Such a strategy enables the reconstruction of the timing, rates, and magnitude of processes driving orogenic evolution, as well as their relationships with mantle, crustal, and surface dynamics.
This session focuses on the intrinsic links between surface and deep-Earth processes in shaping orogenic systems and controlling their spatial and temporal evolution. Topics include the exhumation and surface uplift history of mountain ranges and orogenic plateaus, evolution of foreland and intermountain sedimentary basins, methodological developments on the integration of diverse dataset, landscape evolution, and tectonic plate reconstructions. Research focused on both collisional and subduction-related orogens affected by hinterland extension is welcome.
The influence of deep-seated processes on tectonics and magmatism has been documented at large scale in different orogens, such as the American Cordilleras. Understanding how these processes shape orogens through time is essential to disentangle their interactions with climatically-driven surface processes. The Colorado Plateau experienced a complex Cenozoic uplift and exhumation history, yet the drivers, magnitude and timing of the successive exhumation phases, as well as their role in conditioning late-stage canyon incision, remain strongly debated. In particular, the legacy of Farallon slab subduction, through slab flattening, subsequent rollback, and associated uplift from combined tectonics, magmatism, and dynamic topography, may have fundamentally structured the plateau prior to more recent canyon incision.
We combine apatite (U–Th–Sm)/He dating with apatite fission-track analysis from bedrock samples collected along an elevation profile in the Black Canyon of the Gunnison (eastern Colorado Plateau). By integrating these thermochronological data with the timing of regional erosional unconformities, we provide new constraints on the Cenozoic thermal evolution of basement rocks in this area. Our results reveal an early cooling phase between ca. 70 and 60 Ma. This phase is followed by reheating between ca. 35 and 30 Ma, corresponding to a temperature increase of ~40 °C, and by a subsequent cooling phase from 30 to 25 Ma of similar magnitude. A final cooling phase occurring after ~5 Ma is required to reach present-day surface temperatures. We interpret the early cooling phase as exhumation related to Laramide deformation associated with Farallon slab flattening. The reheating phase is contemporaneous with a widespread mid-Cenozoic magmatic flare-up interpreted to reflect slab rollback processes. The reheating may be specifically associated with a regional increase in the geothermal gradient or burial beneath volcanic sequences, or a combination of both. The final cooling phase is attributed to Plio-Quaternary incision of the Black Canyon, which generated ~800 m of relief.
Together, these results highlight how the sequence of slab flattening and subsequent rollback exerted a first-order control on Colorado Plateau surface uplift, exhumation and magmatism, thereby preconditioning the landscape on which Plio-Quaternary canyon incision developed. These thermochronological data will be integrated with existing thermochronological datasets to assess at larger scale the spatio-temporal variability of exhumation and reheating in response to changes in the geometry of the downgoing slab.
How to cite: Margirier, A., Stanley, J. R., Thomson, S., Valla, P. G., Stübner, K., Huppert, K., and King, G. E.: Thermochronological record of slab flattening and roll-back in the eastern part of the Colorado Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13259, https://doi.org/10.5194/egusphere-egu26-13259, 2026.
The Betic Cordillera of southeastern Spain experienced kilometer-scale surface uplift since the late Miocene, leading to widespread emergence of marine sedimentary units and contributing to the isolation of the Mediterranean Sea from the Atlantic Ocean at the end of the Miocene. Previous geophysical studies have linked this uplift to deep lithospheric processes, particularly the evolution and detachment of a subducted slab beneath the region. However, the geomorphic imprint of these processes across the Betic Cordillera has not been comprehensively characterized.
Here, we investigate the landscape response to late Cenozoic uplift using quantitative geomorphic analysis. We combine high-resolution topography with river longitudinal profile analysis, knickpoint mapping, and river network metrics such as normalized channel steepness (ksn) and χ-values. This approach allows us to assess spatial patterns of landscape disequilibrium and to infer the evolution of surface uplift.
Our results reveal a clear obliquity between the trend of maximum topography and the main tectonic structures of the Betics, a relationship that differs from other Mediterranean orogens. This anomalous elevation pattern spatially coincides with the region of lithospheric slab detachment previously identified by seismic tomography, suggesting a strong coupling between mantle dynamics and surface deformation. River profile metrics show strong contrasts in ksn and χ-values across the main drainage divide, indicating a transient, orogen-scale landscape and asymmetric erosion. These contrasts imply active migration of the principal drainage divide toward the Atlantic-facing basins, supported by the presence of wind gaps and river capture features.
Knickpoint distributions further indicate increasing landscape disequilibrium toward the southwestern Betics, consistent with a laterally propagating uplift signal. Together, these geomorphic observations provide independent evidence for epeirogenic uplift driven by slab tearing beneath the Betic Cordillera, with westward propagation rates estimated at approximately 100–160 km per million years.
This work is funded by GEOADRIA (PID2022-139943NB-I00) and MAPA (PIE-CSIC-202430E005) from the Spanish Government and the Generalitat de Catalunya Grant (AGAUR 2021 SGR 00410).
How to cite: Viaplana-Muzas, M., Vergés, J., Jiménez‐Munt, I., Torne, M., Struth, L., Cruset, D., Najafi, M., and García‐Castellanos, D.: Linking Surface Geomorphology to Deep Lithospheric Processes beneath the Betic Cordillera (SE Spain), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20678, https://doi.org/10.5194/egusphere-egu26-20678, 2026.
The landscape evolution of forearc ranges along accretionary convergent margins, such as the southern Chilean Coastal Cordillera, is strongly influenced by deep-seated accretion dynamics, enhancing reactivation of inherited upper-plate structures. The Nahuelbuta Range is the fastest uplifting and exhuming sector of the southern Chilean subduction margin. Stratigraphic markers and uplifted marine terraces indicate dome-shaped uplift across a ~100-km-wide zone since ~2 Ma. However, uplift mechanisms remain debated, and rates are resolved only for the last ~0.3 Myr. Furthermore, dense vegetation and weathering have hindered fault mapping, limiting the understanding of the Nahuelbuta Range deformational history.
We combined new surface geomorphic mapping, morphometric drainage analysis, and river inversion modeling to explore the tectonic and climatic influences on the Nahuelbuta Range landscape evolution. We identify a regional low-relief relic surface atop the Nahuelbuta Range, now warped and dissected by fluvial incision and faults. Drainage morphometric anomalies and microseismicity align with WSW- and ENE-trending faults, indicating ongoing trench-parallel shortening. River inversion analysis shows uplift and topographic rejuvenation between 3 and 2.5 Ma approximately, followed by two later discrete uplift episodes. Uplift transients correlate with Late Pliocene to Pleistocene Patagonian glacial expansion periods, suggesting that glacially intensified sediment flux to the trench enhanced basal accretion of sedimentary material. The location and wavelength of surface uplift events match depth and scale expected for slices of basal acreeted material. Seismic imaging of the sediment-rich subduction channel and microseismicity patterns supports this interpretation. We propose glacially driven tectonic underplating drives the oscillatory uplift history of the Nahuelbuta Range, while ongoing trench-parallel shortening enhance trench-parallel shortening and fault reactivation.
How to cite: Vega-Ruiz, A., Delgado, V., Racano, S., Clementucci, R., Véliz-Borel, V., Espinoza, M., Encinas, A., Melnick, D., Asenjo, C., Zambrano, P., and Larregla, R.: Tectono-Climatic Controls on Uplift Transients of the Nahuelbuta Forearc Range, Northern Patagonian Andes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-373, https://doi.org/10.5194/egusphere-egu26-373, 2026.
