The reliable appraisal of the diversity of geomorphic, structural, magmatic, metamorphic and sedimentary processes at work during orogeny as well as the 3D-4D conceptual and numerical modeling of the evolution of orogens require a multisource approach encompassing field geology, geomorphology, geophysics, petrology and geochemistry as well as advanced laboratory techniques. In order to constrain the timing, sequence, duration, rates of strain localization in the crust and orogenic growth, determining the age and longevity of structures - folds and thrusts in fold-and-thrust belts and foreland basins and ductile shear zones in the deeper crust - is key. Adding to the petrochronological toolbox applied to metamorphic minerals from the ductile realm, recent advances in K–Ar illite and U–Pb calcite geochronology applied to fault zones and mesoscale brittle structures have allowed for deeper insights into the upper crust mechanics.
This session aims at bridging the gap between spatial - from shallow depth to lithospheric scale- and temporal -short-term vs long-term- scales for a better understanding of mountain building and to provide a forum for all disciplines concerned with orogenic wedges to meet and discuss their views. We welcome contributions reporting topical works on mountain belts including seismology, rheology and mechanics, structural geology, dating deformation, thermochronology, geomorphology, thermicity or fluid rock-interactions. We encourage integrated studies highlighting the respective role of plate tectonics, crust-mantle interactions and surface processes in shaping the architecture of the continental crust. Analogue or numerical modeling work as well as regional case studies are welcome. Furthermore, applied studies aiming at linking structure development and crustal dynamics with hydrogeology and generation of carbon-free energy resources such as geothermal energy or natural H2 are also encouraged.
Orals: Tue, 29 Apr | Room G2
During the last decade, the U-Pb geochronology of fracture-filling carbonates has been used to reconstruct the tectonic and diagenetic history of fold and thrust belts, worldwide. These studies unequivocally show the potential of the U-Pb dating method to quantify geological processes in compressional settings such as activity and duration of fluid migration, folding and faulting, duration of thrust sheet emplacement, and calculation of shortening rates. Here, some examples from the SE Pyrenean fold and thrust belt and from the Andean-Neuquén Basin are presented.
U–Pb ages measured in fracture-filling carbonates from the SE Pyrenean fold and thrust belt reveal Late Cretaceous to Oligocene compressional ages ranging from 71.2 to 25.7 Ma and a minimum duration for the emplacement of the thrust sheets of 18.7 Ma (Bóixols–Upper Pedraforca), 11.6 Ma (Lower Pedraforca) and 14.3 Ma (Cadí). These ages also show that piggy-back thrusting occurred coevally with the post-emplacement deformation of the upper thrust sheets above the lower ones during their south-directed tectonic transport. The duration of the thrust sheet emplacement combined with well-balanced cross sections of the SE Pyrenees allow to calculate shortening rates of 0.6, 3.1 and 1.1 mm/yr from the older to younger thrust sheets, which agree with previous estimations based on the magnetostratigraphic and biostratigraphic studies of syn-orogenic deposits.
In the SE Pyrenees, geochronological results also reveal the long-lasting tectonic history of fault zones and folds. As an example, at Bóixols thrust sheet, dating of multiple samples along the Abella de la Conca thrust fault zone at the frontal Sant Corneli anticline reveals multiple reactivations from 66.9 to 36.55 Ma spanning ∼30 Myr of tectonic activity. Furthermore, systematic dating of fracture-filling carbonates along the whole Sant Corneli anticline, combined with the structural analysis of fractures, constrain its evolution for ∼62 Myr: 1) layer-parallel shortening and folding (from 71.2 to 56.9 Ma); 2) fold tightening (from 55.5 to 27.4 Ma); and 3) post-folding extension (from 20.8 to 9 Ma).
In the Agrio, Chos Malal and Malargüe fold and thrust belts in the Neuquén Basin along the front of the Andes in Argentina, the dating of bed-parallel fibrous calcite veins “beef” reveals mild tectonic pulses that triggered fluid overpressures and oil migration from 116.7 to 78.8 Ma, partly coevally with the Late Cretaceous syn-tectonic deposition of the Neuquén Group. U-Pb dates determined in veins cutting calcite beef register Late Cretaceous to Palaeocene period of layer-parallel shortening in the Neuquén Basin from 72.8 to 60.9 Ma and early-middle Eocene and middle-late Miocene stages of folding and thrusting from 52.0 to 42.2 Ma and from 13.9 to 6.2 Ma, respectively.
This research was funded by the DGICYT Spanish Project PID2021-122467NB-C22, the Grups de Recerca reconeguts per la Generalitat de Catalunya “Modelització Geodinàmica de la Litosfera” (2021 SGR 00410) and ”Geologia Sedimentària” (2021 SGR-Cat 00349).
How to cite: Cruset, D.: Deciphering the tectonic deformation history in fold and thrust belts using U-Pb dating of fracture-filling carbonates. The Pyrenean and the Andean-Neuquén Basin case studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6799, https://doi.org/10.5194/egusphere-egu25-6799, 2025.
In this contribution, we present a kinematic reconstruction for the Tyrrhenian back-arc basin–central Apennines fold-and-thrust belt system during the last 25 Myr, illustrating how its evolution is driven by the interplay between slab rollback and the inherited rifted margin architecture of the lower plate.
After an initial stage of oceanic subduction and slab rollback, which led to the formation of the Liguro-Provençal back-arc basin and the development of the thin-skinned Liguride accretionary wedge, soft collision was established around 20 Ma with the arrival of Adria’s rifted margin at the subduction zone. The transition from subduction to soft collision altered the orogenic system’s dynamics, decelerating slab rollback and slowing down the velocity of thrust migration. By 12–10 Ma, with the hard collision stage already established, the subduction interface migrated from the base of the sedimentary cover into the ductile middle crust, coevally with the onset of lower crust delamination, the renewal of slab rollback, the acceleration of forelandward thrust propagation, and the onset of back-arc extension in the axial zone of the belt. Since then, extensional and compressional deformation are migrating toward the foreland at a constant velocity. We propose a "zip-like" tectonic model for the Apennines over the last 10 Myr, in which delamination of the lower crust spreads from a forelandward-migrating singularity point. Areas of compression and extension are pinned to this migrating singularity point, providing a unified explanation for the seismicity patterns, low-angle normal faults, and Moho depth variations observed in the Apennines.
How to cite: Tavani, S., Maresca, A., Carminati, E., Cavinato, G. P., Granado, P., Manatschal, G., and Muñoz, J. A.: Linking thrust system, back-arc extension, rift inheritance, and crustal delamination in the Tyrrhenian basin–Apennines thrust belt system., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3856, https://doi.org/10.5194/egusphere-egu25-3856, 2025.
The Late Carboniferous to Permian is a crucial time epoch that witnessed multiple-stage icehouse-to-greenhouse transitions and amalgamation of the Pangea supercontinent in geological history. In the North China Block (NCB), a sequence of Late Carboniferous to Permian successions preserves dramatic changes related to these climatic and tectonic shifts. Here, we conducted a comprehensive study of sandstone petrology, mudstone wholerock geochemistry, and detrital zircon U-Pb geochronology on Late Carboniferous to Permian strata in the Wuqi Oilfield, central Ordos Basin of the western NCB. Mudstone geochemistry and sandstone modal composition data indicate that sediments in the central Ordos Basin were deposited in arc/orogen-related tectonic backgrounds, with sources dominantly from erosion of intermediate-acid rocks. Detrital zircon U-Pb analyses yielded 3 major age populations of 2600–2200 Ma, 2100–1700 Ma, and 470–260 Ma, matching well with a northern Inner Mongolia Continental Arc (IMCA) source instead of a southerly Qinling/Qilian source. Three climate warming events were identified by increased levels of continental weathering. The τNa, CIA, and Ln (Al2O3/Na2O) values manifest two positive increasing events and, by reference, climate warming events, represented by high chemical weathering intensity (e.g., CIA >90 and τNa < − 0.96), at ca. 302–298 Ma and ca. 292–290 Ma. The first event coincided with the deglaciation event of Gondwana triggered by the Skagerrak-Centered Large Igneous Provinces (LIPs). The second event was associated with the ca. 290 Ma large-scale glacial retreat in Gondwana that was synchronous with the Tarim LIP, Panjal LIP. The zircon Eu/Eu* empirical equation data indicates that the crustal thickness of the IMCA thickened from 40-43 km–50 km between approximately 320 Ma and 285 Ma. The increasing relief of the IMCA was recorded by ca. 280–260 Ma craton-wide sedimentary hiatus in the NCB interior. Subsequently, the high relief of the IMCA led to orographic rain shadow and aridification, which caused the third climate warming event, as indicated by the change in mudstone color from black to red.
How to cite: Tao, H. and Cui, J.: Late Carboniferous to Permian paleoclimatic and tectono-sedimentaryevolution of the central Ordos Basin, western north China Block, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10657, https://doi.org/10.5194/egusphere-egu25-10657, 2025.
The late-stage evolution of the Central European Alps is recorded by the Cenozoic sediments of the Swiss Molasse Basin (SMB). From a sedimentary perspective, deep marine Flysch sedimentation transitioned to shallow marine and terrestrial Molasse deposition around 30 Ma (Schlunegger & Kissling, 2022 and references therein). Shallow marine conditions were re-established around 20–18 Ma, after which terrestrial sedimentation continued until 10–5 Ma. From a tectonic perspective, the Flysch and Molasse deposits were continuously accreted by the advancing Alpine nappe stacks from late Eocene times onwards. The tectonic exhumation of the External Crystalline Massifs occurred around 22–20 Ma (Herwegh et al., 2023), after which the Molasse units were thrusted on top of each other and tilted towards the south thereby forming the Subalpine Molasse (Kempf et al., 1999). Around 16 Ma, southward-oriented back-thrusting resulted in the formation of a Triangle Zone (von Hagke et al., 2012) where Molasse units dip northwards, marking the structural transition from the flat-lying Plateau Molasse situated in the north, to the tilted and thrusted Subalpine Molasse in the south and adjacent to the Central Alps. The Subalpine Molasse units were then further thrusted and exhumed between 12–4 Ma (Mock et al., 2020).
Nowadays, large parts (c. 2/3) of the Subalpine Molasse are covered by the so-called Helvetic and Prealpine nappe stacks, preventing a complete exposure. Only a SW–NE oriented stretch is exposed, while subsurface information is fragmentary (e.g., from seismic surveys or deep wells). Despite extensive research, we lack an understanding about the present-day lateral and longitudinal geometry of the Subalpine Molasse adjacent to and beneath the Central Alps. In addition, the timing of initial thrusting and emplacement has not been fully resolved at the scale of the entire SMB. This study addresses these objectives through the construction of a large-scale 3D geological model of the Subalpine Molasse, particular of its major lithostratigraphic and tectonic boundaries. The model is based on the Tectonic Map of Switzerland and integrates an input dataset compiled from numerous published geological-mapping, seismic-survey, and drilling campaigns.
The model allows a revised interpretation of the geometry of the Subalpine Molasse in Central Switzerland. The homogenised map shows that the 39+ individual thrust sheets are laterally and frontally displaced by thrust- and fault-complexes, both along strike and across the SMB. We also observe that the steeply dipping (20–30°) frontal thrusts of the Flysch and Molasse units root in depths of 5–7 km below the exhumed External Crystalline Massifs. Where these basement massifs are absent, the frontal thrusts are more gently dipping (10–20°) and likely rooting in Mesozoic fault-zones. Furthermore, palinspastic restorations of reference cross-sections provide insights into the style of deformation and the evolution of thrusting within the Subalpine Molasse.
REFERENCES
Herwegh, M. et al. (2023). Wiley, London.
Kempf, O. et al., (1999). Int J Earth Sci., 88(2).
Mock, S. et al., (2020) Solid Earth, 11.
Schlunegger, F., & Kissling, E. (2022). Geosciences, 12(226).
Von Hagke, C. et al., (2012). Tectonics, 31(5).
How to cite: Garefalakis, P., Herwegh, M., Schlunegger, F., Berger, A., Kempf, O., Kurmann, E., Furlan, M., Drvoderić, S., and Musso Piantelli, F.: A 3D geological model of the Subalpine Molasse in Switzerland: Insights into its subsurface geometry and spatial evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15954, https://doi.org/10.5194/egusphere-egu25-15954, 2025.
