ophiolite slivers belonging to the North Calabria Unit (Basilicata region, southern Italy). The North Calabria Unit represents a strongly dismembered association of mantle, mafic, and continental crustal rocks incorporated into the southern Apennine orogenic system. These units are interpreted as remnants of the Jurassic Alpine Tethys, later affected by Alpine–Apennine convergence and tectonic reworking.
We investigate three ophiolite slivers using a multiscale approach integrating detailed field observations, petrological and geochemical analyses, zircon geochronology, and plate-kinematic reconstructions. Particular emphasis is placed on the characteristics of key lithologies and, critically, on the nature of their contacts, which provide first-order constraints on the original tectonic setting of these slivers.
Key observations include: (i) Mid-Jurassic cherts stratigraphically overlying MOR-type basalts, sealing tectonic contacts between depleted mantle and gabbros affected by crustal contamination; (ii) amphibolite and gneiss tectonically juxtaposed with gabbros, with zircon age and composition compatible with a pre-rift lower continental crustal origin; and (iii) the possible circulation of Cr-rich, mantle-derived fluids along low-angle faults at the top of continental crustal rocks.
When integrated with kinematic reconstructions, these observations indicate that the studied ophiolite slivers originated in an OCT setting developed during Jurassic rifting of the European side of the Alpine Tethys, possibly near Sardinia, rather than in a fully oceanic MOR or SSZ environment.
Our workflow provides a framework to locate fragmented ophiolites in rifted margins and can be applied to interpret dismembered ophiolites in orogenic belts worldwide.
How to cite: Frasca, G., Manatschal, G., Prosser, G., Rubatto, D., Ulrich, M., Barale, L., Curetti, N., and Compagnoni, R.: A systematic approach to reconstruct ophiolite tectonic setting and paleo-position from outcrop analysis and geochemistry: the example of the North Calabria Unit (Southern Apennines, Italy), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17950, https://doi.org/10.5194/egusphere-egu26-17950, 2026.
The Variscan (~370–290 Ma)–Alleghanian (~335–265 Ma) orogen was fragmented during the Mesozoic opening of the Atlantic Ocean, resulting in a complex margin architecture shaped by both extensional processes and inherited tectonic structures. This complexity challenges orogen reconstruction, as current models often underestimate the influence of tectonic inheritance and superimposed rifting. Understanding the interaction between extension and inherited crustal features is therefore essential.
Remnants of this orogen occur offshore in the West Iberian Margin (WIM) and Newfoundland Margin (NM), which form conjugate margins with marked along-strike variability. We restore the marine domains to their pre-breakup configuration and examine how basement characteristics, inferred from geophysical data, controlled extension patterns. We quantify margin extension, its partitioning between upper and lower crust, and its balance with total crustal stretching.
Our reconstruction correlates onshore and offshore basement domains and proposes a new zoning of the Variscan–Alleghanian basement. Results indicate that Mesozoic rifting was oblique to the inherited orogenic architecture, providing new insights into the structural variability of the WIM–NM system. This highlights the role of lithological composition in the Variscan basement and Avalon terranes in shaping rift geometry.
How to cite: Amigo Marx, B., Fernandez, O., and Poblet, J.: Influence of Tectonic Inheritance on the Extensional Architecture of the Iberia–Newfoundland Margins , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6672, https://doi.org/10.5194/egusphere-egu26-6672, 2026.
The origin of hot ocean-continent back-arc regions with very thin mantle lithosphere and very high surface heat flow in both extensional and contractional ocean-continent subduction systems is highly enigmatic and unresolved. These first order characteristics have often been explained with either convective mantle lithosphere removal or by back-arc extension. However, it is unclear what may cause the proposed convective thinning and/or delamination of eclogitic lower crust over very wide regions, whereas back-arc extension is either not observed or insufficient to explain the observed very thin mantle lithosphere. Notably, many of these ocean-continent systems have a long history of terrane accretion. Here we show, using thermo-mechanical model experiments, that terrane accretion provides a consistent explanation for the observed key characteristics and naturally leads to rheologically weak back-arcs with continental crust directly on top of hot sub-lithospheric mantle.
Associated article:
Erdős, Z., Huismans, R.S., Wolf. S., Facenna, C. (2025), Terrane accretion explains thin and hot ocean-continent back-arcs. Science Advances 11, eadq8444. https://doi.org/10.1126/sciadv.adq8444
How to cite: Huismans, R. S., Erdős, Z., Wolf, S. G., and Faccenna, C.: Terrane accretion explains thin and hot ocean-continent back-arcs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9138, https://doi.org/10.5194/egusphere-egu26-9138, 2026.
Posters on site: Tue, 5 May, 16:15–18:00 | Hall X2
Subduction is a key driving mechanism in Plate Tectonics, but how it initiates is still poorly understood.
Subduction initiation is thought to be a complex and evolving tectonic process. It consists of stages of lithospheric contractional deformation that may reactivate inherited structures, potentially localizing deformation in a proto-plate boundary and leading to subduction.
During the Cenozoic, the most common site to initiate subduction was at passive margins (Lallemand and Arcay, 2021). Hence, the importance of understanding the main controlling mechanisms that lead to subduction initiation at these locations. These processes are thought to be dependent on various factors, such as the presence of a weak zone (e.g., a serpentinized exhumed mantle layer, serpentine-filled normal and detachment faults), a pre-existing stress/strain field, and the structure/architecture of the rifted margin.
Using high-resolution 2D geodynamic numerical models carried out with the code LaMEM, this work investigates the mechanisms that may control the reactivation on magma-poor rifted margins. In particular, by testing different parameters (e.g., length of the passive margin, presence of a serpentinized layer), different deformation regimes (e.g., strain-rates) and the thermomechanical state of the system that may lead to subduction initiation in these locations.
