TS8.2 | Analogue and numerical modelling of tectonic processes
EDI PICO
Analogue and numerical modelling of tectonic processes
Co-organized by GD10/GM9/SM8
Convener: Frank Zwaan | Co-conveners: Ágnes Király, Valentina Magni, Riccardo Reitano, Michael Rudolf
PICO
| Wed, 26 Apr, 08:30–10:15 (CEST), 10:45–12:30 (CEST)
 
PICO spot 3b
Wed, 08:30
Geologic processes are generally too slow, too rare, or too deep to be observed in-situ and to be monitored with a resolution high enough to understand their dynamics. Analogue experiments and numerical simulation have thus become an integral part of the Earth explorer's toolbox to select, formulate, and test hypotheses on the origin and evolution of geological phenomena.

To foster synergy between the rather independently evolving experimentalists and modellers we provide a multi-disciplinary platform to discuss research on tectonics, structural geology, rock mechanics, geodynamics, volcanology, geomorphology, and sedimentology.

We therefore invite contributions demonstrating the state-of-the-art in analogue and numerical / analytical modelling on a variety of spatial and temporal scales, varying from earthquakes, landslides and volcanic eruptions to sedimentary processes, plate tectonics and landscape evolution. We especially welcome those presentations that discuss model strengths and weaknesses, challenge the existing limits, or compare/combine the different modelling techniques to realistically simulate and better understand the Earth's behaviour.

PICO: Wed, 26 Apr | PICO spot 3b

Chairpersons: Ágnes Király, Frank Zwaan
5-minute convener introduction
Keynote
08:30–08:40
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PICO3b.1
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EGU23-6318
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ECS
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solicited
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On-site presentation
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Attila Balazs, Ana Gomes, Claudio Faccenna, and Taras Gerya

The subsidence history of forearc and back-arc basins reflects the relationship between subduction kinematics, mantle dynamics, magmatism, crustal tectonics, and surface processes. The distinct contributions of these processes to the topographic variations of active margins during subduction initiation, oceanic subduction, and collision are less understood.

We conducted a series of 2D and 3D thermo-mechanical numerical models with the codes 2DELVIS and 3DELVIS, based on staggered finite differences and marker-in-cell techniques to solve the mass, momentum and energy conservation equations. Physical properties are transported by Lagrangian markers that move with the velocity field interpolated from the fix Eulerian grid. We discuss the influence of different subduction obliquity angles, the role of mantle flow variations and their connection with sediment transport and upper plate deformation. Furthermore, slab tearing and the gradual propagation of slab break-off is modelled during collision.

The models show the evolution of wedge-top and retro-forearc basins on the continental overriding plate, separated by a forearc high. They are affected by repeated compression and extension phases. Compression-induced subsidence is recorded in the syncline structure of the retro-forearc basin from the onset of subduction. The 2–4 km upper plate negative residual topography is produced by the gradually steepening slab, which drags down the upper plate. Trench retreat leads to slab unbending and decreasing slab dip angle that leads to upper plate trench-ward tilting. Back-arc basins are either formed along inherited weak zones at a large distance from the arc or are connected to the volcanic arc evolution leading to arc splitting. Backarc subsidence is primarily governed by crustal thinning that is controlled by slab roll-back and supported by the underlying mantle convection. High subduction and mantle convection velocities result in large wavelength negative dynamic topography. Collision and continental subduction are linked to the uplift of the forearc basins; however, the back-arc records ongoing extension during a soft collision. During the hard collision, both the forearc and back-arc basins are ultimately affected by the compression. Our modeling results are compared with the evolution of Mediterranean subduction zones.

How to cite: Balazs, A., Gomes, A., Faccenna, C., and Gerya, T.: The coupled evolution of forearc and back-arc basins: inferences from 2D and 3D numerical modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6318, https://doi.org/10.5194/egusphere-egu23-6318, 2023.

Regular 2-minute-madness programme (block 1)
Extension
08:40–08:42
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PICO3b.2
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EGU23-113
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ECS
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On-site presentation
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Nuno Rodrigues, Filipe Rosas, João Duarte, Afonso Gomes, Jaime Almeida, and Nicolas Riel

Numerical modelling of rifting has been focused on cases involving extension and breakup of the continental lithosphere. However, the oceanic lithosphere has also been known to undergo rifting in specific geo-tectonic settings, as in the case of the Terceira ridge in the Azores triple junction (N-Atlantic). The rift-to-drift evolution of a segment of oceanic lithosphere potentially bears major implications for the Wilson cycle evolution of an oceanic basin, justifying the importance of carrying out the present numerical modelling study.

We used the Underworld geodynamic code to carry out 2D numerical models of oceanic rifting. To this extent, we systematically tested two main parameters which control the timing of the evolution from initial oceanic extension to breakup and drifting, namely: a) different total extension rates between 4 mm/yr and 160 mm/yr, and b) different oceanic plate ages ranging between 10 Myr and 90 Myr, which act as proxies for the lithospheric thickness.

Our results show that during oceanic rifting, the time required to achieve breakup of the extending oceanic lithosphere decreases logarithmically with an increasing extensional rate (i.e., the time needed to achieve breakup reaches a plateau). Our modelling also shows that lithospheric thickness plays a secondary, yet significant role in the type of oceanic rift that is formed (i.e., its structural configuration). This oceanic rift structure can comprise either a unique major graben or two main grabens, as preferable sites of extensional strain localization. Furthermore, when two main grabens develop, one of them often accommodates the bulk of the deformation, while the other wanes and eventually aborts. In this case, a more distributed pattern of extensional strain (comprising two main grabens) seemingly implies some delay in achieving full oceanic break-up, when compared with the single major graben scenario.

Acknowledgements: numerical modelling was financed by Projeto GEMMA - PTDC/CTA-GEO/2083/2021, Fundação para a Ciência e Tecnologia. 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- IDL.

How to cite: Rodrigues, N., Rosas, F., Duarte, J., Gomes, A., Almeida, J., and Riel, N.: Numerical modelling of intra-oceanic rifting: the rift-to-drift transition time frame, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-113, https://doi.org/10.5194/egusphere-egu23-113, 2023.