Foreland fold-and-thrust belt (FAT), as the dynamic junction between hinterland and foreland, adjusts the evolution of orogeny. Back thrusts (BT) also play a crucial role in the evolution processes of FAT, such as settling deformations. 16 published sandbox analogue modelling, which have different setting background on material and thickness of detachment, number of detachment layer, velocity and direction of baffle, and deformation stages, were collected and re-explained to clarify the structural style, forming and progressive processes of back thrusts which may provide the clues on active fault discussion. We find that: (1) it is easier for a back thrust to initiate from the root part of a fore thrust (FT). If the elder BT move with FT, the new-born BT will form on the previous position of the elder BT, which corresponding to the new foot-wall of the elder BT. On the contrary, when an elder BT does not move with the hanging wall of FT, there will be no enough space in the foot wall, thus the new-born BT will form on the hanging-wall of the elder BT. (2) Space is an important factor during BT group progressing. Obvious space barrier makes the BT group progress out-of-sequencely, while abundant progressive space provide an environment of in-sequencely propagation. (3) A strong detachment with enough thickness provides an opportunity to transfer the deformation forwardly and preferentially, until the deformation comes across barrier. (4) Detachment can de-couple the deformation above and below it as a soft barrier, make the deformations form in different neighbor structural level alternatively.
How to cite: Yang, W.-X., Yan, D.-P., Zhou, Z., Sun, M., and Zhu, L.: Forming condition, position and evolution of back thrusts in the sandbox analogue modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14170, https://doi.org/10.5194/egusphere-egu25-14170, 2025.
Salt-detached fold-and-thrust belts have been described as having an extremely narrow cross-sectional taper, a regular structural spacing, and lack of a dominant structural vergence. However, detailed evaluation of several natural examples shows unclear structural geometries and intricate salt-sediment contacts. Geometries associated with these systems include overturned panels, large-transport thrust sheets, frequent changes in structural orientations and fold plunges, missing stratigraphic units, abrupt thickness changes and geological contacts either omitting or repeating stratigraphy marked strained evaporites and welds. The main reasons for these are: the inherent weakness of salt and the presence of early salt structures (i.e. pre-shortening) associated with a non-layer cake stratigraphy developed on salt-bearing rifted margins.
Based on both analogue and numerical models inspired in several natural case studies (Alps, Pyrenees) we here provide structural and stratigraphic templates to recognize such salt-related structures: downbuilding is represented by vertical aggradation of syn-kinematic strata, erosional truncation of megaflaps and resedimentation of salt-sediment debris. Salt-detached extension is represented by the sharp truncation of minibasin strata against triangular diapirs, while the widening of minibasins by means of shoulders, growth wedges and secondary minibasins illustrate the progressive transition from downbuilding to salt-detached extension in the evolving thermal phase. Truncation of syn-kinematic strata within the expanding wedges along with the occurrence of cusps at the salt-sediment contact also mark the transition from downbuilding into salt-detached extension.
Recognition of these features in geological maps, seismic data or through the interpretation of well intersections provide geometrical constrains to lower the uncertainty in building balanced cross-sections, and are key for reconstructing the depositional history of salt-bearing rifted margins.
How to cite: Granado, P., Santolaria, P., Strauss, P., Bakhtibar, M., Estiarte, M., Canova, D., Castro, V., Ruh, J. B., Snidero, M., Ferrer, O., Roca, E., and Muñoz, J. A.: Diagnostic criteria of salt-bearing rifted margins structures on fold-and-thrust belts: insights from modelling applied to natural case studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20909, https://doi.org/10.5194/egusphere-egu25-20909, 2025.
The Orobic Thrust is a prominent regional-scale fault zone extending over 80 km, recognized as one of the largest structures in the retro-belt of the European Alps. It represents a significant tectonic boundary where the Variscan basement is thrust southward over the Upper Carboniferous to Lower Triassic volcano-sedimentary cover of the Southalpine Domain. Several well-exposed cross sections of the entire fault zone, approximately 250-300 m thick, allow a comprehensive reconstruction of its architecture and evolution.
A distinctive 20-25 m protomylonitic band at the top of the fault zone, coupled with thermal maturity analyses of clay minerals in the footwall, indicates temperatures of at least 300 °C during the early stages of activity. Field and microstructural analysis identified four distinct Brittle Structural Facies (BSF) within the fault zone: cataclasites, foliated cataclasites, pseudotachylyte-bearing cataclastic bands, and incoherent fault gouges. With the exception of fault gouges along undeformed planes, these facies exhibit mutual crosscutting relationships, evidencing a history of alternating seismic slip and aseismic creep.
SEM imaging, minerochemical analyses and quantitative microstructural analyses were performed in order to better characterize the BSF. Our results show that multiple BSFs can be observed at the microscale, with up to five seismic slip events recorded within a single thin section. Analyzing selective clast survival from melting, the clast-to-matrix ratio, grain size distribution, and mineralogical content can help discriminate between different rheological behavior during coseismic slip. Geochronological data provide absolute age constraints on fault activity. Pseudotachylytes yield 40Ar-39Ar ages ranging from 83 to 64 Ma, while illite from gouge material along a reverse fault plane at the core of the zone gives a K-Ar age of 53 Ma. Notably, pseudotachylyte ages show older values (79–83 Ma) at both the top and bottom of the fault zone, with younger ages (76–64 Ma) displaying a bottom-forward trend. These findings illustrate the fault's prolonged activity, with discrete illite gouge-decorated planes extending the activity to the Early Eocene.
The Orobic Thrust, active from the Late Cretaceous to the Early Eocene, functioned as a pre-collisional fold-and-thrust belt within the upper plate of the Alpine Tethys subduction system. Its extended 30-million-year history highlights the capacity of regional-scale fault systems to undergo multiple reactivations under changing thermal and stress conditions.
How to cite: Zanchi, A., Favaro, S., Rocca, M., Chiara, M., Giulio, V., Luca, A., and Stefano, Z.: The Orobic Thrust: A Long-Lived Regional Fault Zone in the European Alps – Architecture, Evolution, and Geochronological Insights, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20196, https://doi.org/10.5194/egusphere-egu25-20196, 2025.
The research was conducted in the Dinarides in two test areas, Posušje and Jajce in Bosnia and Herzegovina, where bauxite has been intensively exploited since the second half of the 20th century. The explored bauxite deposits were formed in two emersions, terrestrial geological phases in the geological history. In the Jajce area, the deposits originate from the horizon within the Middle Cretaceous, while in the Posušje area they were formed in the emersion between the Upper Cretaceous and Paleogene rocks. Two basic goals of the research in the test areas were set. The first goal is to determine the possibility of directly discovering bauxite deposits, and the second is to determine lithological and structural relationships in very complex geological models. The expected result of the research is to increase the efficiency of geophysical methods and thus reduce the overall costs of exploring bauxite deposits. Ground geophysical methods (GGM) were applied, that could contribute to solving the problem, on the basis of previous experiences in exploring karst areas. These are the methods based on the determination of the inverse resistivity model, electrical resistivity tomography (ERT) and the magneto-telluric method (Controlled Source Audio-frequency Magnetotellurics - CSAMT), and seismic refraction which gives an inverse velocity model.
Research at already discovered bauxite deposits at several micro-sites in the Posušje area showed the deposits are outlined as geophysical anomalies on inverse resistivity and velocity models, that is, bauxite deposits can be directly detected by ERT and seismic refraction if Paleogene limestones are in the hanging wall. However, if there are clastic Paleogene-Neogene deposits, it is very difficult to discover bauxite deposits. In the Jajce area, bauxite deposits could not be recognized on geophysical models, since the hanging wall of the deposits mainly consists of clastic rocks whose resistivities and velocities overlap with the bauxite deposits.
GGM can significantly contribute to the determination of very complex geological models in bauxite exploration. In both research areas, Jajce and Posušje, it was shown that ERT should be considered as a basic research method in determining generally very complex geological models. In combination with other geological data, from the surface and from boreholes, the effectiveness of overall investigations can be significantly increased. One of the main tasks is the mapping of the weathered carbonate bedrock with possible bauxite deposits, especially when clastic rocks, Cretaceous or Paleogene-Neogene, are found in the hanging wall. In the case of a deeper carbonate bedrock, greater than 90 m, the CSAMT method should be applied due to the limited depth penetration of ERT.
Acknoledgments
This exploration was carried out in the AGEMERA project (Agile Exploration and Geo-modelling for European Critical Raw Materials) - the European Union's Horizon Europe research and innovation programme - grant agreement No 101058178.
How to cite: Šumanovac, F., Kapuralić, J., Perković, L., and Grbeš Babić, A.: Exploration of karst bauxite deposits in the Dinarides using ground geophysical methods - possibilities and limitations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1638, https://doi.org/10.5194/egusphere-egu25-1638, 2025.
Sixty years ago, the advent of plate tectonics (Wilson, 1965; Le Pichon, 1968; Morgan, 1968) provided a framework to account for the relationship between lithospheric plate convergence and orogenic evolution. Metamorphic belts with gradients ranging from high-pressure/low-temperature (HP/LT) to low-pressure/high--temperature (LP/HT) nourished the concept of alpinotype and hercynotype orogens (Zwart, 1967) and of hot vs cold orogens (Chardon et al., 2009) attributed to secular cooling of the Earth (Brown, 2007). It also led to the distinction between subduction-type orogens, currently represented by the Cordilleras along the Pacific Ocean, and collision-type orogens exemplified by the Alpine-Himalayan belt (Dewey and Bird, 1970). In this view, plate convergence is first accommodated by subduction and is followed by continental collision, which marks the end of the Wilson orogenic cycle (Wilson, 1966) owing to the low density of the continental crust that impedes subduction (McKenzie, 1969). The concept of subduction-type orogen has been extended in the one of accretionary orogens marked by prolonged subduction of an oceanic plate and successive opening and closure of back-arc basins and associated tectonic accretion of terranes (Collins, 2001; Cawood et al., 2009). In turn, the concept of collision-type orogen has fed the model of indentation based on the India-Asia collision (Molnar & Tapponnier, 1975). This description of the orogenic cycle has been challenged by the documentation of UHP metamorphism attributed to continental subduction (Chopin, 1984) and of extension of previously thickened crust in zones of active plate convergence (Coney & Harms, 1984) ascribed to gravitational collapse (Dewey, 1988; Rey et al., 2001).
These discoveries called for a reassessment of the orogenic cycle in order to capture the variety of orogenic belts as a function of plate kinematics, the fate of the crust along convergent plate boundaries, and the thermal-mechanical evolution of the orogenic crust (Vanderhaeghe, 2009; Vanderhaeghe & Duchêne, 2010; Vanderhaeghe et al., 2012). Convergent plate boundaries are marked, at the lithospheric scale, by slab advance or retreat associated to crust/mantle mechanical coupling or decoupling. Slab advance is characterized by distributed deformation across sutures between former continental blocs and corresponds to indentation. In turn, slab retreat promotes subduction of the continental crust and HP/LT metamorphism, but also exhumation of these units, owing to their buoyancy, into the space induced by extension of the overriding plate. In this case, the orogenic wedge is predominantly constructed by tectonic accretion and vertical extrusion of terranes mechanically decoupled from the downgoing plate. After tectonic accretion, slab retreat induces concomitant thickening of the orogenic crust and thinning of the lithospheric mantle, which favor the construction of a hot, buoyant and weak orogenic crust. Partial melting and gravity-driven flow of the orogenic root control the transition from an orogenic wedge to an orogenic plateau. If plate kinematics changes and/or if the 3D geometry of the plate boundaries comprises a free boundary, lateral flow of the orogenic crust might result in gravitational collapse of the orogenic belt. These different stages of orogenic evolution are pictured examples in the Alpine and Variscan orogenic belts.
How to cite: Vanderhaeghe, O.: A reappraisal of the orogenic cycle : thermal mechanical evolution of orogens along convergent plate boundaries, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3341, https://doi.org/10.5194/egusphere-egu25-3341, 2025.