Furthermore, seismic reflection lines were interpreted in order to better understand and characterize the magma-poor rifted margin archetype (West Iberian rifted margin) and its tectonic structure distribution. The data interpreted helped constrain fault distribution and their geometry in numerical models conducted.
Preliminary results show that serpentine-filled tectonic structures (e.g., inherited normal and detachment faults from the rifting process) facilitate the reactivation of the rifted margin by localizing compressive-induced deformation. Additionally, models show that the presence of serpentinized exhumed mantle in a hyperextended domain, constrain the localization of deformation in this section, leading to an earlier subduction initiation. Therefore, we can infer that the presence of serpentinized exhumed mantle and/or the existence of rift inherited tectonic structures, deeply weakens the passive (or rifted margin). Notwithstanding, results also show that there is a first order dependence on the thermal age of the continental lithosphere (e.g., strength and thickness) for the locus of strain localization. Followed by a second order dependence on passive margin length as a constraining mechanism for the locus of subduction.
How to cite: João, M., Cadenas, P., Duarte, J., Rodrigues, N., Gomes, A., Pereira, R., Rosas, F. M., Riel, N., and Welford, J. K.: 2D thermomechanical numerical models of passive margin reactivation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1221, https://doi.org/10.5194/egusphere-egu26-1221, 2026.
The Chamrousse ophiolite, located in the French External Alps, has long been considered as the suture of an ocean opened during the Cambro-Ordovician (496 ± 6 Ma, Ménot et al., 1988). This has been recently challenged by new U–Pb zircon results revealing a dual geological history, occurring in the Cambro-Ordovician (520-460 Ma) and in the Devono-Carboniferous (360-345 Ma), see Gunia et al., 2025. Futhermore, this complex is bounded by North-Gondwana flysch units (Fréville et al., 2018). Additional information is needed to define geodynamic interpretations. Here, we present combined zircon U–Pb/Hf and trace element signatures obtained on these two igneous populations via in-situ approaches.
Zircon showing Cambro-Ordovician U–Pb dates, identified in meta-trondhjemites and amphibolites, feature elemental geochemistry of U and Yb contents indicative of continental affinities. ε176Hfinitial of ca. +5 point to a mantle source intermediate between depleted and enriched end-members. We interpret these results as indicating zircon crystallisation during the continental rifting of the North of Gondwana.
Zircon that crystallized during the Devono-Carboniferous event, identified in mafic-ultramafic units, show trace-element characteristics and an ε176Hfinitial of ca. +12 suggestive of an oceanic zircon origin from a chemically depleted mantle source. This Devono-Carboniferous event is interpreted as reflecting the actual oceanic opening, facilitated by pre-thinned Cambro-Ordovician continental crust.
In addition, new structural data suggest the opening occurs through the development of an asymmetric detachment that enabled exhumation of mantle-derived rocks with limited magma production, followed rapidly by its closure during the Variscan collision (330-300 Ma, Jacob et al., 2023). The new results presented here highlight the two-stage tectonic evolution, making this short-lived oceanic basin an exceptional case study before the final assembly of Pangea.
Reference list:
Fréville, K., Trap, P., Faure, M., Melleton, J., Li, X. H., Lin, W., ... & Poujol, M. (2018). Structural, metamorphic and geochronological insights on the Variscan evolution of the Alpine basement in the Belledonne Massif (France). Tectonophysics, 726, 14-42.
Gunia, M., Cordier, C., Janots, E., Vezinet, A., Milloud, V., Jacob, J. B., & Guillot, S. (2025). The Chamrousse Ophiolite (Western Alps, France): Relict of a Devono‐Carboniferous Ocean. Terra Nova.
Jacob, J. B., Janots, E., Cordier, C., & Guillot, S. (2023). Discovery of Variscan orogenic peridotites in the Pelvoux massif (western Alps, France). BSGF-Earth Sciences Bulletin, 194(1), 2.
Ménot, R. P., Peucat, J. J., Scarenzi, D., & Piboule, M. (1988). 496 My age of plagiogranites in the Chamrousse ophiolite complex (external crystalline massifs in the French Alps): evidence of a Lower Paleozoic oceanization. Earth and Planetary Science Letters, 88(1-2), 82-92.
How to cite: Gunia, M., Vezinet, A., Cordier, C., Janots, E., and Plunder, A.: Two-stage oceanic opening with its continental margins, revealed by elemental zircon U–Pb/Hf/TE signatures: the case of the Chamrousse ophiolite in the Western Alps., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17186, https://doi.org/10.5194/egusphere-egu26-17186, 2026.
Microplates are widely distributed at plate margins and within plates, playing vital roles in the Wilson Cycle. However, their dynamic behaviour and feedback mechanisms across different stages remain poorly constrained. This study synthesizes insights from numerical modelling and geological observations, focusing on the roles of microplates in three key tectonic settings of the Wilson Cycle. Firstly, at divergent plate margins, microplates disrupt the continuity and uniformity of continental rifting, leading to asymmetric rift propagation and complex mid-ocean ridge reconfigurations. Secondly, at convergent plate margins, microplates may undergo crust-mantle decoupling during subduction, induce slab dip angle variation, terminate subduction process and facilitate new subduction initiation. Finally, in intraplate orogens, the heterogeneity of microplates during continental collision could lead to variations in strain distribution and lithospheric deformation, making it a key factor in driving the differential evolution of orogenic processes. This review highlights rheological strength as the primary control on the dynamic behaviour of microplates. Strong microplates transmit tectonic stress, whereas weak ones promote strain localization and accommodate major deformation. Natural cases align with model predictions, highlighting microplate strength as a key factor in shaping divergent plate margins, subduction geometry, and intraplate deformation. Overall, microplates significantly modulate the spatial complexity and temporal rhythms of the Wilson Cycle by controlling local rheological structure and strain localization tendencies. They may play critical roles in better understanding the global tectonic activities, as well as the further development of plate tectonics theory.