08:42–08:44
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PICO3b.3
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EGU23-6598
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ECS
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On-site presentation
Jaime Almeida, Nicolas Riel, Marta Neres, Hamzeh Mohammadigheymasi, Susana Custódio, and Stephanie Dumont

Despite extensive research, intraplate earthquakes and required intraplate deformation remain relatively unexplained. To explore this problematic, we tested the possibility that these could derive from the dynamic interaction between the lithosphere and the upper mantle. This was performed by conducting a thorough geophysical exploration of a region with both low plate velocities and clear asthenosphere dynamics, specifically the Gulf of Guinea (GOG) and adjacent Western Africa.

In this work, we developed 3D numerical geodynamic models of the asthenosphere-lithosphere interaction in the GOG, ran with the state-of-the-art LaMEM modelling code. To assess the contribution of individual intraplate deformation sources, we tested various initial/boundary conditions namely: (a) the spreading rate of the individual segments of Central Atlantic mid-ocean ridge, (b) the presence/absence of weak zones, such as the Romanche or Central-African shear zones, as well as (c) the stress contribution by an active mantle plume head with varying width. Seismicity data was utilized as a criterion to assess the validity of the modelled stress/strain localization sites.

Our results suggest that intraplate deformation within the GOG is mostly controlled by the spreading rate of the mid-ocean ridge, with different localization sites deriving from their relative proximity to the shear zones and plume head. This work aims to expand our knowledge of intraplate deformation mechanisms and to contribute towards improving seismic hazard assessment away from plate boundaries.

This work was supported by the European Union and the Instituto Dom Luiz (IDL) Project under Grant UIDB/50019/2020, and it uses computational resources provided by C4G (Collaboratory for Geosciences) (Ref. PINFRA/22151/2016). It was also partly supported by the Fundação para a Ciência e a Tecnologia (FCT) in the content of the Project SHAZAM “Sismicidade e Perigosidade da Margem Atlântica sub-Saariana,” with the reference PTDC/CTA/GEO/31475/2017; POCI-01-0145-FEDER-031475, co-financed by FEDER-COMPETE/POCI 2020.

How to cite: Almeida, J., Riel, N., Neres, M., Mohammadigheymasi, H., Custódio, S., and Dumont, S.: Lithosphere-asthenosphere interaction as the source for intraplate deformation in the Gulf of Guinea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6598, https://doi.org/10.5194/egusphere-egu23-6598, 2023.

08:44–08:46
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PICO3b.4
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EGU23-691
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ECS
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Virtual presentation
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Yaoyao Zou, Giacomo Corti, Daniele Maestrelli, Chiara Del Ventisette, Liang Wang, and Chuanbo Shen

Along with other parameters (e.g., plate kinematics), the presence of pre-existing structures at all lithospheric scales has been proven to be of primary importance in controlling the evolution and characteristics of continental rifts. Indeed, observations from many natural examples show that even in conditions of orthogonal rifting (when extension should result in simple fault patterns dominated by normal faults orthogonal to the extension vector) the presence of inherited fabrics may result in complex arrangements of differently-oriented extension-related structures.

Here, we explored the influence of pre-existing fabrics on the evolution and pattern of rift-related structures by conducting a series of analogue models deformed in an enhanced gravity field produced by a centrifuge apparatus. The crustal models reproduced a brittle-ductile system and considered the presence of pre-existing discrete fabrics in the upper, brittle crust under conditions of orthogonal narrow rifting. These fabrics were reproduced by cutting the brittle layer at different orientations with respect to the extension direction.

Modelling results show that pre-existing fabrics have a significant influence on the rift-related fault pattern. These fabrics cause curvature of extension-related faults, resulting in S-shaped faults and -in some cases- en-echelon arrangement of oblique fault segments. In addition, the presence of these heterogeneities influences the rift floor subsidence by inducing significant segmentation and development of isolated depocenters. These effects are more visible during initial rifting and less pronounced for more advanced rifting stages. Similarly, increased syn-rift sedimentation tends to decrease the impact of pre-existing structures. Model results show many significant similarities with the fault pattern in many rift basins worldwide, and these findings have important insights into the development of continental rift systems in nature.

 

How to cite: Zou, Y., Corti, G., Maestrelli, D., Del Ventisette, C., Wang, L., and Shen, C.: Enhanced-gravity Analog Modelling of the Influence of Pre-existing Brittle Fabrics on Continental Rifting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-691, https://doi.org/10.5194/egusphere-egu23-691, 2023.

08:46–08:48
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PICO3b.5
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EGU23-380
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ECS
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Virtual presentation
Daniele Maestrelli, Pietro Facincani, Federico Sani, Marco Bonini, Domenico Montanari, Chiara Del Ventisette, and Giacomo Corti

Collapsed calderas are circular to elongated large depressions originating from the subsidence induced by depletion and/or migration of magma from a shallow or deep reservoir during eruptions. Despite being distributed in all tectonic settings, they are particularly important in extensional settings where are often associated with rifting processes, e.g., the East African Rift System. Therefore, their structural architecture can be strongly perturbed by extensional faults associated with regional extension or related to earlier stages of caldera formation. Calderas often bear an elongated shape in plain view, and have been considered valuable proxies for the regional stress (e.g., Nakamura, 1977) and regional strain (e.g. Casey et al., 2006). Moreover, other authors have related the elongated calderas to the influence of preexisting structures reactivated during extension (Acocella et al., 2003). We therefore aim to investigate the mechanical interactions between collapsed calderas and regional extension leading to elongated edifices. Analogue models of caldera collapse were performed by placing a circular magma chamber (simulated with poly-glycerine) placed below a sand-mixture package. We induced the collapse by draining out the analogue magma from the base, reproducing the classical fault architecture observed at many collapsed calderas (i.e., early inner outward-dipping reverse faults and late outer inward-dipping normal fault). Once completed, the collapsed depression was stretched such that normal faulting produced caldera elongation and segmentation. Finally, we compared the elongation and the structural pattern deriving from the interacting caldera-related and rift-related structures with natural examples from the East African Rift System. Our results suggest that different interacting factors may contribute to the development of elongated calderas, thereby questioning whether elongated calderas can be considered as a fully reliable proxy for the regional strain.

