Transform faults represent one of three classes of plate boundaries and show strike-slip tectonism where one plate moves past another and are considered to be conservative plate margins where crust is neither formed nor destructed. The other two types of plate boundaries are divergent and hence extensional plate boundaries where new crust is formed (mid-ocean ridges, MOR) and convergent or destructive plate margins (subduction zones) where crust is recycled back into Earth’s interior. Researcher focused their attention on MOR and subduction zones, but transform faults got rather little attention over the last decades, especially in ocean basins where they outline the direction of plate motion supporting the Wilson cycle.
Oceanic transform faults (OTF) are gigantic features – up to 900 km long – and without oceans masking the seafloor, they would be among the most prominent features on Earth, offsetting mid-ocean ridges, forming tens of kilometres wide and up to 7 km deep valleys on the ocean floor. Yet, they are defined as simple strike-slip faults, but how can a transcurrent plate boundary, generating magnitude 7+ strike-slip earthquakes, promote extension forming the deep and wide valleys? Interestingly, for over half a century, researchers failed to appreciate that OTF are always deeper than adjacent oceanic features of an older age, challenging a major concept of plate tectonics. Thus, instead of showing the predicted age-dependent subsidence, the seafloor shallows at ridge-transform intersections (RTI). It therefore might be reasonable to question if they are indeed conservative plate boundaries.
We will provide observational evidence suggesting that OTFs are highly dynamic features, showing both features of accretion and the occurrence of tensional tectonics, indicating that we have to revise our understanding of how OTFs operate. We will provide constraints from a global compilation of bathymetric data, show predictions from numerical simulations and show observational evidence from micro-seismicity at slowly slipping OTFs in the Atlantic Ocean. Micro-earthquakes outline a diffuse activity over a broad area, cutting across the inside corner domain between the spreading centre and the transform fault before focusing along the trace of the fault. In the vicinity of the ridge-transform intersection, focal mechanisms reveal transform-normal extensional tectonics instead of supporting transcurrent motion, while strike-slip tectonics occurs only away from adjacent spreading segments. These observations support a scenario based on numerical simulations showing that at RTIs the right-angular plate boundary at the seafloor develops into an oblique shear zone at depth, causing crustal thinning and consequently forming transform valleys. However, before turning into a tectonically inactive fracture zone magmatic activity at RTIs buries transform valleys, suggesting that OTFs and fracture zones differ structurally from each other. Therefore, tectonic processes shaping transforms are divers, arguing for a revision of the concept of conservative plate boundaries to account for their morphology, strong lateral differences in seismic behaviour, and crustal structure.
How to cite: Grevemeyer, I., Ruepke, L., and Chen, M.: Oceanic transform faults and fracture zones “in modern dress”, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2798, https://doi.org/10.5194/egusphere-egu25-2798, 2025.
Orogenic Bridge Theory proposes that orogens striking highly oblique to orthogonal to active rifts hinder rifting and breakup. The highly oblique character and low angle geometry of the thrust systems and shear zones in these orogens make them unable to efficiently accommodate crustal thinning and transform faulting which are necessary for breakup. Thus, upon intersecting such orogens, rifts step, and/or locally reorient, and/or bypass the oblique orogen. While breakup and seafloor spreading occur in adjacent areas, the orogenically thickened crust at oblique orogens continues to stretch and thin until breakup occurs there also or until rifting stops. Unlike historical theoretical “land bridges”, orogenic bridges are dynamic features and they deform together with adjacent oceanic and anorogenic continental crust.
Orogenic bridges where full breakup has not yet occurred are continuous domains of orogenically thickened continental crust, which were (hyper) extended during rifting. They may be separated from adjacent oceanic crustal domains by major transform faults, which form along inherited rift-orthogonal orogenic thrusts. Examples of continuous orogenic bridges are the late Paleoproterozoic Laxfordian–Ammassalik–Nagssugtoqidian–Torngat Orogen, which gave rise to the Greenland–Iceland–Faroe Ridge and Davis Strait, and possibly to the late Neoproterozoic Timanian Orogen in the Fram Strait.
Should sufficient extension occur, orogenic bridges eventually rupture. Ruptured orogenic bridges generally form hyperextended salients of continental crust offshore and coincide with major steps and/or reorientation of the main rift axis. Examples of ruptured orogenic bridges include the Permian Cape Fold Belt in South Africa and the Falkland Plateau and Maurice Ewing Bank, the late Neoproterozoic East African–Antarctica Orogen in southeastern Africa and Antarctica, and the latest Neoproterozoic–early Paleozoic Delamerian–Ross Orogen in eastern Australia and Antarctica.
Orogenic bridges have significant implications for several branches of marine Earth science, including but not limited to the biogeodynamics, plate tectonics, structural geology, and natural resource distribution and geohazards. For example, orogenic bridges provide prolonged topographical links between continents during supercontinent breakup, thus allowing continued exchanges of terrestrial fauna and flora between rifted continents, e.g., prolonged faunal exchanges between Greenland and Europe and western Africa and Brazil. Conversely, they form topographical barriers, which prevent biological exchanges of marine fauna and flora between oceanic domains across orogenic bridges, e.g., discrete early Paleozoic trilobite assemblages in Svalbard and Scandinavia.
Orogenic bridges explain the occurrence of anomalously thick crust offshore as remnants of oblique (hyper) extended orogenic crust and localize the formation of major transform faults. In addition, Ridge–Ridge-Ridge triple junctions localize at the intersection of two orogenic bridges. Thus, orogenic bridges have a considerable impact on plate tectonics and paleogeographic reconstructions.
Orogenic bridges extend the continent–ocean boundary farther offshore at various margins worldwide. Thus, they have significant implications for offshore mineral deposits, hydrocarbon exploration, and the Law of the Sea. Furthermore, the mapping of orogenic structures connected with orogenic bridges will further aid geohazard risk assessment, and exploration for white and orange hydrogen and geothermal resources along fault zones.
How to cite: Koehl, J.-B. P., Fouger, G. R., and Peace, A. L.: Introduction to Orogenic Bridge Theory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2604, https://doi.org/10.5194/egusphere-egu25-2604, 2025.
Continental rifting, as the initial and critical phase of the Wilson Cycle, has been extensively observed and studied using 2D and 3D analogue and numerical models. These studies have effectively reproduced the characteristics of wide and narrow, symmetric and asymmetric rift structures, through horizontal multi-layered models with variable strength parameters. One prominent natural case is the South China Sea (SCS), which began its rifting and subsequent seafloor spreading at ~32 Ma. The SCS then underwent a shift in its spreading direction from a north-south to a northwest-southeast orientation at ~23 Ma. Despite resembling a typical wide rift, the SCS poses specific challenges in explaining its complex synchronous basins with detachments , non-flat Moho surface, inland hyper-thinned continental crust extending over 500 km from the continent-ocean boundary (COB), and the wide asymmetric geometry with narrow OCT (ocean continent transition) observed in the Southwest Subbasin (SWSB). Former 1D and 2D simulations have shown that wide continental rift can be produced either by rift migration, i.e. sequential basins associated with non-flat Moho, or in post orogenic context, i.e. synchronous basins form over a flat Moho due to the weakness of the lower crust. They equally fail at capturing the synchronous basins and non-flat Moho of the SCS. Considering the SCS's pre-rift fore-arc environment with thrusts featuring strong and weak crust due to tectonic events such as the Pacific subduction and the Proto South China Sea (PSCS) plate subduction, we applied 2D numerical models to replicate these features. Our models incorporate a dipping layered continental crust structure composed of strong and weak layers with varying dipping angles and thickness of lower crust, alongside temperature variations at the lithosphere-asthenosphere boundary (T_LAB). This setup successfully reproduced the margin style observed in the SWSB. Our models show four distinct rifting styles: pure single spreading center, single spreading center with hyper-thinned continental crust, single spreading center with exhumed mantle, and double spreading centers style, and three styles of Moho surface, including flat Moho, hummocky Moho and wavy Moho. Model with synchronous basins with detachments, single spreading center with inland hyper-thinned crust/exhumed mantle and hummocky Moho style fits well with observations in SWSB. This suggests that by incorporating structural, compositional and thermal variations from surrounding tectonic events, new insights into the diverse rifting features seen in SCS and a robust framework to understand wide asymmetric margins across complex geologic settings can be expected.
How to cite: Zhou, F., Le Pourhiet, L., Pubellier, M., and Delescluse, M.: Impact of structural inheritance and mantle potential temperature on wide asymmetric rifts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4287, https://doi.org/10.5194/egusphere-egu25-4287, 2025.
The Wilson Cycle, a cornerstone of plate tectonic theory, describes the cyclical evolution of ocean basins, from their formation through rifting and spreading, to their eventual closure via subduction and continental collision. While this model has significantly advanced our understanding of tectonic processes along plate boundaries, it remains limited in addressing the dynamics of intraplate deformation. This study revisits the Wilson Cycle by examining the interplay between inherited geological structures, intraplate deformation, and the partitioning of tectonic activity. Using low-temperature thermochronology, specifically apatite fission-track analysis, we investigate the timing, magnitude, and controls of deformation across the (Pre)Cambrian terranes of Southeast Brazil, Southeast Colombia, and Peninsular India, regions traditionally considered stable since their assembly within Gondwana.
