Despite considerable progress in monitoring natural subduction zones, key aspects of megathrust seismicity remain puzzling, mainly due to the temporally incomplete and spatially fragmented available record. Scaled seismotectonic models yield valuable insights by spontaneously creating multiple stick-slip cycles in controlled, downscaled three-dimensional laboratory replicas. Here we report recent progress in analog modeling of the megathrust seismicity, particularly focusing on a meters-scale elasto-plastic model featuring a frictionally segmented, granular fault that mimics the subduction channel at natural subduction zones. We showcase how by employing analog materials under low-stress conditions, the potentialities of monitoring can be maximized using three diverse techniques: 1)  Precise monitoring of surface spatial deformation over time is achieved through digital image correlation techniques, mirroring a uniformly distributed dense geodetic network spanning land to trench in real subduction zones. 2) A Micro-Electro-Mechanical (MEMS) accelerometric network, emulating a seismic network, captures seismic wave propagation at the model surface. 3) Embedded piezoelectric sensors within the granular analog fault capture near-field acoustic signatures of frictional instabilities. These diverse monitoring techniques allow for investigating the consistency between continuous seismic activity and surface deformation data, offering insight into both micro and macroscopic features of analog seismic cycles. At the macroscopic level, the models' frictional behavior can be numerically reproduced via rate and state numerical simulations, considering earthquake fault slip as a nonlinear dynamical process dominated by a single slip plane. At smaller scales, the model accounts for complexities in fault slip emerging from grain interactions, reflecting nonlinearities that arise when considering faults as distributed three-dimensional volumes. These fundamental attributes, coupled with their capacity to create extensive catalogs of small labquakes, make scaled seismotectonic models exceptional apparati for employing Machine Learning (ML) in comprehending multi-scale spatiotemporal seismic processes. Cutting-edge Deep Learning methods are employed to predict the spatiotemporal evolution of surface deformation, where regression algorithms not only forecast timing but also the propagation and magnitude of analog earthquakes across diverse spatiotemporal scales. Given that one of the monitoring systems used in seismotectonic analog models mimics a geodetic-like network in nature (GNSS data-Global Navigation Satellite Systems), an attempt to generalize the promising outcomes achieved in the laboratory to natural subduction faults is proposed.  Such promising avenues emphasize the potential for ML to bridge the gap between laboratory experiments and real-world seismic events. These initial findings, combined with advancements in the instrumentation of fault laboratories in nature and expanding data reservoirs, reinforce the belief that ML can significantly augment our understanding of the multiscale behaviors of natural faults.

How to cite: Mastella, G., Corbi, F., Bedford, J., Latypova, E., Pignalberi, F., Scuderi, M., and Funiciello, F.: Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6869, https://doi.org/10.5194/egusphere-egu24-6869, 2024.

Fold-and-thrust belts (FTBs) evolve over a mechanically weak basal décollement that separates overlying intensely deformed rocks from the underlying less deformed or undeformed rocks. Although fold-and-thrust belts are often considered laterally cylindrical in nature, a closer inspection reveals remarkable variations in structural style (e.g., fold geometry) both along and across the strike of mountain belts. Using crustal scale thin-sheet laboratory experiments, this study focuses on the role of laterally varying coupling strength of the basal décollement on the evolution of structural styles in natural FTBs. In this study, we used a rectangular slab of silicon putty, a linear viscous material, of uniform thickness in all experiments to simulate the crustal section and the models were deformed at a uniform convergence velocity of ~7.649 × 10^-5 ms^-1. Analyses of experimental results show remarkable changes in the wedge growth with the introduction of along strike variations in décollement strength. The segment of the deforming wedge over weakly coupled décollement propagates at a faster rate towards the frontal direction compared to the laterally continuous segment over a strongly coupled décollement, leading to an overall sinuous geometry of the deformation front. In contrast, an approximately linear deformation front represents a condition of uniform along-strike coupling strength at the basal décollement. Based on our experimental results, we argue that the broad arcuation of the mountain front along the eastern margin of the Zagros fold-thrust belt (i.e., Fars arc region) might have resulted due to along strike variations in the décollement strength, while the occurrence of a linear deformation front from the central to western margin of the fold-and-thrust belt represents a segment of the wedge with a uniform coupling strength at the basal décollement. Our experimental results can be carefully used to explain the cause of strike-wise segmentation of tectonic processes in orogenic belts, variations in topography and earthquake activities.   