Acocella, V., Korme, T., Salvini, F., and Funiciello, R. (2003). Elliptic calderas in the Ethiopian Rift: control of pre-existing structures. J. Volcanol. Geotherm. Res., 119, 189–203.

Casey, M., Ebinger, C., Keir, D., Gloaguen, R., and Mohamed, F. (2006). Strain accommodation in transitional rifts: extension by magma intrusion and faulting in Ethiopian rift magmatic segments. Geol. Soc. Lond. Spec. Publ., 259(1), 143–163.

Nakamura, K., (1977). Volcanoes as possible indicators of tectonic stress orientation— principle and proposal. Journal of Volcanology and Geothermal Research 2, 1–16

How to cite: Maestrelli, D., Facincani, P., Sani, F., Bonini, M., Montanari, D., Del Ventisette, C., and Corti, G.: Stress-strain relationships at elongated calderas in extensional settings: what analogue models say, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-380, https://doi.org/10.5194/egusphere-egu23-380, 2023.

08:48–08:50
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PICO3b.6
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EGU23-14818
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On-site presentation
Yuan Li, Adina Pusok, Timothy Davis, Dave May, and Richard Katz

Dykes are tensile fractures that rapidly transport magma from the hot, ductile asthenosphere across the cold, brittle upper lithosphere. They play an important role in tectonic extension settings by drastically reducing the force needed for rifting (Buck, 2004). Yet the balance of mechanisms that drive dyke propagation and how they promote rift initiation remain unclear. Here we investigate the physics of dyke propagation in a two-phase continuum model that can approximate both faults and dykes in an extensional tectonic setting.  

Dykes are fluid-filled fractures, typically modelled as discrete inclusions in an extended elastic continuum.  These models suggest that dyking is dominated by magma buoyancy and that its direction can be altered according to the competition between tectonic stress and the topographic load (Maccaferri et al., 2014). However, this method assumes a constant background stress field in the lithosphere during dyking. Therefore this method cannot capture the interaction between dykes and the long-term deformation of the lithosphere. To resolve this issue, dyking has been prescribed as a weak material in a continuum, one-phase rifting model in which dyking is included in the conservation of mass, momentum and/or energy (Liu and Buck, 2018). This method respects the scale separation between dyking and long-term dynamics, but still neglects the feedback of dyking on the stress field.

We present a geodynamic model that incorporates a novel poro-viscoelastic–viscoplastic rheological formulation with a hyperbolic yield surface for plasticity. With this model, both dyking and faulting can be simulated consistently (Li et al., in review). We validate our theory by comparing the stress field at the tip of the dyke with that from the linear elastic fracture mechanics theory. We then investigate dynamics of dyking in a geodynamic rifting model. We show that dyking assists rifting and its localisation. First, it reduces the yield strength in the brittle layer as the pore pressure balances the compressive stress; second, it promotes the development of near-surface normal faults localised in a relatively narrow rift region near the rift axis. We investigate the physics of dyke propagation with respect to the balance between buoyancy and tectonic forcing, and the effect of topography.

References

Buck, W .R., (2004). Consequences of asthenospheric variability on continental rifting. In Rheology and deformation of the lithosphere at continental margins, chapter 1, pages 1–30. Columbia University Press. doi: 10.7312/karn12738-002.

Maccaferri, F., Rivalta, E., Keir, D., and Acocella, V., (2014). Off-rift volcanism in rift zones determined by crustal unloading. Nature Geoscience 7, 297–300. doi: 10.1038/ngeo2110.

Liu, Z. and Buck, W. R., (2018). Magmatic controls on axial relief and faulting at mid-ocean ridges. Earth and Planetary Science Letters, 491:226–237. doi: 10.1016/j.epsl.2018.03.045.

Li, Y., Pusok, A., Davis, T., May, D., and Katz, R., Continuum approximation of dyking with a theory for poro-viscoelastic–viscoplastic deformation, in review of Geophysical Journal International.

How to cite: Li, Y., Pusok, A., Davis, T., May, D., and Katz, R.: Dyke propagation and dynamics during rift initiation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14818, https://doi.org/10.5194/egusphere-egu23-14818, 2023.

08:50–08:52
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PICO3b.7
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EGU23-11554
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ECS
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On-site presentation
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Mahdi Bakhtbidar, Jonas B. Ruh, Pablo Santolaria Otín, Pablo Martinez Granado, and Oscar Gratacos Torra

Due to their high economic (natural resources) and scientific (e.g., global archive of climate changes) potential, rifted margins have been studied using different approaches including sequence stratigraphy, high-resolution mapping, structural analysis, or seismic imaging. Sandbox analogue modelers have also assessed rifted margins and tested the driving and controlling parameters that determine their structural styles and evolution. In this research, we present a series of physical analogue models aimed at testing the influence of downbuilding and dominant gliding instabilities on the evolution and configuration of salt-bearing rifted margins. Being aware of the limitations of this experimental technique we go a step further and use numerical modelling to implement parameters that are not easy to simulate using analogue modelling. Several numerical experiments have been defined to test the main governing mechanisms (differential loading vs dominant gliding) and different key parameters such as the rheology of salt and temperature.

Comparison of the two approaches yields valuable insights into the processes that control the evolution and structural styles of salt-bearing rifted margins as well as clarifies the limitations and complementarity between both techniques. Our models provide stratigraphic, structural and kinematic templates to better understand salt-bearing rifted margins worldwide.

How to cite: Bakhtbidar, M., B. Ruh, J., Santolaria Otín, P., Martinez Granado, P., and Gratacos Torra, O.: Numerical and Analogue Modelling of Salt-Bearing Rifted Margins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11554, https://doi.org/10.5194/egusphere-egu23-11554, 2023.