In Southeast Brazil, the study integrates results from three key areas: the Brasília Orogen, the São Francisco Craton (SFC), and the Araçuaí Orogen. The findings reveal three major phases of exhumation: (i) the Paleozoic, linked to reactivations in the Brasília Orogen and SFC; (ii) the Early Cretaceous to Cenomanian, in the Araçuaí Orogen; and (iii) the Late Cretaceous to Paleocene, with widespread reactivation across all domains. These results highlight contrasting tectonic behaviors: the SFC concentrated deformation within narrow weak zones, the Brasília Orogen displayed lithospheric rigidity and stability, while the Araçuaí Orogen experienced extensive reactivation, particularly during (post-)rift phases associated with the opening of the South Atlantic.
In the Amazonian Craton in Southeast Colombia, AFT data reveal a rapid basement cooling event during the early Cretaceous, driven by extensional tectonics associated with a back-arc setting. This extensional regime facilitated basement uplift, erosion, and exhumation, followed by a shift to contractional Andean tectonics in the late Cretaceous, which slowed cooling rates.
In Peninsular India, a comparison of the eastern and western passive margins underscores the role of cratonic inheritance in tectonic reactivation. Along the eastern margin, the Dharwar Craton underwent significant exhumation during the Late Jurassic to Early Cretaceous, driven by Gondwana’s breakup, whereas the western margin, with its thicker lithosphere, exhibited subdued deformation. Eastward tilting of the Indian plate during the Cenozoic, combined with Bengal Fan sedimentation, further influenced fault reactivation and intraplate exhumation along the eastern margin.
This study underscores that neither cratons nor orogens conform to a single tectonic behavior, revealing significant variability in their responses to geological processes. While some cratons, such as the Amazon and Dharwar cratons, demonstrate unexpected tectonic activity and exhumation driven by extensional tectonics, others, like the São Francisco Craton, exhibit localized reactivations along weak zones but remain largely stable. Similarly, orogens can follow distinct evolutionary paths: some, like the Brasília Orogen, become resistant to further deformation, effectively stagnating the Wilson Cycle, while others, such as the Araçuaí Orogen, experience reactivation, even far from ancient suture zones, enabling renewed tectonic activity. These examples challenge the traditional Wilson Cycle, demonstrating that intraplate deformation, influenced by lithospheric inheritance, plays a critical role in sustaining or altering the cycle. By integrating these insights, this study contributes to an updated framework for the Wilson Cycle that incorporates the complexities of intraplate deformation.
How to cite: Fonseca, A. C. and De Grave, J.: Intraplate deformation and the Wilson cycle: Insights from the thermo-tectonic basement history from several Gondwana terranes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2015, https://doi.org/10.5194/egusphere-egu25-2015, 2025.
Rift-inversion orogens such as the High Atlas, Pyrenees, and Greater Caucasus exhibit strain localization primarily due to contractional reactivation of lithospheric weaknesses inherited from continental rifting, rather than from long-lived subduction leading to continental collision along a major plate boundary. These orogens thus experience a transition from extension to compression distinct from their plate-boundary counterparts that impacts georesource development and seismic hazard. It is widely recognized that the initial conditions prior to rift inversion strongly control the structural and thermal evolution of such orogens, yet it is difficult to derive initial conditions from available structural and thermochronologic data.
Here, we present geodynamic numerical modeling designed to capture the structural and thermal evolution of rift-inversion orogens. We complement our study with new Python routines to calculate synthetic low-temperature thermochronometric ages from the model results. This enables directly comparing our numerical results with thermochronometric data collected in natural rift-inversion orogens. Our initial results (Vasey et al., 2024) indicate three end-member structural styles in model orogens: 1) asymmetric underthrusting reminiscent of the Pyrenees and Greater Caucasus, 2) distributed thickening reminiscent of the High Atlas, and 3) polarity flip in which the vergence of the orogen varies over time. Synthetic apatite (U-Th)/He and fission track thermochronometric ages record regions of focused exhumation on the flanks of the initial rifts and in the hanging walls of major thrust faults in the final orogens, mirroring similar relationships between major structures and areas of greater exhumation observed in natural orogens.
These results demonstrate how geodynamic modeling can extend the ability of structural data and low-temperature thermochronology to help distinguish between competing models of pre-orogenic initial conditions.
Reference Cited:
Vasey, D.A., Naliboff, J.B., Cowgill, E., Brune, S., Glerum, A., and Zwaan, F., 2024, Impact of rift history on the structural style of intracontinental rift-inversion orogens. Geology, v. 52, no. 6, 429-434, doi:10.1130/G51489.1
How to cite: Vasey, D. A., Naliboff, J. B., Scully, P. M., Brune, S., Glerum, A., and Zwaan, F.: Modeling structural styles and thermochronometric ages in rift-inversion orogens to test pre-orogenic conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4863, https://doi.org/10.5194/egusphere-egu25-4863, 2025.
A thorough understanding of structural inversion and the positive or negative impacts of inversion tectonics on hydrocarbon trap development is crucial in geological investigations and petroleum exploration. To characterize the occurrence of inversion tectonics and its controlling effects on the spatial distribution of oil and gas fields located in the southern Dezful Embayment (SW Iran), this study describes the structural characteristics and deformation history of the Rag-e-Sefid oil/gas field and its surrounding areas through the structural and tectono-sedimentary analyses. Based on the results obtained from the integration of aeromagnetic, seismic, and well data, the strike-slip basement faults with the Pan-African or Arabian trend (N-S to NE-SW) and the Najd trend (NW-SE) modified the evolutionary history of the sedimentary basin in the southern Dezful Embayment. The geological interpretation of seismic profiles and the investigation of the geometry and thickness changes of the sedimentary layers across the growth structures indicate that the minimum time of the strike-slip faults formation with the Najd and Pan-African trends is related to the Neoproterozoic-Cambrian rifting of the northern Gondwana margin. These faults experienced activity at least during seven different extensional and compressional deformation events that include Cambrian rifting, Hercynian compressional deformation in the Late Devonian-Carboniferous, Permo-Early Triassic rifting, and Zagros orogeny cycle in the Late Cretaceous and Cenozoic. Three-phase inversion tectonics along the strike-slip basement faults occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries. Inversion affected hydrocarbon trap development at the Late Cretaceous and controlled the final geometry and distribution of the oil and gas fields in the southern Dezful Embayment. Considering the hydrocarbon migration from the Miocene to the present day and the strong sealing of the Gachsaran Formation (Early-Middle Miocene) in the southern Dezful Embayment, the inversion tectonics event has a positive impact on hydrocarbon trap development. Also, the activity of the segmented strike-slip basement faults with the Pan Africa and Najd trends has an important effect on hydrocarbon migration and charging. These faults control the channel of hydrocarbon migration and the horizontal and vertical distribution of oil and gas in the region. The results of this study could add data to worldwide examples of the positive impact of tectonic inversion on hydrocarbon accumulation in the foreland of a collisional orogen.
Keywords: Inversion tectonics; Strike-slip fault; Tectono-sedimentary analysis; Hydrocarbon trap; SW Iran
How to cite: Tajmir Riahi, Z. and Soleimany, B.: Tectonic inversion of strike-slip fault system and its effects on hydrocarbon trap development in the southern Dezful Embayment, SW Iran, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13999, https://doi.org/10.5194/egusphere-egu25-13999, 2025.
The seafloor between Newfoundland and Iberia is unusually devoid of fracture zones compared to other parts of the Atlantic Ocean. As oceanic fracture zones often spatially correlate with inherited lithospheric weaknesses onshore, their absence may be suggestive of margins with stronger, broader, and more homogeneous inherited lithospheric structures. Herein, the smooth fracture-free seafloor is attributed to the long-lived influence of the massive St. Lawrence Promontory, which a) formed during Paleozoic Iapetan rifting, b) subsequently controlled the spatial and temporal evolution of Appalachian orogenesis, and c) ultimately pre-determined the geometry of the Grand Banks continental shelf and the location of the Newfoundland-Azores Fracture Zone during Atlantic rifting and seafloor spreading. Further still, based on the spatial distribution of the adjacent Precambrian cratons and orogenic belts within ancestral Laurentia, the formation of the St. Lawrence Promontory itself is attributed herein to inheritance from earlier episodes of Paleoproterozoic orogenesis during the building of Laurentia and during the amalgamation of the Rodinian supercontinent, suggesting that the influence of lithospheric inheritance on subsequent tectonism may persist and be detectable for almost two billion years and through multiple Wilson cycles.
How to cite: Welford, J. K.: The potential impact of compounding tectonic inheritance since the Paleoproterozoic on seafloor morphology in the southern North Atlantic between Newfoundland and Iberia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2300, https://doi.org/10.5194/egusphere-egu25-2300, 2025.