Abstract: Hinterland mountains serve as the pivotal link that spatially and temporally couples deep lithospheric processes with surface responses in orogenic systems. The Qinling Mountains, situated in the continental interior of East Asia, form a significant natural boundary that separates China into distinct north-south climatic and geographical zones. A key unresolved issue is the origin of the Qinling Mountains-specifically, the timing and mechanisms of their initial uplift and exhumation. The basin-range structure of the East Qinling provides a natural archive for elucidating this problem, as its formation records the onset of mountain building. This study employs multiple thermochronological techniques, including apatite and zircon fission-track and (U-Th)/He analyses of both basin sediments and bedrock samples across basin-bounding faults. Through analyses of lag-time, elevation profiles, and thermal history modeling, the exhumation history of East Qinling is reconstructed. Results elucidate an early-phase cooling event during ~120-100 Ma, with a rate of 5.9-3.4 °C/Ma. Following a prolonged thermal stagnation until ~80 Ma, a renewed phase of accelerated cooling occurred between 80 and 60 Ma, with cooling rates ranging from 5.3 to 1.0 °C/Ma. Integrating these new results with existing geological evidence, we propose that the Qinling Mountains underwent multi-stage uplift and orogenic processes, driven by far-field tectonic stresses associated with the convergence of surrounding plates. The early Cretaceous rapid cooling and exhumation are correlated with intracontinental deformation stage in the eastern China during the Yanshanian period. However, prolonged erosion and planation resulted in low-relief topography in the Qinling Mountains before the late Cretaceous (~80 Ma). During the late Cretaceous-early Cenozoic, under the far-field influence of Pacific Plate subduction, the East Qinling region experienced intense hinterland extension. This process broke up the pre-existing planation surface and formed a series of alternating basins and ranges, signifying the onset of the mountain building in Qinling mountains. Furthermore, the Qinling Mountains exhibit a spatio-temporal pattern of progressive mountain growth from south to north. This study provides a typical case study for understanding the uplift and tectonic evolution of hinterland mountains.
How to cite: Yuxiong, M., Zhao, Y., Xiaohui, S., Jiali, Y., and Dali, J.: Onset of mountain building in the Qinling Mountains: Evidence from bedrock and detrital low-temperature thermochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6495, https://doi.org/10.5194/egusphere-egu26-6495, 2026.
This study presents a new regional-scale 3D reconstruction of the major Plio–Pleistocene tectonostratigraphic surfaces of the Po Plain Basin (Italy), providing new constraints on the deformation history of this key Mediterranean foreland basin. The model was constructed by interpreting several thousand 2D pre-stack time-migrated (PSTM) seismic profiles, calibrated with an extensive wellbore database. This approach enables a robust regional mapping of structural elements and defined Plio-Pleistocene unconformities.
The results show that the Plio-Pleistocene architecture of the Po Plain is controlled by the interaction of two different geodynamic systems, resulting in a complex source-to-sink system. Since the Plio-Pleistocene, the advancing Northern Apennines (NA) thrust belt has mostly generated accommodation space, whereas most of the sediment supply came from the Southern Alps (SA).
Isobath maps provide new temporal constraints on the timing and style of deformation, particularly in the central sector of the Po Plain, where the outermost buried fronts of the NA, belonging to the Emilian Arc fold system, are nearly in direct contact with the outermost fronts of the SA. Our reconstruction demonstrates that the evolution of the NA thrust front was strongly influenced by the presence of the buried SA to the north. Where the NA collided with the SA, out-of-sequence thrusting was triggered within the internal sector of the NA from the middle to late Pliocene, locally persisting until the late Pleistocene. In contrast, where this interaction did not occur, the NA thrust front evolved following a classical in-sequence style, highlighting significant along-strike variability in the structural evolution of the Northern Apennines.
The detailed 3D reconstruction of the entire Po Plain subsurface further allows a robust analysis of the progressive reorganization of basin depocenters through time via the calculation of isochore maps. Beyond providing a three-dimensional depiction of this evolution, these maps enable quantification of sediment volumes deposited between successive unconformities and, subsequently, the calculation of sedimentation rates across the basin.
Decompacted volume analysis reveals a marked increase in sediment accumulation during the Pleistocene, from approximately 31,041 km³ for the entire Pliocene, with a rate of 10.594 km³/Ma to about 60,646 km³ for the Pleistocene, with a rate of 25.269 km³/Ma, based on a 50% sand–50% shale decompaction model. This increase occurred despite an overall reduction in tectonic activity during the Pleistocene within the Alps, the primary sediment source region. This apparent paradox is interpreted as the result of strong climatic forcing associated with progressive climate deterioration and the onset of major Alpine glaciations, which dramatically enhanced erosion in the surrounding orogenic belts. The resulting increase in sediment flux, together with a major marine regression, drove rapid basin infilling and large-scale eastward progradation of the Po Basin system. These findings highlight the fundamental role of climate–tectonic coupling in controlling the evolution of the Po Plain over the last 5 Myr.
How to cite: Barrera, D., Toscani, G., and Di Giulio, A.: How Two Orogens Shaped and Filled a Foreland Basin: Plio-Pleistocene Tectonic and Climatic Controls on the Po Plain Basin (Italy) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8275, https://doi.org/10.5194/egusphere-egu26-8275, 2026.
The contact between the northern edge of the Higher Himalayan Crystalline (HHC) and the overlying Tethyan Sedimentary Sequence (TSS) has long been debated as either a thrust or a normal fault. Initially thought to be a thrust contact, it was later recognized as a zone of crustal-scale normal faults dipping to the north, known as the South Tibetan Detachment System (STDS). This suggests that the overlying TSS has moved northward along the contact relative to the HHC footwall. The cause of the initiation of such a crustal-scale normal-fault system in a convergent setting remains poorly understood, which motivates the present study to re-examine the structure of the HHC-TSS contact in the Dhauliganga valley of the Garhwal Himalaya. Nevertheless, we identified a series of normal faults cutting across the regional foliation of the HHC-TSS rocks during our field investigation, characterized by intense brecciation and gouging, consistent with upper-crustal brittle deformation. Our field observations suggest that these faults primarily formed during the waning phase of Himalayan growth and are unrelated to the northward slip of the TSS over HHC, as these normal faults cut across all dominant structural elements, including the migmatitic layering of HHC at high angles. In addition, we found a spectacular ductile shear zone within the Milam Formation of the TSS, located directly above the HHC. This zone provides strong evidence of south-vergent thrusting along the contact, as indicated by fold asymmetry, C-S structures, and low-angle Riedel shears, consistent with the Himalayan deformation. Microstructural studies of shear-zone samples reveal that quartz grains are predominantly stretched as we expect in a ductile shear zone, forming lenticular ribbons with high aspect ratios and undulose extinction, whereas the occurrence of smaller, unstrained grains along the edges of larger grains is indicative of subgrain rotation recrystallisation typical of high temperatures (~400°-500°C). XRD analysis further confirmed the presence of graphite in the mylonitized samples, and the alignment of graphite along shear fabrics suggests the influence of shear heating during their formation. Our new findings of deformation structures along the HHC-TSS contact recognize the importance of reevaluating and expanding our understanding of the structural evolution in this area, particularly in the context of the India-Eurasia collision. Based on field and microstructural observations, we suggest that the collision between India and Eurasia caused the TSS to thrust over the HHC, while steeply dipping normal faults that have affected all previous structural features in the HHC and TSS are a later phenomenon that helped the Himalayan mountain belt attain stability of the Himalayan wedge from a supercritical stage.
How to cite: Das, A. and Bose, S.: Deformation at the contact between the Higher Himalayan Crystalline and the Tethyan Sedimentary Sequence: Thrusting versus normal faulting conundrum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9016, https://doi.org/10.5194/egusphere-egu26-9016, 2026.