Compression
08:52–08:54
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PICO3b.8
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EGU23-11040
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On-site presentation
Oriol Ferrer, Eloi Carola, and Ken McClay

The structural style of inverted rift basins is controlled by the inherited structures and stratigraphic elements but also by the presence of salt layers or welded equivalents. Salt acts as a main detachment during extension and, depending on its thickness, different degrees of linkage develop between the basement and overburden. The presence and distribution of salt structures, the linkage between the basement and overburden, and the continuity of salt on these salt-bearing rifted basins have a strong impact on thick- to thin-skinned deformation during inversion. As the weakest rock of the basin infill, salt acts as a contractional detachment and buried diapirs rejuvenate during early inversion. With increasing shortening thick-skinned deformation folds and uplifts the basins while the diapirs are squeezed and welded by thin-skinned deformation.

Using an approach based on systematic analogue models, this work analyses how extensional basins develop above a pre-rift salt layer and how the inherited salt structures evolve during subsequent inversion. A first set of models only affected by extensional deformation was carried out examining how the variation of different parameters such as salt and overburden thicknesses impact the structural style of salt structures developed during thick-skinned extension. Afterwards, some of these models were repeated to understand how pre-existing extensional and salt structures condition the evolution during total inversion tectonics. The experimental apparatus consists of five metal fault blocks simulating a domino basement-fault system that rotate counter-clockwise during extension and clockwise during inversion. Deformation was transferred to the blocks by a motor worm-screw at a constant velocity of 4.6 mm/h until reaching 10 cm of total extension. During the inversion phase, the same velocity was applied until reach total inversion of the basins. A layered unit of sand capped by a uniform-thickness polymer layer and additional layers of sand simulated the pre-kinematic unit. While different sand layers were added during extension, no syn-inversion sedimentation was considered.

The results of this study show that the structural style during inversion is highly conditioned by the inherited extensional configuration but also by the salt thickness that condition the degree of coupling/decoupling of the pre- and syn-kinematic successions. The study also revealed that the thickness of the overburden has a minor impact during the inversion of the basins. Such is the case that in models with either thin or thick overburden succession, the extensional geometry might be preserved if the salt is thick independently of the overburden thickness. Contrary, models with a thin salt layer are characterized by a total inversion of the ramp-syncline basin that as an inversion anticline is developed, crestal collapse extensional faults minimize the developed structural relief. Finally, the analogue modelling allowed to understand how compression caused primary weld reactivation, diapir rejuvenation, salt thickening and/or thrust emplacement. The reactivation of some of these salt-related structures is extremely impacted by the salt thickness distribution that resulted from the extensional phase. Therefore, to characterize structural style and understand the evolution of the basin it is needed an understanding of the inherited salt-related structures.

How to cite: Ferrer, O., Carola, E., and McClay, K.: Experimental approach (analogue modelling) of thin- to thick-skinned inversion of extensional basins with pre-rift salt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11040, https://doi.org/10.5194/egusphere-egu23-11040, 2023.

08:54–08:56
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PICO3b.9
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EGU23-10149
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ECS
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On-site presentation
Anindita Samsu, Weronika Gorczyk, Fatemeh Amirpoorsaeed, Timothy Schmid, Eleanor Morton, Peter Betts, and Alexander Cruden

The inversion of rift basins is commonly associated with the reactivation of normal, basin-bounding faults or shear zones. Analogue models have shown how the reverse reactivation of these pre-existing structures facilitates the uplift of a basin’s sedimentary infill. However, few of these models examine the viscous processes occurring beneath the brittle crust, which may or may not drive basin inversion. In our study, we use lithospheric-scale analogue experiments of orthogonal extension followed by shortening to simulate rifting followed by inversion and orogenesis. Here we explore how the flow behaviours of ductile layers underneath rift basins promote or suppress basin inversion.

In our experiments, we simulate rifting by extending a multi-layer, brittle-ductile lithosphere which floats on a fluid asthenosphere, creating a system of distributed basins. This extension is followed by shortening of the model, during which strain is accommodated by the reactivation of basin-bounding faults and folding or upwelling of the ductile layers. These experiments reveal that the rheology of the ductile lower crust and lithospheric mantle, modulated by the imposed bulk strain rate, determine: (1) how rift basins are distributed during extension and (2) whether all or only some of these basins are inverted during shortening. We interpret that this selective basin inversion is related to the superposition of crustal-scale and lithospheric-scale boudinage during the basin-forming extensional phase. Our findings demonstrate that lithospheric-scale analogue models can be a powerful tool for investigating the interaction between brittle and viscous deformation during basin inversion.

How to cite: Samsu, A., Gorczyk, W., Amirpoorsaeed, F., Schmid, T., Morton, E., Betts, P., and Cruden, A.: Not all basins are created equal: Lithospheric-scale analogue experiments of selective basin inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10149, https://doi.org/10.5194/egusphere-egu23-10149, 2023.

08:56–08:58
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PICO3b.10
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EGU23-13434
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ECS
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On-site presentation
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Fatemeh Amirpoorsaeed, Anindita Samsu, Peter Betts, Alexander Cruden, and Robin Armit

Craton margins undergo intense deformation influenced by the pre-existing crustal and lithospheric architecture, rheology, and far-field kinematics. The role of rheological contrasts and weak zones at the edge of the craton has been discussed, but it is unclear whether deformation in the upper crust is influenced by the geometry of the craton margin itself (i.e., whether the margin dips towards or away from the interior of the craton). Our analogue experiments are aimed at studying the influence of craton margin geometry on structures formed during rifting and inversion, as craton margins are prone to reworking and reactivation during superimposed tectonic events.

The experiments are designed based on the geometries of the eastern and southern margins of the North Australian Craton which has experienced multiple stages of extension and shortening. The inward vs. outward dipping craton margins in these areas were interpreted from crustal-scale seismic reflection data.  In our experiments, we see that strain and deformation style varies with proximity to the craton margin. During the extensional phase of both inward and outward dipping experiments, we observe that rifts are mainly formed by boudinage and necking in the lower crust. The inward dipping model prevents the propagation of a major normal fault at the margin, resulting in a number of smaller faults. Subsequent shortening of the inward dipping model results in modest basin inversion above the craton margin, suggesting that the majority of strain is accommodated by reactivation of normal faults away from the margin. In contrast, the outward dipping model shows the propagation of a single major normal fault along the craton margins, leading to significant thinning of the lower crust. A major rift is also being formed away from the craton margin in this model. Inversion of the outward dipping craton margin model shows more intense inversion at the margin compared to the inward dipping model, with lower strain and smaller reactivation of normal faults away from the margin. We can therefore conclude that the geometry of a craton margin exerts a first-order control on the deformation of the upper crust during rifting and subsequent inversion.