Obduction causes overthrusting of dense oceanic rocks on top of lighter continental units at convergent margins. Despite many conceptual models addressing both its initiation and the counterintuitive significant horizontal displacements of large and heavy rafts of oceanic lithosphere, obduction is only partially understood and remains quite an enigmatic process. Uncertainty remains on the triggering mechanisms and the emplacement modes under mechanically unfavourable frameworks, with recent contributions stressing the role of far-field boundary conditions, such as the impact of bursts of “plate acceleration”. The processes governing convergent margin deformation and the structuring of an orogenic wedge in association with obduction and ophiolite emplacement also remain mostly unexplored. In that setting, complex orogenic architectures may form during the imbrication of mobile and deformable continental crust slivers underneath advancing, and possibly several kilometre-thick, ophiolitic successions.
The northeastern Oman Mountains allow studying one such orogenic wedge in the Jabal Akhdar Dome (JAD), an Arabian Plate related domain that is now exhumed to the surface from beneath the allochthonous and far-travelled Semail Ophiolite. At odds with the general view, recent and ongoing studies indicate that parts of the Arabian Plate therefrom experienced a complete cycle of subduction-exhumation broadly concurrent with the Semail Ophiolite obduction in the Late Cretaceous, thus recording high pressure-low temperature (HP-LT) blueschist facies conditions of ≥ 0.9 GPa (based on the presence of aragonite in carbonates) and ≃ 350 °C. Preservation of such a metamorphic signature in the relatively undeformed external portion of the Arabian Plate calls for a re-evaluation (i) of the regional picture framing HP-LT metamorphism formation in the absence of obvious links with long-lived subduction or major continental collision and (ii) of the mechanisms capable to exhume the HP-LT rocks and accrete them beneath the Semail ophiolitic sequence.
Our on-going structural, stratigraphic and metamorphic investigations within the JAD document a twofold history sequentially encompassing: 1) Cenomanian top-to-the NE imbrication and accretion under HP-LT conditions in the subduction channel of a SW-dipping Arabian Plate-directed subduction zone nucleating on transitional passive margin crust; 2) Late-Cretaceous top-to-the SW lower-grade shearing during SW-ward thrusting and imbrication of the Hawasina nappes and the obduction of the Semail Ophiolite. This would have been triggered by an embryonic NE-ward intraoceanic subduction close to the Semail spreading centre, which set in motion the ophiolite basal thrust that, through >400 km of SW-ward transport, overrode the by-then failed subduction zone of (1); 3) Finally, the current NE-ward Makran subduction zone initiated farther outboard in the Paleogene.
How to cite: Viola, G., Degl'Innocenti, S., Zuccari, C., Sanguettoli, T., Giuntoli, F., Callegari, I., and Vignaroli, G.: Orogenic wedge formation during obduction: insights and perspectives from the Oman Mountains , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2744, https://doi.org/10.5194/egusphere-egu25-2744, 2025.
The nature of the overriding plate plays a major role for subduction zone processes. In particular, the highly heterogeneous continental lithosphere modulates intra-plate tectonics and the surface evolution of our planet. However, the role of continental heterogeneity is relatively under-explored for the dynamics of subduction models. We investigate the influence of rheological and density variations across the overriding plate on the evolution of continental lithosphere and slab dynamics in the upper mantle. We focus on the effects of variations in continental plate margin and keel properties on deformation, topographic signals, and basin formation. Our results show that the thickness, extent, and strength of the continental plate margin and subcontinental keel play a crucial role for the morphology and topography of the overriding plate, as well as the retreat of the subducting slab. We show that this lateral heterogeneity can directly influence the coupling between the subducting and overriding plate and determine the partitioning of plate velocities across the overriding plate.
These findings suggest that back-arc extension and subsidence are not solely controlled by slab dynamics but are also influenced by continental plate margin and keel properties. Large extended back-arc regions, such as the Pannonian and Aegean basins, may result from fast slab rollback combined with a weak continental plate margin and a strong and extended continental keel. Narrow margins, like the Okinawa Trough in NE Japan, may indicate a comparatively stronger continental plate margin and weaker or smaller continental keel. Additionally, continental keel properties may affect the overall topography of the continental lithosphere, leading to uplift of the deformation front and the formation of intermontane basins.
How to cite: Grima, A. G. and Becker, T. W.: The role of continental heterogeneity on the evolution of continental plate margin topography at subduction zones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3143, https://doi.org/10.5194/egusphere-egu25-3143, 2025.
The westernmost Mediterranean basins formed in a supra-subduction system during the Miocene. We have found that since the late Miocene, the previously extending region has been deformed by contractional and strike slip fault systems due to the Iberia – Africa tectonic plates convergence, producing the reorganization of the main tectonic structures.
The westernmost Mediterranean realm is seismically active because it hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which plate convergence is absorbed by minor to moderate-size tectonic structures, each absorbing a comparatively small part of the deformation. However, the understanding of the crustal configuration and the evolution of this basin was limited due to the limited penetration and resolution of the images of the subsurface.
We collected and processed >3.000 km of a modern seismic dataset to characterized for the first time 1) the deep structure and the crustal domains of the Alboran Basin, 2) the sedimentary infill and as a consequence, the basin evolution, and 3) the main active faults of the basin. Based on these results, we were able to identify the main fault systems and quantify the total slip accommodated by those prominent tectonic structures of the area, late Miocene - early Pliocene in age.
Our results show that the estimated total slip accommodated by the main fault systems is similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on those faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin.
These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. We performed a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed.
How to cite: Gómez de la Peña, L., Ranero, C., Gràcia, E., Grevemeyer, I., Kopp, H., Booth-Rea, G., Azañón, J. M., Maesano, F., and Romano, F.: A revision of the Westernmost Mediterranean: its crustal configuration, tectono-sedimentary structure and implications for seismic and tsunamigenic potential, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9369, https://doi.org/10.5194/egusphere-egu25-9369, 2025.
Suture zones mark the final closure of oceanic domains through subduction and subsequent continental collision [1]. These zones are typically characterized by inherited crustal shear zones and the fossil subduction interface in the mantle lithosphere. The orientation of the suture reflects the preceding subduction polarity. While the presence of hydrated lithosphere in older sutures is somewhat contested, the upper plate peridotite portion of the lithosphere certainly involves significant hydration and metasomatism.
Reactivation of suture zones triggered by post-collisional extensional episodes can result in lithospheric thinning, rifting and associated magmatic activity. Large-scale suture reactivation linked to continental breakup is well-documented [2], whereas localized post-collisional extension is sometimes invoked in order to explain less voluminous magmatic events. An example of the latter is the enigmatic Late Cretaceous magmatism along Sava-Vardar suture Zone (e.g. Klepa, Ripanj, Jelica) which is recently argued to be the product of a transtensional regime imposed onto the suture that lead to opening of pull-apart basins alongside lithospheric thinning and emplacement of basaltic magma [3].
Here, we present our results of numerical 3D modelling of a transtensionally reactivated suture. To this end we use the petrological-thermo-mechanical code I3VIS [4]. The code implements a marker-in-cell approach with conservative finite differences and a multigrid method. The model consists of upper and lower continental crust, lithospheric and sublithospheric mantle down to 250 km depth. Two continental blocks are translated along the transfer zone in the middle of the model domain resulting in transtension. The suture consists of a fossil slab represented by oceanic lithosphere and a hydrated mantle wedge in the upper plate.
Our results demonstrate that the step-over distance between the two weak crustal zones governs the development of the pull-apart basins accompanied by crustal and lithospheric thinning and asthenospheric uplift. Partial melting of the suture's metasomatized mantle yields primary melts which ultimate derivatives are emplaced at the surface. The model provides important new insights into magmatic processes assosciated with suture reactivation in the Sava-Vardar Zone and in other similar tectonic settings.
[1] J. F. Dewey, “Suture zone complexities: a review,” Tectonophysics, vol. 40, no. 1-2, pp. 53–67, 1977.
[2] S. J. Buiter and T. H. Torsvik, “A review of wilson cycle plate margins: A role for mantle plumes in continental break-up along sutures?,” Gondwana Research, vol. 26, no. 2, pp. 627–653, 2014.
[3] D. Prelević, S. Wehrheim, M. Reutter, R. L. Romer, B. Boev, M. Božović, P. van den Bogaard, V. Cvetković, and S. M. Schmid, “The late cretaceous klepa basalts in macedonia (fyrom)—constraints on the final stage of tethys closure in the balkans,” Terra Nova, vol. 29, no. 3, pp. 145–153, 2017.
[4] T. V. Gerya and D. A. Yuen, “Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties,” Physics of the Earth and Planetary Interiors, vol. 140, no. 4, pp. 293–318, 2003.
How to cite: Stanković, N., Balázs, A., Cvetković, V., Mladenović, A., Cvetkov, V., Prelević, D., and Gerya, T.: Transtensional Reactivation of Suture Zones: Insights from 3D Numerical Modelling of Pull-Apart Basins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3086, https://doi.org/10.5194/egusphere-egu25-3086, 2025.