How to cite: Li, Z.-H., Yu, S., Cui, F., and Luo, P.: Microplate Dynamics Through the Wilson Cycle: Insights from Modelling and Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3648, https://doi.org/10.5194/egusphere-egu26-3648, 2026.
The transition from continental rifting to oceanic accretion - and the related initiation of the spreading ridge - remains one of the least understood phases in plate tectonics. This study presents new seismic reflection observations from the Møre and Vøring margins offshore Norway, revealing a series of deep dome-like structures in the outer rifted domain. These features, identified across multiple profiles, are interpreted as crystallized magmatic bodies - possibly gabbroic sills or lenses -emplaced during the rift-to-drift transition. The domes are associated with high seismic reflectivity and velocity, and spatially correlate with the boundary between sills and lava flows, suggesting a strong magmatic control.
It is proposed that these domes represent proto-magma chambers or magma mush zones, potentially marking early, stuttering attempts at ridge initiation. Their alignment sub-parallel to the continent-ocean boundary (COB) implies a broader magmatic axis at the margin scale. These findings challenge the conventional notion of a sharp COB and support a more transitional, structurally complex Continent-Ocean Transition Zone (COTZ). The study highlights the need for revised mapping protocols and further investigation into the thermal and temporal evolution of these magmatic features to better understand the onset of oceanic spreading.
How to cite: Peron-Pinvidic, G.: Magmatic domes and the initiation of oceanic processes at the Mid-Norwegian rifted margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2508, https://doi.org/10.5194/egusphere-egu26-2508, 2026.
The Cretaceous High Arctic Large Igneous Province (HALIP; 135 – 75 Ma) is a massive magmatic province preserved in the circum-Arctic region through a series of volcanic flows, sills, and dykes. The plumbing geometry of LIPs, often showcased through the dyke swarms, can inform the paleo-stress regime, rheological behaviour, and tectonic history of the region. Pre-drift plate tectonic reconstruction models have identified the presence of HALIP’s signature 1600 km diameter, quasi-circular circumferential dyke swarm which encloses a radial dyke swarm extending onshore to continental masses including the Queen Elizabeth Islands of the Canadian Archipelago. The foci of the swarms are debated to be derived via mantle plume, continental rifting, or combined mechanisms, producing three major pulse events and resulting in the intrusion of the associated dykes. The earliest dykes are thought to bare economic concentrations of Ni-Cu-PGE sulfides, specifically in Axel Heiberg Island and western Ellesmere Island, Canada. Despite HALIP’s massive extent and prospectivity for Ni-Cu-PGE deposits, it remains one of the least explored LIPs on Earth based on its remote location, limited surface exposure, extensive glacial coverage, and scarce, discontiguous geophysical data.
In particular, the presence of HALIP dykes in northeastern Ellesmere Island is suspected, yet remains unmapped. The Paleogene Eurekan deformation and orogeny (63 – 35 Ma) has been hypothesized to have reworked the dykes in the region, overprinting the extent of HALIP with orogenic deformation. Here, we test the theory that unmapped HALIP dykes extend into northeastern Ellesmere Island and are subsequently impacted by the Eurekan deformation, suggesting an increased geographical presence and prospectivity of the LIP.
To test this theory, we present a series of three-dimensional numerical models to investigate the presence, impact, and prospectivity of HALIP dykes in northeastern Ellesmere Island. Utilising the open-source geodynamic code Advanced Solver for Planetary Evolution, Convection, and Tectonics (ASPECT), we superimpose a range of dyke configurations to evaluate the structural controls of HALIP dykes on host rocks at depth during the convergent plate tectonic boundary conditions that took place during Eurekan deformation. The range of dyke configurations are collated from a comprehensive review of dyke and host rock samples from neighbouring regions to accurately parameterize and configure the models to HALIP and the High Arctic, allowing for a direct link between outsourced field data and our numerical modelling.
The suite of Eurekan deformed HALIP dyke models are then critically contrasted to available geological and geophysical data in the region. Finally, we produce an analysis of the likelihood that HALIP intrusions were overprinted by Eurkean deformation, or that the HALIP extent is not as significant as previously thought. Our work here provides new insights into an understudied area of the Canadian Arctic, which may be a future site for critical mineral prospectivity.
How to cite: Nielsen, J. P. and Heron, P. J.: The influence of orogenesis on a large igneous province: a focus on Eurekan deformation on HALIP in the Canadian High Arctic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8113, https://doi.org/10.5194/egusphere-egu26-8113, 2026.
Rifted margins form through multi-phased periods of rifting, stretching and thinning of the continental lithosphere until breakup is complete and oceanic lithosphere is formed. It is widely accepted that rifted margins can be partitioned into distinct structural domains (proximal, necking, distal (hyperextended and exhumed), outer and oceanic), which are characterized by their architecture and associated rift stages. However, no consensus has been reached yet on how the different domain boundaries should be defined. As a result, the terminology used to describe rifted margin domains remains inconsistent across studies, hindering comparison between margins and limiting the development of a unified conceptual framework.
A key challenge for establishing robust nomenclature is the dependency of the domain boundary on the constraining data type. Structural, geophysical and magmato-stratigraphic data inherently result in different boundaries. The oversimplistic concept of a Continent Ocean Boundary (COB) is a classic example of this, where the definition is heavily dependent on the method and data utilized. A similar ambiguity is present for the various structural domains, such as the boundary between the necking and distal domains. The inconsistency in terminology highlights the need for unification of the nomenclature through a novel classification framework.