How to cite: Amirpoorsaeed, F., Samsu, A., Betts, P., Cruden, A., and Armit, R.: The effects of inward and outward dipping craton margin geometry on upper crustal deformation: Insights from analogue modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13434, https://doi.org/10.5194/egusphere-egu23-13434, 2023.

08:58–10:15
Chairpersons: Michael Rudolf, Riccardo Reitano
10:45–10:50
Compression (continued)
10:50–10:52
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PICO3b.1
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EGU23-432
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ECS
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Virtual presentation
oumaima badraoui, Chiara Del Ventisette, Daniele Maestrelli, Mohamed Najib Zaghloul, and Federico Sani

Earlier extended continental margins are frequently involved into late compressive deformation during mountain building (i.e. orogenesis). This process gives rise to positive inversion of previous extensional faults, but these structures may also play different roles during late compressive phases, interacting in various ways with inherited structures from older tectonic stages.

Moreover, different orientation of compression direction related to different phases affecting extended continental margins may give rise to complex structural settings whose evolution is often difficult to reconstruct. To address this problem, we performed an analogue model experimental series aiming at extending a continental margin and then imposing on the same margin differently oriented compressive phases. Models were quantitatively analyzed through particle image velocimetry (PIV) to highlight fault interaction, and by using Digital Elevation Models reconstructed with Structure from Motion (SfM) techniques. Our results show that well developed and favorably oriented normal fault systems drive the location of successive compressive structure, often through inversion processes, but they also condition the final geometrical setting without inversion. Moreover, an important role is also played by the orientation of the direction of compression (obliquity angle a varied from 0° to 90°), which gives rise to different structural patterns when is superimposed to extensional structures as a first compressive phase or is superimposed to already formed compressive structure as second compressive phase. The resultant complex structural patterns show differently oriented structures cutting each other even at high angles, a feature often seen in nature. Therefore, these experiments may be applied to a variety of natural cases, helping to decipher geological evolution of the analyzed areas basing on the geometrical relationships among structures.

How to cite: badraoui, O., Del Ventisette, C., Maestrelli, D., Zaghloul, M. N., and Sani, F.: analogue modelling of multiple compressive phases deforming and extended margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-432, https://doi.org/10.5194/egusphere-egu23-432, 2023.

10:52–10:54
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PICO3b.2
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EGU23-7248
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On-site presentation
Filipe Rosas, Afonso Gomes, Nicolas Riel, Wouter Schellart, Joao Duarte, and Jaime Almeida

Subduction of an oceanic plate beneath either an oceanic, or a continental, overriding plate requires two main conditions to occur in a steady state: i) a high enough subduction rate (~5 cm/yr, Schellart in print); and ii) a weak (efficiently softened/lubricated) subduction channel (Gerya and Meilick, 2011). The first requirement prevents thermal diffusive re-equilibrium of the subducting slab within the asthenospheric ambient mantle, maintaining the slab cold and dense enough to provide the slab-pull subduction driving force. The second condition, is achieved with the contribution of a strong dehydration of the serpentinized oceanic plate, with resulting pervasive fluid circulation in the subduction channel significantly promoting its weakening, thus preventing strong coupling between the subducting and the overriding plate. Avoiding such a coupling has been shown to be key to maintain stable subduction, since it generally leads to a halt in the subduction process and to slab break-off (Duarte et al., 2015). Both these conditions are seemingly not favoured in a continental subduction scenario, since continental lithosphere is positively buoyant and much less, or not al all, serpentinized. Hence, the (geo)dynamics governing continental subduction is still not fully understood.

We thus carried out a set of geodynamic numerical modelling experiments to further understand the first order geodynamic constraints governing continental subduction in the specific scenario that considers the subduction of a continental plate beneath an oceanic one, i.e., upon the arrival of a continental plate at an intra-oceanic subduction zone. The 2D numerical experiments were conceived and constructed using the Underworld code (Moresi et al., 2007), to better understand the influence on continental subduction efficiency, as well as on related synthetic ophiolite obduction, of considering either a scenario of dominant trench retreat (roll-back) or trench advance (roll forward) subduction regime. Roll-back subduction was prescribed in our models by fixing the trailing edge of the overriding plate, whereas roll-forward subduction was favoured (allowed) by leaving it free to move. Our experiments ensure dynamic self consistency in all cases.  

Our preliminary results show that, although synthetic obduction is possible to achieve in both situations, the overall first order (geo)dynamic differences implied by the two different simulated regimes, bear important consequences on the timing, overall kinematic configuration and local stress/strain distribution of the considered continental subduction-exhumation cycle in each case.

Acknowledgments

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- IDL

References

Duarte, J.C., Schellart, W.P., Cruden, A.R., 2015. How weak is the subduction zone interface? Geophysical Research Letters 42, 2664–2673. doi:10.1002/2014GL062876.

Gerya, T.V., Meilick, F., 2011. Geodynamic regimes of subduction under an active margin: effects of rheological weakening by fluids and melts. Journal of Metamorphic Geology 29, 7–31. doi:0.1111/j.1525-1314.2010.00904.x.

Moresi, L., Quenette, S., Lemiale, V., Mériaux, C., Appelbe, B., Muhlhaus, H.B., 2007. Computational approaches to studying non-linear dynamics of the crust and mantle. Physics of the Earth and Planetary Interiors 163, 69–82. doi:10.1016/j.pepi.2007.06.009.

Schellart, W.P., in print. Subduction zones: A short review, in Dynamics of Plate Tectonics and Mantle Convection, Editor: João Duarte, ISBN: 9780323857338.