Many rifted margins form in regions that have previously undergone oceanic subduction and continent-continent collision. This implies that rifting occurs in the presence of inherited compressional features, rather than in homogeneous lithosphere, which may influence the resulting rift structures. The degree of compressional inheritance is increased in subduction systems that involve the accretion of oceanic plateaus, continental fragments, and microcontinents. In this case, a more intricate structural, rheological, and thermal inheritance is present at the onset of rifting compared to continent-continent collisions without terranes. In this study, we employ 2D thermo-mechanical numerical models to explore how such complex inherited features influence subsequent phases of continental rifting. Our models simulate orogenesis through ocean subduction, microcontinent accretion, and continental collision, followed by a quiescent phase before rifting initiates. We investigate the resulting rifted margin structures and assess the extent to which inherited compressional features are reactivated during rifting.
We find that a dynamic interplay exists between structural and thermal inheritance, which exerts a primary control on rifted margin architectures. In smaller, colder orogens, structural inheritance predominantly governs rifting, whereas in larger, warmer orogens, thermal inheritance plays a more significant role. To illustrate these contrasts, we present two end-member models and compare their resulting conjugate rifted margin architectures with natural examples from the opening of the North and South Atlantic Oceans. Our experiments demonstrate a diverse array of features, including the formation of continental fragments, allochthons, and hyper-extended segments, which arise due to the presence of inherited compressional features. These results highlight the critical role of deformation history and accreted terranes in shaping the evolution of continental rifting.
How to cite: Erdős, Z., Buiter, S., Peron-Pinvidic, G., and Tetreault, J.: Patterns of extensional reactivation of compressional features in rifted margins – insights from thermo-mechanical modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3603, https://doi.org/10.5194/egusphere-egu25-3603, 2025.
Ocean spreading is an intergral part of the Wilson cycle and its dynamics crucially reflects global tectonic processes. Ocean age-dependent cooling subsidence with seafloor deepening is traditionally described by models of thermochemical buoyancy of oceanic plates with globally constant parameters, that specify a linear correlation between square-root of seafloor age, sqrt(age), and bathymetry.
Here I present a worldwide analysis of the ocean floor split into 94 segments, delineated by wide-offset transform faults and mid-ocean ridges, to demonstrate a strong heterogeneity of sediment-corrected isostatic cooling subsidence both between and within normal oceans. Subsidence parameters for individual ocean segments significantly deviate from global constants in conventional models and show a large variability of subsidence rate and zero-age depth with plate thickness estimated between 50 and 160 km for cooling models with constant mantle properties.
Statistically strong correlations (R2=0.80–0.94) between major characteristics of cooling subsidence and spreading rate indicate that ocean evolution is essentially controlled by spreading rate, despite this factor is not included in conventional models of ocean subsidence.
- Normal oceans with slower spreading rate have, statistically, higher subsidence rate which implies faster gravitational collapse caused by faster plate cooling with moderate-to-low mantle temperatures at mid-ocean ridges.
- Fast-spreading oceans have the opposite characteristics.
- The ultraslow SW Indian and the fast-spreading Central Pacific Oceans are the end-members in ocean cooling subsidence trends, with the Atlantic/NW Indian Oceans tending towards the ultraslow end, and the Pacific/SE Indian Oceans being closer to the fast-spreading end.
- The Arctic Ocean and the Atlantics north of the Charlie-Gibbs Fracture Zone with an atypical subsidence behavior often deviate from the global trends.
Strong correlation between spreading rate, ocean half-width and the type of ocean margins indicates the roles of slab-pull and ridge-push in the Wilson cycle:
- ridge-push dominates tectonic forces in slower-spreading, narrower oceans with passive margins,
- slab-pull at active margins is a dominant tectonic force in faster-spreading oceans with half-width exceeding 4250 km.
The age of bathymetry departure from cooling subsidence, controlled by distribution of hotspots on ocean floor, correlates (R2=0.76) with spreading rate, and thus is not fully random.
- Slower-spreading oceans follow normal cooling subsidence to older ages (7.5–9.5 Ma1/2) than faster-spreading oceans (5–7 Ma1/2).
Recognition that spreading rate controls ocean evolution with formation of active or passive ocean margins dominated by
slab-pull or ridge-push contributes to advances in understanding driving forces in geodynamics.
Reference:
- Artemieva I.M., EPSL, 2024; https://doi.org/10.1016/j.epsl.2024.119017
How to cite: Artemieva, I. M.: Heterogeneous cooling subsidence of spreading oceans controlled by spreading rate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3064, https://doi.org/10.5194/egusphere-egu25-3064, 2025.
The geochemical characteristics of the mantle during continental breakup and the initial spreading of marginal sea basins remain poorly understood. Mid-ocean ridge basalt (MORB) samples from Hole U1500B and Hole U1503A in the northern margin of the South China Sea (N-SCS), obtained during IODP Expeditions 367 and 368X, provide crucial insights into mantle evolution of the nascent oceanic basin subsequent to continental breakup. This study analyzes major and trace elements, as well as Mo–Sr–Nd–Hf isotopes, in these MORB samples to explore variations in their mantle sources. MORB samples from Hole U1500B, closer to the continent, exhibit higher 87Sr/86Sr ratios, along with lower εNd and εHf values compared to the depleted mantle. Additionally, their δ98/95Mo values correlate positively with Mo/Ce and Mo/Nb ratios, indicating the influence of recycled oceanic crust (ROC) melts in the mantle source. In contrast, MORB samples from Hole U1503A, nearer to the oldest fossil ridge, show a broader range of δ98/95Mo values, reflecting varying extents of contribution of terrigenous sediment melts alongside ROC melts. The differing trace element and Mo–Sr–Nd–Hf isotope compositions of MORBs from the two sites highlight a significant transition in the mantle beneath the nascent mid-ocean ridge of the SCS. During the initial stages of seafloor spreading in the SCS, the mantle source experienced continuous replenishment from enriched components derived from shallow recycling of metasomatized SCLM. This process significantly contributed to the rapid transition from continental rifting to seafloor spreading in the SCS. The enrichment of the asthenospheric mantle, likely induced by previous subduction processes, facilitated rapid rifting and extensive magmatism in the SCS, distinguishing it from magma-poor margin basins. This research provides critical geochemical insights into the mantle evolution beneath nascent mid-ocean ridges, enhancing our understanding of the early processes in marginal sea basins.
How to cite: Huang, X.-L., Yang, F., Cai, Y.-X., and Yu, Y.: Rapid transition in the mantle composition beneath the nascent mid-ocean ridge in the northern margin of the South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3408, https://doi.org/10.5194/egusphere-egu25-3408, 2025.
The Mid-Atlantic Ridge (MAR) is the longest divergent plate boundary in the world, with evident seafloor spreading, transform faults, and hydrothermal vents generating earthquake swarms as tectonic plates move apart. Earthquake swarms are generally defined as a sequence lacking a mainshock event (e.g., a number of similar magnitude events occurring close in space and time). Previous work on swarms on the Mid-Atlantic Ridge have focussed on specific events, where recording equipment generate a local view of an earthquake swarm. Although these studies provide high-resolution information into an event, the work is limited in space (local area) and time (days or months). As a result, there is currently no up-to-date large-scale analysis across the length of the ridge which would provide regional information on Wilson Cycle processes of rifting. Here, we apply a clustering algorithm to an earthquake database across the MAR to identify spatially and temporally correlated swarms to establish a regional analysis of earthquake swarms on the Mid-Atlantic Ridge.
For our study, we use the available United States Geological Survey (USGS) earthquake database to analyse earthquake events across four different sections of the MAR (Reykjanes Ridge, Northern, Central, and Southern MAR) over the past 25 years (7,000+ earthquakes in total). Within this database, we find over 800 swarm events (compared to around 150 swarms in the past 50 years of published literature). We explore the spatial and temporal links between earthquakes and establish some similarities throughout the ridge. Specifically, swarm events are short lived, often starting and finishing within a day. Furthermore, the earthquakes within a swarm are mainly between 10-20 km of each other. An advantage of this large-scale approach to identifying swarms through cluster analysis is that we can begin to establish swarm characteristics and provide quantifications on spatial and temporal values.
Notably, we have identified 600+ swarms not discussed in the current literature with our work providing a standardised output for comparing swarms across the whole ridge. We highlight that MAR is not a homogenous entity, with Reykjanes Ridge behaving fundamentally different to the rest of the ridge. The large-scale analysis from our work here provides future studies with a benchmark to exploring spatial and temporal changes on this significant Wilson Cycle feature on our planet.
How to cite: Heron, P., Zhong, R., and Rich, J.: Cluster analysis can identify differences in earthquake swarm patterns along the Mid-Atlantic Ridge, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7389, https://doi.org/10.5194/egusphere-egu25-7389, 2025.
