TS9.1

Tectonic modelling is a very wide area of application over a large range of time scale and length scale. What mainly characterize this modelling field is the coexistence of brittle fractures which relates to the field of fracture mechanics and plastic to viscous shear zones which belongs to the two main branch of continuum mechanics (solid and fluid respectively).

This type of problems arises sometimes in engineering but material do not change their behavior with loading rate or with time or with temperature, and rarely are engineers interested in modelling large displacement in post failure stage.  As a result, tectonicists cannot use commercial packages to simulate their problems and need to develop methodologies specific to their field.

Historically, the first tectonics models made use of simple analogue materials and corresponded more to modelism than actual analogue models. While the imaging of the models, and the characterization of the analogue materials have made a lot of progress in the last 15 years, up to recently, most analogue models still relied on sand and silicone putty to represent the brittle and viscous counter part of tectonic plates.

Since the late 80’s, but mostly during the years 2000, numerical modelling has exploded on the market, as contrarily to analogue modelling, it was easier to capture the thermal dependence of frictional-viscous transition, I use frictional here because most models in tectonics use continuum mechanics approach and in fine do not include brittle material s.s. but rather frictional shear bands. Some groups run these types of simulation routinely in 3D today but this performance has been made at the cost of a major simplification in the rheology: the disappearance of elasticity and compressibility which was present in late 90’s early 2000 simulations and is still very costly because the treatment of “brittle” rheology seriously amped code performances.

Until recently, in both analogue and numerical modelling, I have some kind of feeling that we have been running the same routine experiments over and over again with better performance, or better acquisition.  

We are now entering a new exciting era in tectonic modelling both from experimental and numerical side: a ) emergence of complex analogue material or rheological laws that efforts in upscaling from micro-mechanical process observed on the field to plate boundary scale, or from earthquake cycle to plate tectonics, b) emergence of new interesting set up’s in terms of boundary conditions in 3D, c) development of robust numerical technics for brittle behavior d) development of new applications to make our field more predictive that will enlarge the community of end-users of the modelling results

I will review these novelties with some of the work develop with colleagues and students but also with examples from the literature and try to quickly draw a picture of where we are at and where we go.

How to cite: Le Pourhiet, L.: Tectonic modelling state of the art and future challenges, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14923, https://doi.org/10.5194/egusphere-egu21-14923, 2021.

We are interested in reconstructing the time evolution of 2D plane deformation of analogue models of tectonic processes. Under relevant forcings, these models develop internal deformation, such as faults, and broader zones of deformation. We use Particle Image Velocimetry (PIV) to derive incremental displacements from top-view images that we use in subsequent steps to calculate the shape changes that come with large deformation. Because PIV describes displacement in a spatial reference, and material moves through the area in view, displacements at any given time refer to fixed locations in space, and not to specific material points. By reconstructing the path of material, we can follow small regions of material while they translate, rotate and change shape.

To aid the qualitative interpretation of this deformation, we have developed a novel method that can qualitatively describe shape changes coming from extensional, shortening and horizontal shearing (strike-slip) deformation or combinations of these. This method is based on a logarithmic measure of stretch and results agree well with the visual interpretation of structures that we observe in our models. Thus, we provide tools with which the evolution of 2D tectonic deformation can be interpreted in a physically meaningful manner, but our method may be useful outside the realm of tectonics. Our software to compute deformation is freely available and can be used to post-process incremental displacements from PIV or similar autocorrelation methods.

How to cite: Broerse, T., Krstekanic, N., Kasbergen, C., and Willingshofer, E.: Classifying large strains from digital imagery: application to analogue models of lithosphere deformation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6046, https://doi.org/10.5194/egusphere-egu21-6046, 2021.