The life cycle of orogenic belts is governed by the competition between compressional tectonic forces that build topography and gravitational forces that destroy it through extension. In mature orogens, extension is commonly thought to involve viscous flow within a weak crustal channel (WCC), driven by topographic gradients between mountain belts and their margins. This process is expressed in the upper crust as normal faulting atop high mountain belts, such as the Tibetan Plateau and the Apennines. However, the mechanical link by which flow within the WCC drives extension in the brittle upper crust remains poorly understood. In previous work (Dawood et al., 2025 EGU), we designed an analytical model predicting the instantaneous, characteristic rate of brittle extension enabled by WCC flow. Here, we extend and test this framework by coupling it with two-dimensional numerical simulations to investigate the time-dependent dynamics of orogenic collapse. While the analytical model captures the static force balance and provides a snapshot estimate of extension rates for a given orogenic state, the numerical approach resolves the temporal evolution of topography, crustal-channel flow, and fault activity. Our simulations show that topographic gradients drive viscous flow within the WCC, which generates basal shear tractions that promote extension along upper-crustal normal faults. We find that sustained orogenic extension requires both a sufficiently weak WCC (ηwcc ≤ 1021 Pa.s) and an orogenic elevation exceeding a critical threshold height, hmin. This threshold is controlled by the frictional strength of the brittle crust and the magnitude of basal shear stress transmitted from the WCC. Extension rates scale systematically with fault strength, orogenic height, and WCC viscosity and thickness: high extension rates occur for weak faults and high topography (h >>hmin), especially in the presence of a thick, low-viscosity WCC. In contrast, stronger faults, lower elevations, or thinner and more viscous channels suppress extension. Together, these results validate our analytical scaling laws, indicating that while a static force-balance description predicts the instantaneous extensional behavior, numerical models capture the longer-term, time-dependent, self-limiting evolution of collapsing orogens.
How to cite: Dawood, R., Olive, J.-A., and Aharonov, E.: Dynamics of Orogenic Collapse Controlled by Coupled Brittle–Ductile Deformation , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3563, https://doi.org/10.5194/egusphere-egu26-3563, 2026.
The shallowing of subducting slabs within the upper ~200 km of the mantle, commonly referred to as flat slab subduction is associated with extensive petrological and structural modification of the continental lithosphere. Anomalously buoyant oceanic lithosphere, upper-plate overthrusting, and interactions with cratonic keels have all been proposed as mechanisms promoting shallow slab geometries, yet the dynamics governing the initiation and duration of flat slab subduction remain to be fully understood. Here, we investigate self-consistent flat-slab subduction dynamics using the finite element code ASPECT with adaptive mesh refinement and a free surface boundary condition. We explore the influence of the overriding plate structure, including the presence of continental keels, as well as the role of heterogenous subduction interface strength on shallow slab dynamics. Our results show that flat slab geometries develop when a weak, sediment-rich subduction interface is combined with a positively buoyant overriding continental lithosphere. Substantiating previous studies, we further find that the presence of a strong cratonic keel near the continental plate margin enhances shallow slab underthrusting and encourages flat slab configurations. Importantly, we show that the timing of interface weakening, such as due to influx of sediments, exerts a first-order control on the onset and the longevity of slab flattening. As the slab flattens, pronounced subsidence, extension and transient marine inundation develop within the foreland region of the upper plate, superimposed on broader, large-scale subsidence of the continental interior. Regional uplift and subsidence are thus not solely linked to flat slab emplacement and removal, but also reflect evolving slab dynamics within the shallow upper mantle. Our results provide new constraints on the geodynamic controls of flat slab evolution and their role in driving continent-scale deformation and sediment redistribution.
How to cite: Grima, A. G. and Becker, T.: How interface weakening and continental structure promote flat slab subduction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5782, https://doi.org/10.5194/egusphere-egu26-5782, 2026.
The Eastern Anatolian Plateau is a broad, high-elevation (~2 km), low-relief collisional plateau in eastern Turkey that developed following the Arabia-Eurasia collision and the transition to a post-collisional tectonic setting. It occupies a central position between the Bitlis-Zagros suture to the south and the Eastern Pontides-Lesser Caucasus mountain ranges to the north and is associated with widespread Neogene volcanism. Since the Early-Middle Miocene, uplifted regions along the Bitlis segment of the Arabia-Eurasia convergence zone, including parts of the Eastern Anatolian Plateau, were drained toward the northern Eastern Mediterranean, delivering large volumes of sediment to the deep sea and forming thick flysch successions. These deposits archive the crustal inventory exposed at the time and provide a valuable record of the tectono-magmatic evolution of the convergence zone. Here, we present detrital zircon U-Pb-Hf data from Late Miocene sediments recovered from DSDP Sites 375/376 and ODP Site 968 in the northern Eastern Mediterranean to constrain the sequence of tectono-magmatic events associated with Arabia-Eurasia convergence, with particular emphasis on the timing of the establishment of a post-collisional regime. Detrital zircon U-Pb-Hf data record Upper Cretaceous and Eocene magmatic flare-ups related to Neotethys subduction, as well as a prominent Miocene magmatic flare-up with distinct age modes at ~17, ~11, and ~6 Ma associated with the transition to a post-collisional regime. Hf isotope compositions of Miocene detrital zircons reveal a systematic shift from highly variable, evolved signatures before ~13 Ma to predominantly juvenile signatures thereafter. This shift indicates an increasing contribution of mantle-derived sources to magmatism since the mid-Miocene, relative to earlier evolved or mixed mantle-crustal sources. We interpret this transition to indicate that Neotethys slab break-off or lithospheric mantle delamination beneath Eastern Anatolia had largely progressed toward completion by ~13 Ma, signaling the establishment of post-collisional tectonic conditions. Notably, this transition slightly predates the inferred onset of plateau uplift at ~11 Ma, suggesting that mantle reorganization beneath Eastern Anatolia preceded, and was not synchronous with, the surface expression of uplift.
How to cite: Glazer, A., Avigad, D., and Morag, N.: Dynamic Mantle Support Beneath the Eastern Anatolian Plateau Since ~13 Ma Inferred from Zircon Hf Isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11098, https://doi.org/10.5194/egusphere-egu26-11098, 2026.
The mechanisms of stress transfer across continental plate interiors during continent-continent collision, as well as the timing and the style of far-field fault system responses, remain poorly constrained. The collision between the Indian subcontinent and what is now Tibet began in the Eocene and has involved still on-going north-south convergence throughout southern Tibet and the Himalayas, providing an exceptional natural laboratory for studying continental collision processes.
The Altyn Tagh Fault (ATF), a >1600-km-long lithospheric-scale strike-slip fault marking the northern boundary of the Tibetan Plateau, is a key structure for investigating how deformation propagated following the India-Asia collision. However, the timing of its (sinistral?) initiation remains uncertain, with proposed ages ranging from the Mesozoic to the Miocene. These uncertainties largely reflect the involved structural complexities and the difficulty of directly dating the fault's protracted brittle activity. To address this long-standing problem and to better understand the ATF’s evolution and its role in the Plateau build-up, we conducted detailed structural investigations of two significant outcrops in the Old Aksay region (Gansu province). These exposures preserve a complex fault internal architecture containing numerous Brittle Structural Facies (BSFs), that is, distinct rock domains defined by characteristic fault rocks, mineralogy, textures, and kinematics. Repeated faulting at those outcrops localized deformation into weaker zones, creating thick foliated gouge layers, and along discrete slip surfaces, while lithons from earlier slip events were locally preserved. Their juxtaposition records the temporal and spatial evolution of the ATF, including its deformation mechanisms, physical conditions during initial faulting and subsequent reactivations. We combined multiscalar structural analysis with multi-grain-size K-Ar dating of synkinematic illite separated from BSFs at both outcrops.