Magnetic data, along with their associated chrons, have played a crucial role in deepening our understanding of oceanic crust formation and seafloor spreading dynamics. Over the past 25 years, the Geological Survey of Norway has conducted extensive magnetic surveys, acquiring more than 172,846 km of new aeromagnetic profiles in the Norwegian-Greenland Sea (NGS). This contribution presents our latest regional compilation of the NGS, shedding light on the complex tectonic evolution of the region since the onset of continental breakup. The NGS witnesses diverse tectonic regimes and structural features, including sub-oceanic basins of different ages, microcontinents, and conjugate volcanic passive margins, between the Greenland-Iceland-Faroe Ridge in the south and the Arctic Ocean in the north. The new aeromagnetic compilation suggests that the highly magmatic breakup in the NGS was diachronous and initiated as isolated and segmented seafloor spreading centres. The early seafloor spreading system, initiating in the Early Eocene, gradually developed into atypical propagating systems, with subsequent breakup(s) following a step-by-step thinning and rupture of the lithosphere. Newly formed spreading axes initially propagated towards local Euler poles, died out, migrated or jumped laterally, changed their propagation orientation, or eventually bifurcated. The final line of lithospheric breakup may have been controlled by highly oblique extension, associated plate shearing, and/or melt intrusions before and during the formation of the Seaward Dipping Reflectors (SDRs). The Inner SDRs and accompanying volcanics formed preferentially either on thick continental ribbons or moderately thinned continental crust. The segmented and diachronous evolution of the NGS spreading activity is also reflected by a time delay of 1–2 Myrs expected between the emplacement of the SDRs imaged at the Møre and Vøring margins. Further north, the initiation of spreading that led to the formation of the Knipovitch Ridge began around C6 (~20 million years ago) within a distinct and oblique oceanic segment in the Fram Strait region. Magnetic observations indicate a broader continent–ocean transition, interpreted as exhumed lower continental material adjacent to the Barents Sea margin, which significantly reduces the mapped extent of the oceanic domain expected in the Fram Strait. This configuration also suggests the presence of a failed oceanic basin east of the Boreas Basin, which helps explain the resulting asymmetry in the spreading system. Meanwhile, several significant changes in spreading kinematics were recognised in the Norway Basin, with the first occurring in the Middle Eocene around 47 Ma (magnetic chron C21r), initiating rifting in the southern part of the Jan Mayen Microplate Complex. Inheritance and magmatism likely influenced the complex reorganisation of rifting, ultimately leading to the final dislocation of the Jan Mayen Microplate Complex from Greenland during the Late Oligocene/Early Miocene. The mechanism behind this final dislocation, likely triggered by overlapping rift systems, also raises questions about the controversial nature of crust and lithosphere stretching between the Faroes and Iceland.
How to cite: Gernigon, L., Dumais, M.-A., Nasuti, A., and Olesen, O.: The Formation and Evolution of the Norwegian-Greenland Sea: A 25-Year Aeromagnetic Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10759, https://doi.org/10.5194/egusphere-egu25-10759, 2025.
The Circum-Arctic region is a highly active geological region, with repeated opening and destruction of oceans alongside massive intrusive and extrusive volcanic and magmatic events. Although repeated episodes of rifting have been documented in the Arctic region over the past 500 million years and more, a fundamental understanding of the geodynamic processes involved is lacking. For instance, what are the tectonic triggers in the region for the most recent continental breakup via rifting? And, what is the role of earlier deformation events in structural inheritance? A number of different tectonic models describing the opening kinematics of the Arctic Ocean have emerged for post Pangea-times, with many using the opening of the Canada Basin (part of the Amerasia Basin) as a starting point.
To study the opening of the Arctic Ocean, methods such as geological mapping, geophysical surveying, geochemical analysis, and plate reconstruction models have been employed to better understand the rifting dynamics of Arctic Pangea, which has produced varying interpretations of how and when the Canada Basin first opened. However, the use of high-performance computing and lithospheric numerical modelling has yet to be fully adopted to investigate Arctic rifting.
In this work, we hypothesize that past orogenesis from the assemblage of Arctic Pangea may play a role in subsequent Arctic rifting dynamics and the opening of the Canada Basin. For the first time, we test this hypothesis using lithospheric numerical models with the open-source geodynamic code ASPECT by applying a range of plausible inherited structures to the pre-rift conditions of the Arctic region. Given the uncertainty with the tectonic history of the region, we apply a number of different structural inheritance scenarios to our numerical models – changing lithospheric rheological and rift velocity conditions, as well as simulating different deformation styles from a range of ancient tectonic boundaries in the region. We then critically compare the different rifting styles produced from our suite of models against the data available. Given the limited availability of direct data across this region, for this presentation we welcome community discussion on which key components of continental rifting that may indicate a potential successful modelling of the opening of the Canada Basin. As a rifting community, we want to work toward establishing a set of ‘non-negotiable’ tectonic features to better constrain numerical models of Arctic dynamics that will help push the understanding on tectonic triggers for Arctic plate tectonic processes.
How to cite: Rich, J., Shephard, G., and Heron, P.: Exploring the opening of the Arctic Ocean using lithospheric numerical modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13024, https://doi.org/10.5194/egusphere-egu25-13024, 2025.
Earth is a dynamic planet with its surface constantly recycled by plate tectonics and surface processes. Subduction of oceanic lithosphere and delamination of continental lithosphere are two of the main mechanisms by which the Earth’s lithosphere is recycled back into the mantle. Delamination in continental regions typically occurs below collisional belts due to the separation of the lithospheric mantle from the overlying lighter crust, aided by the existence of weak layers within the continental lithosphere. The oceanic lithosphere is classically pictured as a rigid plate with a strong core that should not allow for delamination to occur at pristine segments of oceanic plates. We will present what may be the first case of oceanic delamination offshore Southwest Iberia. The process seems to be triggered by plate convergence and assisted by a thick serpentinized layer that allows the lower part of the lithosphere to decouple from the overlying crust. Tomography images of a high-velocity anomaly support the hypothesis of ongoing oceanic delamination. We also present a set of numerical models that reproduce the process and suggest that it may facilitate subduction initiation. We further propose that such oceanic delamination is responsible for some of the highest-magnitude earthquakes in Europe, including the M8.5-8.7 Great Lisbon Earthquake of 1755 and the M7.9 San Vincente earthquake of 1969.
This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). JCD is supported by an FCT contract CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002 (https://doi.org/10.54499/CEECINST/00032/2018/CP1523/CT0002).
How to cite: Duarte, J. C., Riel, N., Civiero, C., Silva, S., Rosas, F. M., Schellart, W. P., Almeida, J., Terrinha, P., and Ribeiro, A.: Evidence of oceanic plate delamination in the Northern Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6706, https://doi.org/10.5194/egusphere-egu25-6706, 2025.
We use a new approach to quantify magmatic addition on the S. American and African rifted margins of the S. Atlantic south of the Florianopolis Fracture Zone. At magma-rich and magma-normal rifted margins, decompression melting starts before the continental crust is thinned to zero thickness. This results in a crustal “sandwich” of volcanics underlain by thinned continental crust, underlain by magmatically intruded continental basement and mantle. Usually all that can be imaged seismically is the top and base of extrusive volcanics and the seismic Moho, with no reliable indication of the quantities of remaining continental crust and magmatic addition. While the individual thicknesses of remaining continental crust and magmatic addition cannot be geophysically determined, their combined isostatic response controls margin bathymetry. We show using a simple isostatically balanced rifted margin model for thermally re-equilibrated lithosphere that the TWTT of first-proximal-volcanics provides a proxy for quantifying the total magmatic addition on a rifted margin, and distinguishing magma-rich from magma-normal rifted margins. The model predicts that the TWTT of first-proximal-volcanics correlates inversely with the timing of first magmatism with respect to crustal thinning.
We measure the TWTT of first-proximal-volcanics for a set of deep long-offset seismic reflection lines. The TWTT of first-proximal-volcanics for the highly magmatic northern Pelotas and conjugate Namibian margins is between 1 and 2 s; these margin segments have SDRs with thicknesses in excess of 15 km. Southwards, the TWTT of first-proximal-volcanics increases to between 6 and 7 s, corresponding to a magma-normal margin type. Despite this large north to south variation in first-proximal-volcanics TWTT, the interval TWTT of first oceanic crust varies little between 2.4 and 2.0 s from north to south, corresponding to normal thickness oceanic crust. Application of the Warner 10 s Moho TWTT rule for thermally equilibrated lithosphere indicates that decompression melting starts when crustal basement interval TWTT is between 8-9 s in the magma-rich north and at 3-4 s TWTT (β = 3) in the magma-normal south. Margin volcanic width, measured between first-proximal-volcanics and the landward limit of oceanic crust (LALOC) is approximately 300 km in the north, decreasing southwards to approximately 50 km width, and correlates inversely with the TWTT of first-proximal-volcanics. TWTT measurements of first-proximal-volcanics show that the very magma-rich margin type is restricted to the north adjacent to the Florianopolis Fracture Zone and rapidly decreases southwards to magma-normal in less than 300 km.
Our TWTT measurements and comparison with the simple isostatic margin model predictions indicate that magma-rich margins are explained by timing advance of decompression melting with respect to crustal thinning rather than melt magnitude increase. This together with the very rapid along-strike Pelotas margin decrease in magmatic addition, and the relatively normal thickness of first oceanic crust is difficult to reconcile with magma-rich margin formation due to mantle plume elevated temperature. Our observations are more consistent with magma-rich margin formation by rifting and decompression melting of inherited locally enriched mantle.
How to cite: Kusznir, N., Manatschal, G., Sauter, D., Cassel, M., and Chenin, P.: Along Strike Variation of Magmatic Addition on the Austral South Atlantic Rifted Margins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13028, https://doi.org/10.5194/egusphere-egu25-13028, 2025.