The collapse of orogenic belts is commonly thought to involve viscous flow in a mid-crustal channel, and manifests as extensional faulting in the upper crust. Recent observations in some orogenic belts have indicated a power-law relationship between local elevation and extensional strain rates. Simple mechanical considerations predict that the flow of the weak crustal layer beneath these belts is driven by topographic gradients, suggesting that the observed extension is linked to this flow. To test this hypothesis and examine the temporal evolution of collapsing orogenic belts, we developed a 2-D numerical model simulating how topography-driven viscous flow in the weak mid-lower crust induces, and is affected by, orogenic belt extension. Our results show that flow of a weak mid-lower crust triggers orogenic collapse via normal faulting, provided mountain height exceeds a critical threshold (hmin). The simulated faults form within the highest regions of the orogen, where the weak crustal layer flow originates. Once the mountain collapses so much that its height falls below hmin, extension ceases, where hmin depends on both the thickness of the weak layer and the strength of the upper crust. Additionally, we find that collapse rates increase with hotter and thicker weak channels, taller orogens, and weaker upper crustal faults, while stronger upper crust restricts fault distribution, concentrating deformation within smaller areas, leading to a core complex extension mode. Finally, a strong agreement between our numerical and analytical (detailed in companion abstract: Aharonov et al., (2025) EGU General Assembly 2025) models demonstrates that orogenic collapse rates and their temporal evolution are jointly controlled by the brittle and ductile properties of the continental crust.
How to cite: Dawood, R., Olive, J.-A., and Aharonov, E.: How Coupled Brittle-Ductile Deformation Controls the Rates and Temporal Evolution of Orogenic Collapse, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16632, https://doi.org/10.5194/egusphere-egu25-16632, 2025.
The Cadomian Orogeny, an accretionary orogen around Gondwana, was extensively reworked during the Paleozoic Variscan Orogeny. In SW Iberia, a structural, geochronological and tectonometamorphic study of the Mina Afortunada Massif identified two Cadomian deformation phases. The first phase (DC1; ~586 Ma, U-Pb dating of inherited garnet) represents the ophiolite acrection during the closure of a back-arc or intra-arc basin, identified as the Cuartel Ophiolite. This phase is preserved as internal foliation in Ediacaran metasedimentary rocks. The second deformation phase (DC2; 515–485 Ma) is marked by a penetrative foliation in the Mina Afortunada Gneiss (~515 Ma) and the absence of deformation in overlying Ordovician sediments (~485 Ma). Extensional tectonics during DC2 facilitated early exhumation of the Cadomian suture zone, evidenced by telescoped metamorphic isograds and low-angle normal faults. Later Variscan deformation overprinted Cadomian structures and played a significant role in further exhumation. Geochronological and structural correlations link the Cuartel Ophiolite to the Mérida ophiolite (SW Iberian Massif), being fragments of a single Cadomian suture zone located at the northern margin of Gondwana. This work highlights the potential duplication of suture zones in reworked orogens, especially after ophiolite accretion.
How to cite: Moreno-Martín, D., Díez Fernández, R., Albert, R., Sánchez Martínez, S., Rojo Pérez, E., Gerdes, A., and Arenas, R.: Tectonometamorphic evolution and structural overprinting of a Cadomian suture zone in SW Iberia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3615, https://doi.org/10.5194/egusphere-egu25-3615, 2025.
The Taiwan orogeny, a notable example of arc-continent collision, features complex geological structures, rapid exhumation, and dynamic deformation. To better understand these processes, we developed advanced thermomechanical models incorporating dehydration and hydration of serpentinite, partial melting and magma migration in the mantle wedge, elasto-visco-plastic rheology, lithology-dependent erosion, and observed boundary geometries. These models successfully replicate key features of the Taiwan orogeny, including fault distributions, seismicity patterns, and metamorphic temperature profiles. They align with thermochronological records, accurately reflecting rates of exhumation and cooling, and reproduce strain distributions and structural complexities consistent with geodetic and geological data. This study highlights the effectiveness of thermomechanical modeling in capturing the evolution of arc-continent collision zones, offering insights into the driving mechanisms of mountain building. These findings provide a valuable framework for exploring similar tectonic settings globally.
How to cite: Tan, E., Lee, Y.-H., Chen, C.-H., Hung, S.-H., Zheng, M.-J., Chang, J.-B., and Shyu, C. J.: Arc-continent collision and mountain building processes of the Taiwan orogeny, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10300, https://doi.org/10.5194/egusphere-egu25-10300, 2025.
Tomotectonics hindcasts paleo-trenches, through the spatiotemporal superposition of subducted lithosphere (slabs imaged in the earth’s mantle) with plate reconstructions (constrained by seafloor isochrons). The two geophysical datasets are linked through the tomotectonic null hypothesis, that oceanic lithosphere sinks vertically down after entering in the mantle. This linkage permits simple and testable predictions about the location and lifespan of volcanic arcs, and specifically about arc-continent collisions, switches in subduction polarity, and switches from consuming to transform plate boundaries. In a second stage, tomotectonics uses land geological observations from the accretionary orogen in order to test predictions arising from the geophysical data sets.
We have applied the tomotectonic method to the North American Cordillera, where lower-mantle slab geometries indicate the nearly simultaneous initiation (~200-180 Ma) of three intra-oceanic archipelagos in the northeastern proto-Pacific (figure: MEZ, ANG, and CR slabs). Westward subduction beneath 10,000 km-long MEZ and ANG pulled North America from Pangaea, opening the Central Atlantic. Coeval eastward convergence of Farallon plate beneath intra-oceanic CR is predicted from Pacific seafloor isochrons. This configuration of subduction zones facing each other across an archipelago is analogous to today’s southwest Pacific, where Australia, embedded in Indian/Tethys Ocean floor, and the Pacific Ocean are drawn in by double-sided subduction.
Each slab must be associated with a paleo-arc. Central and controversial in formation accounts of the Cordilleran has been the Insular microcontinent (INS, comprising Peninsular, Alexander, Wrangellia superterranes of Alaska and B.C.) and its southward extension of Guerrero superterrane (GUE) of Mexico. When, where and in what style did MEZ accrete to North America? Did INS subsequently translate thousands of kilometres along the margin (the “Baja-BC” debate between geology and paleomagnetism)? How did INS unite with the remainder of accretionary terranes that form Alaska?
We demonstrate how tomotectonics hindcasts the INS journey. Massive MEZ slab wall fixes INS-GUE’s initial, stationary, offshore position – in an accretionary regime. Full consumption of North American oceanic lithosphere, pulled beneath INS-GUE arcs, caused diachronous collision from ~155 Ma to ~90 Ma (Nevadan-Sevier deformation), leaving a trail of collapsed basins. Subduction was gradually forced outboard of MEZ: flip to Farallon subduction, eastward beneath INS-GUE (now attached to North America), brought another accretionary episode of Franciscan and Chugach subduction complexes, linked to Sierra Nevada and Coast Mountain batholith arcs.
Northward translation of INS by ~2000 km between 90-50 Ma (the “BajaBC” regime) corresponds with a lack of subduction (slab) beneath the paleo-margin. A key result is that both tomotectonics and paleomagnetic observations, which are completely independent, support large-scale translation.
Simultaneously, INS and North Americal collided obliquely with Central Alaska and Farallon arcs in a second collisional phase ~100-50 Ma, again in double-sided subduction. Since 170 Ma, Insular micro-continent experienced all regimes of modern double-sided archipelagos: subduction accretion, collision, subduction flip, and transform.
Reference: Sigloch, K. & Mihalynuk, M.G. (2025), Tomotectonics of Cordilleran North America since Jurassic times: double-sided subduction, archipelago collisions, and Baja-BC translation. In review (revision) with GSA Books. Preprint: https://eartharxiv.org/repository/view/7460/
How to cite: Sigloch, K. and Mihalynuk, M. G.: Journey of the Insular micro-continent through accretionary, collisional and translational regimes in the North American Cordillera since 170 Ma: a tomotectonic case study., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7466, https://doi.org/10.5194/egusphere-egu25-7466, 2025.
We use a wide database of pressure (P), temperature (T) and petrochronological data from late Neoproterozoic to early Mesozoic metamorphic rocks together with a review of compressive and extensional tectonic cycles to evaluate and correlate the tectonothermal and temporal evolutions of the Mongolian and the Tarim–North China collages forming the Central Asian Orogenic Belt. In the Mongolian Collage, metamorphic pressure–temperature (P–T) and timing reveal a one-stage evolution defined by a duality of late Neoproterozoic–Ordovician subduction-related low T/P metamorphism and suprasubduction high T/P metamorphism recorded in the Mongolia–Manchuria and Baikal–Sayan belts. This was followed by gradual prevalence of suprasubduction high T/P metamorphism towards the late Paleozoic corresponding to the Altai and South Altai cycles. In the Tarim–North China Collage, metamorphic P–T and timing reveal a two-stage evolution, from dominant intermediate T/P metamorphism possibly resulting from Ordovician–Devonian amalgamation and Andean-type evolution of the collage, to dual low and high T/P metamorphism in the Carboniferous–Permian reflecting subduction–collision processes along the South Tianshan suture in the west and a suprasubduction evolution along the Solonker suture in the east. Altogether, the Paleozoic tectonometamorphic evolution of the two collages shows remarkable differences, with the Mongolian Collage displaying features typical of peripheral accretionary cycle reflecting recurrent tectonic switches that can be regarded as a single orogenic system, and a two-stage evolution of the Tarim–North China Collage with features of both peripheral–accretionary and interior–collisional orogenic cycles, but mostly related to recurrent subductions of interior oceans. Furthermore, the Paleozoic tectonic cycles recognized in the Mongolian and Tarim–North China collages are tentatively correlated to distinct retreating and advancing subduction dynamics of Paleozoic oceanic domains.
Funding: This research was funded in part by the Polish National Science Centre (Grant DEC-2023/51/D/ST10/02611/R). K.S. and P.S. acknowledge the support of the Czech Science Foundation (grant number 19-27682X to K.S.) and of an internal grant of the Czech Geological Survey (number 329805 to K.S.). J.S. acknowledges the support of project No. 2021/43/P/ST10/02996 co-funded by the National Science Centre and the EU H2020 research and innovation program under MSCA GA No. 945339.
How to cite: Soldner, J., Schulmann, K., Štípská, P., and Jiang, Y.: Paleozoic tectonothermal history of the amalgamation of theTarim–North China and Mongolian collages, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8647, https://doi.org/10.5194/egusphere-egu25-8647, 2025.
The Altaids, (also termed as Central Asian Orogenic Belt, CAOB), world’s largest Phanerozoic accretionary orogen, is characterized by multiple collages of juvenile crust, and whether significant tectonic contraction occurred or not during its amalgamation with old continents on its south is unclear. Here, we present zircon U-Pb-Hf and whole-rock geochemical study on middle-late Permian high silica granites in Siziwangqi area of the northern margin of North China Craton (NCC). These rocks from the batholith were formed at ~262-267 Ma, and those from adjacent or individual stocks at ~255-257 Ma. All these granitic rocks were mainly derived from late Archean to Mesoproterozoic rocks of the NCC and similar cases documented commonly along the northern margin of the NCC, indicating a widespread crust-reworking there. Together with coeval compressional structures, accompanying sedimentary records and continental uplift there, this crust-reworking probably resulted from crust shortening by intensive tectonic contraction there. We propose that this tectonic contraction was caused by a collisional event related to closure of the Paleo-Asian Ocean (PAO), supported by: (1) rock change with significant decrease of arc-related magmatism in the northern NCC at ~250-270 Ma, (2) roughly coeval mixing of the Tethyan and Boreal realm fauna of marine strata in the southern CAOB, (3) disappearance of marine strata replaced by continental strata there after ~260 Ma, and (4) occurrence of significantly closer paleolatitudes (~0-5°) between the North China and Mongolia collages after ~260 Ma. Comparatively, the wide CAOB accretionary zone has insignificant contraction, commonly occurred in accretionary orogens. We infer that such difference is due to different crust architecture resulted from different directions of subduction of the PAO.
This research was financially supported NSFC Project (42102260), Hong Kong RGC GRF (17307918), and HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100), Fundamental Research Funds for the Central Universities, CHD (300102272204), Croucher Chinese Visitorship (2022-2023) from Croucher Foundation, and the Youth Innovation Team of Shaanxi Universities.
How to cite: Zhou, H., Zhang, Q., Zhao, G., Han, Y., and Wu, Y.: Significant crust remelting and accompanied continental uplift during contraction of the amalgamation of world's largest Phanerozoic accretionary orogen (Altaids) with North China Craton, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-53, https://doi.org/10.5194/egusphere-egu25-53, 2025.