In this contribution, we compile and synthesize published contributions to construct this set of unifying definitions for rifted margin domain boundaries. Through an extensive literature review, we highlight the existing terminology discrepancies. We focus on the Northeast Atlantic region, including the NE Greenland & Norway and the SE Greenland & Faroe-Hatton-Rockall margins, as an ideal test laboratory for our work. The regional tectonic history captures a complete evolution from Devonian post‑orogenic collapse through multiple rifting phases and finally Cenozoic breakup and magmatism. The area has been extensively studied because of past hydrocarbon exploration, providing ample constraints. Finally, local complexities including microcontinents (e.g., Jan-Mayen), failed rift basins (e.g., Rockall Basin) and anomalous ridges (Greenland-Iceland-Faroe Ridge) ensure that our framework will capture the full spectrum of rifted margin architectures.
Our preliminary results confirm that domain boundaries shift systematically depending on the dataset used, reinforcing the need for a unifying classification approach. We present the foundations of a novel framework for defining rifted margin domain boundaries, showcasing its application to the NE Atlantic. This framework aims to bridge across the rifting terminology, ultimately improving cross‑margin comparisons and fostering greater consistency within the rifting community.
How to cite: Ammerlaan, F., Peron-Pinvidic, G., and Welford, J. K.: Unifying rift terminology in the northeast Atlantic: towards a harmonized framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5365, https://doi.org/10.5194/egusphere-egu26-5365, 2026.
Small-volume, alkaline mafic intrusions of Tithonian age (~148 Ma) in north-central Newfoundland form the Notre Dame Bay Magmatic Province (NDBMP) representing a useful onshore expression of early North Atlantic rift-related magmatism in the Newfoundland–Iberia-Ireland rift system. Over the past decade, a diverse body of new work has emerged combining structural geology, geochronology, palaeomagnetism, geochemistry, petrology, and geophysics. Here, we synthesise these results to develop an integrated regional framework for the timing, emplacement, and tectonic significance of this magmatic episode.
High-precision CA-ID-TIMS U–Pb zircon and 40Ar/39Ar phlogopite ages constrain emplacement of the NDBMP to a short-lived Tithonian pulse at ca. 148 Ma, contemporaneous with early offshore rifting and basin development. Structural mapping and field studies demonstrate that lamprophyre dykes preferentially exploited pre-existing Appalachian structures, including faults linked to an Iapetus suture, and locally record post-emplacement reactivation. Joint inversion of airborne gravity gradiometry and magnetic data reveals the 3-D geometry of the intrusions at shallow crustal levels and highlights structural focusing at the intersection of inherited fault systems and likely penetrating to Moho-scale structures. New petrochemical and isotopic data indicate derivation from low-degree partial melting of a metasomatised lithospheric mantle source, whereas palaeomagnetic results are consistent with coherent motion of the Newfoundland block with North America during Late Jurassic rifting.
These complementary datasets emphasise the importance of structural inheritance, lithospheric architecture, and distal extension-driven upwelling in generating early rift magmatism along magma-poor margins. However, key uncertainties remain regarding magma transport pathways at depth, the relationship between radial dyke swarms and regional stress evolution, and links to conjugate margin processes. We outline future research directions that integrate offshore data, improved geochronology, and plate-scale reconstructions to further refine models of North Atlantic rift initiation, whilst also considering the implications for rift evolution globally.
How to cite: Peace, A. L., Sandeman, H., McCausland, P. J. A., Welford, J. K., Keefe, E., Guna, A. G., Dunning, G., and Geng, M.: Early rift-related Mesozoic magmatism in Newfoundland: A synthesis of recent work and links to North Atlantic opening, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8254, https://doi.org/10.5194/egusphere-egu26-8254, 2026.
The Mexican Orogen is the most important tectonic event recorded during the Late Cretaceous-Paleocene in Mexico. This orogen conforms to the majority of the Mexican territory, and its origin is probably related to the subduction dynamics in the western margin of the North American plate. Many studies had concentrated their efforts in the foreland fold-thrus belt toward the eastern part of Mexico. However, the geometry, kinematic, and amount of shortening to the hinterland part of the orogen are unknown. Additionally, the age and kinematics of the shortening structures associated with the inversion of the early Cretaceous Arperos basin, now in the hinterland part, remains an enigma. In this work, we present a detailed structural analysis of the shortening structures and U-Pb detrital zircon ages of sedimentary rocks located in the western-central part of Mexico, with the proposal to know the main features of the contractional deformation and resolve the enigma about the Arperos basin inversion during the Mexican Orogen. The rocks of the western sector of the Arperos basin are composed of a sequence of volcaniclastic sandstone interbedded with shale and thin layers of limestone with a maximum depositional age of 133.3 ±1.1 to 110.27±0.77 Ma. This sequence is unconformably covered by a synorogenic turbidite package with a maximum depositional age of 101 ±1 Ma. All these rocks are strongly deformed by folding with a pervasive sub-horizontal axial plane cleavage and 70% shortening. Although, the Arperos basin rocks record a less pervasive second cleavage. The mesoscopic folds are asymmetric with a subhorizontal axial plane, and are class 1C, 3, and 2 based on Ramsay's classification. There is a second fold generation in the rocks of Arperos basin that refolds the firs folds. The refolded folds are type-3 mainly. The reverse faults dip 30–60° to the NE and SW, having displacements of tens of centimeters and are penetrative on the scale of tens of meters.
The data obtained in this work suggest that the hinterland part of the Mexican Orogen is represented by sedimentary rocks of Arperos Basin and synorogenic turbidites. These rocks were folded and thrusted during the late Cretaceous when the Arperos basin closed. Their complex deformation can be explained by a progressive deformation accommodated during the development of orogen.