Continental rifting is often oblique, influenced by the strain localization effects of the various structural, compositional and thermal heterogeneity zones pre-existing in the lithosphere. Oblique rifting generates strain partitioning and leads to the along-strike segmentation of the rift structure, including the development of strike-slip transfer zones and en echelon fault geometries. While previous modelling studies have explored the relation between the rift obliquity and crustal fault patterns, its effects on the syn-rift magmatism and the oceanic spreading initiation have remained underexplored.
In this study, we conducted a series of high resolution 3D numerical models using the I3ELVIS-FDSPM numerical code to compare the continental rift evolution and spreading initiation in orthogonal and oblique rift settings. The code handles visco-plastic rheologies, staggered finite differences and marker-in-cell techniques to solve the mass, momentum and energy conservation equations for incompressible media. Oblique rifting is linked to strain localization along a pre-defined hydrated weak zone in the mantle lithosphere that simulates an inherited suture zone, while the applied two-way coupling between the thermo-mechanical and surface processes models allows for the quantification of the dynamic feedbacks between rift obliquity, crustal strain patterns, magmatism, and the erosion-sedimentation processes.
The models show that oblique rifting delays the onset of melting and continental break-up. Due to the feedbacks between crustal deformation, thermal evolution and melting, increasing rift obliquity leads to the non-linear reduction of the crustal melt supply, while at higher rift obliquity (α>30°), the en echelon arrangement of the elongated magma chambers in the crust suggests a strong structural control over the spatial distribution of crustal melts. When the rift evolution enters the spreading stage, first continental break-up occurs along the offset sub-orthogonal rift segments, and the individual embryonic oceanic segments are subsequently merged by the two-directional along-strike propagation of the incipient spreading ridges. The rate of this propagation changes in space and time, driven by the variable efficiency of strain localization. Above 30° obliquity, deformation along the offset spreading ridges is accommodated by oceanic transform faults that develop spontaneously, without a precursory lithospheric inhomogeneity in their place during the latest stage of spreading initiation. These inferences are in line with observations from the Woodlark Basin and Main Ethiopian Rift.
How to cite: Oravecz, É., Balázs, A., Gerya, T., and Fodor, L.: Syn-rift magmatism and spreading initiation controlled by rift obliquity: insights from 3D thermo-mechanical modelling and observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13146, https://doi.org/10.5194/egusphere-egu25-13146, 2025.
In the evolutionary history of the Tethys tectonic realm, numerous continental fragments progressively split from the southern hemisphere's Gondwana continent and “unidirectionally” converged and assembled with the northern hemisphere's Eurasian continent, ultimately shifting the center of the Earth's continental masses from the southern hemisphere in the late Paleozoic to the present northern hemisphere. Previous studies have vividly summarized this seemingly unidirectional process of plate fragmentation and reassembly as the “Tethys one-way train.” As a “welcoming ceremony” for this train's arrival, the upper plates' lithosphere, such as in the Tibetan Plateau and Anatolia from different geological eras, records unique tectonic-magmatic responses. For example, tectonic-magmatic activity may first appear in the interior, thousands of kilometers away from the convergence boundary, then expand from the inside out. This can also develop into a “piston-like” cycle of transformations: crustal compression + magmatic quiescence → crustal extension + magmatic peak → crustal compression + magmatic quiescence → and so on. Addressing these typical geological phenomena of the Tethys tectonic realm and combining the tectonic background revealed by plate reconstruction with the contemporaneous multiple episodes of block assembly, we employ forward numerical simulation to interpret the deep driving processes and mechanisms behind these phenomena. By utilizing geological, geochemical, and geophysical observations to constrain model results, we propose that the abrupt changes in the lower-plate movement characteristics (such as subduction angle and rate) caused by the subduction of high-buoyancy blocks significantly control the rapid transition of tectonic-magmatic patterns in regions like Tibet and Anatolia. The multiple episodes of block assembly can explain the accordion-like tectonic-magmatic cycles of the active continental margins. Given that the high-buoyancy blocks require continuous northward driving forces during their journey from Gondwana's fragmentation to their convergence with the Eurasian continent, we further calculated the temperature distribution in today's upper mantle using previous global seismic wave attenuation models to establish a forward geodynamic model, exploring the deep driving mechanisms of the convergence process in the Tethys tectonic realm. The modeling results indicate that the current temperature structure of the upper mantle, with colder northern regions and warmer southern regions, can create sufficiently large lateral mantle density contrasts and trigger the initiation of oceanic plate subduction towards the low-temperature areas, essentially starting the engine of the express train. Subsequently, the demise of secondary ocean basins during convergence often accompanies the subduction and rebound of high-buoyancy blocks, which rapidly returning fragments strongly collide with the rear oceanic plates, triggering a new round of oceanic subduction and further cooling the northern hemisphere's upper mantle, thereby giving the convergence process a chain reaction characteristic. Therefore, although the continental blocks fragmented from Gondwana may be seen as “passengers” of the one-way train, they have played a significant role in both the welcoming ceremony and the sustainable operation of the train.
How to cite: Liu, L., Morgan, J. P., Liu, L., Cao, Z., Chen, L., and Xu, Y.-G.: Upper Plate Responses and Driving Mechanisms of the 'Tethys One-Way Train', EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4949, https://doi.org/10.5194/egusphere-egu25-4949, 2025.
At the onset of convergent tectonics, lithospheric contractional deformation precedes the stages of plate rupture and underthrusting that foster subduction initiation. It is widely agreed that pre-existing lithospheric structural variations favour localisation of deformation and may be critical for subduction inception. Along magma-poor rifted margins, the Continent Ocean Transition (COT) includes structurally complex zones of thinned continental crust and serpentinized exhumed mantle, which are prone to deformation. Incipient contractional deformation during the Alpine Orogeny resulted in the formation of thrusts and folds along the COT of the reactivated magma-poor Iberian Atlantic and Armorican margins. Numerical models testing subduction initiation at magma-poor margins also reproduce thrusting and folding along the COT prior to the formation of a lithospheric shear zone within serpentinized exhumed mantle that initiates underthrusting. However, the distribution of thrusts along thinned continental crust and serpentinized exhumed mantle remains unconstrained, although it may be critical to decipher the localisation of deformation that occurs prior to and during the underthrusting stage.
The North Iberian margin uniquely preserves fossilized Alpine thrusts along the COT that affected underthrust thinned continental crust and serpentinized exhumed mantle at the central part of the margin, and underthrust oceanic crust at its western corner. Thus, it represents an ideal setting for investigating the role of basement type on the formation and distribution of contractional tectonic structures prior to and during underthrusting at magma-poor margins. Based on 2D seismic reflection profiles, we describe the structure of thrusts sheets overlying transitional basement, consisting of highly thinned crust and serpentinized exhumed mantle, and oceanic crust. Our observations support the preservation of an accretionary prism overlying incipiently subducted oceanic crust. Contrastingly, large thrusts led to overthrusting of thinned continental crust and possibly serpentinized exhumed mantle resulting in crustal thickening, landward tilting and uplift of the crust and overlying sediments. Discrete thrusts deformed the upper ultra-thinned basement, leading to the deposition of wider syn-orogenic sediments. We integrate our structural observations with previous numerical and geophysical models to discuss underthrusting vs intraplate deformation and localisation vs distribution of contractional deformation along thinned continental crust and serpentinized exhumed mantle at the onset of convergence.
This work is supported by the Marie Skłodowska-Curie grant agreement No 895895 funded by the European Union´s Horizon 2020 research and innovation programme, the projects ASTRACAN, Ref. PID2021-123116NB and ATLANTIS, Ref. PID2021-124553OB-I00 from the Ministry of Science and Innovation of Spain, and the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025, UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020) and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020).
How to cite: Cadenas Martínez, P., Welford, J. K., Fernández-Viejo, G., C. Duarte, J., and Somoza, L.: Evidence for onset of convergent tectonics within the Continent-Ocean Transition zones of the Atlantic rifted margins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12508, https://doi.org/10.5194/egusphere-egu25-12508, 2025.
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 of one of the plates. One way subduction initiation may occur is through the reactivation of a passive margin.
The processes that generate a self-sustained subduction zone are still debated and are thought to be dependent on various factors, such as the presence of a weak zone (e.g., a serpentinized layer), a pre-existing stress/strain field, the structure of the rifted margin and the age of the subducting oceanic plate.
Using high-resolution 2D geodynamic numerical models carried out with the code LaMEM, this work investigates the mechanisms that may control the reactivation of 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 (e.g., temperature profiles and rheology) that may lead to subduction initiation in these locations.
Our preliminary results show that serpentinized layers facilitate the reactivation of inherited rift structures by localizing deformation. The results also show that the length of the passive margin might influence the location of the subduction nucleation.
How to cite: João, M., Cadenas, P., Duarte, J. C., Rodrigues, N., Riel, N., Rosas, F. M., Welford, J. K., and Gomes, A.: 2D numerical models of passive margin reactivation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11067, https://doi.org/10.5194/egusphere-egu25-11067, 2025.