The results reveal a protracted, episodic faulting history from the Early Cretaceous (~115 Ma) to the Quaternary (~0.6 Ma), documenting at least five reactivation events. The earliest record at ~115 Ma suggests the ATF existed from before collision as a lithospheric weakness inherited from Mesozoic intracontinental deformation. Crucially, we identify an Early Eocene event (~56 Ma) that provides the first direct geochronological evidence for brittle deformation nearly synchronous with the initial India-Asia collision farther south, supporting models of rapid stress transfer to the northernmost plateau margin. A Late Oligocene reactivation at ~26 Ma coincides with rapid, widespread Miocene exhumation and sedimentation across northeastern Tibet. Late Pliocene (~3 Ma) and Middle Pleistocene (~0.6 Ma) events record continuing slip and deformation localization during progressive Plateau expansion.
This intricate >100 Myr archive demonstrates that long-lived lithospheric weaknesses can preserve deformation spanning multiple tectonic regimes. Beyond providing a robust temporal framework for the tectonic evolution of the northern Tibetan Plateau, our results highlight the efficiency of far-field stress transfer through rigid lithosphere even over very large distances, and establish a powerful methodological protocol for integrating geochronological records and structural investigations in intracontinental orogens worldwide.
How to cite: Sun, Z., Viola, G., Liu-Zeng, J., Zheng, Y., Del Sole, L., Shao, Y., Wang, W., Cui, F., and Shen, X.: Lithospheric weakness and episodic reactivation of the Altyn Tagh Fault since the Early Cretaceous: Insights into stress transfer and Tibetan Plateau growth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1155, https://doi.org/10.5194/egusphere-egu26-1155, 2026.
Topography is a direct manifestation of the coupling of tectonic and surface processes and this connection between rapid erosion and high uplift rates is most readily evident in the frontal High Himalayas– an area that provides an excellent opportunity to study the progressive evolution geomorphic features in response to the interplay of these processes. An abrupt topographic break between the low-relief Lesser Himalaya and the high-relief Greater Himalaya has received significant attention, but the processes that govern its evolution remains debated. While it is commonly accepted that active tectonics are required to produce the topographic break, it remains debated whether it is driver by a blind mid-crustal ramp or discrete thrust faulting that daylights at the mountain front. Evidence for out-of-sequence thrusting has been documented along the orogen at similar elevations as the topographic break, suggesting active surface faulting could play a major role in generating and sustaining this marked topographic break. In central Nepal, where the topographic break is most pronounced, thermobarometric data indicate pronounced differences in maximum pressure temperature estimates (>300°C, >4 kbar) experienced by juxtaposed Greater Himalayan units. Consequentially, this structure likely plays a major role in accommodating shortening within the orogen, which is expected to build significant topography. In the Annapurna region, this boundary lacks a thick mylonitic shear zone, suggesting that it may have experienced recent brittle activity. This study investigates neotectonic offsetting and warping of fluvial terraces that record recent thrust activity within the past tens of thousands of years. Newly available two-meter resolution digital elevation data coupled with field observations, provide an unprecedented opportunity for identifying neotectonic deformation of fluvial terrace geometries across the topographic break. We present terrace tread data from the Seti river drainage in central Nepal. An important limitation, however, is that these digital elevation data allow for detailed imaging of terrace tread deposits, rather than bedrock strath terraces, and thus are also influenced by sedimentation processes. We present preliminary interpretations based on first-order changes in terrace tread geometries over kilometers distance, ensuring that evidence is recorded across multiple terrace levels, and in some cases supported by additional bedrock data. Seti River terrace tread profiles suggest divergence upstream of the topographic break, which can be caused by differential uplift or changes in sediment flux. Multiple terrace levels also appear folded near the structural position of the Chamrong thrust, mapped in the neighboring Modi Khola drainage. At this location, we also report evidence of pervasive brittle bedrock deformation. The combination of these features suggests possible tectonic deformation at multiple locations along the Seti River that are consistent with active brittle out-of-sequence thrusting along the mountain front. We plan to combine these data with UAV models of strath terrace geometries to clarify these preliminary interpretations.
How to cite: Preece, M., Stockli, D., Thigpen, R., and Gallen, S.: Insight on recent tectonic deformation in the Himalayas of central Nepal provided by fluvial terrace geometries , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15999, https://doi.org/10.5194/egusphere-egu26-15999, 2026.
The Carpathian Bend Zone is an orocline in the Southeastern Carpathians that links different segments of the Carpathian arc and represents a structurally unique sector of the mountain range. The region experienced Cretaceous to Miocene thick- and thin-skinned nappe stacking as well as post-collisional shortening and out-of-sequence thrusting. Unlike in many other places, these nappe stacks were not overprinted by subsequent back arc extension. In addition to this tectonic inheritance, the bend zone hosts the most seismically active region in Europe, characterized by persistent deep seismicity referred as “seismic nest”. This reflects deep-seated processes that are only partially expressed in the upper crust and are partially manifested through surface uplift and landscape reorganization rather than upper crust faulting.
These factors lead to preserved nappe stacks and ongoing landscape evolution driven by recent uplift. Previous studies aiming to quantify exhumation and uplift rates have so far been limited to regions north and south of the Bend Zone, leaving this key segment poorly constrained. This study aims at closing this knowledge gap by investigating if long-term and short-term uplift rates are comparable. Furthermore, it collates these data with preexisting rates from other segments along the orogen to reveal local differences in exhumation patterns.
To investigate long-term exhumation, six sandstone samples were analyzed using apatite (U-Th)/He thermochronology. Additionally, geomorphometric analyses such as river longitudinal profiles, knickpoints, and χ-maps were used to study topographic evidence of recent uplift and assess drainage divide migration and equilibrium conditions. Furthermore, river terraces were mapped and their relative elevations above the modern riverbed were used to estimate since the Early Pleistocene. By correlating terrace elevations with known dated levels from nearby regions, constraints were placed on the timing of Quaternary incision and rock uplift.
The Apatite (U-Th)/He dates show a variable amount of thermal overprint. Two samples yield (U-Th)/He dates younger than their stratigraphic ages while four samples show dispersed dates older as well as younger than the corresponding Miocene stratigraphic ages. This indicates partial resetting, an inherited thermal history from the grains’ sources, and limited post-Miocene burial. Therefore, assuming a geothermal gradient of 30 °C/km, a maximum amount of approximately 2.7 km of burial since the Middle Miocene can be presumed. The geomorphic signals consistently indicate active uplift within the Bend Zone, particularly in areas where structural controls induce sharp knickpoints and asymmetry in watershed geometry. The average rock uplift rate indicated by river terraces is 1.1 mm/yr since the Middle Pleistocene. In combination with estimated exhumation rates derived from the thermochronological data, a overall stable landscape surface within the Bend Zone is proposed for the last 2.5 Ma. Overall, our results indicate that the Bend Zone has been characterized by low long-term exhumation rates since the mid Miocene and higher uplift rates during the Quaternary.
How to cite: Schönleber, L., Otto, J.-C., Pollhammer, T., Friedrichs, B., Heberer, B., Dremel, F., Villamizar-Escalante, N., and von Hagke, C.: Long- and Short-term Landscape Evolution of the Carpathian Bend Zone – Linking Low-Temperature Thermochronology with Geomorphometric Analyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3918, https://doi.org/10.5194/egusphere-egu26-3918, 2026.