How to cite: Díaz, A. and Vásquez, A.: Complex deformation recorded in the western sector of the Cretaceous Arperos Basin. Late Cretaceous-Paleocene Mexican Orogen, central Mexico., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8831, https://doi.org/10.5194/egusphere-egu26-8831, 2026.
Although continental lithosphere can enter the subduction zone, how buoyant continental crust sinks below 100 km of depth and is then exhumed remains hard to understand. Exhumation of continental lithosphere is testified by the occurrence at the surface of high pressure rocks in several orogenic belts. Despite the existence of different models describing the exhumation of high pressure rocks, they consider only tectonic settings where both upper and lower plates are either continental or oceanic.
In the Oman mountains, high pressure continental rocks crop out in the Saih Hatat Window surrounded by obducted oceanic lithosphere. Here, oceanic obduction occurred during subduction of continental lithosphere, setting a peculiar framework where a denser lithosphere overrides the subducting lighter continental crust.
In this study we used 2D thermo-mechanical geodynamic numerical modelling to investigate the mechanisms that drive exhumation of the continental lithosphere beneath obducted oceanic lithosphere. We validate the geodynamic numerical models with the pressure-temperature-time estimates from the Oman Mountains natural samples and we compare the final architecture reproduced by our models with the regional tomographic models available from the Oman region, which allow to infer the presence of a NE-dipping steep slab beneath the Oman mountains.
Our models reproduce the subduction of continental rocks up to ~150 km, with crustal material returning up to the surface guided by the steepening of the slab dip and by slab roll back. The result is a stack of continental material surrounded by obducted oceanic lithosphere. Concluding, exhumation of continental lithosphere is accompanied by a slight heating at the bottom of the exhumed continental crust, triggered by asthenosphere flow after the slab dip increased.
How to cite: Caso, F., Sternai, P., Petroccia, A., Pilia, S., and Giuntoli, F.: Simulating the role of slab steepening and roll back in exhuming subducted continental lithosphere using 2D geodynamic numerical modelling (Saih Hatat Window, Oman Mountains), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6670, https://doi.org/10.5194/egusphere-egu26-6670, 2026.
Subduction initiation remains one of the critical unsolved problems of modern plate Tectonics (e.g., Stern, 2004; Stern and Gerya, 2018). At passive margins, oceanic lithosphere is old and negatively buoyant, but also thick and very strong. Thus, spontaneous foundering of this lithosphere at these locations requires forces higher than the ones driving tectonic plates in nature (slab-pull and ridge-push, e.g., Cloething et al., 1982, 1989; Mueller and Phillips, 1991). Therefore, different authors have proposed different conceptual processes of induced subduction initiation, in which pre-existent, inherited (mechanical and/or chemical) lithospheric weaknesses, including older subduction zones, might trigger the formation of a new one.
One of these processes is the so-called subduction initiation by transference (Stern, 2004), in which it is argued that a crustal buoyant obstacle (e.g., a continental terrane) could arrive at a subduction zone, causing it to shut down, and triggering a new subduction at the back-end of such a terrane, i.e., causing the subduction zone to be transferred there from its original (frontal) position.
In the present paper, we present new preliminary results of 3D numerical models (LaMEM code of Kaus, 2016) to understand the (geo)dynamic viability of subduction initiation by transference, and to gain new insights on the main parameters governing the possibility of its occurrence in nature. We use buoyancy driven models of continental terrane accretion against the overriding plate (OP) of a subduction zone, to find out if subduction transference is “caused” by the scrapping-off of the continental crustal portion of the terrane against the OP (e.g., Tetreault and Buiter, 2012), or if true front-to-back transference of subduction, critically implying rupture of the lithosphere at the back margin of the terrane, is really possible. Our still preliminary results seemingly suggest that the scrapping-off scenario is more viable, while the true transference one might depend on two key factors: 1) the trench-parallel width of the continental terrane relatively to the width of the oceanic subducting slab; and 2) the existence vs. absence of a weakened (faulted and serpentinized?) zone in the back-end margin of the accreting terrane.
Acknowledgements:
This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2023, LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020) and https://doi.org /10.54499/UID/PRR/50019/2025
How to cite: Lourenço, Â., Rosas, F. M., Duarte, J. C., and Rodrigues, N.: 3D Numerical modelling of induced subduction initiation by transference, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1278, https://doi.org/10.5194/egusphere-egu26-1278, 2026.
New subduction zones may initiate either in intra-oceanic setting or in the vicinity of rifted margins. At both sites, the requirement of subduction initiation is the efficient strain localization and sufficient in-situ external forcing to overcome the shear and bending resistance of the lithosphere. While the age-dependent negative buoyancy of the oceanic lithosphere is the greatest at the ocean-continent boundary and therefore, rifted margin should be more favorable sites for subduction initiation, the increasing mechanical coupling between the oceanic and continental domains and the coeval strengthening of the rifted margin have been suggested to limit subduction initiation along the ocean-continent boundary to the first few tens of million years after continental break-up. This, in particular, suggests that the duration of the transitional interval between rifting and plate convergence plays a crucial role in determining the location of subduction initiation.
In this study, we investigated compression-induced subduction initiation in young and narrow oceanic basins, where the thermo-tectonic age of the rifted margin is low and thus, it is weak and more prone to strain localization. By using the I3ELVIS-FDSPM numerical code, we tested the duration of the plate motion reversal from rifting to convergence, and evaluated the role of the associated structural and thermo-rheological inheritance in controlling the location of subduction initiation. The models tracked the dynamic changes in the lithospheric strength and strain patterns, while the applied two-way coupling between the high-resolution 3D geodynamical and surface processes models allowed for the joint analysis of the crustal tectonics, thermal structure, melting, topography evolution, and the erosion-sedimentation processes.