During the Middle Devonian-earliest Carboniferous, the sedimentation in North-East Greenland was characterised by the deposition of Old Red Sandstone (ORS) molasse in the Hudson Land Basin. In this area, Givetian conglomerates of the Vilddal Group, which postdate a first stage of Caledonian folding, unconformably sit on the core of large-scale anticlines and above a deep erosional surface that exposed Late Silurian migmatitic rocks of the lower part of the Nathorst Land Group. The ORS succession records folding and intrabasinal unconformities that are associated with the activation of extensional faults and subsequent compression and thrusting (Guarnieri 2021).
In Parkinson Bjerg, Middle Devonian sandstones of the Ankerbjergselv Fm rests in tectonic contact with Neoproterozoic metasandstones of the Nathorst Land Group in the footwall of a top-to-SW brittle/ductile extensional fault: the Dybendal Detachment. Rhyolitic and basaltic flows are intercalated within the sedimentary package at different stratigraphic levels and lie in the hanging wall of the detachment. The Dybendal Detachment is probably a splay of the Payer Land Detachment (Gilotti and Elvevold 2002) along which Lower Paleozoic carbonate rocks rest tectonically in contact with Paleoproterozoic gneisses that reached HP/HT granulite facies conditions, along a SW-dipping mylonitic zone. The peak metamorphism was dated at c. 405 Ma (Gilotti and Elvevold 2002) followed by partial melting of metapelites associated with isothermal decompression, probably during the Middle-Late Devonian, leading to the emplacement of a metamorphic core complex.
Tin mineralization associated with granitic intrusions in Parkinson Bjerg has been known since the mid-fifties of the last century (Harpøth et al., 1986) and recent U-Pb ages from cassiterite found in greisen floats, established a Devonian age for the mineralization (Keulen et al., 2024).
The structural setting of the Devonian intrusions in the footwall of the Dybendal Detachment suggests a correlation between magmatism and partial melting of the Payer Land gneisses during the emplacement of the metamorphic core complex.
References
Gilotti, J. A., & Elvevold, S. 2002. Extensional exhumation of a high-pressure granulite terrane in Payer Land, Greenland Caledonides: Structural, petrologic and geochronologic evidence from metapelites. Canadian Journal of Earth Sciences, 39, 1169–1187. https://doi.org/10.1139/e02-019.
Guarnieri 2021. Devonian–Early Carboniferous thrust tectonics in the Old Red Sandstone Molasse Basin, North-East Greenland. Terra Nova 33, 521-528. https://doi.org/10.1111/ter.12544
Harpøth, O., Pedersen, J.L., Schønwandt, H.K. & Thomassen, B. 1986. The mineral occurrences of central East Greenland. Meddelelser om Grønland, Geoscience 17, 139 pp.
Keulen, N., Rosa, D., Heredia, B., Malkki, S., Whitehead, D., Thomsen, T. B. 2025. Tungsten and tin occurrences in East-Greenland, Geology & Ore 39, 12p.
How to cite: Guarnieri, P., Rosa, D., and Baker, N.: Devonian granites and Tin mineralization in the footwall of the Dybendal Detachment in Hudson Land (North-East Greenland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20261, https://doi.org/10.5194/egusphere-egu25-20261, 2025.
Posters on site: Tue, 29 Apr, 10:45–12:30 | Hall X2
A prominent tectonic feature in northeastern Taiwan, the Ilan Plain, has played a critical role in the structural evolution of Oligocene and Miocene strata during the opening of the Okinawa Trough. Despite its significance, the geological map of around this region remains unclear, particularly regarding how backarc extension during the later stages of the Taiwan orogeny affected the faulting and folding of these strata. Dense vegetation has posed significant challenges to field-based structural investigations, limiting our understanding of the region’s tectonic processes. To overcome these challenges, we applied 3D LiDAR mapping, a high-resolution technique capable of removing dense vegetation and providing detailed topographic and structural information. The results of our study have dramatically improved the mapping of sedimentary strata and geologic structures, revealing a previously unrecognized 3–4 km-wide zone of normal faulting in the Oligocene Szeleng and Kankou Formations, while the folded Miocene strata exhibited minimal normal faulting. Furthermore, we identified several new fault systems, including the Dajinmianshan normal fault system, and observed that the faults are characterized by relatively small displacements, as indicated by minor offsets in sedimentary layers. This study underscores the transformative potential of 3D LiDAR mapping in resolving ambiguities in densely vegetated and poorly mapped regions, offering new insights into the structural evolution associated with the Okinawa Trough's backarc opening. Future research should focus on determining the ages of these structures to better understand the timing and mechanisms of extension and exhumation, shedding light on the interplay between tectonic forces and geomorphic processes in shaping this tectonically active region.
How to cite: Chan, Y.-C., Sun, C.-W., Chang, K.-J., and Hsieh, Y.-C.: Enhanced Mapping of Fault Structures and Normal Faulting in Northeastern Taiwan: Insights into Tectonic and Geomorphic Evolution During Okinawa Trough Opening, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2424, https://doi.org/10.5194/egusphere-egu25-2424, 2025.
The Korean Peninsula, in East Asia alongside China and Japan, is tectonically linked to these neighboring regions. Notably, the Qinling-Dabie-Sulu Belt, located between the North China Craton (NCC) and the South China Craton (SCC), includes intervening microcontinents and has been proposed to extend into the Korean Peninsula. However, robust tectonic correlations were not made due to a lack of understanding of detailed geology for both regions. Within the Korean Peninsula, the Western Gyeonggi Massif has been tectonically linked to this belt, preserving evidence of Permo-Triassic orogeny and a related fold-thrust belt associated with a subduction followed by a collision.
The Taean area of the Western Gyeonggi Massif is a part of this Permo-Triassic fold-thrust belt and retains typical contractional fold-thrust belt structures. The Paleoproterozoic Seosan Group, which forms the basement underlying the Paleozoic Taean Formation, shows systematic NE-SW trending repetitions in map view. To decipher the structural geometry of these repetitions in the Taean area, structural geometric interpretations have been conducted based on detailed field mapping. The results reveal that the overall structural geometry of the study area comprises NE-SW trending overturned folds. These folds plunge to the southwest in the northern, southern, and eastern parts of the area, and the northeast in the central part. This multi-plunging asymmetric fold geometry, displaying northwest vergence, can be interpreted as second-order folds within the hanging wall of the regional-scale fault located in the eastern part of the study area. These fault-related folds suggest basement-involved deformation possibly related to the Permo-Triassic collisional orogeny preserved in central-western Korean Peninsula, based on the newly obtained SHRIMP titanite U-Pb age (ca. 205 Ma) of a deformed mafic intrusion in the study area.
Understanding the spatial and temporal evolution of these structures will provide valuable insights into the tectonic significance of the orogenic belt in the Western Gyeonggi Massif of the Korean Peninsula. This, in turn, will enhance our understanding of the role of the Korean Peninsula in the tectonic evolution of the East Asian continent as a whole.
How to cite: Park, S., Kang, M., Jang, Y., Kwon, S., and Samuel, V. O.: Structural geometry of the Taean area in the Western Gyeonggi Massif: Implications for the tectonic evolution of the Korean Peninsula and East Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5517, https://doi.org/10.5194/egusphere-egu25-5517, 2025.
Fold-and-thrust belts (FTBs) usually develop in the external zones of the orogens, between the mountain belt and the foreland basin. The structural style of FTBs varies greatly depends on the mechanical stratigraphy and the influence of inherited tectonic features. Back-thrusts are structures typical of FTBs, but they are commonly less frequent than fore-thrust. The Variscan FTB outcropping in SW Sardinia is characterized by the extensive development of back-thrusts that affect a poly-deformed and mechanically heterogeneous stratigraphic succession, suggesting a cause-and-effect relationship. We investigate the geometry and kinematics of back-thrusts and the role of structural inheritance, in order to better understand the mechanism of their progressive development.
The Variscan FTB of SW Sardinia consists of two stacked tectonic units, the Iglesiente and Arburese units, separated by a regional Variscan structure, the Arburese thrust. The Iglesiente Unit has been overthrusted by the Arburese Unit with a top-to-the-west transport direction during the collisional phase of the Variscan Orogeny, in Early Carboniferous times.
The geological setting of the Iglesiente Unit arises from a complex stratigraphic and tectonic evolution because of the superposition of the lower Cambrian extensional tectonics, the compressional Ordovician Sardic Phase and the Variscan deformation. The following superposed structures characterize the Iglesiente Unit: 1) N-trending normal faults; 2) E-trending Sardic close folds; 3) E-trending Variscan open folds, 4) N-trending Variscan inclined folds; 5) Variscan fore- and 6) back-thrusts. As the back-thrusts are the youngest structures, they develop in a non-layer cake stratigraphic succession, cutting across strata whose steepness ranges from horizontal to vertical and the strike varies from parallel to perpendicular to the thrusts.
Our findings from field surveys and cartographic and structural analysis suggest that the extensive back-thrusting development is due to the occurrence of the structural domes that acted as an inherited buttress that prevents the fore-ward propagation of deformation. The structural domes formed because of the superposed E-trending Sardic and N-trending Variscan folds and consists, at the core, of sandstones, limestone and dolostones of the lower Cambrian succession.
During their progressive emplacement, the back-thrusts cut across the Sardic folds, that have the axes perpendicular to the back-thrusts strike. Thus, back-thrusts cut across vertical strata in the limbs of the fold and sub-horizontal strata in the hinge of the fold. We infer a relationship between steepness and displacement of back-thrusts and the attitude of the strata involved. Moving from the limb to the hinge of the folds, the steepness and the displacement of the back-thrust decrease. The geometry of the thrust surface varies accordingly, taking up either a synformal shape when cut across a hinge of a synform dipping in the same dip direction of the thrust, or an antiformal shape when cut across a vertical limb perpendicular to the thrust strike. Thus, what looks like a folded back-thrust is rather an effect due to the geometric and mechanical anisotropies of the involved stratigraphic succession.
How to cite: Cocco, F. and Funedda, A.: Large-scale back-thrusting development in fold-and-thrust belts: the case study of the Variscan External Zone of Sardinia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16259, https://doi.org/10.5194/egusphere-egu25-16259, 2025.
The Okcheon fold-thrust belt, located in the southern Korean Peninsula, serves as a natural laboratory for understanding the formation and evolution of the orogenic belts along the East Asian continental margin during complex Paleozoic tectonics in East Asia. The belt preserves various sedimentary basins developed at different geological times and tectonic settings, which have experienced various orogenic events forming an area of significant scientific debate. This study integrates biomarker analysis, and U-Pb detrital and igneous zircon geochronology to redefine the stratigraphy of the Okcheon belt. Redefined stratigraphy, cross-section profiled constructions using down-plunge projections, structural interpretations based on detailed field survey, and cross-section balancing were conducted to figure out new insights into the structural evolution of this belt. These together with evidence from previously reported publications, the spatiotemporal scenarios for the evolution of the Okcheon fold-thrust belt could be summarized as follows. (1) The Okcheon Belt was formed during the Neoproterozoic intracontinental rifting resulted in the creation of a rift basin in the Taebaeksan Zone. This is followed by subsequent deposition of miogeoclinal carbonate sediments, known as the Joseon Supergroup. Throughout this time, the Okcheon Zone remained as a basement high without sedimentation. (2) During the Devonian, sporadic magmatic events and contractional deformation in the Gyeonggi Massif supported the higher structural relief of the Gyeonggi Massif than the Okcheon Belt. In addition, the Taebaeksan Zone was higher structural relief relative to the Okcheon Zone in the Okcheon Belt. The differences in basement geometry before deposition of the Carboniferous clastic wedge resulted in differences in depositional environments and lithologic variations in the Okcheon and Pyeongan supergroups. These are supported by previously reported Devonian detrital zircon U-Pb age dates from the meta-sedimentary rocks in the Okcheon Belt, existence of angular unconformity between the Joseon Supergroup and the subsequent supergroups, and distinct lithologic differences between the lower parts of two Supergroups, etc. (3) Finally the Late Permian to Early Triassic marks a significant period in tectonic history of the Okcheon Belt that is characterized by extensive crustal deformation and formation of a complex fold-thrust belt system. Key structural features such as the Bonghwajae Tectonic Window and the Yeongwol connecting-splay duplex support presence of typical fold-thrust features in the central part of the belt. However, other regions like the Gyemyeongsan Thrust and Wachon Klippe display signs of basement-involved deformation, where Proterozoic basement rocks are notably involved in the deformation style. These will provide spatio-temporal evolution of the Okcheon Belt, which will offer significant insight into tectonic processes along the East Asian continental margin during Paleozoic to Early Triassic period.