How to cite: Roy, S., Willingshofer, E., and Bose, S.: Influence of lateral variations of décollement strength on the structure of orogenic wedges: insights from experimental viscous wedge models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3310, https://doi.org/10.5194/egusphere-egu24-3310, 2024.

Fault evolution is influenced by multiple factors, including the reactivation of pre-existing structures, stress transmission within ductile detachment layers, and the growth, interaction, and connection of newly formed fault segments. In the same stress field, displacement vectors of fault strikes, dip-slip vectors, and subtle fractures accommodate strain distributed everywhere. This study employs PIV analysis and model reconstruction to simulate oblique extensional fault systems formed at four different angles. Simulation modelling indicates that oblique extensional reactivation of pre-existing structures controls the linear arrangement of fault segments in the overlying strata. Arcuate faults can be classified into linear master fault segments controlled by pre-existing structures, curved splay faults in termination zones, and normal fault segments responding to regional stress fields. Along-strike displacement is regulated by linear segments within the master strike-slip fault, while progressive bending of splay faults, relay ramps' dislocation, and inclined displacements are regulated by relay ramps within the overlap zone. Small-angle (15°) oblique extension favours the formation of fault segments with distinct step-like features, leading to additional relay ramps. In contrast, high-angle (60°) oblique extension often results in the development of more continuous fault segments. As faults continuously evolve, new fault segments tend to deviate from the control of pre-existing structures, concentrating more on the development of planar and continuous master faults. Finally, we compared the established model with the transtensional fault system within the intraplate rift system in eastern China, demonstrating that the oblique extension angle controls the composite characteristics of the overlying strata faults.

How to cite: Wang, Y. and Yu, F.: The Linkage Evolution of Strike-Slip Faults with Normal Faults—Insights from Analogue Modelling at Various Oblique Extension., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4813, https://doi.org/10.5194/egusphere-egu24-4813, 2024.

This study investigates a fold-and-thrust belt (FTB) beneath the South Yellow Sea Basin, a noteworthy petroleum exploration target, featuring a basement high and a detachment layer. In the central basin, magnetic anomalies reveal the development of the basement high. Seismic reflection data, in conjunction with drilling information, disclose the presence of the Lower Silurian Gaojiabian Formation, exceeding ~500 m, acting as a low-cohesion detachment layer. However, the impact of these features on regional structures and the resulting hydrocarbon preservation conditions remains uncertain. This study explores the kinematic characteristics and deformation localization associated with the basement high and intermediate detachment using four sandbox models and particle velocity analysis within the FTB framework. Model 1, the reference, utilized pure quartz sand without either feature. Model 2 examined the role of the intermediate detachment using glass microbeads, revealing a limited effect in generating typical thin-skinned FTB. Model 3 considered the basement high and found that it strongly influenced the deformation regime of the wedge. Model 4 examined both features and suggested their combined influence on FTB deformation processes. In Model 2, lacking a pre-existing basement high, the intermediate detachment did not contribute to FTB deformation. In Model 3, lacking an intermediate detachment, deformation propagated along the surface of the basement high upon reaching its edge. In Model 4, shortening propagated upward along the edge of the basement high and then into the intermediate detachment, producing comparable structural geometry to the prototype, including both thick- and thin-skinned FTBs in nature. The results indicate that in the central South Yellow Sea Basin, structural layers between the basement high and detachment are likely to experience weak deformation; thus, favorable hydrocarbon preservation conditions can be anticipated in this region. This study holds significant importance in guiding future petroleum exploration efforts in the central South Yellow Sea Basin.

How to cite: Zhang, P., Fu, Y., and Yan, B.:  Influence of Basement High and Detachment on the Kinematics of a Fold-and-Thrust Belt in the Central South Yellow Sea Basin with Implications for Hydrocarbon Preservation: Insights from Analog Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8859, https://doi.org/10.5194/egusphere-egu24-8859, 2024.

Eastern Sichuan fold belt, a prolific hydrocarbon province in China, shows the similar fold styles to the Swiss Jura Mountain fold belt, which’s therefore called as Jura-type fold by Chinese geologists. However, it’s still a matter of geologist’s debate on the formation mechanism of the eastern Sichuan fold belt.