The Wilson Cycle describes the periodic nature of supercontinent formation through amalgamation and break-up of continents. This cycle is driven by the dynamic interaction between the lithosphere and mantle. To investigate the role of plate-mantle interactions during the supercontinent cycle, we have performed a series of high-resolution, 2D global numerical simulations using the ASPECT geodynamic code. We explicitly include continental lithosphere with pressure- and temperature-dependent visco-plastic rheology. The models are conducted in a self-consistent way without imposing velocity boundary conditions at the surface. They include a free surface to simulate realistic topography which we use to quantify gravitationally induced stresses.
Our simulations reveal a complex interaction between, subduction, mantle and lithosphere dynamics as continents collide, and break apart during 600 My of model evolution. We quantify the plate tectonic driving forces: slab pull, gravitational potential energy gradients, and basal drag, i.e. mantle flow-induced tractions. In our models, we identify slab pull and mantle plumes as key factors in overcoming the strength of the lithosphere to achieve continental break-up. Interestingly, in our models, continental break-up does not occur at the suture zone of colliding continental plates—a region traditionally considered to be structurally weak and with higher GPE. These model results provide new insights into the relative importance of plate driving forces during the Wilson cycle.
How to cite: Dong, M., Pons, M., and Brune, S.: Quantifying super-continent evolution through Wilson cycle phases at global scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12313, https://doi.org/10.5194/egusphere-egu25-12313, 2025.
Inversion of passive margins located within the subducting plate is somewhat unintuitive but widely observed. Situated at the northern African margin, the 1000-km-long Syrian Arc fold system preserves a classic example of such intraplate passive margin inversion that formed during the closure of the Tethys Ocean. Although extensively studied, its evolution is still crudely documented, thus, the dynamic processes that have driven its formation are poorly understood. Here, we present new structural and temporal constraints on the evolution of the Hatira monocline situated at the central part of the arc. Our results suggest that folding occurred at an episodic manner that overlaps long-term background shortening, with one prominent short folding pulse (~79 to ~77 Ma) accounting for 25% of the total accumulated shortening, followed by two additional minor folding pulses. Most of the shortening (~50%) was accommodated by a slow and continuous deformation that started at around 90 Ma and lasted until the Miocene. The pronounced shortening pulse seems to correlate with the secession of the double subduction zone and the obduction of ophiolites along the northern Tethys. Other dynamic processes acting along the subducting slab (e.g., slab interaction with the 660 km discontinuity, slab buckling, etc.) may have triggered the long-term and short-term shortening pulses. The temporal evolution of the central Syrian Arc demonstrated here provides new insights into the role of subduction processes (margin and slab) on the internal shortening of the trailing passive margins.
How to cite: Fisch, G., Granot, R., Marconato, S., Eyal, Y., and Abramovitch, S.: Intraplate episodic shortening within a subducting plate: the case of the central Syrian Arc Fold system , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-219, https://doi.org/10.5194/egusphere-egu25-219, 2025.
The Jabal Akhdar and Saih Hatat tectonic windows in the Oman Mountains are key geological features where to investigate the geological record of the Late Cretaceous subduction, obduction and exhumation cycle that affected the northeastern margin of the Arabian Plate. Indeed, the metasedimentary Autochthon A (pre-Permian) and B (post-Permian) Units exposed therein and separated by the so-called Hercynian Unconformity display well-preserved evidence of many of those processes, as they were spared by the obliterating effects of continental collision once subduction terminated. Research on the structural and metamorphic framework of the Jabal Akhdar tectonic window has been scanty until now. This stems from the fact that, unlike Saih Hatat, which records greenschist to eclogite facies metamorphism, Jabal Akhdar has been traditionally considered a portion of the Arabian Plate only recording anchizone metamorphism (only one site has recently been reported as preserving evidence of high pressure-low temperature (HP-LT) metamorphism dated to the Late Cretaceous). Here, we present new field and thermobarometric data from Jabal Akhdar aimed at better constraining its structural and metamorphic framework on a regional scale and possibly correlating it to the greater subduction-obduction cycle of Oman.
In western Jabal Akhdar, field constraints from newly documented top-to-the ENE shearing indicate the local pervasive structural reactivation of the Hercynian Unconformity as a post-Permian ENE-verging thrust. Multiple Raman spectroscopy findings of metamorphic aragonite infilling Mode I veins support a HP-LT metamorphic imprint associated with such shortening. In the eastern sector of the tectonic window, on the other hand, folding and S-C tectonites in Ediacaran slates indicate NW-verging shear. Our new structural data thus suggest NE- to NW-verging shortening and stacking within and between the Autochthon A and B. Further new structural evidence from the structurally higher Autochthon B in northeastern Jabal Akhdar indicates that inherited structures with top-to-the NE kinematics were later overprinted by lower-grade, localised SW-ward thrusting through interlayer slip recorded in Cretaceous marbles. Finally, extensional reactivation followed, associated with Neogene doming and final exhumation.
We employed a multidisciplinary approach to constrain the P-T conditions associated with the identified structures. Chlorite–white mica–quartz–water multiequilibrium analyses integrated with Raman spectroscopy on carbonaceous material indicate T = 370 °C and P = 0.50 GPa in western Jabal Akhdar, associated with NE-verging S-C tectonites, and T = 330 °C and P = 0.66 GPa, in the eastern domain of the tectonic window, related to NW-verging folds. These thermobarometric results place the investigated deformation in the greenschist and lower blueschist facies metamorphic fields, respectively.
These new structural data and the recorded metamorphic signature call for a re-evaluation of the commonly held notion of a mostly undeformed and non-metamorphic geological record within Jabal Akhdar, questions its correlation (or lack thereof) with the Saih Hatat tectonic window and, ultimately, Jabal Akhdar’s role within the framework of the Oman Late Cretaceous subduction and obduction phases.
How to cite: Degl Innocenti, S., Viola, G., Zuccari, C., Sanguettoli, T., Giuntoli, F., and Vignaroli, G.: Evidence of blueschist facies shortening in the Jabal Akhdar tectonic window, northern Oman, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-665, https://doi.org/10.5194/egusphere-egu25-665, 2025.
Magmatic arc migration, a prevalent feature in accretionary orogens, often aligns with fluctuations in crustal thickness and geochemical properties. Despite their common occurrence, the mechanisms intertwining these processes and their influence on arc magmatism remain largely elusive. The Sikhote–Alin accretionary orogen, as a part of the West Pacific orogenic belt and a long-lived active margin along eastern Eurasia, offers an exceptional window for investigating these dynamics. Our study leverages machine learning-based modelling inversions, revealing a decrease in crustal thickness from 52 ± 9 km to 43 ± 8 km in Northeast Asia during the Early Cretaceous. This thinning was disrupted by two significant thickening events around 130 Ma (peaking at 57 ± 9 km) and 110 Ma (peaking at 56 ± 6 to 59 ± 5 km). The spatial-temporal distribution of magmatism ages indicates an arc migration exceeding 500 km during 135–120 Ma, and a further ~200 km migration around 110 Ma. During the Early Cretaceous (135–120 Ma), the Sikhote–Alin accretionary orogen was predominantly intruded by S-type granitoids, originating from partial melting of pelite-poor, psammite-rich sediments within a thickened accretionary prism, accompanied by muscovite and biotite dehydration. Younger granitoids, with ages of 120–110 Ma were transitional S- to I-type, whereas those aged 110–100 Ma were dominated by I-type, generated through partial melting of igneous rocks in an accretionary prism setting. Linking the data of arc migration, crustal thickness variation, and magmatism, we propose that the arcs in Northeast Asia migrated during 135–120 Ma and around 110 Ma, mainly driven by crustal thinning and accretionary prism emplacement, respectively. Variations in crustal thickness significantly impacted the magmatic evolution by influencing magma transport, the likelihood and location of magma stagnation, and the pressure conditions for magma differentiation. Arc migration events further accentuated the spatial heterogeneity of crustal composition and thickness, ultimately affecting magma sources and evolution.
How to cite: Liang, Y., Zheng, H., He, Z., and De Grave, J.: Linking arc migration, crustal thickness variation, and magmatism in the Early Cretaceous Sikhote–Alin accretionary orogen, NE Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4084, https://doi.org/10.5194/egusphere-egu25-4084, 2025.
The North Iberian Margin (NIM) constitutes an example of a former plate boundary where to explore the role played by geological inheritance during the alpine convergence between Iberia and Europe in the Paleogene. The convergence, which resulted in the partial and asymmetric closure of the Bay of Biscay, resolved in major tectonic differences along this boundary, depending on the previous tectonic history of the crust: short-lived south directed subduction of oceanic crust in the West under the crystalline basement of Iberia (Variscan), continental collision in the Pyrenees in the East, shortening of a previously hyperextended margin in the middle part.
The Picos de Europa massif (Cantabrian Mountains, CM), is located in this middle region between the continental collision and the arrested subduction, and from the structural point of view represents part of the leading edge of the Variscan orogenic wedge, the forefront of the Variscan thrusts over the foreland. The area reflects a history of deposition where synorogenic thick carbonate platforms are affected by thrusting during the Variscan collision between Gondwana and Laurussia.