How to cite: Kim, C., Noh, J., Kim, D., Kwon, S., and Jang, Y.: Tectonic Evolution of the Okcheon Fold-Thrust Belt, southern Korean Peninsula: Insights into Paleozoic Tectonics and Orogenic Processes along the East Asian Continental Margin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5451, https://doi.org/10.5194/egusphere-egu25-5451, 2025.
Orthogonal vein sets, orientated perpendicularly to the bedding, are present in fold-and-thrust belts; yet the date of their origin in relation to orogeny is ambiguous. This research aims to clarify the formation of perpendicular orthogonal vein sets from the iconic outcrops in northern Almograve in SW Portugal, referred to as “Chocolate-Tablet Structures,” which are influenced by the Variscan Orogeny. Establishing whether these vein sets developed earlier than to and/or during the folding associated with the main deformation (i.e., Variscan) requires many independent lines of evidence. Previous investigations, based on limited outcrops, indicate that these veins are vertical and parallel to the Variscan folded strata. We provide a comprehensive structural analysis using drone photogrammetry (with resolutions ranging from a few cm to m) of inaccessible sections of the coastline zone. This research has structurally studied a practically continuous and much longer section of the coast at Almograve and Zambujeira do Mar. Field observations and stereographic projections of several vein sets and the refolded host rock reveal a continuous perpendicular connection between two vein sets, both of which are also perpendicular to the bedding. A genetic relation to the Variscan folding is tempting, but our recent research challenges such prior findings. This study proposes that the perpendicular orthogonal vein sets are the result of hydraulic fracturing, formed during the early phase of the Variscan Orogeny, either via sedimentary loading (hydraulic fracturing) and simultaneously veining or through the stretching of the initial foreland basin due to forebulge-foredeep dynamics.
How to cite: Huseynov, A. A. O., Andeweg, B., and van der Lubbe, J.: Orthogonal extensional quartz veins in a famous 'Chocolate-Tablet Structure' from Almograve (SW Portugal), associated with early Variscan Orogeny, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19399, https://doi.org/10.5194/egusphere-egu25-19399, 2025.
Accretionary orogens grow through frontal accretion and crustal underplating, that contribute to crustal thickening by scraping slices of continental crust from the downgoing plate. Although geophysical data provide insights into the deep structure of these orogens, understanding the modes of crustal accretion in retreating subduction systems and the surface responses to these processes, remains challenging.
This study focuses on the Albanides-Hellenides, a long-lived subduction orogen in the Mediterranean resulted from the eastward subduction of the Adria plate beneath Eurasia since the Late Cretaceous. In the orogenic front, modes of crustal accretion have been influenced by along-strike variations in basal coupling, associated with the increasing thickness of Triassic evaporites toward the south. In the hinterland, extensional tectonics, associated with the retreating slab, led to the development of graben and half-graben structures. This geological setting provides an ideal framework to investigate the combined effect of different tectonic processes on the spatial and temporal patterns of exhumation from the foreland to the orogenic interior. By integrating tectono-stratigraphic and structural data with new and existing low-temperature thermochronological data, we aim to clarify the relationships between cooling patterns, major tectonic structures, and variations in the thickness of the evaporitic décollement level.
In the northern part of the orogen, high basal coupling resulted in crustal-scale structures that confined middle/late Miocene-Pliocene exhumation to the foreland. In contrast, toward the south, low basal coupling conditions limited exhumation related to frontal accretion, while deep crustal-scale structures focused late Miocene–Pliocene exhumation more toward the orogenic interior. In the hinterland, existing data show extension-related exhumation that progressively rejuvenated toward the foreland, from middle Miocene to Pliocene, suggesting slab rollback as dominant geodynamic driver.
Overall, our results demonstrate that from the middle/late Miocene to Pliocene crustal accretion through deep crustal-scale structures occurred at the same time as hinterland extension triggered by slab rollback. This tectonic phase likely marks the most recent stage of a long-term accretionary cycle that has driven orogenic growth by accreting slices of continental crust, contributing to significant crustal thickening in an orogen with retreating subduction boundaries.
How to cite: Rossetti, F., Fellin, M. G., Ballato, P., Faccenna, C., Crosetto, S., Balestrieri, M. L., Muceku, B., Bazzucchi, C., Durmishi, C., and Maden, C.: Deformation styles and exhumation patterns in a long-lived orogen: Insights from the Albanides-Hellenides, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11321, https://doi.org/10.5194/egusphere-egu25-11321, 2025.
In the Andes, reactivated inherited crustal faults play a key role in influencing regional tectonic styles and the areal extent of deformation. Determining the timing of fault activity is essential to reconstruct the sequence of deformation events and their implications for the orogenic evolution of the region. To investigate the history of brittle deformation prior to Cenozoic compressional reactivation in the southern Andean Plateau (Puna), we applied K-Ar illite dating to fault gouges. This method provides insights into the cooling and deformation history of fault systems, offering valuable temporal constraints on tectonic processes. Our study yielded 12 ages from 4 samples, ranging from 299.4 Ma to 122.3 Ma. We interpret these results to document the onset of brittle deformation in the realm of the future southern plateau during the Permian and an early Cretaceous event in the adjacent region where the thick-skinned Eastern Cordillera later evolved during Cenozoic mountain building.
How to cite: Espinoza, D., Strecker, M., Giambiagi, L., Sobel, E., Wemmer, K., and Jaldin, D.: Pre-Cenozoic brittle deformation in the southern Central Andes: K-Ar Illite dating of fault gouge suggest pre-straining of crust in the region of the Andean Plateau and Eastern Cordillera , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15637, https://doi.org/10.5194/egusphere-egu25-15637, 2025.
The Betic Cordillera is a collisional orogen developed during Cenozoic times by the tectonic inversion of a former Mesozoic hyperextended rift system. The region contains an extensive Upper Triassic salt unit that enabled the development of salt withdrawal minibasins and diapirs during rift, post-rift, and inversion stages. Diapir squeezing and the resulting salt extrusion during orogenesis culminated with the advance of a hundreds-of-kilometers-scale salt canopy in the frontal part of the cordillera. Even so, the primary minibasins are exceptionally well-preserved, providing a rare opportunity to analyze their tectono-stratigraphic architecture and the associated salt weld systems.
Based on geological maps, cross-section restoration, and outcrop observations, this communication provides an overview of the structural framework and the sedimentary infill of Sierra Mágina, located in the Central Betic Cordillera. It exposes a set of welded primary minibasins, making it possible to study in outcrop their evolution and their relation to the surrounding salt sheets. Six main asymmetric primary Jurassic to Cretaceous minibasins, developed above Upper Triassic salt, have been identified (south to north: Gargantón, Mata Bejid, Mágina, Almadén, Carluco, and Cuadros). They exhibit a synformal geometry, with sizes ranging from 5-50 km in length and 2.5-5 km in width. Strata steepen and thicken southwards, consisting of 2-3 km of Lower Jurassic carbonates for the southern minibasins (Gargantón, Mata Bejid, Mágina, and Almadén), and 1-2 km of Jurassic and Lower Cretaceous carbonates and pelagic facies for the northern minibasins (Carluco and Cuadros).
The primary minibasins were reactivated during contractional deformation, and the surrounding diapirs were squeezed, creating vertical welds. In the central parts of Sierra Mágina, vertical welds frequently include smears of salt and incorporate folded Lower-Middle Miocene detrital limestones and turbiditic sandstones, which reveal their contractional origin. Vertical welds transition into thrust-welds to the north and northwest, towards the foreland. To the south and southeast, the minibasins are surrounded by allochthonous salt. In the southernmost portion, the Gargantón minibasin exhibits a panel of vertical to overturned strata, with the lower boundary being concordant with the top salt. This extends for several hundreds of meters and displays a hook geometry, which is associated with flaring salt and likely played a significant role during salt sheet extrusion.
At the orogen scale, the minibasins in Sierra Mágina are thinner and have experienced greater reactivation than their equivalents in the main depocenter of the precursor rift system (approximately 5 km thick), currently buried beneath the salt canopy. Shortening was accommodated by salt expulsion and the stacking of minibasins, with moderate thrust-weld displacements of a few kilometers. We hypothesize that the smaller thickness and weaker mechanical behavior of the minibasins in Sierra Mágina favored salt expulsion and localized shortening during contractional deformation.
These outcomes enhance our understanding of the South-Iberian paleomargin's salt tectonic framework and provide new insights into the role of structural inheritance in the evolution of collisional orogens.
How to cite: López-Mir, B., García Senz, J. M., Ramos, A., and Pedrera Parias, A.: Evolution and architecture of reactivated primary minibasins and salt weld systems: outcrop analogues from Sierra Mágina (Central Betic Cordillera, Southern Spain), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7095, https://doi.org/10.5194/egusphere-egu25-7095, 2025.
Fold-and-thrust belts (FTBs) serve as crucial structural elements in regulating crustal shortening and deformation within continental interiors. They exhibit intricate geometric and kinematic characteristics, encompassing various fault-related folds and multiple sets of primary (active) detachment planes at varying depths. It is crucial to determine the sequence of deformation and the interaction between shallow and deep structures within the multiple detachment systems to comprehend geological processes fully in fold-and-thrust belts (FTBs). However, the kinematic model involving the interaction of multiple sets of active detachments, remains unexplored. This study focuses on the western segment of the Southern Junggar fold-and-thrust belt (SJT, also known as the Northern Tianshan FTB), comprising three nearly parallel thrust-fold belts with an east–west trend. We established a four-dimensional evolution model of the SJT based on the interpretation of two‐dimensional seismic reflection profiles and surface mapping, along with forward modeling of shallow and deep structures. The results revealed two sets of active detachments: upper (SJTU) and lower (SJTL) detachment. The SJTU contained the South Anjihai tectonic wedge and the “shallow” Huoerguos anticline while the SJTL contained the Halaand, Dunan, and “deep” Huoerguos anticlines. A comparison of the deformation patterns between the growth strata in the forward modeling and reflection profiles revealed a complex interaction and linkage between the shallow and deep structures. The tectonic landforms on the surface were a result of this interaction. The total amount of shortening remained relatively constant while the shortening accommodated by the SJTU and SJTL exhibited a 24.5% decrease (from west to east) across the transfer zone. Our study contributes to the quantification of shortening transfer between the shallow and deep structures in FTBs and advances the current literature on the mechanisms of crustal shortening. Finally, based on shallow and deep structural interactions and cascading rupture, a multi-scale seismic rupture model for the SJT was proposed, and maximum magnitude was estimated. The cascading rupture of multiple faults raises the upper limit earthquake magnitude, and leads to a greater variety of energy accumulation mechanisms as more faults interact, resulting in the occurrence of strong earthquakes. This also necessitates a reassessment of the seismic hazards associated with such complex foreland thrust belts.
How to cite: Yao, Y., Chen, J., Li, T., Xiao, W.-J., Yang, W., and Di, N.: Interaction between shallow and deep structures in the Southern Junggar fold-and-thrust belt, northern Tianshan, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5545, https://doi.org/10.5194/egusphere-egu25-5545, 2025.
The Calabrian forearc separated from Sardinia ~10 Ma and migrated to the ESE, creating an oceanic basin (the Tyrrhenian Sea) in its wake and colliding obliquely with Apulia to build the southern Apennines. The time transgressive, spatially asymmetric nature of oblique collisions leads to along-strike migration of active geologic processes. Lack of evidence for large thrust earthquakes and conflicting geodetic evidence of Calabria-Apulia convergence contribute to the predominant belief that this process has completely ceased. Indicators of thrusting and steady state uplift from the Pleistocene into the Holocene are evident from field observations in the southernmost internal Apennines (Pollino Massif) and marine terrace ages on the external Apennines along the Gulf of Taranto (Metaponto). Terrace uplift rates increase dramatically southward, reaching a maximum of 1 mm/yr at the boundary between Pollino and Metaponto. Uplift rates may continue to increase southward in tandem with the structural and topographic relief across the Apenninic core, but correlation of marine terraces southward to the Sibari Plain becomes problematic because of steep slopes, erosion, and mass wasting. Any chronology of marine terrace ages used for determination of uplift rates and variability will need confirmation by abundant independent age constraints. Constraining uplift rates may be further complicated by a “corrugated detachment” (CD), a regionally exposed kinematic contact along the topographic axis of the southern Apennines between underlying carbonate and overlying flysch. This surface is believed to represent an active gravity-driven detachment with ESE tectonic transport down–slope of the collision wedge. Ductile deformation features within the exposed carbonate suggest burial depths of 1-2 km, and thus a currently active CD might be buried beneath the marine terraces ESE of the Pollino Massif. An active detachment above a rising footwall could lead to underestimates of tectonic uplift rates, and consequently misinterpretations of seismic risk. Recent advances in InSAR technology can resolve elastic deformation preceding seismogenic fault ruptures, as well as aseismic motion on faults, folds, and slumps through high-resolution velocity fields derived from accumulated datasets over the past decade. A coordinated effort coupling field-based observation, a detailed geochronology of marine and fluvial deposition, and high resolution InSAR analyses is needed to determine whether the current deformation is consistent with a continued Calabria-Apulia collision and to better constrain the seismic hazard in south Italy.