To unravel how this type of fold trains form, a systematic scaled 2D contractional analogue experiments with composite materials were conducted. Silica-sand represents the overburden with added mica-flakes, and a stiff plasticine interlayer introducing different mechanical anisotropies. Viscous silicone rubber represents the salt detachment. The following 3 main issues have been investigated: 1) what type mechanical stratigraphy can form the fold train during lateral contraction; 2) what are the mutual interaction between faulting and folding during the formation process of detachment fold; 3）what are kinematics and its related strain distribution patterns for a detachment fold system.

The modelling results indicate that the presence of a stiff plasticine layer is the key perquisite for the formation of a concentric fold train for the following reasons: 1) it encourages the shortening to be periodically accommodated by sinusoidal-symmetric buckle folds at the inceptive folding stage; 2) it can keep the break-thrust ramps from being activated with further shorting delaying the development of faulted detachment folds at the later folding stage. As for silicone detachment, it mainly plays a role in the amplification of detachment folds via the redistribution of ductile material between the syncline and anticline domain.

DIC strain data show that the main sections of detachment fold-the limbs, especially in the forelimb, and the hinge are easily strained. More specifically, the normal faults and breakthrusts can form in the anticlinal hinge and limbs, respectively, when the detachment fold cannot be tightened any more. However, the strain is not easily accumulated in the syncline domain.

Our modelling result together with the latest interpretation of seismic reflection suggest that the eastern Sichuan fold belt is a result of faulted detachment folds, mainly controlled by the competence contrast within the overburden and the thickness of both the weak viscous detachment and strong brittle overburden.

Keywords: Eastern Sichuan Basin; Analogue modelling; DIC; Fold-thrust belt; Detachment fold

How to cite: Feng, G., Adam, J., Chen, S., and Wang, X.: Key controlling factors on the formation of Jura-type fold in eastern Sichuan Basin, South China: insights from analogue modelling with optical strain monitoring (Digital Image Correlation), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13637, https://doi.org/10.5194/egusphere-egu24-13637, 2024.

The Reykjanes Peninsula (RP) in southwestern Iceland represents a zone of oblique rifting where the divergent boundary of the Mid-Atlantic ridge is offset to the eastern Iceland along a left-lateral transform fault - the South Iceland Seismic Zone (SISZ). RP and the SISZ represent regions of the most abundant earthquake activity on Iceland, development of fissure arrays and occasional lava eruptions. A series of earthquake swarms at RP in the 2021-2023 period indicates development of distributed fracture networks along ENE direction of the transform fault and two new fissure arrays trending NE divided by a gap in seismicity. In the last 3 years, the volcanic activity culminated two times in volcanic eruptions, bringing magmas from Moho depth at 15 km.

Inspired by the recent tectonic activity at RP, we conducted a series of analogue experiments consisting of a silicone magma chamber embedded in a photoelastic gelatine crust. The aim of our study is to constrain the links between the depth level of the magma chamber, the crustal scale fracture arrays, faults, magma pathways, superficial fractures and the location of related potential volcanic activity in a transform setting. Inducing strike slip deformation of the system, we explored the influence of shape and orientation of the magmatic chamber on the evolution and pattern of progressively developed fractures along the central shear domain. During the experiment, we captured the stress fringe patterns in the fractured gelatine. The surface deformation was traced by a stereoscopic digital image correlation (DIC) system employing two high-speed LaVision cameras. Analog magma spreading was traced using fluorescent dye mixed to the silicone or into the gelatine interlayer.

Modelling results show that decoupling of the crust above the magma reservoir in strike-slip setting produces a domain with higher vorticity bounded by a conjugate set of tensional fractures. The largest open fractures initiate at and propagate from the intersection of the principal strike-slip fault plane with the vertical contact of the magma chamber and the surrounding crust. Including other open fractures, the orientation of the fracture set is oblique (~ 60°) to the fault plane. With formation approximately coeval to those of the fractures, fine wrinkles at the crust surface are observed with orientation of ~ 120° with respect to the fault plane.

How to cite: Staněk, M., Závada, P., and Krýza, O.: Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18656, https://doi.org/10.5194/egusphere-egu24-18656, 2024.