How to cite: Rosas, F., Gomes, A., Riel, N., Schellart, W., Duarte, J., and Almeida, J.: Geodynamic modelling of continental subduction beneath oceanic lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7248, https://doi.org/10.5194/egusphere-egu23-7248, 2023.

10:54–10:56
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PICO3b.3
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EGU23-7370
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ECS
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On-site presentation
Afonso Gomes, Filipe Rosas, João Duarte, Nicolas Riel, Wouter Schellart, and Jaime Almeida

Ophiolites are exposed remnants of oceanic lithosphere that are emplaced onto a continental domain, and Tethyan-type ophiolites, specifically, are those that are emplaced within a continental passive margin. The emplacement process for this type of ophiolites occurs when a continental passive margin subducts, and subsequently exhumes, beneath an oceanic overriding plate (future ophiolite). It is the exhumation of the passive margin’s crust that triggers both the separation of the ophiolite from the remaining oceanic overriding plate (OP) and its ensuing emplacement within the continental domain.

Analogue and numerical models have demonstrated the feasibility of this process (Chemenda et al., 1996; Duretz et al., 2016; Porkoláb et al., 2021); however, its specific geodynamic constraints are still poorly understood. For example, the geological record appears to be heavily skewed towards the fast emplacement of very young lithosphere, but it is unclear whether it is possible to emplace older lithosphere via the same process. Here we use 2D numerical models to test the sensitivity of this process to three key parameters: a) overriding plate age (10-60Myr), b) width of ocean-continent transition (OCT, 0-500km), and c) existence/absence of a serpentinization layer in the OP. The models use temperature and strain-rate dependent visco-plastic rheologies, are driven by buoyancy forces (without imposed non-zero velocity conditions), and are run using the Underworld code (Moresi et al., 2003).

Preliminary results show that the continental subduction/exhumation cycle and the ophiolite emplacement process are highly sensitive to variations in initial model conditions. Nevertheless, the emplacement process is physically viable under a somewhat wide range of conditions, being optimized for a narrow OCT and adjacent continental margin subducting beneath a young and serpentinized OP. A 10 Myrs old OP leads to a fast continental subduction-exhumation cycle (15-20 Myrs), while a 60 Myrs old OP induces a slow (>30 Myrs) cycle, but still leads to ophiolite emplacement. A long and tapered margin (OCT, 500km) also promotes a slow (>30 Myrs) cycle, with only a thin melange of exhumed crust, which hinders the formation and emplacement of individual ophiolite klippen; the reverse is true for a very short OCT. The existence of a serpentinization layer greatly facilitates the emplacement of the ophiolite klippe.

Acknowledgments

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia I.P./MCTES through national funds (PIDDAC)–UIDB/50019/2020-IDL and through scholarship SFRH/BD/146726/2019.

References

Chemenda, A., Mattauer, M., Bokun, A. (1996). Continental subduction and a mechanism for exhumation of high-pressure metamorphic rocks: New modelling and field data from Oman. EPSL, 143, 173–182.

Duretz, T., Agard, P., Yamato, P., Ducassou, C., Burov, E., Gerya, T. (2016). Thermo-mechanical modeling of the obduction process based on the Oman Ophiolite case. GR, 32, 1–10.

Moresi, L., Dufour, F., Mühlhaus, H. B. (2003). A Lagrangian integration point finite element method for large deformation modeling of viscoelastic geomaterials. Journal Comp. Physics, 184, 476–497.

Porkoláb, K., Duretz, T., Yamato, P., Auzemery, A., Willingshofer, E. (2021). Extrusion of subducted crust explains the emplacement of far-travelled ophiolites. Nature Commun., 12, 1499.

How to cite: Gomes, A., Rosas, F., Duarte, J., Riel, N., Schellart, W., and Almeida, J.: 2D numerical modelling of Tethyan-type ophiolite emplacement: The role of overriding plate age, serpentinization, and OCT width., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7370, https://doi.org/10.5194/egusphere-egu23-7370, 2023.

10:56–10:58
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PICO3b.4
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EGU23-2782
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ECS
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On-site presentation
Thomas Geffroy, Guillaume Benjamin, Replumaz Anne, Simoes Martine, Lacassin Robin, Kermarrec Jean-Jacques, and Habel Tania

Plates and the convective mantle interact with each other over geological time scales, leading to mantle flow, plate motion, and deformation along plate boundaries.  At convergent boundaries undergoing subduction, the role played by mantle drag remains poorly understood despite its potential impact on subduction dynamics, and in turn on the deformation regime of the overriding plate. Previous studies were generally conducted in two dimensions, limiting their ability to faithfully reproduce processes taking place on Earth. Instead, in this study, we present 11 three-dimensional analog models of subduction at the scale of the upper mantle, including an overriding plate, and in which we control mantle drag at the base of the lower or upper plate by imposing a controlled unidirectional background mantle flow perpendicular to the trench. We systematically vary the velocity and the direction of the imposed horizontal mantle flow and quantify its impact on horizontal and vertical upper plate deformations, plate and subduction velocities, and the geometry of the slab. The geometry of the slab is only marginally affected by the velocity and direction of the mantle flow. In the absence of mantle flow, slab rolls back and deformation is accommodated by trench-orthogonal stretching in the upper plate. Instead, the addition of a background flow dragging the lower or upper plate toward the trench  systematically results either in the absence of upper plate deformation, or in trench-orthogonal shortening with strain rates that increase linearly with increasing mantle flow. We show that the upper plate strain rate is primarily controlled by the velocity of the free plate in the model, which itself results from the drag exerted by the mantle at the base of the plate. Coupling between mantle and plate is larger for models with flow directed toward the upper plate, resulting in strain rates that are about three times larger than for equivalent models with flow directed toward the lower plate. This systematic study provides a better understanding of the effect of mantle drag on plate displacements and deformation along subduction zones, leading to a better understanding of the ingredients required to form Andean-type mountain ranges.