The results show that abrupt plate motion changes lead to ridge-inversion and subsequent intra-oceanic subduction initiation along the extinct spreading ridge, controlled by the inherited thermal- and melt-induced weakening effects of the shallow lithosphere-asthenosphere boundary. In contrast, when the transition between rifting and plate convergence exceeds a few million years, strain localization is linked to inherited lithospheric-scale weak zones, such as pre-existing suture zones underneath the continental margin, while the inherited thermal structure no longer exerts a substantial influence on the location of subduction initiation. These modeling inferences align with observations from natural subduction initiation sites, such as the Algerian margin and the eastern Japan Sea.
How to cite: Oravecz, É., Gerya, T., and Balázs, A.: Structural versus thermal inheritance controlling the location of compression-induced subduction initiation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9854, https://doi.org/10.5194/egusphere-egu26-9854, 2026.
On Earth, the long-term development of plate tectonics is often explained by the Wilson cycle, which spans hundreds of millions of years and involves the repeated opening and closing of ocean basins through lithosphere recycling and continental movement. These cycles feature alternating phases of supercontinent assembly and breakup. Their dynamics are fundamentally connected to mantle convection and to subduction. Subduction networks are essential for both supercontinent breakup and rapid plate movements. We suggest that the development and longevity of Earth's global subduction networks are affected by water-rich sediments resulting from continental erosion. These sediments can accumulate at convergent margins and reduce their frictional strength, promoting long-lasting subduction and sustained slab rollback. As individual subduction systems expand and link together, they can create a global subduction network that increases plate mobility and promotes large-scale plate reorganizations, ultimately supporting a return to continental assembly. To test this hypothesis, we use the ASPECT numerical code, combined with the Geodynamic World Builder to run a suite of three-dimensional global geodynamic models by prescribing an initial plate configuration using GPlately. We examine two end-member Earth-like scenarios: (i) models without initial prescribed subduction zones and ridges, where plume-driven regional subduction evolves into a global subduction network, and (ii) a setup with pre-defined plate boundaries and subduction zones corresponding to the GPlates-derived configuration at 1 Ga, demonstrating that sustained subduction can be maintained when friction is locally reduced. On Earth, such frictional weakening may vary over time in response to climatic conditions, such as Snowball Earth episodes, which enhance erosion, sediment flux at plate boundaries. Our results highlight the fundamental role of surface water and sediment supply in regulating the longevity of subduction systems and, ultimately, the emergence and maintenance of large-scale plate tectonics.
How to cite: Pons, M., V. Sobolev, S., Jain, C., and Fraters, M.: Formation of global subduction networks and large-scale convection facilitated by climate-induced weakening of convergent plate boundaries. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11861, https://doi.org/10.5194/egusphere-egu26-11861, 2026.
The Carboniferous-Permian evolution of the Variscan belt, marking the transition from continental collision to post-collisional extension, is particularly difficult to investigate because the post-collisional metamorphism overprints the previous history of subduction and collision. In fact, the collision is followed by widespread high- to ultra-high-temperature metamorphism in the early Permian (e.g., Schuster and Stüwe, 2008), interpreted as the expression of a large-scale transtensional regime linked to active shear zones across Pangea (Muttoni et al., 2003). In addition, uncertainties in Pressure-Temperature (PT) estimates and metamorphic geochronology complicate the discrimination of successive events.
In this study, we focus our analysis on the Valpelline area where the Variscan post-collisional evolution is well preserved. The rocks in the area offer the possibility of integrating high-precision age determinations with robust PT constraints, allowing the discrimination of two closely spaced metamorphic events (M1 and M2) separated by only a few Myr (Filippi et al., 2025). We compare these PT constraints with predictions obtained from 2D thermo-mechanical numerical models performed with the FALCON code (Regorda et al., 2023), to investigate the evolution of convergent–divergent tectonic systems, with particular emphasis on post-collisional processes. In particular, we developed three models characterised by different durations of an intermediate gravitational phase before the beginning of the extension.
Our simulations indicate that the onset of post-collisional divergence promotes the reactivation of structures inherited from the preceding convergence phase. In fact, extension in the upper crust is accommodated by normal faulting associated with the reactivation of pre-existing compressional structures. This evolution leads to the progressive thinning of the thickened continental crust, driven by asthenospheric upwelling beneath the slab. This process is enhanced by relatively high temperatures and reduced viscosities at the base of the subducting plate compared to that of the mantle wedge, which favour efficient strain localization. In addition, the agreement between model predictions and high-precision PT estimates and geochronological data indicates that the initiation of a divergent tectonic regime shortly after collision (within a maximum of 5 Myr) is required to explain the observed metamorphic evolution of the Valpelline rocks.
References
M. Filippi, F. Farina, M. Ovtcharova, F. Caso, M. Roda, C. B. Piloni, and M. Zucali. High-precision zircon geochronology constrains early permian exhumation of the deep adriatic crust in the western italian alps. Earth and Planetary Science Letters, 671:119689, 2025. doi:10.1016/j.epsl.2025.119689.
G. Muttoni, D. V. Kent, E. Garzanti, P. Brack, N. Abrahamsen, and M. Gaetani. Early permian pangea ‘b’ to late permian pangea ‘a’. Earth and Planetary Science Letters, 215(3):379–394, 2003. doi:10.1016/S0012-821X(03)00452-7.
A. Regorda, C. Thieulot, I. van Zelst, Z. Erdős, J. Maia, and S. Buiter. Rifting venus: Insights from numerical modeling. Journal of Geophysical Research: Planets, 128(3): e2022JE007588, 2023. doi:10.1029/2022JE007588.