The structural and tectonic interactions between the S-verging Southern Alps and the NE-verging Northern Apennines fold-and-thrust belt, and their shared Po Plain foreland basin, represents a classic and long-debated issue in Alpine–Apennine geodynamics. We here investigate a cross section from the Bobbio Tectonic Window (BTW) in the Emilian Northern Apennines, to the central Po Plain subsurface, which records these important relationships. Previous studies focused on fault slip-rate measurements of the buried Northern Apennine thrust fronts, but a comprehensive tectono-thermal study of the Lower Miocene turbiditic sequence outcropping in the BTW is still lacking. In this work, we investigate the relationship between BTW development and the interaction of the Northern Apennines and Southern Alps thrust fronts buried below Pliocene-Pleistocene sediments in the central Po Plain. We analysed the cooling/exhumation history of rocks exposed at the core of the BTW by means of low-T thermochronology (apatite fission-track and U-Th/He) on samples from the Lower Miocene (Burdigalian) Bobbio Fm. and compared them with the slip-rate history of the Northern Apennines buried thrust front along the Emilian Arc. Our thermochronological results from the BTW show a maximum temperature of ca. 85-90°C (apatite fission-tracks partial annealing zone) reached soon after depositional age, followed first by a relatively slow cooling in the Early Miocene- Early Pliocene time window (17-6 Ma), and then by a fast cooling starting between ca. 6 and 4 Ma. By comparing these results with the slip-rate trend of the buried Apennines thrust front, we interpret them as the signal of an out-of-sequence thrusting reactivation within the inner Northern Apennine fold-and-thrust belt due to the interaction between the Northern Apennines outermost fronts and the Southern Alps. This study shows how far-field geological structures can influence the general kinematics of the thrust-fold belt, promoting out-of-sequence reactivation of internal tectonic structures and the exposure of deep tectonic units within the BTW.
How to cite: Stendardi, F., Barrera Acosta, D., Carrapa, B., Toscani, G., Albino, I., and Di Giulio, A.: Tectono-thermal evolution of the Northern Apennines-Alpine knot: a case study from the Bobbio Tectonic Window, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5387, https://doi.org/10.5194/egusphere-egu26-5387, 2026.
The Korean Peninsula is located along the eastern margin of the Eurasian Plate and is characterized by a pronounced east-high, west-low topography, commonly attributed to Cenozoic tectonic processes associated with the evolution of the East Sea (Sea of Japan). The East Sea is a back-arc basin that opened from the Early Oligocene (ca. 32 Ma) to the late Middle Miocene (ca. 12 Ma) and has been subjected to an E–W compressional stress regime since the Early Pliocene (ca. 4 Ma). Quaternary marine terraces indicate rapid uplift along the east coast (200–300 m/Myr), whereas the western coast shows relative stability or subsidence, suggesting strong spatial heterogeneity in recent crustal deformation. However, low-temperature thermochronological data generally indicate more moderate long-term Cenozoic exhumation rates, implying that the rapid Quaternary uplift reflects late-stage acceleration rather than long-term average behavior.
To investigate the long-term cooling and exhumation history of the Korean Peninsula, we conducted zircon and apatite fission-track (FT) dating on 21 samples from 12 plutonic bodies. Zircon FT ages range from ca. 173 to 51 Ma, and apatite FT ages range from ca. 46 to 12 Ma, with mean track lengths of 12.94–14.61 μm, indicating no significant post-cooling thermal disturbance. Apatite FT ages are generally older in inland regions (av. ~37.5 Ma) than along the east coast (av. ~25.0 Ma), suggesting long-term differences in cooling and exhumation histories. Assuming a geothermal gradient of ~30 °C/km, average exhumation rates are estimated to be ~90 m/Myr for inland regions and ~150 m/Myr for the east coast. However, fission-track data alone cannot uniquely constrain the timing of possible uplift acceleration. To better resolve late Cenozoic exhumation and assess the role of Quaternary tectonics, apatite (U–Th)/He dating is currently being conducted on selected samples.
How to cite: Chae, Y.-U., Ha, S., Lee, Y. I., Choi, T., Jeen, S.-W., Lim, H. S., and Shin, S.: Reconstructing the Cenozoic uplift history of the Korean Peninsula using fission-track thermochronology: implications for East Asian tectonics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16211, https://doi.org/10.5194/egusphere-egu26-16211, 2026.
Oroclines are orogenic belts that have been subjected to bending and are a common feature of mountain ranges worldwide. Despite their widespread occurrence, there is ongoing debate surrounding the geodynamic processes responsible for their development. Specifically, there is uncertainty as to whether these orogens involve upper-crustal (i.e, thin-skinned) or large-scale lithospheric (i.e., thick-skinned) deformation, as well as whether their curvature evolves contemporaneously with mountain growth (i.e., progressive orocline) or post-orogenesis (secondary orocline). Such spatial and temporal deformation means that unraveling the tectonic signature of oroclines may significantly enhance our understanding of orocline formation and provide broader insight into the evolution of mountain systems and convergent plate boundaries worldwide.
Given the widespread occurrence of oroclines, identifying their tectonic signatures requires analyzing their attributes and geodynamic framework within a global context. However, oroclines have primarily been studied individually - which presents a challenge for their comparison. To address this, we present a global catalogue of oroclines and their tectonic signatures based on map-view characteristics, structural deformation style (e.g., thin- or thick-skinned), and kinematic classification (e.g., primary arc, progressive or secondary orocline).
Our catalogue is generated by analyzing published literature and newly derived data on orocline attributes, collating 30+ oroclines from around the world. Within our dataset, we observe a wide range of tectonic characteristics, including curve lengths, width-to-length ratios, and interlimb angles. However, we also find a specific signature for oroclines that are classified as thin-skinned or thick-skinned – allowing for a clear identification of such geodynamic processes within our catalogue. In our study, we provide an orocline classification system based on the tectonic signatures highlighted in our dataset. This classification system and identified signatures may have several implications for our understanding of lesser-studied oroclines and the evolution of mountain systems worldwide.
How to cite: Hamid, A. A., Heron, P. J., and Johnston, S. T.: Unraveling the tectonic signatures of thin and thick oroclines through a global catalogue, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8121, https://doi.org/10.5194/egusphere-egu26-8121, 2026.
The analysis of clastic sequences is fundamental for understanding plate dynamics, as it record variations in depositional environments and source-to-sink systems. Since the late Paleozoic, contemporaneous with the convergence between the paleo-Pacific plate and Gondwana, sedimentary basins developed in both forearc and retroarc positions of the Gondwanide orogenic system. The Beacon Supergroup in Antarctica and the Parmeener Supergroup in Tasmania represent the sedimentary infill of the Transantarctic Basin, located in a retroarc setting. These successions are mainly composed of fluvial sandy and muddy deposits, which are poorly deformed and currently unconformably overlie older units. Deposition began in the Devonian and ended in the Early Jurassic, spanning more than 200 Myr and encompassing key events in the history of the Earth, such as the Late Paleozoic Ice Age, the subsequent transition from icehouse to greenhouse conditions, and the Permian-Triassic mass extinction. The composition of sandstones within the Beacon and Parmeener supergroups varies through time and space, correlating with major tectonic processes driven by subduction dynamics, which ultimately controlled the source-to-sink systems feeding these clastic units. Variability in sandstone composition is documented through a quantitative analysis of all available published data, integrated with new datasets from the Transantarctic Mountains and Tasmania. The results reveal a shift from quartz-feldspar-dominated sandstones, indicating derivation from crystalline basement, to volcanic lithic fragment rich sandstones, reflecting a provenance from coeval volcanic arc rocks. This provenance shift occurred diachronously along the basin, whit volcanic component appearing in the central Transantarctic Mountains during the Permian and in Victoria Land and Tasmania during the Triassic. Sandstone composition further indicates that the Victoria Land region evolved from an intracratonic basin in back-bulge position to a foredeep basin setting.
How to cite: Zurli, L., Fioraso, M., Perotti, M., Di Giulio, A., Olivetti, V., Pezzoli, S., Corti, V., Stendardi, F., and Cornamusini, G.: Tracing the evolution of the Transantarctic Basin (southern Gondwana) through sandstone petrography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8585, https://doi.org/10.5194/egusphere-egu26-8585, 2026.