How to cite: Geffroy, T., Benjamin, G., Anne, R., Martine, S., Robin, L., Jean-Jacques, K., and Tania, H.: A systematic study of mantle drag effect on subduction dynamics and overriding plate deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2782, https://doi.org/10.5194/egusphere-egu23-2782, 2023.

Geodynamics and applications
10:58–11:00
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PICO3b.5
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EGU23-10353
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ECS
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Virtual presentation
Qihang Wu and Shoufa Lin

We present a new numerical method to simulate the structural patterns emerging from the long-term large-deformation tectonic flows in both two and three spatial dimensions.  The domains of different material properties are each represented by a level set function discretized on a Eulerian mesh with the discontinuous Galerkin method. The level sets are advected by a velocity field provided by a coupled Stokes flow solver. Our method accurately captures the material interface by the adaptive mesh refinement, reduces the computational expenses compared to the traditional particle-in-cell method and offers straightforward handling of geometric splitting and merging.  Under the unified finite element framework, our method promises the flexibility in the choice of mesh geometry as well as the potential for extending to complex rheology.  With passive tracers geat and around areas of interest, the finite strain of the flow field can be integrated through any time interval within the total simulation time.  The strain ellipsoids thus obtained offers the possibility for ground-truthing the simulated deformation patterns with the field structural analysis.  Our results demonstrate identical physical behaviour when compared with established structural geology and geodynamic benchmarks.

The style of the crustal dynamics on the Archean Earth has been subject to controversy on whether a vertical tectonic style in the form of Rayleigh-Taylor instability, induced by an inverted density profile, prevails in the early history of the Earth and if so, how the transition to the present-day plate tectonics, characterized by dominantly horizontal movement, is manifested in the rock record.  Equipped with our modelling scheme, we construct numerical models to simulate the lithological distributions and deformation patterns resulted from a synchronous operation of vertical tectonism and horizontal shearing. The latter can be viewed as a possible result of some far-field tectonic boundary condition (e.g. oblique convergence).  Many aspects of the simulation in terms of the map pattern, foliation/lineation trend and strain distribution compare favorably with the field observations in Neoarchean granitoid-greenstone terranes in the Superior Province as well as worldwide.  Therefore, it is concluded that the vertical and horizontal tectonism are not mutually exclusive tectonic regimes  The symbiosis of both tectonic processes is a viable mechanism for establishing the crustal architecture and the deformation pattern we see today in many Neoarchean terranes and might represent a transition from the former to the latter in the Neoarchean.

How to cite: Wu, Q. and Lin, S.: Modelling tectonic flow with discontinuous Galerkin level set method: Case studies and applications  for the Neoarchean crustal dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10353, https://doi.org/10.5194/egusphere-egu23-10353, 2023.

11:00–11:02
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PICO3b.6
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EGU23-122
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Virtual presentation
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xianwu xin

Abstract.

In this paper, the physical simulation of the meridional movement of the crust is carried out by experiments; According to the geometry relationship between the peak point of the earth's crust and the earth's rotation under the action of tidal force, a mathematical model of the meridional movement of the crust is established. The velocity field of global continental drift is calculated using the meridional motion equation derived from the model, and is compared with the measured value of ITRF2000. It can be seen from the comparison between adjacent calculated values and measured values that the magnitude and direction of the two velocity vectors are basically the same. It follows that the meridional movement of the crust is a reciprocating harmonic movement. The continent and the ocean floor, under the action of the reciprocating harmonic dynamic process, float back and forth along the meridian. Due to the difference between forward and reverse resistance, there will be fixed displacement in one direction. So far, the series of papers on "Harmonic dynamic of the Earth (C)" have completed the kinematic analysis, driving force calculation, energy conversion calculation and verification of observation results of the earth harmonic dynamic process. Velocity field, driving force and energy consumption are the three basic indicators of mechanical power process. Many possibilities of geophysical evolution mechanism determine that the study of its main dynamic mechanism is inseparable from the detailed discussion of the three major indicators.

How to cite: xin, X.: Harmonic dynamic of the Earth (C), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-122, https://doi.org/10.5194/egusphere-egu23-122, 2023.

11:02–11:04
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PICO3b.7
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EGU23-4245
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ECS
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On-site presentation
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Ruiqing Yang, Fengli Yang, and Panpan Hu

 Abstract

The Nanchuan region is located on the southeastern margin of the Sichuan Basin, South China. Silurian Wufeng-Longmaxi Formation, buried between 2000-4500m deep in this area, is an important shale gas-producing formation. Influenced by multi-phase tectonic action during Mesozoic- Cenozoic [1], the maximum compressive horizontal principal stress (σHmax) directions are complex and the orientation changes rapidly (55°-135°). Therefore, effectively predicting the maximum compressive horizontal principal stress (σHmax) is important for improving the shale gas production capacity and optimizing the fracturing scheme development.

In this paper, the SHELLS finite element stress field modeling [2] was introduced and used to understand the above problems. Based on the increased and improved resolution of its program, and faults topography, heat flow, petrophysical parameters, and boundary conditions in the shale gas target layer, the σHmax directions in the study area were modeled and calculated. The prediction results show that σHmax directions in the Nanchuan region vary multi-directionally (0-180°), and are consistent with 11 of the 13 drilled wells, with only two drilled wells having minor differences (Figure 1). 85% of the predicted wells are consistent with the measured wells, achieving significant geological results and laying the foundation for the effective development of shale gas production capacity and optimized fracturing schemes in the area.

Keywords: Stress field modeling, maximum compressive horizontal principal stress directions, shale gas, mid-deep, the Nanchuan region

Figure 1 σHmax directions in the Nanchuan region compared to actual drilling

References:

[1] Tang J G., Wang K M., Qin D C., Zhang Y., Feng T., 2021. Tectonic deformation and its constraints to shale gas accumulation in the Nanchuan area, southeastern Sichuan. Bulletin of Geological Science and Technology. 40(5), 11-21. ( in Chinese version).

[2] Bird, P., 1999. Thin-plate and thin-shell finite-element programs for forward dynamic modeling of plate deformation and faulting 1. Comput. Geosci. 25, 383–394.