How to cite: Sincavage, R., Seeber, N., Filice, F., Piluso, E., Shen, L., Steckler, M., and Gorski, A.: The progressive southeastward advance of the Calabria-Apulia collision recorded by uplifted Ionian marine terraces, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11734, https://doi.org/10.5194/egusphere-egu25-11734, 2025.
Whether or not the slip rate of intracontinental faults varies through time is of fundamental importance for the spatiotemporal distribution of strain, the strain release during earthquakes and the growth of fault-related topography; however, fault systems for which slip rate estimates over high-resolution scales ranging from millions to thousands of years are lacking (Hetzel et al., 2019). Here, we focused on the Huoerguosi fold-and-thrust belt, Northern Tianshan. Through field geological-geomorphological mapping, drone photography, differential GPS measurements, and analysis of petroleum seismic-reflection profiles, we studied the geometric and kinematic characteristics of the Huoerguosi anticline. It was found that the deep South Junggar Thrust (SJT) along the gypsum bearing Anjihaihe Formation (E2-3a) detachment horizon, characterized by arcuate bending and faulting, controlled the growth of the Huoerguosi anticline, forming a wide and gentle active synclinal curve hinge zone in the southern limb of the anticline. All terraces near the active curve hinge zone exhibited folding deformation, resulting in broad, gentle fold scarps facing south. Through modeling and forward simulation of the growth strata and deformed terraces in the active curve hinge zone of the southern limb of the anticline, a geometric model for the growth strata and sporadically terraces was established, constraining the shortening of the SJT at different time periods. By using the optically stimulated luminescence dating method on fine sand fluvial sediments and granite cobbles, a chronological framework was established for these late Quaternary growth strata and deformed terraces. Combining previous Magnetochronological ages (Charreau et al., 2009) and cosmogenic nuclide ages (Puchol et al., 2017), the slip rates of the SJT at million-to-thousand-year scales were estimated. It was found that the slip rate of the SJT remains almost constant at the million-year scale and exhibits strong fluctuations at the tens of thousands to thousand-year scale, similar to the characteristics of normal faults at different time scales (Mouslopoulou et al., 2009). Comparing to climate records, it seems that there is a strong coupling relationship between the SJT deformation and climate change over the past 300 ka.
References
Charreau, J. et al., 2009, Neogene uplift of the Tian Shan Mountains observed in the magnetic record of the Jingou River section (northwest China): Tectonics, v. 28, p. 2007TC002137, doi:10.1029/2007TC002137.
Hetzel, R., Hampel, A., Gebbeken, P., Xu, Q., and Gold, R.D., 2019, A constant slip rate for the western qilian shan frontal thrust during the last 200 ka consistent with GPS-derived and geological shortening rates: Earth and Planetary Science Letters, v. 509, p. 100–113, doi:10.1016/j.epsl.2018.12.032.
Mouslopoulou, V., Walsh, J.J., and Nicol, A., 2009, Fault displacement rates on a range of timescales: Earth and Planetary Science Letters, v. 278, p. 186–197, doi:10.1016/j.epsl.2008.11.031.
Puchol, N., Charreau, J., Blard, P.-H., Lavé, J., Dominguez, S., Pik, R., Saint-Carlier, D., and ASTER Team, 2017, Limited impact of quaternary glaciations on denudation rates in central Asia: Geological Society of America Bulletin, v. 129, p. 479–499, doi:10.1130/B31475.1.
How to cite: Di, N., Chen, J., Li, T., Li, K.-C., Liu, Q., Pu, Y.-C., Yang, W.-X., and Yao, Y.: Variations in slip rates at the Million to Thousand-Year scale: A Case Study of the Huoerguosi Fold-and-Thrust Belt, Northern Tianshan, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15125, https://doi.org/10.5194/egusphere-egu25-15125, 2025.
The Eaux-Chaudes massif (ECM) of the French Pyrenees consists of a nappe stack located in the western Axial Zone formed during Alpine times. It features a basement-cored recumbent fold nappe with a large overturned limb in Upper Cretaceous carbonates ductily deformed. Paleotemperatures of ~350°C for an autochthonous succession and for the overturned limb, and ~310°C for the normal limb were recorded during the main deformational event, which is equivalent to burial depths of 8-10 km. During the main deformation, syn- and post-deformation calcite veins formed, which could be dated by calcite LA-ICP-MS U-Pb. The whole nappe stack was eventually affected by late backthrusting on top of the Gavarnie thrust.
The rare occurrence of such a fold nappe in the Alpine Pyrenees and the observed ductile strain makes necessary to understand under which conditions it was developed, and to put an age constraint on the ductile event within the history of the massif. Here, we present the results of 2D parametric simulations to address changes between thrust nappes (plastic/brittle-localisation) and recumbent fold nappes (viscous/ductile-distributed) using the thermomechanical staggered finite-difference code LaMEM. The simulations were carried out using a linear viscoelastoplastic rheology with the Drucker-Prager criterion for plasticity. We also present a systematic study of syn- and post-tectonic calcite veins as well as the deformation and exhumation history for the Eaux-Chaudes massif, constrained by means of U-Pb geochronology on veins, low-temperature zircon (U-Th)/He thermochronology and QTQt time-temperature simulations.
Modelling results show that in all cases a footwall backstop causing stress concentration in the stiff Upper Cretaceous (key because allows to identify an alpine recumbent fold) layer (an underlying granite massif in the Eaux-Chaudes case) was necessary to induce recumbent folding. Deep burial and the combination of a thick, weak upper decoupling unit and a lower detachment level are essential features favouring viscous behaviour and spatially distributed deformation, enabling the formation of fold nappes by progressive hinge migration (material particles travel from the normal to the overturned fold limb). On the other hand, shallower conditions, shorter lengths of the stiff layer and lower friction angles of the key layer reduces hinge migration, enhancing instead reverse limb stretching and shearing, which eventually results in strain localisation and thrusting.
Geochronology results indicate that the ductile folding and thrusting event occurred between 48.87±5.66 Ma and 38.14±5.99 Ma (mid Eocene). Cooling ages indicate that the exhumation of the Eaux-Chaudes massif occurred later between ~40-20 Ma, coinciding with the known activity of the Gavarnie and Guarga basement thrusts that raised the Axial Zone of the Pyrenees.
How to cite: Guardia, M., Griera, A., Teixell, A., Caldera, N., Kaus, B., Piccolo, A., Chatterjee, R., Stockli, D., and Stockli, L.: Time constraints and evolution of the Eaux-Chaudes fold nappes (Pyrenees): a study combining 2D numerical simulations, U-Pb geochronology and zircon (U-Th)/He thermochronology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16440, https://doi.org/10.5194/egusphere-egu25-16440, 2025.
The interaction of the lithosphere with surface processes in fold-and-thrust belts often leads to the formation of mineral ore deposits, including economically significant resources like bauxites. These interactions are driven by complex geological dynamics, including crustal deformation, sedimentation, and erosion, which create favourable conditions for ore deposition. Bauxite, an essential ore for aluminium production, has become increasingly critical due to global demand and is now included in the European Union's fifth list of critical raw materials. The Dinarides, a branch of the Alpine Belt in south-eastern Europe, are notable for their multiple bauxite levels, making them an important case study for understanding bauxite ore deposits. The External Dinarides are traditionally divided into two tectonic units: the High Karst Unit and the Dalmatian Unit. Historically, these external Dinarides have been interpreted as a thin-skinned fold-and-thrust belt, characterized by significant horizontal shortening and detachment along sedimentary layers.
This study proposes a new model for the evolution of the Dinarides, mapping the spatial and temporal distribution of bauxites providing valuable insights into the processes that control their formation, with the ultimate aim to provide broader implications for exploration strategies in similar geological settings.
The new model is based on regional balanced and restored cross-section through the External Dinarides of Bosnia and Herzegovina and Croatia that integrates offshore 2D seismic data, borehole data, fieldwork and remote sensing to determine style of deformation, and paleogeographic evolution of this portion of the belt.
The balanced and restored cross-section revises the traditional view, proposing a mixed thin-skinned/thick-skinned tectonic model that emphasizes the role of deep-seated structures and salt tectonics in shaping the region, with much less shortening than previous models. Salt tectonics, involving the deformation of evaporite layers, plays a critical role both in the passive margin stage and its subsequent inversion, localising the deformation and controlling the structural style. In this revised tectono-stratigraphic framework, potential scenarios for bauxite generation, accumulation and preservation are outlined. The combination of surface processes and tectonic activity creates zones where bauxite deposits are likely to be concentrated, both at local (thrust ramp anticlines, diapir roof uplift or extensional footwall uplift) and regional (see level fluctuation, forebulge migration) scales. Understanding these scenarios not only enhances the exploration potential in the Dinarides but also offers valuable analogues for bauxite exploration in other fold-and-thrust belts worldwide.
How to cite: Saura, E., Casini, G., Pavičič, I., and Šumanovac, F.: Geodynamic control on bauxite deposit distribution in fold and thrust belts and their associated foreland basins: the External Dinarides (Croatia and Bosnia-Herzegovina), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18430, https://doi.org/10.5194/egusphere-egu25-18430, 2025.
Bauxites, a key source of multiple critical raw materials, including aluminum, rare earth elements (REEs), titanium, and gallium, have gained renewed interest due to Europe's ambition of becoming the first carbon-neutral economy by 2050. The External Dinarides, part of the Alpine orogenic system, provide an ideal setting for examining the interplay between lithospheric deformation and surface processes in fold-thrust belts, with a particular focus on the formation and preservation of karst bauxite deposits. Multiple emersions with associated bauxite deposits and occurrences have been reported from the Adriatic microplate throughout its tectonio-stratigraphic evolution from rifting to passive margin and tectonic inversion, including Triassic, Jurassic, Lower and Upper Cretaceous, and Paleocene-Eocene age deposits.
This study investigates the tectono-stratigraphic evolution of a portion of the External Dinarides and its controls on the generation and preservation of Late Cretaceous-Paleogene karst bauxites in the Posušje area, Bosnia and Herzegovina.
A 3D geological model was developed using detailed geological maps, borehole data, and remote sensing, integrating structural interpretations and cross-section analyses to determine deformation style, and tectonic control over basin evolution and paleogeography.
The study reveals a complex structural history characterized by both thin- and thick-skinned tectonics, with multiple detachment levels and the inversion of inherited normal faults. Late Cretaceous-Paleogene bauxite deposits are closely associated with the Late Cretaceous to Early Paleocene forebulge uplift and subsequent erosion, where karst-related depressions served as primary traps for bauxite accumulation and preservation. Paleocene to Oligocene syn-orogenic deposits are reviewed in the context of the Dinaric Foredeep Basin's evolution and its progressive migration towards the foreland. Finally, the 3D-modeled top Cretaceous unconformity highlights extensive underexplored areas where bauxite deposits might exist at mineable depths, offering improved targeting efficiency for future exploration campaigns.
Through the integration of tectono-stratigraphic data within a validated structural model, this work provides new insights into the evolution of the External Dinarides and valuable information on the formation and preservation of Late Cretaceous-Paleogene karst bauxites. These findings contribute to enhancing exploration strategies for critical mineral resources in this portion of the fold-thrust belt and other regions with similar geological settings.
How to cite: Casini, G., Saura, E., Pavičič, I., and Šumanovac, F.: Tectono-stratigraphic evolution of the Posušje area, External Dinarides, Bosnia and Herzegovina: controls on bauxite formation and exploration potential, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16074, https://doi.org/10.5194/egusphere-egu25-16074, 2025.