The Campanian/Maastrichian to Lutetian Alpine flysch sequences of the Schlieren- and Gurnigel nappes record deposition in an ocean-continent subduction setting related to Alpine orogenesis. Despite extensive studies of these flysch deposits, the existence of a source-to-sink relationship between the two units remains debated. Here, we logged 50-70 m-thick successions of the Gurnigel and Schlieren deposits at two sites, respectively, at a scale of 1:20. The ages of the analysed sediments range from the Thanetian to the Lutetian. We measured the paleoflow directions using sole marks and cross-bedding, and conducted drone surveys to document the large-scale depositional architecture. Our aim was to reconstruct a potential proximal-to-distal relationship between the two sequences.
In the Schlieren nappe, the analysed sediments are dominated by coarse-grained (grain size up to 2 mm) sandstone beds <5 m thick, characterised by a matrix-supported fabric and sole marks at their bases. The finer-grained sandstone beds (grain size up to c. 0.6 mm) are <50 cm thick. They display a massive, grain-supported fabric with normal grading at the base, followed by parallel lamination and occasionally ripple marks at the top. Mudstone beds (clay and silt fraction) are up to 30 cm thick. They are massive to parallel-laminated and locally show bioturbation. Mudstone beds contribute to <10% to the entire suite. Paleoflow directions scatter between the NE and SE. Drone surveys disclose the presence of troughs up to 7 m deep and ten meters wide. They are cut into sandstone beds and backfilled with coarse-grained, massive to laminated sandstones.
By contrast, the Gurnigel sequences are dominated by a succession of sandstone beds with mudstone interbeds. Sandstone beds are <1.5 m thick. They have a planar base, are medium- to fine-grained (grain size ranging from c. 0.1 to 0.6 mm) and show a fining-up trend. Individual beds display a succession of sedimentary structures occasionally starting with a massive fabric. It is followed by mm-scale plane lamination, ripple marks with convolute bedding and sub-mm laminations towards the top. Mudstone interbeds, up to 30 cm thick, are massive to parallel laminated and strongly bioturbated, comprising up to 40% of the surveyed outcrop. Drone imagery shows that laterally continuous, horizontally layered beds dominate the overall architecture. However, lenticular sandstone beds with scours up to 50 cm deep occur locally. Sole marks and cross bedding indicate paleoflow toward the S and W.
The sedimentary structures indicate that the Schlieren sediments were deposited predominantly by (hyper)concentrated, friction-controlled flows and concentrated currents where grain-grain interactions dominate. In contrast, the Gurnigel sediments most likely accumulated from surge-like turbidity flows driven by dynamic pressure. Although the inferred surges recorded in the Gurnigel sediments could, in principle, have resulted from flow separation – with coarse-grained material accumulating in the more proximal Schlieren area and finer-grained fractions being deposited in a more distal setting such as the Gurnigel realm – we discard this interpretation. This conclusion is supported by the opposite paleoflow directions, which indicate that no source-to-sink relationship existed between the two depositional systems.
How to cite: Swaton, S. J., Bozetti, G., Schmidt, C. L., Epprecht, B. L., Graf, G. L., Hermann, J., and Schlunegger, F.: Sedimentary architecture of Late Cretaceous to Early Eocene flysch sequences in the Swiss Alps, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9943, https://doi.org/10.5194/egusphere-egu26-9943, 2026.
The Prealps represent a complex nappe system consisting of Mesozoic to early–middle Cenozoic sediments deposited in the Penninic domains, detached from its substratum during the Alpine orogeny. During subsequent phases of subduction and collision, these nappes were transported along the active plate interface between Adria and Europe far to the north. Today, they lay above the transition between the Helvetic Nappes and the Subalpine Molasse. As a result of long-term displacement and successive deformation, the Prealps exhibit a complex structural architecture that records the cumulative tectonic evolution. We developed a 3D model to yield a high-resolution visualization of the structural architecture and its spatial changes within the Préalpes Romandes. These observations allow us to correlate nappe internal deformation with movements of underlying nappes, which is the goal of this work.
The Préalpes Romandes are crosscut by predominantly north–south–oriented sinistral strike-slip faults. These structures range from large-scale faults that transect the entire Prealps nappe stack and accommodate offsets of several kilometers, to minor faults with displacements of only a few meters to tens of meters. Smaller faults are commonly linked by lateral offsets to form continuous step-over fault systems and typically terminate within the detachment horizon. In contrast, larger strike-slip faults must breach the basal detachment of the Prealps to maintain a kinematic balance and are therefore rooted in deeper structural units. Despite a regional change in stratigraphic orientation of approximately 30° from east to west, the orientation of sinistral strike-slip faults remains largely unchanged. An increasing number of NW–SE–oriented dextral strike-slip faults in the eastern Préalpes Romandes indicate a change in the regional kinematic regime.
Based on our results, we interpret that the Préalpes Romandes experienced a young (Miocene) phase of deformation following early stages of subduction related nappe transport. We relate this Miocene phase of deformation to the uplift of the Aar Massif. This caused differential motion beneath the Prealps, which is expressed by strike-slip deformation, rotation and back-thrusting within the Préalpes Romandes. We additionally invoke this motion to have controlled the differential migration within the nappe stack, resulting in ~30° counter-clockwise rotation and a general northwestward displacement of the eastern Préalpes Romandes. In addition, the presence of a northern backstop subsequently promoted the occurrence of a lateral escape along local dextral strike-slip faults. A correlation of our 3D model with seismically active zones at greater depth discloses the occurrence of structures that were offset in response to the uplift of the Aar massif during Miocene times. These observations document a complex multistage deformation sequence associated with late-stage collision and uplift tectonics in the subsurface, where the initial sinistral movement has been disrupted and partially reoriented by the latest tectonic evolution. It also highlights the role of strike-slip structures as key elements for understanding the long-term tectonic evolution of the region.
High-resolution 3D modelling therefore provides a powerful framework to unravel internal structural relationships, integrate them with surrounding geology, and develop coherent palaeogeographic reconstructions through space and time.
How to cite: Drvoderić, S., Herwegh, M., Berger, A., Schlunegger, F., Furlan, M., Kurmann, E., Dall’Agnolo, S., Garefalakis, P., Monti, R., and Musso Piantelli, F.: Indentation tectonics in the Swiss Préalpes Romandes caused by the uplift of the Aar Massif: insights from high-resolution 3D structural modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12076, https://doi.org/10.5194/egusphere-egu26-12076, 2026.
One of the main ways in which deep seated tectonic or geodynamic processes influence the Earth's surface is by driving rock uplift. Variations in rock uplift through space and time combine with surface processes, such as erosion in rivers and on hillslopes, to shape the surface landscape. These relationships imply that, if we can adequately parameterise surface processes, we may be able to infer rock uplift histories from observations of present day topography. Efforts to do so formally using inverse modelling have mostly focused on the shapes of river profiles. Such approaches can reproduce well observed profiles, and yield uplift histories broadly consistent with independent constraints. However, they generally assume a fixed drainage planform, and neglect any information stored in the rest of landscape (i.e., in hillslope topography). Landscape evolution models, which include descriptions of hillslope processes and allow drainage planforms to evolve, may address these issues, but come with their own challenges. In particular, a strong dependence of modelled drainage planforms on the initial condition, which is generally poorly constrained, complicates direct comparison of observed and modelled topography.
Here, we explore the utility of hypsometric curves – cumulative distribution functions of elevation within a domain – in inverse landscape evolution modelling (we also include equivalent functions for slope and curvature). These curves' integrative nature should make them relatively insensitive to the precise positions of individual valleys and ridgelines. By comparing hypsometric curves from many simulations, with and without added noise, we assess their sensitivity to initial conditions, erosional parameters and uplift histories. We confirm that hypsometric curves are insensitive to initial conditions, particularly when normalised by the mean – rather than, as is traditional, the maximum – value in the domain. For landscapes in a dynamic equilibrium with the imposed uplift rate, the main control on the normalised hypsometric curve is the relative importance of fluvial and hillslope processes. Multiple erosional parameters influence this balance, introducing trade-offs to the misfit space. Nevertheless, individual parameters do have subtle secondary effects that allow them to be determined independently, at least for relatively low noise levels. In transient landscapes, features of simple uplift histories – such as timings and amplitudes of step changes in uplift rate – also appear to be recoverable. We conclude that hypsometric curves can form useful bases for inverse landscape evolution modelling, which could in turn provide novel insights into the tectonic and geodynamic processes that drive rock uplift.