How to cite: Yang, R., Yang, F., and Hu, P.: Prediction of the maximum compressive horizontal principal stress directions of medium to deep shale gas in the Nanchuan region, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4245, https://doi.org/10.5194/egusphere-egu23-4245, 2023.

New advances in modelling methodology
11:04–11:06
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PICO3b.8
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EGU23-7357
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On-site presentation
Marcin Dabrowski

Flow perturbation can deflect the layering of the host rock around slip surfaces in shear zones resulting in the development of flanking structures. The details of flanking structure geometry can provide important clues about shear sense, flow kinematics, and finite strain, although not without ambiguities. The developing structures share similarities to fault-related folds that play an important role in sedimentary basins.

Mechanical anisotropy has been shown to have a major influence on both the slip rate and flow perturbation. Willis (1964) derived an analytical solution for an elliptical inclusion embedded in a homogeneous anisotropic elastic matrix subject to a uniform load in the far field. The solution can be reduced to the case of an incompressible viscous medium and an arbitrarily oriented inviscid slit (slip line). The reduced solution, which is exact for the initial state of homogeneous planar anisotropy, provides useful insights into the initial stages of deformation and it can be used to approximately study finite strain deformation of a power-law host. However, anisotropic fluids such as ductilely deforming foliated rocks keep a ‘memory’ of deformation due to their evolving microstructure, which affects the flow field. In this study, I will use different numerical modeling techniques to examine the impact of host layering on the perturbing flow and structure development around a slip surface in shear zone.

How to cite: Dabrowski, M.: Numerical modelling of flanking structures in layered viscous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7357, https://doi.org/10.5194/egusphere-egu23-7357, 2023.

11:06–11:08
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PICO3b.9
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EGU23-6125
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On-site presentation
Lorenzo Bonini and Nicolò Bertone

During the last decades, analog models have taken extraordinary advantage of new technologies. High-resolution cameras, analytical methods to extract quantitative data from the experiments (e.g., Digital Image Correlation), and new analog materials are only a few examples of the new improvement. The ease of extraction of quantitative data means that the modeling results can be used to provide new views on natural processes. Reducing unwanted uncertainties is crucial to propose robust new theories. One of the main difficulties for analog modelers is reducing the uncertainties related to the initial setup arrangement. Most of these uncertainties are classically referred to the handmade processes, such as handling analog materials. In the Analog Modeling laboratory of the University of Trieste, we tested the use of a cobot (a cobot is a robot for direct physical interaction with a human user within a shared workspace) to simulate pre-existing faults in wet clay boxes. We present two different sets of experiments. The first set has been designed to evaluate the kinematic efficiency of Riedel shears. The second reproduces differently oriented inherited dip-slip faults in an experimental box reproducing extension. In both cases, we reproduced the same setup more than one time. The collaborative robot reduced the variability of the results, demonstrating the effectiveness of the use of cobots in analog modeling laboratories.

How to cite: Bonini, L. and Bertone, N.: The use of collaborative robots (cobots) in an analog modeling laboratory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6125, https://doi.org/10.5194/egusphere-egu23-6125, 2023.

11:08–11:10
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PICO3b.10
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EGU23-4555
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ECS
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On-site presentation
Megan Withers and Alexander Cruden

Continental transform faults transition to a new plate boundary type when strike-slip, transpression or transtension are no longer the most efficient way to accommodate plate motion. In some instances, rather than the transform fault ‘transforming’ plate motion directly to its connecting plate boundary, the continental transform fault can become ‘misaligned’ with its connecting plate boundary. Where a plate boundary misalignment occurs, plate motion that was localised on the transform fault can become distributed over a broad, intervening transition zone between the two major plate boundary faults. In this study we use scaled analogue models to investigate the development of fault networks in regions of localised and distributed simple shear and the transition between the two. We use digital image correlation (DIC) to analyse the surface deformation of the analogue model experiment and present results as incremental shear strain maps of the surface of the analogue models.  The results are compared to natural examples of plate boundary transition zones (e.g., Alpine Fault, New Zealand; North Anatolian Fault, Turkey; San Andreas Fault, USA).  In our previous analogue model experiments, regions of localised and distributed simple shear have been generated in an analogue shear box using a four-way stretchable fabric to adjust the basal boundary conditions. These experiments were limited by the elasticity of the stretchable material, which cannot deform infinitely. Here we will present preliminary results from a new shear box apparatus that uses carbon fibre rods to adjust the basal boundary conditions. This new apparatus has been designed to minimise the boundary effects caused by the limitations of the four-way stretchable fabric in our previous experiments.

How to cite: Withers, M. and Cruden, A.: A new shear box apparatus for investigating distributed deformation at the termination of continental transform faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4555, https://doi.org/10.5194/egusphere-egu23-4555, 2023.

11:10–11:12
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PICO3b.11
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EGU23-7077
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ECS
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On-site presentation
Jasper Smits, Fred Beekman, Ernst Willingshofer, and Ivan Vasconcelos

We present and demonstrate our new application of a geophysical seismic technique to acoustically characterise and image layers with different impedance contrast in analogue models. A high-powered pulsed laser in combination with a mirror galvanometer is used to generate a powerful acoustic shockwave at any point of the surface of the analogue model. Reflections, refractions, and diffractions of the acoustic source wave, induced by internal structures inside an analogue model, produce vibrations of the top surface of a model, which are measured by laser vibrometer.

Using our setup, we acquire seismic receiver gathers in less than a minute. Interpretation of the gathers allowed to identify the presence of internal reflecting and refracting material interfaces. In a series of test models, we determined the speed of both P-waves and surface waves in a multitude of brittle analogue materials. In uniform layered models we performed 1D inversion using the gathered waveform data. The results are validated by simulating the test experiments in a finite-difference solver. The novel method will be developed further, aiming to determine stress build-up in the material prior to fault formation or activity.

How to cite: Smits, J., Beekman, F., Willingshofer, E., and Vasconcelos, I.: Laser-based seismic imaging of analogue models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7077, https://doi.org/10.5194/egusphere-egu23-7077, 2023.

11:12–12:30