A significant part of accommodated localized deformation in continent-continent collision zones occurs along mechanically weak fault zones inherited from earlier tectonic events, in particular through polyphase rifting of continental margins. Besides the pre-existence of weak zones, the inherited thermal, rheological and geometric characteristics of continental plate margins may affect collision dynamics and promote or impede the subduction or accretion of continental lithospheric slivers. Therefore, the implication of previous rifting dynamics is required when investigating the structural and mechanical evolution of continental collision systems.
In this work, we test the impact of rift-inherited rifted margin architecture on continental collision by using geodynamic numerical modelling. We apply the two-dimensional finite difference numerical code Norma with a locally refined fully staggered Eulerian grid measuring 1000 x 150 km and a Lagrangian marker field tracking deformation. The numerical experiments undergo initial extension of continental lithosphere, followed by a phase of tectonic quiescence and subsequent convergence, ultimately culminating in continental collision. Depending on the amount of extension and whether oceanic lithosphere developed or not, the initial phase of convergence is characterized by oceanic subduction. Our parametric study includes the variation of the thermal conditions of the continental lithosphere, the amount of extension, and the duration of tectonic quiescence, all affecting the rheological and morphological characteristics of the tectonically accreted rifted continental margins.
Modelling results demonstrate that a warmer initial geotherm produce highly-extended wide (>100 km) continental margins with several individual continental crustal slivers in contrast to narrow rifted margins in case of a cold and strong lithosphere. Upon tectonic inversion, a short previous phase of thermal relaxation of the rifting-related mantle upwelling leads to subduction initiation at the former spreading ridge, while >20 Myr of tectonic quiescence results in subduction along one of the continental margins. Ultimately, the inherited crustal and rheological architecture of the extended lithosphere and its thermal state influence the dynamics during orogeny, resulting in either single- or double-verging orogenic wedges. Our study provides further insight into the specific conditions of pre-collisional rifted margins of natural orogens.
How to cite: Ruh, J. B. and Granado, P.: Importance of rifted margin inheritance during continental collision revealed by numerical modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3664, https://doi.org/10.5194/egusphere-egu25-3664, 2025.
Continental margins are generally sites of massive material redistribution related to processes that drive continental erosion. This redistribution in form of large sedimentary fluxes (i.e. increased sediment accumulation rates) and a rapidly adapting submarine topography is responsible for major mobilization and re-mobilization of sediments in the sense that they move under their own means, without direct impact of tectonic forces. In basins with deeply-buried fine-grained clastic sediments, excess pore pressure may result in the formation of mobile shale that deforms in a ductile manner at critical state. Such mobile shale horizons can act as major décollements to gravity-driven fold-and-thrust belts that undergo extension in the proximal part of the margin and horizontal shortening farther offshore. In this study, we investigate the effect of variable pore-pressure distribution on the mechanical and structural evolution of gravity-driven fold-and-thrust belts during delta progradation by applying geodynamic numerical modelling.
Numerical experiments are conducted by a two-dimensional finite-difference mechanical model with a visco-elastic-plastic rheology. The model employs a fully staggered Eulerian grid of 500 km width and 25 km height, and a Lagrangian marker field to track deformation. All across-boundary velocities are set to zero. Elastic rigidity of the base allows for lithospheric flexure related to the load of the prescribed prograding delta. Mobile shale forms when material undergoes pore-pressure-dependent brittle failure, following a Bingham-type rheology (i.e., viscous deformation above brittle strength threshold).
Preliminary results reveal that delta progradation and deep shale mobilization lead to the formation of gravity-driven tectonics with three distinct structural domains: landward fault-bounded extensional basins, a transitional zone of shale beneath a mostly undeformed continental slope, and a seaward fold-and-thrust belt at the delta toe. These features are consistent with structural patterns observed in gravitationally unstable Cenozoic deltas, such as the Niger Delta. This study provides insights into the fundamental links between deltaic sedimentation, fluid pressure profiles, and margin-scale gravity spreading, with implications for understanding passive margin tectonics and hydrocarbon exploration.
How to cite: Roy, W. and Ruh, J.: Numerical modelling of gravity-driven fold-and-thrust belts at passive continental margins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6538, https://doi.org/10.5194/egusphere-egu25-6538, 2025.
Oceanic domains can be characterised by lithological heterogeneities, such as microcontinents and continental ribbons, with dimensions vary from tens to hundreds of kilometres. In particular, microcontinents are completely detached from continental margins and isolated by oceanic lithosphere (Gaina & Whittaker, 2020). While previous works have analyzed the impact of various rhological parameters on the evolution of subduction systems characterized by oceanic plateaus, seamounts, or microcontinents (e.g., De Franco et al., 2008; Tetreault & Buiter, 2012), these models typically focused on very large terranes located at significant distances from the initial trench (150-200 km), emphasizing mechanical effects with less attention to thermal effects. Here, our goals are 1) to evaluate the effects on the microcontinent subductability of different lengths (ranging from 25 to 100 km long) of microcontinents located at varying distances from the upper plate (ranging from 25 to 100 km) and of different velocities of the plates; and 2) to analyze the thermo-mechanical effects induced by the collision or the subduction of the microcontinents.
We observed that four different styles of subduction can develop when microcontinents are introduced into the system: (1) continuous subduction; (2) continuous subduction with jump of the subduction channel; (3) interruption and reinitiation of the subduction; (4) continental collision. Our results show a direct dependence between the length of microcontinents, the length of the inner ocean, and the capability to be subducted or accreted. In general, continuous subductions after the collision of the microcontinent do not occur if the microcontinent is equal to or longer than its initial distance from the trench. We also observed that subductability of the microcontinent is favored for higher velocities of the upper plate, while it is more difficult in case of higher velocities of the lower plate. Therefore, the velocity of both plates and the length of a microcontinent are significant parameters to consider for better constraining geodynamic reconstruction in the case of exhumed rocks characterized by contrasting maximum pressure recorded (Regorda & Roda, 2024).
References
C. Gaina & J. Whittaker, 2020. Microcontinents. Encyclopedia of Solid Earth Geophysics. Ed. by H. K. Gupta. Encyclopedia of Earth Sciences Series. Springer, Cham, doi:10.1007/978‐3‐030‐10475‐7_240‐1.
R. De Franco, R. Govers & R. Wortel, 2008. Nature of the plate contact and subduction zones diversity. Earth and Planetary Science Letters, 271, 245–253, doi:10.1111/j.1365‐246X.2008.03857.x.
A. Regorda & M. Roda, 2024. Thermo‐Mechanical Effects of Microcontinent Collision on Ocean‐Continent Subduction System. JGR: Solid Earth, 129, e2024JB029908, doi:10.1029/2024JB029908.
J. L. Tetreault & S. J. H. Buiter, 2012. Geodynamic models of terrane accretion: Testing the fate of island arcs, oceanic plateaus, and continental fragments in subduction zones. Journal of Geophysical Research: Solid Earth, 117, doi:10.1029/2012JB009316.
How to cite: Regorda, A. and Roda, M.: 2D numerical analysis on microcontinents subductability: subduction or collision?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3298, https://doi.org/10.5194/egusphere-egu25-3298, 2025.
The Andaman and Nicobar region is a geologically complex area characterized by active subduction and tectonic activities, including the collision of the Indian Plate with the Burma Plate. Seismological studies suggest that differential subduction and rollback velocities in this region may lead to tearing of the subducting plate, potentially dividing it into three distinct segments. Slab tearing plays a critical role in influencing various geodynamic processes such as earthquakes, volcanism, uplift rates in mountain ranges. While lithospheric tears are typically identified through seismic tomography and seismicity trends, gravity anomalies provide a valuable complementary approach. In this study, we employ a 3D thermo-mechanical visco-plastic model, I3ELVIS, to simulate the subduction and tearing processes. We will explore the interaction between subduction, rollback, and tearing of the plate and its influence on the gravitational field of the region. Forward simulation of Gravity anomaly is conducted on different modeled geodynamic scenarios, and resulting 2D profiles of gravity anomalies are compared with observed gravity data from the region to assess the validity of the plate tearing hypothesis. Our findings indicate that slab tearing indeed plays a crucial role in subduction dynamics in the Andaman-Sumatra subduction zone.
How to cite: Singh, J., Kumar, S., Gerya, T., and Mannu, U.: Insights into Plate Tearing and Subduction Dynamics in the Andaman Nicobar Region through 3D Geodynamic and Gravity Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8790, https://doi.org/10.5194/egusphere-egu25-8790, 2025.
Accretionary wedges, formed at convergent plate boundaries, are influenced by complex interactions between incoming deformation, fluid dynamics, and mineralogical changes. The smectite-illite transformation, driven by increasing temperature and pressure, releases bound water, creating fluid overpressure and altering wedge rheology. Post-transition illite strengthens wedge material while increasing fault stability, influencing the development of the décollement and wedge morphology. The depth of this transformation often aligns with the onset of interplate seismicity, highlighting its role in earthquake generation. Our study investigates the impact of smectite-illite transformation on wedge dynamics, incorporating phase transitions and models of empirical fluid overpressure into geodynamic models to assess their role in wedge evolution and seismicity. Using I2VIS for a visco-plastic rheology framework, this study models thermal gradients and kinetic phase transitions to simulate their effects on wedge dynamics. Parameters such as fluid pressure, and internal friction are systematically varied to evaluate the influence of smectite-illite phase transition on wedge stability and morphology. Numerical simulations reveal that fluid overpressure and mineralogical transitions significantly shape wedge geometry and contribute to zones of seismic hazard. Model predictions are validated against data from subduction zones such as the Nankai Trough, improving our understanding of wedge behavior and seismic hazards. These findings highlight the critical role of mineralogical transformations in subduction zone mechanics and their broader implications for earthquake and tsunami risk assessment.
How to cite: Mannu, U., Choubey, S., Miyakawa, A., and Gerya, T.: Geodynamic Models of Accretionary Wedges with Smectite-Illite Transformation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8538, https://doi.org/10.5194/egusphere-egu25-8538, 2025.
The Eastern Pyrenees mark the transition of the Pyrenean Range towards the Mediterranean Sea. Because of this specific structural location, crustal geometries in this area register a significant along-strike change, mainly resulting from the overprint of Neogene extension on the Late Cretaceous-Cenozoic orogenic structure. Along-strike crustal changes in the Eastern Pyrenees are mainly marked by the lateral termination of the Iberian lower crust subduction and the progressive eastwards thinning of both the Iberian and European crusts. Although Moho depth studies in the area are abundant and agree on the main crustal architecture, they show significant depth differences that locally reach ca. 10-12 km underneath the Axial Pyrenees. Besides, these previous works rarely evaluate lower crust geometries and their relationship to upper crustal features.
To address both issues (differences in Moho depths and lower crust geometries), we have collected previous crustal data along three cross-sections and modelled them in 2.5D using available gravity and magnetic information. Constructed models (i) are tightly constrained at upper crustal levels by surface geology, exploration wells, petrophysical data and preceding studies on cover and basement units and (ii) compile and test various Moho geometries derived from an extensive compilation of available geophysical data. For lower crustal levels, the modelling of previous Moho surfaces has constrained the geometry of the upper-lower crust boundary (i.e., the Conrad discontinuity).
Models challenge some of the previously proposed Moho surfaces, which provide geologically inconsistent Conrad discontinuities. Besides, they highlight a progressive shallowing and Moho/Conrad topography decrease to the East. In the West, modelled Conrad discontinuities depict a lower crust that thickens significantly from the foreland domains towards the Axial Pyrenees. These lower crust geometries align with upper crust orogenic shortening values from the literature, without requiring the subduction of the Iberian plate. In the East, the modelled lower crust thins moderately underneath the Axial Pyrenees. Obtained geometries indicate a significant lower crustal thinning, consistent with an increased crustal extension eastward.
How to cite: Izquierdo Llavall, E., Ayala, C., Mochales, T., Clariana, P., Santolaria, P., Soto, R., Rubio, F. M., Margalef, A., Gamisel-Muzas, A., and Torné, M.: Lateral changes in the crustal architecture of the Eastern Pyrenees: Assessing Moho and Conrad geometries using potential field data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11900, https://doi.org/10.5194/egusphere-egu25-11900, 2025.