How to cite: McNab, F., van der Beek, P., Schildgen, T., and Turowski, J.: Inferring uplift histories from landscapes using hypsometric curves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11459, https://doi.org/10.5194/egusphere-egu26-11459, 2026.
When aseismic ridges carried by the subducting oceanic plate enter a subduction zone, the trench depth and hence the margin relief is reduced, which increases the compression of the upper plate. The increase in compression may be relevant for understanding surface uplift and mountain building in response to ridge-subduction, but detailed effects remain to be explored. Here we use analytical and two-dimensional finite-element force-balance models to investigate the effects of relief changes and other parameters that may change during ridge subduction, including the initial trench depth, the megathrust dip angle, the slab curvature, the submarine surface slope angle, the density structure of the upper plate, the initial mountain height and the surface topography of the upper plate.
Our modeling results indicate that the increase in upper-plate compression mainly depends on the total relief change, the trench depth prior to ridge subduction and the submarine surface slope angle during ridge subduction. Secondarily, the increase in compression also depends on the average dip angle and curvature of the plate interface, as well as on the density structure of the upper plate and the mountain height prior to subduction. The enhanced upper-plate compression due to ridge subduction promotes mountain building in the upper plate until the increase in elevation leads to stress conditions comparable to those before the entrance of the ridge. We investigate this aspect for the subduction of the Cocos Ridge, based on additional finite element models that approximate the setting along the Central American margin near Costa Rica before and after the entrance of the ridge. The models indicate that the mere decrease in trench depth of ~3.3 km due to ridge subduction promoted an increase in mountain height of ~0.6 km. This corresponds to one-third of the maximum uplift inferred for Costa Rica. We further find that the remaining elevation increase of up to 1.4 km cannot be explained by changes in the slab dip angle or upper-plate density structure but may indicate an increase in shear stress along the plate interface. Taken together, our analysis shows that the decrease in trench depth during ridge subduction increases the compression of the upper plate, which promotes surface uplift and mountain building even at greater distances to the ridge.
How to cite: Leng, Y., Dielforder, A., and Hampel, A.: Impact of decreasing trench depth during aseismic ridge subduction on the forearc stress state: Insights from analytical and finite-element force-balance models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5077, https://doi.org/10.5194/egusphere-egu26-5077, 2026.
First-order orogenic arcs are often divided into second-order curves, termed salients and recesses (convex and concave to the transport direction, respectively). Although several studies have analysed the supracrustal factors controlling this festooned geometry, the potential role of deep-seated mechanisms has received little attention.
In the northern branch of the Gibraltar Arc, the orogenic grain of the central and western Betics external fold and trust belt (FTB) draws two secondary arcs, connected by a salient-recces transition segment, whose southernmost limit is the Torcal shear zone (TSZ). The central FTB salient consists of WSW-ENE to W-E thin-skinned shortening structures involving post-Burdigalian, syn-orogenic sequences in its deformation front. Thrust surfaces are dominantly SE to S-ward dipping and slickenlines suggest NNW-SSE to N-S transport directions. At the SW end of this salient, just east of the TSZ, the shortening structures trend becomes N-S. The westernmost FTB salient, within the Gibraltar Arc hinge, is defined by NW to W-ward verging, shortening structures with radial transport direction. Arc-parallel extension occurred coeval with arc-orthogonal shortening. Both salients are connected by the aforementioned transitional domain, an E-W to ENE-WSE transpressive band, dominated by dextral strike-slip deformation. This transpressive zone is significantly segmented into scattered topographic highs due to orogen-paralell extension, mainly accommodated by NW-SE normal and dextral faults.
These three tectonic domains seem to have been differentiating since the upper Miocene to Holocene suggesting a decoupling between the W-ward migrating hinge of the Gibraltar Arc and the rest of the arcuate chain. Such decoupling would fit well with the existence of a W-E trending STEP fault, whose easternmost tip were located under the transition between the central and western Betics. Thus, the dominantly dextral, significantly stretched TSZ, located just north of the betic FTB/hinterland boundary, would be the expression in the FTB of such deep STEP fault. In this context, the recent FTB deformation in the central Betics would respond mainly to the current NW-SE shortening undergone by the Iberian Peninsula, whereas the kinematic features of both the transitional transpressive band and the westernmost FTB are consistent with a WNW-ESE directed far field vector associated with the arc westward migration. Interestingly, the recent intraplate deformation in the Betics foreland has produced greater relative uplifts in front of the central Betics, mostly accommodated in overall WSW-ENE faults, than in westernmost sectors. Additionally, the kinematics of reactivated structures in the westernmost sector of the foreland is compatible with a WNW-ENE convergence. Assuming some amount of mechanical plates coupling along the northern branch of the Betics, these foreland deformation features would agree with the proposed difference in the convergence angle along the central and western Betics FTB.
This work is supported by projects PID2024-159481NB-I00 and by ERDF/EU.
How to cite: Expósito, I., Díaz-Azpiroz, M., Jiménez-Bonilla, A., and Balanyá, J. C.: Kinematic Decoupling and Orogenic Trend Variations in Arcuate Fold-and-Thrust Belts: Exploring Possible Deep Controls, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13851, https://doi.org/10.5194/egusphere-egu26-13851, 2026.
At 30º South, the western Central Andes are comprised by the Coastal Cordillera, a seemingly little-deformed zone containing Mesozoic volcanic arc and back arc-related rocks . To the east, the Vicuña fault separates the Coastal Cordillera from the Principal Cordillera and the Frontal Cordillera. Those two units display relatively small areas of Mesozoic sedimentary cover that have been preserved despite the uplift which exposes mainly Carboniferous to Triassic plutonics. Further east in the Precordillera, deformation involves increasingly recent Cenozoic sedimentary units.
Based on 2025 campaign field data acquisition and the revision of previous geological maps, we present a structural cross section along a 30ºS, E-W transect and its restoration . During the Mesozoic, extension in the Coastal Cordillera was mainly accommodated by the west-dipping Vicuña fault from the Jurassic to Late Cretaceous. Constraints from pluton emplacement depths and stratigraphic relationships suggest that significant uplift and topographic growth might have interrupted this extension in the Early Late Cretaceous in the Coastal Cordillera. Uppermost Cretaceous syn-orogenic deposits mark the onset of contraction. Upon shortening, the Vicuña fault was folded and reactivated as a west-vergent thrust during the uplift of the Principal Cordillera. This shortening episode also created the present-day relief in the Coastal Cordillera although the timing of this uplift is not well constrained. Subsequently, shortening propagated eastwards into the foreland of the orogen, forming the folds and thrusts of the Precordillera.
Our cross section suggests successive phases of extension and compression which can alternate at variable timescales and operate in different locations. This tectonic evolution raises numerous questions: Which geodynamic factors drive the occurrence of contraction or extension? What is the relationship between surface and deep crustal structures? In a non collisional context, what controls the localization of deformation?...
How to cite: Munday, W., Santolaria, P., and Muñoz, J. A.: Andean Cross Section at 30ºS: A Window Onto the Tectonic Evolution of a Non-Collisional Orogen, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14604, https://doi.org/10.5194/egusphere-egu26-14604, 2026.