R. Schuster and K. Stüwe. Permian metamorphic event in the Alps. Geology, 36:603–606, 2008. doi:10.1130/G24703A.1.
How to cite: Regorda, A., Filippi, M., Roda, M., Caso, F., Piloni, C. B., Farina, F., and Zucali, M.: 2D numerical models of the Variscan post-collisional evolution:example from the Valpelline Series (western Alps), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4503, https://doi.org/10.5194/egusphere-egu26-4503, 2026.
Collisional systems mark the end of a Wilson cycle, where after a period of oceanic subduction two continental plates collide. In response to intense crustal deformation, high topographic features are developed and orogens are formed. Orogens can display multiple architectonic styles, shifting between compressional/extensional episodes and transitioning from wedges to plateaus. The large-scale processes that control different orogenic growth modes are greatly influenced by lower crustal rheology, which can enable and promote switches in tectonic modes and allow orogenic plateaus to be formed.
In the present study we use geodynamic numerical modelling to investigate the control of lower crustal rheology in different orogenic growth processes, using the geodynamic code LaMEM (Kaus et al., 2016) to perform high-resolution (512 x 128 x 256) 3D buoyancy-driven models. For realistic density variations, we couple LaMEM with the thermodynamic code MAGEMin (Riel et al., 2022). Using this modelling setup, we specifically assess the role of different continental crust rheological configurations in determining the dynamic feedbacks that control orogenic growth and architecture (for ca. 50 Myr).
Here, we obtain the P-T-t paths in our models and compare them to those recorded in different natural orogenic settings. We attempt to establish a correlation between different orogenic growth modes and natural analogues that record similar burial and exhumation patterns. In this sense, we seek to constrain which geodynamic scenarios can better produce the P-T-t paths observed in natural orogenic settings.
References:
Kaus, B., et al., 2016. Forward and inverse modelling of lithospheric deformation on geological timescales. In: Proceedings of the NIC Symposium, (John von Neumann Institute for Computing (NIC), NIC Series vol. 48.
Riel, N., Kaus, B. J. P., Green, E. C. R., & Berlie, N. (2022). MAGEMin, an Efficient Gibbs Energy Minimizer: Application to Igneous Systems. Geochemistry, Geophysics, Geosystems, 23(7). https://doi.org/10.1029/2022GC010427
This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025
How to cite: Rodrigues, N., Riel, N., Rosas, F., Gerbault, M., Almeida, J., Gomes, A., and Duarte, J.: Influence of lower crustal rheology on orogenic growth modes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12412, https://doi.org/10.5194/egusphere-egu26-12412, 2026.
The Vahic Unit represents a critical tectonic element of the Western Carpathians, proposed as the oceanic suture zone that separates the Central Western Carpathian (CWC) block from the North Europeanplatform. Interpreted as the eastern continuation of the South Penninic (Alpine Tethys) oceanic domain, the Vahicum is primarily represented by the Belice Unit, which preserves a sedimentary record of the Vahic Ocean's evolution. This sequence includes Upper Jurassic radiolarites and Lower Cretaceous pelagic limestones, conformably overlain by Upper Cretaceous flysch.
Structurally, the Vahicum occupies the lowermost position in the orogenic wedge, situated beneath the Tatric crystalline basement. It is believed that the closure of the Vahic Ocean occurred during the Late Cretaceous (Late Turonian to Maastrichtian), marked by the subduction of oceanic and attenuated continental crust beneath the prograding CWC overriding plate. This process was supposed to result in high-pressure/low-temperature (HP/LT) metamorphism, typical of Penninic-type subduction zones, although these signals are often fragmented due to subsequent tectonic reworking, and in larger scale non existent.
In this study, six sandstone samples were collected from the Vahic Unit to investigate, through a detrital rutile geochronological campaign, its tectonic and sedimentological evolution. From each sample, approximately 200 rutile grains were extracted, with roughly half selected for detailed age and trace element analysis.
These findings are compared with previously acquired data from the Magura and Silesia supernits to constrain regional provenance better. In the Magura transect, prominent age peaks align with Variscan (c. 400–280 Ma) and Alpine (c. 160–90 Ma) events, including dominant Alpine maxima at 137–126 Ma and 115–105 Ma. In contrast, the Silesian samples consistently exhibit a prominent Variscan peak, with Alpine tectonic signatures (e.g., a dominant peak at 95 Ma) appearing only in the young, Oligocene deposits. Integrating the rutile age data from the Vahic Superunit into this regional framework allows for a more comprehensive reconstruction of the evolving paleodrainage and tectonic maturation of the Carpathian orogenic wedge.
How to cite: de Doliwa Zieliński, L., Potočný, T., Kośmińska, K., and Majka, J.: Detrital rutile geochronology of the Vahic Superunit helps to understand the closure of the Alpine Tethys in the Western Carpathians, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13859, https://doi.org/10.5194/egusphere-egu26-13859, 2026.
Arc kinematics is mostly oblique, such that deformation at different parts of their orogenic wedges responds to specific combinations of rotational and non-rotational strains. To inquire about the influence of obliquity evolution in orogenesis, we propose a kinematic model that helps to understand bulk strain distribution along arcuate wedges, which is essential to interpret their structural patterns. Our model set-up considers one branch of a progressive arc, where curvature increases with arc evolution, in this case from an initial straight configuration. Displacement vectors are parallel along the arc and normal to the arc chord. This configuration imposes convergence with increasing obliquity towards the arc tips and along time at any point along the arc but its apex, where it is always orthogonal. We have applied the unsteady vorticity analytical model of Alonso-Henar et al. (2025) to reproduce bulk strain kinematics along an orogenic wedge developed in such a progressive arc. We consider the deformation zone boundary is defined by a vertical backstop, which results in monoclinic transpressional kinematics. We define ten sectors along the arc branch from the apex to the tip. Each sector is defined by its final obliquity, which ranges from α = 90º at the apex to α = 0º at the tip, with 10º variations. Sectional kinematic vorticity (Wk) increases accordingly from 0 to 1, and also along time. Maximum shortening normal to the backstop is 0.8 at the apex, and progressively decreases toward the tip, where it is 0.4. Arc evolution is divided into eight stages, each one defined by 0.1 increase of the frontal shortening.