The dominance of carbonate rocks in Picos de Europa over the shales in the surrounding Variscan foreland sediments, together with its subsequent alpine tectonic history, contributed to its current orography. It is the area of the Cantabrian Mountains with the highest concentration of peaks above 2000 m.
A temporal local network of 10 broadband seismic stations was deployed in the area to study its seismicity and produce a high-resolution tomography of the upper crust in order to gain insight into its tectonic structure. A previous tomography at regional level, revealed the existence of a low velocity zone dipping north interpreted to represent the frontal thrust of the CM. Although scarce, seismicity associated to this major tectonic structure has an impact at the surface as Picos de Europa, in its hanging wall, is well known by the steepness of its slopes, with the main river incising over 2000 m. As well as being the first Spanish Natural Park is one of the most visited. The increasing touristic pressure over this protected space has highlighted the importance of constraining natural hazards in mountain areas.
Results from ambient noise data recorded during six months are presented. The cross-correlation technique was used to retrieve the empirical Green functions of the subsurface between all station pairs, showing the emergence of Rayleigh waves. After measuring dispersion velocities, Rayleigh-wave group velocity tomography maps were computed at different periods and then inverted in order to calculate S-wave velocities as a function of depth, reaching the upper 8-9 km of the crust. The tomography shows the presence of a relative high velocity body at 5-6 kms in the northern part of Picos de Europa, and the presence of two low velocity bodies at 6-9 km aligned NW-SE. Preliminary interpretation points to likely Variscan structures underlying the geometry of the velocity patterns.
How to cite: Fernández-Viejo, G., Acevedo, J., Llana-Funez, S., Lopez-Fernandez, C., Gutierrez-Medina, M., and Gonzalez-Cortina, J. M.: Preliminary results from a temporary high-resolution broadband network around Picos de Europa (Cantabrian Mountains): ambient noise tomography and seismicity distribution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8743, https://doi.org/10.5194/egusphere-egu25-8743, 2025.
When two continents collide different surface expressions can be produced. Triangular wedges are relatively narrow, while plateaus are high topographic features extending over large areas. Several studies have focused on the transition from wedges to plateaus, but the dynamic conditions of their growth remain elusive. Although different models for orogenic growth have been proposed, the link between theoretical/experimental models and natural analogues proves to be an outstanding task yet to be resolved.
Here, we present 2D high resolution (2048 x 512) buoyancy-driven numerical models, coupled with density phase diagrams, of sustained continental collision and subduction. We explore how crustal rheology controls the development of different types of orogenic growth and their subsequent final orogenic architecture, while further benchmarking our results to natural analogues.
Our results show that continental subduction can be sustained without the need for external forces and that three types of orogenic growth modes can be identified: i) forward; ii) backward; and iii) thermally induced. We show that the different types of orogenic growth are highly dependent on crustal rheology that, under high stresses, can allow large-scale lower crustal detachments to be formed and delamination processes to be developed.
For weak lower crust rheologies, our results always show the development of a lower crustal detachment that connects both continents. In turn, subducting crustal material is thrusted onto the overriding continent, leading to compression of the two continents. In this case, a progressive uplift of the orogen in direction of the overriding continent is observed (forward orogenic growth).
For a strong lower crust, no large-scale lower crustal detachment connecting both continents is formed. As such, the incoming crustal material is progressively stacked at the collision zone and the deformation is propagated backwards. Thus, the orogen continuously grows in direction of the subducting continent (backward orogenic growth).
However, backward orogenic development can only occur over large periods of time if the strength of the subducting continental crust is sufficiently low to sustain continuous deformation of the crustal material. While a weak upper crust enables steady backward orogenic growth, a strong upper crust halts continental subduction and collision. Due to a stronger upper crust, the slab pull force is not sufficient to continuously deform the crustal material while maintaining high subduction velocities to conserve slab integrity.
Thus, for a strong upper crust, after an initial stage of backward orogenic growth, slab break-off ensues, promoting the rise of hot asthenospheric mantle through the subduction channel and peel-back delamination. In this sense, the orogen grows due to a thermally induced isostatic response of a post-collisional peel-back delamination process (thermally induced orogenic growth).
Finally, we benchmark our models to natural analogues and show that forward orogenic growth models comply well with the width and heights of natural orogenic plateaus.
This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020), and through scholarship UI/BD/154679/2023.
How to cite: Rodrigues, N., Riel, N., Rosas, F., Almeida, J., Gomes, A., and Duarte, J.: Modes of collisional orogenic growth: forward, backward and thermally induced, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12306, https://doi.org/10.5194/egusphere-egu25-12306, 2025.
Myanmar is located south of the Eastern Himalayan Syntaxis, where tectonic activity is driven by the northward indentation of the Indian Plate into Asia and the oblique eastward subduction of India beneath the western margin of the Burmese microplate. Dextral motion along the Sagaing Fault separates the eastern margin of the Burmese microplate from the Asian Plate. The associated lithospheric structure is complex and three-dimensional, featuring a transition from an oceanic-transitional subduction slab to continental subduction and collision, likely involving plate tearing and bending. Additionally, intermediate-depth seismicity and volcanism are linked to processes associated with the ongoing subduction. We use finite-frequency teleseismic P-wave tomography to explore the relationship and interaction of these different tectonic elements. Our input data is derived from approximately 480 teleseismic earthquakes that occurred between 2019 and 2021, recorded by around 140 regional seismic stations, primarily from temporary deployments. These include stations of the 6C (2018–2022, MySCOLAR) network, operated by GFZ and DMH, and the XR (2018–2022, Tripartite BIMA) network, operated by the University of Missouri with partners, as well as stations deployed by the Earth Observatory of Singapore (EOS). The dataset is further augmented by permanent stations from the China National Seismic Network (SEISDMC), the Geophysical Broadband Observation Network (GEOFON), and other regional permanent stations accessible through the Incorporated Research Institutions for Seismology (IRIS). Travel-time residuals were calculated via cross-correlation in three frequency bands (0.1, 0.3, and 0.5 Hz central frequency). The resulting P-wave velocity models are derived from around 70,000 residuals, covering the area between 90° to 101°E and 18° to 30°N, down to approximately 600 km depth. Data coverage and resolution are best in central and northern Myanmar. This enables the illumination of the geometry and characteristics of the different lithospheric units involved in the subduction/collision transition and slab bending towards the Eastern Himalayan Syntaxis.
How to cite: Kufner, S.-K., Tilmann, F., Schurr, B., Yuan, X., Heit, B., Than, O., Wei, S., Sandvol, E., Li, W., van der Beek, B., Gaherty, J., and Persaud, P.: A slab’s journey from subduction to collision: Lithospheric structure of Myanmar from finite-frequency tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13089, https://doi.org/10.5194/egusphere-egu25-13089, 2025.
As one of the most immense orogenic belts, the Altaids (or southern Central Asian Orogenic Belt) primarily comprises Kazakhstan, Mongolia, and Tarim-North China cartons collage systems. The Chinese Altai-East Junggar orogenic collage in the northern Xinjiang, NW China, links the Mongolia collage system to the east with Kazakhstan collage system to the east, occupying a critical tectonic position and retaining the fundamental architecture of the southern Altaids. The Erqis tectonic belt, situated at the junction of the Chinese Altai and East Junggar, originated through the subduction of the Ob-Zaisan Ocean, playing a pivotal role in unraveling the tectonic evolution of the southern Altaids.
Tectonic and provenance analyses of the Erqis tectonic belt discern three distinct arcs: the Chinese Altai, a Japan-type island arc, in the north, exhibits a protracted history from the late Cambrian to early Permian with a slender accretionary complex (AC) termed the Supute AC; The Kuerti intra-oceanic arc in the middle eemerged in the late Silurian to Devonian with a minor coeval AC as the Tesibahan AC; The Dulate arc in the south predominantly evolved from the middle Devonian to Permian, giving rise to the Fuyun AC that independently developed on its northern margin at least until ~273 Ma.
Our findings indicate the existence of multiple arcs within the Ob-Zaisan Ocean, forming an archipelago paleogeography in the Paleo-Asian Ocean (PAO). Provenance studies lead us to propose that cryptic sutures demarcating the Chinese Altai, Kuerti, and Dulate lie approximately along the Kuerti and Tesibahan faults, respectively. In addition, the tectonic facies matching between accretionary complex and the corresponding parental island arcs demonstrate that he oceanic branches between these arcs subducted northward beneath the Chinese Altai and Kuerti arcs and southward beneath the Dulate arc. Additionally, our work demonstrates the closure of the Ob-Zaisan Ocean most probably postdates ~273 Ma. Combining our data with previous research, we present a novel tectonic evolution model, elucidating several arc amalgamations with multiple subduction polarities between Chinese Altai and East Junggar throughout the late Cambrian to Permian.
How to cite: Gan, J., Xiao, W., and Sang, M.: Paleozoic amalgamation of the Chinese Altai and East Junggar: Insight from the anatomy of Erqis tectonic belt, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14447, https://doi.org/10.5194/egusphere-egu25-14447, 2025.