In the northern Andean block the subducting Nazca plate contains a flat slab segment that notably influences the structural styles of the mountain belts of the Southamerican plate. A seismotectonic break at approximately 4°N is often referred to as the Caldas Tear. In contrast to the obvious aseismic ridges associated with the southern edges of the Peruvian and Chilean flat slab segments, there is no distinct single oceanic feature that limits the size of the North Andean flat slab segment. Instead, a ridge-transform system can be extrapolated into the inboard domain of the trench. This explains the presence of the Istmina Transverse Range along a transform-parallel sector, as well as the Miocene Combia volcanic province where this transform-parallel sector turns into the ridge-parallel discontinuity of the Caldas Tear. Folding of the forearc basins and the Eastern Cordillera of the retroarc domain provides evidence of a margin-wide, NW-SE contractional regime, which has been independently documented by regional paleostress determinations. Further structural evidence for oblique convergence comes from a clear collisional feature formed by a sweeping linear transform fault, which is now situated beneath the Istmina Transverse Range. This feature resulted in a triangular re-entrant of the Western Cordillera, causing it to bend around the Transverse Range. On the retroarc side, the southward propagation of the flat slab segment is evident in fold terminations within the Eastern Cordillera, as well as in the relay pattern of frontal thrust faults at its foothills. The southern morphotectonic break of the Caldas Tear juxtaposes the intramontane Bogotá basin, which belongs to the flat-slab segment, with a folded flank of an E-vergent anticlinorium that marks the deformational style related to the steeply dipping Nazca plate. In our contribution, we depict representative, but less evolved transverse lineaments of the Eastern Cordillera and characterize their deformation style. We also observe the local presence of salt nappes and compare the retarded vs. accelerated intrusive ascent of magmatic manifestations, discussing their relevance with respect to possible plate configurations that suggest lithospheric tearing or bending. The guiding question that informs our research is whether these surface processes provide insight into time slices of the evolving flat slab segment.
How to cite: Kammer, A., Zeilinger, G., Quintero, C. E., and Cifuentes, W. D.: Evolution of the northern Andean Flat Slab Segment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21961, https://doi.org/10.5194/egusphere-egu26-21961, 2026.
The Hellenides constitute a long-lived convergent system resulting from oceanic–continental subduction and subsequent continental collision between Apulia and Eurasia. Their external domain developed above inherited sectors of a hyperextended Mesozoic passive margin, composed of alternating thick carbonate platforms including the Apulian (and Pre-Apulian) and Gavrovo units, and thin basinal domains such as the Ionian. Such inherited structural and stratigraphic architecture exerted a first-order control on thrust localization, wedge geometry, and foreland basin evolution. Since the Late Cretaceous, convergence was accompanied by significant slab retreat, producing a strongly asymmetric orogen with outward thrust propagation in the prowedge and coeval extension in the Aegean region.
We present three E-W, regionally balanced cross sections across the External Hellenides, sequentially restored to constrain the pre-contractional configuration of the sedimentary cover, the kinematic evolution of the thrust belt, and its relationship with inherited rift-related domains and salt-related deformation. The cross sections run through the western Hellenides and are roughly parallel to the main transport direction. The northernmost section crosses the Corfu area, whereas the southernmost profile is located south of the Kefalonia Fault, where the tectonic regime transitions from continental collision to active oceanic–continental subduction.
The sections are based on detailed field surveys along the Ionian structural unit, integrated with published seismic profiles and exploration wells. In the eastern Ionian zone, synclines affecting Jurassic to Oligocene–Miocene flysch are generally broad, whereas toward the west, folding becomes tight to isoclinal, locally forming box-type folds with overturned limbs. Anticlines are tight, variably elongated, doubly plunging, and locally associated with breakthrough thrusts. This structural contrast reflects variations in pre-orogenic stratigraphic thickness and mechanical behaviour: tight folds involve a thin sedimentary cover detached on Triassic salt, while broader synclines record deformation of thicker, locally welded successions. The pre-contractional Ionian basin consisted of a salt-influenced deeper-water carbonate system with salt pillows and plateaus, and subsident areas receiving episodic carbonate debrites from adjacent shallow-water domains. The absence of halokinetic sequences in the pre-orogenic succession suggests that diapirism in the study area was exclusively syn- to post-shortening and controlled by shortening-related uplift and erosion.
During contraction, all the Ionian structural units show regionally consistent allochthonous behaviour, detached along Triassic evaporites and overthrusting the autochthonous structural units together with Aquitanian deposits, as documented by tectonic windows. Progressive Miocene deformation involved thicker sub-thrust units, producing broader structures that subsequently controlled deformation of the overlying thinner Ionian units.
Sequential restoration from the Oligocene to the present reveals forward-propagating thrusting consistent with a prowedge-dominated orogen above a retreating slab. This supports an evolution in which thin-skinned deformation above Triassic evaporites and subsequent reactivation of sub-thrust structural units was driven by underplating of Adriatic crust beneath the External Hellenides. Our balanced cross sections provide quantitative constraints on the relative proportions of accreted versus subducted continental crust of the former hyperextended margin, and allow prosing a tentative location for the transition between the Pre-Apulian ramp and the Ionian basinal domain, which acted as precursor for thrust nucleation.
How to cite: Snidero, M., Martinez Granado, P., Santolaria, P., and Muñoz, J. A.: Thrust tectonics in the External Hellenides: from a salt-bearing rifted margin to convergence in a retreating subduction zone , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22451, https://doi.org/10.5194/egusphere-egu26-22451, 2026.
Unravelling the tectonic evolution of collisional orogens and the forces driving the exhumation of high-grade metamorphic rocks requires constraining the kinematics and timing of major fault systems. The Main Mantle Thrust (MMT) in the Swat Valley (northern Pakistan) marks the Eocene suture between the Indian Plate and the Kohistan–Ladakh Island Arc. Its later reactivation is critical yet debated, with models ranging from dominantly dextral strike-slip faulting with minor normal offset (typically less than a few meters) to significant normal faulting facilitating regional exhumation of high-grade metamorphic rocks. This research integrates structural geology with a new, multi-method low-temperature thermochronology dataset—including zircon and apatite (U–Th)/He and apatite fission-track ages—to contribute to this debate. Structural analysis of over 150 kinematic indicators collected along the MMT and its footwall shows that the MMT experienced semi-ductile to brittle reactivation dominated by top-to-the-north normal faulting. Structures formed under greenschist- to sub-greenschist facies conditions (e.g., C′ shear bands) in the footwall record progressive exhumation, with purely brittle cataclastic deformation marking the final stages. Our new thermochronometer dateset includes zircon (U–Th)/He (ZHe) single-grain ages (14.9 ± 1.2 to 24.4 ± 2.0 Ma), apatite (U–Th)/He (AHe) single-grain ages (7.6 ± 0.4 to 15.9 ± 1.0 Ma), and apatite fission-track (AFT) central ages (15.3 ± 2.4 to 16.4 ± 3.2 Ma). This dataset, alongside its thermal history modelling, reveals a consistent cooling signal across the Swat Valley. Following the Eocene collision and peak metamorphism, a major tectonic shift occurred in the Early Miocene. Our data indicate the onset of rapid cooling at ~20 Ma, with a slightly later initiation at ~18 Ma in the eastern Loe Sar Dome. This distinct phase of rapid cooling records the top-to-the-north normal reactivation of the MMT, which lasted until ~15–14 Ma. Collectively, our results provide structural and timing constraints supporting a model of protracted, normal-sense reactivation of the MMT between ~20 and 15 Ma. This event facilitated the final unroofing of high-grade metamorphic rocks in the Swat Valley.
How to cite: Hernández Chaparro, D. R., Faccena, C., Olivetti, V., Fellin, G., and Ghani, H.: Constraining Early Miocene Reactivation of the Main Mantle Thrust (Swat Valley, Pakistan) through Integrated Structural and Thermochronologic Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12696, https://doi.org/10.5194/egusphere-egu26-12696, 2026.