Our model reproduces similar results (strain accumulation along time and along the arc) to those obtained through more classical steady models. However, some of our results are specific to unsteady vorticity evolution, thus inherent to progressive arcs. For instance, there is not a unique relationship between some strain parameters (e.g., the orientation of the maximum horizontal stretching axis) and the obliquity of one arc segment, because the path followed by the orogenic wedge to attain such obliquity is also relevant. Unexpectedly, our model also suggests that passive lines rotate faster than strain ellipsoids. Therefore, at any sector along the arc and any evolutionary stage, the angle that such lines make with the displacement vector is larger than the angle that the main structural traces make with the arc chord. This result poses questions on the interpretations of the so-called orocline test.
References:
Alonso-Henar, J., Fernández, C., Díaz-Azpiroz, M., Druguet, E. (2025) Unsteady transpression: How progressive variations in kinematic vorticity influence finite strain in shear zone evolution. Journal of Structural Geology 198, 105462.
How to cite: Díaz-Azpiroz, M., Alonso-Henar, J., Fernández, C., Balanyá, J. C., Jiménez-Bonilla, A., and Expósito, I.: What unsteady transpression models tell us about orogenic wedge kinematics of progressive arcs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7866, https://doi.org/10.5194/egusphere-egu26-7866, 2026.
The Saharan metacraton was assembled during pre-Neoproterozoic to Neoproterozoic times and was strongly remobilised during the Pan African orogeny. The Ouaddaï massif in eastern Chad represents the core of the Saharan metacraton, yet its geological history remains poorly documented. In this study, we combine of field observations, petrological analysis of metamorphic rocks, and geochemical and geochronological constraints to reconstruct the tectono-metamorphic evolution of the Ouaddaï massif. The study area is dominated by collision-related plutonic rocks and migmatitic gneisses, within which inliers of older basement occur. Geochemical data indicate a transition from active-margin to collisional magmatism, with a compositional evolution from diorite to granite. This suite is cross-cut by syenogranites and alkaline granites with shoshonitic affinities, interpreted as post-collisional granitoids derived from tonalitic rocks to sedimentary protoliths. Geochronological data (U-Pb on zircon and monazite) point to a ca. 1000 Ma age for orthogneisses inliers. Granitoids of the Ouaddaï massif record emplacement ages from 620 to 590 Ma, coeval with high-temperature metamorphism characterized by peak pressure-temperature conditions of 1.2 GPa and 850°C (mafic granulite) and around 0.8 GPa and 700°C (sillimanite-garnet bearing migmatites). Integrating our new results with regional data, we discuss the existence and geodynamic evolution of the Saharan Metacraton. Our findings emphasize the significance of the Saharan Metacraton as a key region for understanding the extensive reworking of cratonic lithosphere during both a Tonian magmatic phase prior and the assembly of Gondwana.
How to cite: Plunder, A., Blein, O., Isseini, M., Ousman Al-Gadam, I., Chevillard, M., Djedouboum, E., Lach, P., Lahfid, A., Melleton, J., Rouzeau, O., and Vic, G.: A window on the amalgamation of Western Gondwana: Geological history of the Ouaddaï massif (E. Chad), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5345, https://doi.org/10.5194/egusphere-egu26-5345, 2026.
One efficient driver for atmospheric CO2 removal over 10-100 Ma timescales is silicate-rich rock weathering, which is notably favored in the context of arc magmatism (Gernon et al., 2021). The modeling of the past evolution of atmospheric CO2 therefore requires to finely reconstruct the evolution of past subduction zones, which is challenging due to the permanent recycling of oceanic lithosphere. One difficulty notably resides in the reconstruction of intra-oceanic arcs, which leave almost no direct imprints in the geological record, although they could significantly contribute to the atmospheric CO2 removal through silicate weathering, especially in the tropics (Gaillardet et al., 2011).
We propose to test how the variability of intra-oceanic arcs can affect the amount of CO2 removed from the atmosphere through supercontinent cycles. To do so, we use 3D numerical models of whole-mantle convection self-generating Earth-like plate tectonics in order to quantify the temporal evolution of the number and length of intra-oceanic arcs, in a fully-dynamic context, independent of any plate reconstructions. We use the automatic plate tessellation algorithm MAPT3 based on the open-source library Topology ToolKit (Janin et al., 2025) to detect intra-oceanic subduction zones. We show that the total length of intra-oceanic arcs varies significantly depending on the continental configuration in the models. We then test the sensitivity of atmospheric CO2 absorption level through silicate weathering to mantle convective parameters, to the latitudinal distribution of the intra-oceanic arcs, their width and fraction above sea-level, and the potential effect of True Polar Wander. We show that in a fully-dynamic model, it is possible to reach the amount of extra-weathering required to possibly explain the atmospheric CO2 and temperature drops observed, especially during periods of continental aggregation. Nevertheless, the amount of intra-oceanic subduction zones in the geodynamic models varies over longer timescales than in the plate reconstruction, and cannot explain alone, rapid cooling events, such as during the Hirnantian (Marcilly et al., 2022).
How to cite: Arnould, M., Janin, A., and Merdith, A.: How does ocean arcs’ silicate weathering affect the atmospheric CO2 budget through supercontinent cycles?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16797, https://doi.org/10.5194/egusphere-egu26-16797, 2026.