In subduction systems, asthenospheric flow, generated by subducting slabs, is considered as one of the key forces contributing to the deformation of the overlying lithosphere. Previous analogue modelling studies predominantly focused on understanding the kinematics and dynamics of subduction roll-back-driven asthenospheric flow, without looking at the influence of that flow on upper-plate deformation due to the modelling setups or methodological limitations. We developed a novel analogue modelling approach where gravity-driven asthenospheric flow represents the main driver for upper plate deformation. Volume-constant flow within the deformation box is achieved by an inlet-outlet system. In the models, we gradually increase the setup complexity from single-layer asthenosphere-only models to 4-layer asthenosphere-lithosphere models to test flow velocity distribution and its sensitivity to the outlet size, model thickness and rheological stratification of the model, as well as the transfer of deformation from the asthenosphere to the overlying lithosphere. Furthermore, we study the effects of the inherited lithospheric structures, such as weak zones representing old sutures, on deformation transfer. The results are compared with the Pannonian-Carpathians system of south-eastern Europe, where the large Pannonian back-arc basin formed during the Miocene retreat of the Carpathians slab.

For the methodological approach, the results show that asthenospheric flow can be fully controlled by the inlet-outlet system by adjusting the outlet size, which provides an efficient mechanism for the deformation of the overlying mechanically stratified lithosphere. The models also demonstrate that the back-arc extension is initiated farther away from the asthenospheric flow origin (i.e., the outlet in the models or slab-roll back in nature). The subsequent deformation propagates in two directions, towards the flow origin, and farther away from it, both directions controlled by the shape of an indenter located laterally to the subduction zone. Most of the back-arc extension and the lithospheric thinning are accommodated in the area farther to the “slab” due to the strain shadow effect of the indenter. The indenter also contributes significantly to the strain partitioning in its closer proximity where a complex pattern of bi-directional extension, transtensional, strike-slip and transpressional deformation forms. The weak zones accommodate the onset of back-arc extension or act as transfer zones between areas with different extension rates, depending on their orientation relative to the asthenospheric flow. These models show several similarities with the Pannonian-Carpathians system, where most of the Pannonian lithospheric thinning is located at a significant distance from the subducting Carpathians slab, bypassing the Transylvanian-Apuseni area. This extension started by reactivation of the Neotethys suture zone, while the Mid-Hungarian Fault zone transferred the deformation between areas of higher extension to the south and lower extension to the north. Furthermore, several triangular-shaped sub-basins within and at the margin of the Pannonian Basin are radially located around the Moesian NW corner, similar to our modelling results. The complex pattern of the bi-directional extension and strike-slip observed in the models were recorded by the Carpathians-Balkanides orocline in the vicinity of the Moesian indenter.

How to cite: Krstekanic, N., Willingshofer, E., Auzemery, A., Matenco, L., and Smits, J.: Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12468, https://doi.org/10.5194/egusphere-egu24-12468, 2024.

The deformation associated with the evolution of fold-thrust tectonic (FTT) wedge has been in the focus of research due to their association with hydrocarbons resources. Analogue sandbox modelling has been proven to be useful in characterizing FTT wedge. However, it is less convenient to interpret the influence of complex boundary conditions and material rheological parameters and to derive the stress distribution pattern from the analogue models. Nonetheless, these challenges can be accomplished competently by means of an exact numerical equivalence of those analogue models. Therefore, we undertook a numerical replication of the analogue sand-box with an absolute identical set up. This makes the attempt unique from earlier approaches, where lengths, rheology, and/or cohesive strengths were likely varied for converging the solutions in codes. Here, propagation parallel profile of sandbox experiments is numerically modelled in a 2-dimensional (2D) space with a plain strain assumption. For simplicity, the models are devoid of complex geological phenomena such as isostasy, pore fluid pressure and surficial processes. The present model enforces an elastoplastic constitutive relationship having exactly same rheology as our sand-box model. The model comprises cover material resting over a rigid decollement with frictional interaction. The cover material is subjected to asymmetrical push from one end as in physical experiment. With the identical rheology, dimensions, and geometry our numerical model successfully produced comparable results with our physical sandbox models. The measured kinematic attributes of the wedge such as taper angle, wedge width, thrust spacing, displacement along thrust from our numerical model are found in good agreement both qualitatively and quantitively with their analogue counterparts. The dynamics of deformation has also been investigated by extracting the magnitudes of stresses from each node of the numerical mesh of the present models.  From the dynamic analysis, the spatial distribution of stresses revealed that within a deforming wedge all the stress parameters are maxed periodically at a certain distance away from the pushing end boundary. The position of maximum stress is found consistent with the zone localized failure. Monitoring the periodic peaks of stress approximate the location of failure, in return leading to measure the thrust spacing. Furthermore, empirical relationships for stress distribution within a collisional wedge have been successfully developed from the observed stress distribution patterns. With the help of these relationships, mathematical expressions were developed for predicting 2D curvature of a thrust plane within a tectonic wedge. 