The Matese-Sannio region in Southern Italy represents a crucial sector to analyse the processes that characterized the formation of Apennines and its current structural setting. This area is also of great interest from a seismotectonic point of view, hosting the epicentres of multiple historic destructive earthquakes.
Our study presents part of the results of a multidisciplinary project (MOSAICMO) that integrates multiscale approaches to produce: a regional-scale model of this part of the orogen, a detailed reconstruction of the shallow subsurface of the Quaternary Bojano intramountain basin located in the central part of the study area, and detailed seismological and geophysical analyses.
In this work, we present the 3D subsurface reconstruction of the Matese-Sannio region, exploring the orogen structure to a depth of ca. 10 km by using a dense network of seismic reflection profiles tied with well-logs drilled for hydrocarbon exploration.
We tested the reliability of our geological reconstruction by performing numerical kinematic forward models that provide independent geometrical and temporal constraints to our conceptual model. We then compared our results with previous paleogeographic reconstructions of this sector of the Apennines to shed light on the complex interaction among different paleogeographic domains insisting in a relatively limited region.
Our results provide an updated picture of the present-day structure of the transition between Central and Southern Apennines and represent a reference framework for more detailed applications within the MOSAICMO project.
How to cite: Maesano, F. E., Buttinelli, M., Maffucci, R., and Vico, G.: The boundary between Central and Southern Apennines as a laboratory of the transition between accretionary and collisional orogens., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12470, https://doi.org/10.5194/egusphere-egu25-12470, 2025.
In northeastern Mexico, within the Coahuila Block, lies the Las Delicias Terrane, where a Triassic plutonic body previously referenced as the Acatita intrusive suite is exposed. This suite has been interpreted within a post-orogenic collapse context and is observed emplaced in a deformed volcanosedimentary sequence of the Las Delicias Formation. Associated with both units are some questions about the transition and magmatic diversity, as well as the petrogenetic evolution of the suite. To address these questions, cartographic, geochemical, isotopic, petrographic, and geochronological analyses were conducted.
Our results suggest that the Las Delicias Formation is primarily composed of volcaniclastic deposits, rhyolites, and andesite-dacite rocks from the Carboniferous-Permian (327–270 Ma). On the other hand, the Acatita intrusive suite (223–211 Ma) consists of granodiorites, tonalites, and quartz monzodiorites, including hornblende-rich gabbroic and dioritic enclaves. Zircon Hf analyses from both units reveal variation during the magmatic transition, potentially representing different stages in the evolution of Pangea.
The geochemical signatures of the suite exhibit a typical arc pattern. However, a depletion in HREE, significant negative anomalies in Nb and Hf, and Sr enrichment are observed. These patterns, in conjunction with the disequilibrium textures observed in the petrographic analysis, suggest a simultaneous process involving mixing, assimilation and fractional crystallization, which defines the compositional variation of the intrusive suite.
How to cite: Brito Mejía, L., Maldonado-Villanueva, R., Vásquez-Serrano, A., and Orozco-Esquivel, T.: The Magmatic Evolution Between the Late Paleozoic and Triassic of the Las Delicias Terrane, Coahuila, Mexico., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5324, https://doi.org/10.5194/egusphere-egu25-5324, 2025.
The lower structural levels of the Variscan orogen exposed in the Eastern Pyrenees reveal three genetically associated magmatic suites: (i) a batholitic sized calc-alkaline granitoid (Sant Llorenç–La Jonquera, SL–LJ); (ii) minor mafic intrusions with local ultramafic cumulates (Ceret and Mas Claret mafic complexes); and (iii) peraluminous leucogranite bodies. The granitoids and the mafic complexes underwent variable degrees of lower crustal assimilation as demonstrated by the Sr and Nd isotopic ratios of SL–LJ granitoids and mafic rocks. Contaminated gabbro-diorites are high in Fe and Zr and contain magmatic garnet in equilibrium with an Fe–Mg amphibole. A supra-subduction metasomatized mantle source for the mafic complexes is inferred. The magma that formed the SL–LJ granitoids was of intermediate composition and may have formed by differentiation of magmas derived from partial melting of a subduction-metasomatized mantle caused by active subduction or mantle delamination or by partial melting of the lower crust triggered by underplating of mantle-derived mafic magmas. Leucogranite magmas formed later by partial melting of crustal rocks with compositions similar to the outcropping metapelites and orthogneisses.
The interference pattern resulting from the superposition of Variscan (F2) and Alpine (F3) folding in the Eastern Pyrenees gives an exceptional field example to infer the 3D geometry of the SL–LJ pluton and its associated igneous rocks. The intrusion feeder zones are located in the northern flank of the antiform where the mafic complexes crop out, cutting the deeper structural levels of the Roc de Frausa and L'Albera series. The floor of the pluton is located above the Upper Proterozoic – Mid- Ordovician sequence, which is largely parallel to the S1 foliation, and the roof is slightly oblique to the Upper Ordovician-Silurian sequence (S0). This parallelism together with a well-developed magmatic and magnetic fabric parallel to S1 suggests that initial phases of intrusion of SL–LJ magmas took place at the end of D1, at ca. 314–311 Ma. The lack of stratigraphic continuity above and below the pluton suggests that the stratigraphic succession of the L'Albera massif was laterally displaced, and the intruding magma progressively grew while cutting through the entire sequence and filling the available space. This placement of the magmas is compatible with a local extensional setting that favored the ascent of the SL–LJ magmas from a lower crustal reservoir through vertical feeder zones in the footwall of the extensional faults where lithostatic pressure was minimal. The coeval development of NW-SE to NNW-ESE extensional faults with the NE-SW trending D2 contractional structures and the horizontal attitude of the mineral lineations, once restored the Alpine deformation, is compatible with a regional dextral strike-slip tectonic setting that took place during and after the emplacement of the igneous bodies. This strike-slip system is consistent with late-Variscan shear zones displacing Gondwana to the west with respect to Laurasia during the orogenic collapse.
How to cite: Aguilar, C., Liesa, M., Castro, A., Gisbert, G., Reche, J., Muñoz, J.-A., and Vilà, M.: Emplacement mechanisms of the calc-alkaline Variscan magamtism and its prevailing regional tectonic regime in the Eastern Pyrenees, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21939, https://doi.org/10.5194/egusphere-egu25-21939, 2025.
The formation of oceans along north Gondwana in lower Paleozoic times is usually ascribed to an inheritance of the Cadomian orogen back-arc system followed by the generation of epicontinental seas during the initial lithospheric breakup. In the Iberian Massif, evidence of a ca. 30 Ma magmatic flare-up – from the Furongian to the Middle Ordovician – involving crustal- and lithospheric mantle-derived partial melts, with different grades of magmatic differentiation and magma mixing/mingling, are described in the different tectonic domains. Extensive anatexis have been recently described in the south-central Central Iberian Zone (CIZ), documenting partial melting of the continental crust, with inputs of lithospheric mantle-derived melts, related to fast crustal thinning during the formation of a passive margin that overprints the Cadomian Orogen in north Gondwana. Along this CIZ-segment, we describe new evidence that supports the presence of this Cambrian-Ordovician magmatic flare-up, represented by the Fundão Pluton. Among other contemporaneous plutonic bodies exposed in this sector, the Fundão Pluton is a composite-zoned system comprising different granitoid facies which compositional attributes document interaction between basal crustal and metaigneous-derived melts produced from ca. 499Ma to 465Ma. The available dataset confirms the importance of this CIZ-segment to unravel the magmatic phenomena and the paleogeographic meaning of the preexisting continental margin during the lower Paleozoic, to form the Rheic Ocean and the drifted continental masses. We propose a geodynamic and paleogeographic model that incorporates field, geochemical and geochronological datasets. In this model, an inherited NE to ENE pre-Variscan structure, following the continental margin configuration of Gondwana in the lower Paleozoic, might have assisted the mid-to-upper crustal emplacement of successive tonalitic-granitic melts with calc-alkaline affinities. This structure could be rooted in flat-lying extensional shear zones that enabled the fast crustal thinning and triggered the exhumation of the lithospheric mantle towards shallow conditions, favoring the formation of adiabatic melts further intruded the mid-to-upper crust along major upright discontinuities. This model impacts the current understanding of events preceding the Variscan Orogeny in Iberia, with direct influence in the definition and distribution of a large-scale magmatic flare-up in this sector in northern Gondwana hyperextended margin. Also, this crustal architecture had a major impact on the distribution and nucleation of the Variscan structures responsible for the orogenic thickening during the accretionary and collisional processes that formed the Pangea supercontinent in the Devonian and Carboniferous periods.
This work was supported by MOSTMEG project (ERA-MIN/0002/2019 ) and by FCT I.P./MCTES (Portugal) through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). IDS is supported by the researcher contract DL57/2016/CP1479/CT0030 (https://doi.org/10.54499/DL57/2016/CP1479/CT0030).
How to cite: Dias da Silva, Í., Andrade, A. R., Mateus, A., Cambeses, A., and Pereira, B.: The lower Paleozoic magmatic flare-up in the Iberian Massif: the Fundão Pluton case-study (Castelo Branco, Portugal), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5846, https://doi.org/10.5194/egusphere-egu25-5846, 2025.
In Hokkaido, northern Japan, the westward migration of the Kuril forearc sliver (KFS) that started in the late Miocene due to the oblique subduction of the Pacific Plate along the Kuril Trench results in a "collision" between the KFS and the western part of Hokkaido, the northern extension of the Northeast Japan Arc. The "collision" rapidly uplifted the arc crust, forming the present-day Hidaka Mountains, and tectonically forced delamination occurred beneath the mountains. Based on the depth conversion of seismic wave velocities and geological observations, the delamination has occurred in the upper lower crust, ~23 km depth of the original crustal section. The central to eastern Hidaka Mountains interpret an Eocene-Miocene island-arc crustal section that shallows eastward (Hidaka metamorphic belt; HMB). In the western part, the Poroshiri ophiolite extends approximately 70 km long and <2 km wide, exposing a nearly complete oceanic crust-mantle section that shallows to the west. Both units are bounded by a thrust at the deepest lithologies.
The Uenzaru peridotite complex is a steeply dipping sheet approximately 800 m wide. It lies between the metagabbro of the Poroshiri ophiolite and the pelitic granulites of the HMB. The western part consists mainly of harzburgite, showing metamorphism with abundant amphiboles and complete absence of clinopyroxene. The eastern part consists mainly of fresh spinel lherzolite and plagioclase lherzolite along with pyroxenite and gabbro veins/bands similar to lithologies found in the Horoman peridotite complex, the largest peridotite body in the HMB. The compositional relationship between spinel Cr#[= Cr/(Cr+Al) in atomic ratio] and olivine Fo suggests that the western peridotites are petrogenetically related to the gabbro of the Poroshiri ophiolite. The eastern sample showed a wide range of spinel Cr# consistent with Horoman peridotites. The REE pattern of amphiboles throughout the area shows significantly low abundance and a leftward decreasing pattern in the western part, a spoon or U-shaped pattern at the boundary to the eastern part, and relatively high abundance with an LREE-depleted pattern in the easternmost part. Comparing these patterns with those of the clinopyroxene, the western pattern is consistent with that of the mafic cumulate of the Poroshiri ophiolite, while the eastern part has a similar spoon- or U-shaped pattern. From the plagioclase lherzolite of the Horoman peridotite body, clinopyroxene with spoon- or U-shaped patterns has been reported for spinel lherzolite and harzburgite. Therefore, the trace elements of amphiboles in the Uenzaru Complex reflect the REE pattern of clinopyroxene, indicating that the eastern part belongs to the HMB.
In the HMB, metamorphic pressure and temperature conditions of <970 MPa and <890˚C have been estimated for partial melting of exposed crustal parts. Therefore, the delaminated materials are most likely restites (garnetite and/or garnet-pyroxenite) that could descend in the wedge mantle and passively induce the asthenospheric upwelling that compensates for the removal of the lower crust. Furthermore, the delaminated lower crust may descend even lower than the subducting slab and the fragmented subducting slab (Poroshiri ophiolite) attached to the HMB as part of the passive asthenospheric upwelling.
How to cite: Yamasaki, T. and Shimoda, G.: Delamination-induced conjunction of sub-oceanic and sub-arc mantle peridotites in the Hokkaido, northern Japan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3392, https://doi.org/10.5194/egusphere-egu25-3392, 2025.