How to cite: Behera, A. and Bhattacharjee, D.: The dynamics of fold-thrust tectonic wedge: An insight from impeccable simulation of Physical Sandbox Experiment with Finite Element Model., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14388, https://doi.org/10.5194/egusphere-egu24-14388, 2024.

Simulations of accretionary prisms are most of the time realized either using a simplified set up that cannot account for the evolution of temperature with the growth of the prism nor deformable basement or using a very large size simulation of the complete subduction zone using a larger resolution locally. The first method is over-simplified and discards the possibility to study crustal scale accretionary prism, the second method is very costly numerically.  

Here, we present simulations of accretionary prisms that use 1/ heatflux as boundary condition allowing the temperature at the base of the model to evolve as the accretionary prism grows and 2/ flexural deformation of the basement in response to the growth of the accretionary prism. This new boundary condition is very cheap to compute as we implemented it by solving analytically the flexure equation using sinus decomposition and image method.  

We then present a set of numerical simulations of crustal scale accretionary prism with particular focus on the geometry of the subducting basement in order to better understand how the alternation between period of subduction erosion and accretion affects the geometry of the accretionary prism and its thermal history as a function of the rigidity of the subducting plate. We compare our simulations with a set of east-west trending seismic profiles located southwest of Taiwan showing along strike structural variations of the accretionary prism.    

How to cite: Le Pourhiet, L., Gauthier, A., Cubas, N., Tugend, J., and Mohn, G.: How the rigidity of the subducting plate affects the geometry of accretionary prisms?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16472, https://doi.org/10.5194/egusphere-egu24-16472, 2024.

The Azores archipelago is an integral part of the Macaronesian geographic region (which also includes the volcanic archipelagos of Madeira, Selvagens, Canaries and Cape Verde). This region, located in the centre of Atlantic Ocean, has its individual islands spread around a triple junction, which has been suggested to affected by a plume-ridge interaction (Storch et al., 2020; Beier et al., 2022). One of the major questions surrounding its history concern the why/how the Terceira Rift (i.e., the NW-SE oriented connection between the mid-ocean ridge and the Gloria Fault Zone) was formed.

To explore this issue, we have run sets of 3D viscoelastoplastic models for the region using the state-of-the-art modelling code LaMEM (Kaus et al., 2016). As our objective was to evaluate how the geological data and the suggested evolution for the region fit geodynamic constraints. We based our numerical models on previously established evolutionary models for the region, such as the leaky transform model (Madeira and Ribeiro, 1990).

Preliminary results hint that the formation of the Terceira Rift could be formed as the result of a shift in the regional tectonic forcing, which we attribute to the collision between the Iberian and Eurasian plates. Furthermore, our results suggest that a strong rheological contrast in the region was required to ensure the localization of deformation. Models without this feature tended to maintain a simple E-W connection between the Gloria Fault Zone and the southern part of the mid-ocean ridge.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through projects GEMMA (https://doi.org/10.54499/PTDC/CTA-GEO/2083/2021) and 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) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

References

Beier, C. et al. (2022) ‘The submarine Azores Plateau: Evidence for a waning mantle plume?’, Marine Geology, 451, p. 106858. Available at: https://doi.org/10.1016/j.margeo.2022.106858.

Kaus, B.J.P. et al. (2016) ‘Forward and Inverse Modelling of Lithospheric Deformation on Geological Timescales’, NIC Series, 48, pp. 978–3.

Luis, J.F. and Miranda, J.M. (2008) ‘Reevaluation of magnetic chrons in the North Atlantic between 35°N and 47°N: Implications for the formation of the Azores Triple Junction and associated plateau’, Journal of Geophysical Research: Solid Earth, 113(B10). Available at: https://doi.org/10.1029/2007JB005573.

Madeira, J. and Ribeiro, A. (1990) ‘Geodynamic models for the Azores triple junction: A contribution from tectonics’, Tectonophysics, 184(3–4), pp. 405–415. Available at: https://doi.org/10.1016/0040-1951(90)90452-E.

Storch, B. et al. (2020) ‘Rifting of the oceanic Azores Plateau with episodic volcanic activity’, Scientific Reports, 10(1), p. 19718. Available at: https://doi.org/10.1038/s41598-020-76691-1.

How to cite: Almeida, J., Duarte, J., Rosas, F., Fernandes, R., Geraldes, F., Carvalho, L., and Ramalho, R.: A new geodynamic model of the Azores archipelago: preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13464, https://doi.org/10.5194/egusphere-egu24-13464, 2024.

The recognition of different boudinage patterns is of key importance to the unravelling of the tectono-metamorphic evolution of different domains in different tectonic contexts and at different considered spatio-temporal scales.

The main reason for this is twofold: (1) Boudins tend to preserve the relic metamorphic conditions that characterize deformation prior to the one recorded by matrix fabrics and associated mineral associations. (2) Specially under shear deformation regimes, quarter-structure geometric patterns comprising rotated boudins and folded matrix planar fabrics, can be used to determine the shear sense of the later (sin-boudinage) deformation.

In the present work, we present preliminary numerical and analogue modelling results of boudinage, under non-coaxial (shear strain) deformation. We specifically investigate the potential influence of three main parameters on the genesis of different (boudins-folds) quarter structures patterns: i) the viscosity contrast between the boudin and the matrix; ii) the original position of the non-equidimensional boudin; and ii) the assumed (bulk) shear strain rate.

We proceed by presenting a preliminary comparison of our results with archetypical natural examples of boudinage, in different tectonic-structural contexts and at different scales, further illustrating the potential value of these type of structures in the unravelling of the deformation history in different situations.

Acknowledgements

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES 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) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

How to cite: Rosas, F., Gomes, A., Almeida, J., Duarte, J., Riel, N., and Schellart, W.: Numerical and analogue modelling of boudinage under non-coaxial shear strain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12208, https://doi.org/10.5194/egusphere-egu24-12208, 2024.

Continental collision occurs when two continents are dragged towards each other by the pull of the attached subducting oceanic lithosphere. Previous geodynamic modeling studies of collisional systems focused on first-order processes (such as coupled/decoupled regimes, continental delamination, slab break-off dynamics) and regional or even local scale dynamics (e.g., exhumation of HP/UHP rocks, surface topography). However, continuous subduction of continental lithospheric mantle after the onset of collision and long-term dynamics of continental subduction remains poorly constrained. Long-term continental subduction bears major geodynamic implications for the evolution of past and present collision zones.

To this aim, we use the geodynamic code LaMEM to perform high-resolution (2048 × 512) 2D buoyancy-driven numerical models, coupled with phase diagrams to account for density changes, of continued continental subduction with conditions that favor flake tectonics. We investigate the role of lower crust rheology to assess which rheological scenarios allow continental flaking and, thus, continued subduction of continental lithospheric mantle.

Our preliminary results exhibit long-term continental subduction, due to decoupling of the lower crust from the subducting continental mantle and/or density changes. This separation allows the deformation to be transmitted onto the overriding plate, with the emplacement of the subducting plate crust onto the overriding plate spanning more than 350 km and lasting over 100 Myr.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES 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) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and through scholarship UI/BD/154679/2023.

How to cite: Rodrigues, N., Rosas, F., Riel, N., Almeida, J., Gomes, A., and Duarte, J.: Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13652, https://doi.org/10.5194/egusphere-egu24-13652, 2024.

Ophiolites are exposed remnants of oceanic lithosphere that are critical to our understanding of the structure, composition, and evolution of oceanic plates.

Some ophiolites (e.g., some Tethyan-type ophiolites) originate in the oceanic forearc of an intra-oceanic subduction system (i.e., in the overriding plate). If the trailing edge of the subducting oceanic lithosphere is connected to a continental passive margin, then that passive margin may also be subducted (beneath the forearc and proto-ophiolite) once all the oceanic lithosphere is “consumed” at the trench. The subduction of the continental passive margin means that a buoyant continental crust will underthrust the oceanic forearc (i.e., proto-ophiolite). This crust goes through a burial-exhumation cycle, and as it exhumes it can drag and detach the tip of the overlaying oceanic forearc, creating an ophiolite klippe. The exhumation-emplacement process is, however, still not fully understood, particularly regarding the constraints imposed by the forearc itself. For example, the detachment of the tip of the forearc (ophiolite) from the remainder of the plate should, at least in part, be controlled by the mechanical properties of the forearc (i.e., presumably the tip of a “weak” forearc will detach more easily than the tip of a “strong” forearc).

Present-day intra-oceanic subduction forearcs (i.e., present-day model-types for Tethyan-type ophiolites) experience significant chemical alteration induced by the circulation of metamorphic fluids originating from the dehydration of the underlying subducting plate. This chemical alteration occurs mostly in the form of serpentinization of forearc peridotites, leading to a substantial weakening of the forearc lithospheric mantle. The circulation of these fluids, and hence the serpentinization process, is thought to occur primarily along preexisting deeply rooted fault systems, further weakening these strain-localizing structures, although some diffuse alteration probably also occurs. It is then reasonable to assume that the paleo forearcs that originated Tethyan-type ophiolites were also subject to these chemical and mechanical alterations, which are then expected to have affected the ophiolite emplacement process.  

Here we present novel 2D and 3D dynamic numerical models that investigate the role of forearc weakening on ophiolite emplacement processes. Specifically, we test different mechanical weakening patterns, i.e., localized (serpentinized faults) vs homogeneous (diffuse serpentinization) weakening.

Preliminary results suggest that prior serpentinization of the forearc has a critical control on ophiolite emplacement. Furthermore, differing degrees of forearc serpentinization, as well as serpentinization distribution patterns, result in different tectonic regimes of ophiolite emplacement.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES 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) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020) and through scholarship SFRH/BD/146726/2019.

How to cite: Gomes, A., Rosas, F., Riel, N., Duarte, J., P. Schellart, W., and Almeida, J.: Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10540, https://doi.org/10.5194/egusphere-egu24-10540, 2024.

The continual modification of the topography due to varied processes results in diverse and dynamic terrain. Landscape evolution studies can link the effect of small-scale topographic quantities on long-term landscape evolution. In this study, the evolutionary pattern of the Dibang basin, located at the limb of the Eastern Himalayan Syntaxis stretch along the active tectonic region of northeast India is analysed using the stream power incision model (SPIM). SPIM is an empirical power law equation linking erosion with channel area and bed slope.  With constant tectonic forcing and homogeneous physical properties, river profiles deviate from linearity and exhibit convexity (indicating uplift) and concavity (indicating erosion) in their longitudinal profiles. These deviations indicate the transient responses of the river profile due to tectonics. Here, the landscape is modelled assuming that the Dibang River lying close to the mountain front shows bedrock properties. The evolved topography is seen to exhibit an erosion-dominated landscape with a rapid decrease in the mean elevation. The profile of the Dibang River exhibits a concave-convex-concave shape, indicating that the river channel is in a state of disequilibrium. The steepness index is observed to be varying across the Dibang basin with higher values in the middle and upper right parts of the basin. The χ plot also reveals the transient nature of the river profile.

How to cite: Narayan M, U., Sahu, S. K., Bharti, R., and Nair, A. M.: Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17730, https://doi.org/10.5194/egusphere-egu24-17730, 2024.

The Atlas fold and thrust belt extend from the Atlantic rifted margin of Morocco to Tunisia over a distance of 2500km. Before its inversion in the Cenozoic to the present, the Atlas system evolved initially as a rift basin that opened simultaneously with the Atlantic rift in the west and the Tethys in the north, during the upper Triassic-Jurassic period.

The Western High Atlas is believed to be influenced by the Atlantic Ocean (also known as the Atlantic domain), where the Triassic to Early Jurassic strata are considered to be syn-rift, while the Middle Jurassic to Cretaceous deposits are labelled as post-rift. In contrast, the Marrakech High Atlas (MHA), Central High Atlas (CHA), Middle Atlas (MA), and the Eastern High Atlas (EHA) are assumed to be influenced by the Tethys Ocean (also known as Tethyan domain), where the Triassic to Jurassic sediments are considered to be syn-rift. This implies that the Mesozoic rifting along the Atlas was diachronous, making it difficult to determine the exact timing and kinematic of crustal stretching. Constraining the extensional phases in the Atlas system is crucial for understanding how the Atlas crust was stretched and thinned. Our work aims to quantify the magnitude and regional kinematic of stretching in the Atlas system using various methods, namely, thickness variation method, subsidence analysis and palinspatic reconstruction of 2D cross-sections.

Our preliminary results indicate that the maximum stretching factor (beta factor) in the Atlas is β = 1.25; and that crustal thinning did not exceed 20%, based on tectonic subsidence analysis. While the palinspatic restoration suggest that the Moroccan Atlas system underwent approximately a uniform stretching with β = 1.11 in EHA (Midelt-Errachidia area), β = 1.08 in CHA (Imilchil area), and β = 1.12 in the East Marrakech High Atlas (EMHA: Demnat area). These values indicate that the Moroccan Atlas crustal thickness has been thinned by 9% in EHA, 8% in CHA, and 11% in EMHA. In addition, the geological context of the High and Middle Atlas regions, where the estimated shortening is reported to be less than 20%, the stretching factor (β) was calculated based on the crust thickness. The initial crustal thickness (IC) of the Meseta block, which constitutes one of the Atlasic rift shoulders, considered an undeformed area, served as a reference. Accounting for the observed shortening, the final crustal thickness was deduced by subtracting the reported shortening value representing 7.8 km from the observed crustal thickness (39 km), resulting in a β value of 1.25, which is consistent with the result obtained from the subsidence analysis.

Keywords: Atlas system, extension, stretching factor, Thinning factor,

How to cite: Ankach, M., Gouiza, M., and Amrouch, K.: Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting: , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6667, https://doi.org/10.5194/egusphere-egu24-6667, 2024.

Abstract

Accurate understanding and identification of faults architecture is crucial in seismic data interpretation and earthquake analysis, where fault slip surfaces may interact with damage rocks, forming damage zones with a width larger than hundred meters. We use machine learning (ML) to show 10 kinds of seismic attributes from a seismic survey could be applied in identification and quantification of fault damage zone in northeast Sichuan Basin, China. The results indicate: (1) Six seismic attributes provide highest contribution to the fault characterization, including root mean square amplitude attributes, azimuth angle attributes, reverse attributes, original attributes, chaotic body attributes and ant body attributes; (2) The application of SHAP (SHapley Additive exPlanations) algorithm improves the model's accuracy, as the loss value (Mean Square Error , MSE) of the test data is restored from 17.86% to 16.03%; (3) Width estimation from the kernel density estimation algorithm (KDE) show the fault damage zone ranges from 0.3 to 1.2 km. Our work provides new insights into the interpretation of fault architecture in the subsurface, and we argue the geometrical parameters of the fault damage zone is significant for understanding the evolution of fault and earthquake simulations.

Keywords:  Fault damage zone; Seismic interpretation; Machine learning (ML); Geometrical parameters

Figure1.The seismic attributes of the actual work area entered into the model and the model calculation results: (A) Original attributes of the work area. (B) Variance attribute of the work area. (C) Results calculated by the ML model

Figure2. Thermal diagram presents the structure of the fault damage zone: (A) A vertical line perpendicular to the fault orientation correction; (B) indicates the fault range with a thermal index greater than 1.572; (C) indicates a fault range with a thermal index greater than 2.065; (D) indicates a thermal index greater than 2.401 fault range. The width of the damage zone could be estimated by these figures.

Figure3. Descriptive diagram of fault damage zone width. Fault_1 represents the direction of fault width with thermal index greater than 1.572; Fault_2 represents the direction of fault width with thermal index greater than 2.065; Fault_3 represents the fault width trend map with thermal index greater than 2.401

How to cite: Zhang, J., Chen, S., and Liao, Z.: Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14511, https://doi.org/10.5194/egusphere-egu24-14511, 2024.