The Carpathians subduction system evolved similarly to many Mediterranean systems where extensional back-arc basins and separate large sag basins develop in the overriding plate. The evolution of such basins can be explained in the context of roll-back of narrow oceanic slabs. Their evolution is linked to extensional and sag back-arc basins, retreating orogenic systems and slab detachment. A recent example of slab detachment can be studied by the Vrancea slab beneath the SE Carpathians.
Significant effort has been dedicated to modelling such Mediterranean-style subduction systems, and in most cases the model was set up with a narrow oceanic domain, which has an increased difficulty to create rollback due to reduced buoyancy of the slab.
Our approach is to use a two-dimensional thermo-mechanical numerical model that introduces an inherited oceanic domain, which adds to the younger, narrow ocean developed in the later stages.
Our model can produce sustained subduction of the oceanic slab associated with roll-back and slab detachment. In most of our models a retro-arc sag basin develops, which can be interpreted as the Transylvanian Basin. This sag basin is one of the most consistent features of our model. At larger distances from the subduction zone, the extensional back-arc of the Pannonian basin can be modelled by introducing an lithospheric weakness zone, which represents a suture zone inherited from a previous orogenic evolution. Such a suture zone is compatible with the overall orogenic evolution of the Alps-Carpathians-Dinarides system. We furthermore discuss the limitations of our 2D modeling in the overall 3D settings of the Carpathians system and possibilities of future integration.

How to cite: Bozsó, I., van Dinther, Y., Matenco, L., Balázs, A., and Kovács, I.: Subduction and roll-back of narrow oceanic slabs: Back-arc basin modelling of the Carpathians subduction zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13393, https://doi.org/10.5194/egusphere-egu21-13393, 2021.

Exhumed subduction shear zones often exhibit block-in-matrix structures comprising strong clasts within a weak matrix (mélanges). Inspired by such observations, we create synthetic models with different proportions of strong clasts and compare them to natural mélange outcrops. We use 2D Finite Element visco-plastic numerical simulations in simple shear kinematic conditions and we determine the effective rheology of a mélange with basaltic blocks embedded within a wet quartzitic matrix. Our models and their structures are scale-independent; this allows for upscaling published field geometries to km-scale models, compatible with large-scale far-field observations. By varying confining pressure, temperature and strain rate we evaluate effective rheological estimates for a natural subduction interface. Deformation and strain localization are affected by the block-in-matrix ratio. In models where both materials deform viscously, the effective dislocation creep parameters (A, n, and Q) vary between the values of the strong and the weak phase. Approaching the frictional-viscous transition, the mélange bulk rheology is effectively viscous creep but in the small scale parts of the blocks are frictional, leading to higher stresses. This results in an effective value of the stress exponent, n, greater than that of both pure phases, as well as an effective viscosity lower than the weak phase. Our effective rheology parameters may be used in large scale geodynamic models, as a proxy for a heterogeneous subduction interface, if an appropriate evolution law for the block concentration of a mélange is given.

How to cite: Ioannidi, P. I., Le Pourhiet, L., Agard, P., Angiboust, S., and Oncken, O.: Effective rheology of a two-phase subduction shear zone: insights from numerical simple shear experiments and implications for subduction zone interfaces, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10396, https://doi.org/10.5194/egusphere-egu21-10396, 2021.

Slab rollback-induced mantle flow in retreating subduction zones is known to have a significant geodynamic impact on Earth. The resulting quasi-toroidal circulation can deflect mantle plumes, transport geochemical signatures and have an upwelling component that thereby generates atypical intraplate volcanism near lateral slab edges. Nevertheless, the mantle flow generated by advancing slabs remains unstudied and its geodynamic significance unclear. We therefore conducted analogue buoyancy-driven subduction models to investigate the mantle flow generated in both retreating and advancing subduction modes. We analysed our models using a novel tomographic Particle Image Velocimetry technique, allowing us to compute the 3D velocity field in a volume of the mantle. Our model results show that the advancing subduction mode develops a slab rollover geometry that produces a quasi-toroidal mantle flow with mantle material displaced from the mantle wedge domain to below the subducting plate, opposite to mantle flow during the retreating mode. This slab rollover-induced mantle flow generates an upwelling component that is laterally offset from the subducting plate and is located some ~1000 km from the trench on the subducting plate side. Such newly imaged mantle flow may have implications for intraplate volcanism and the distribution of mantellic geochemical signatures associated with advancing subduction zones, such as the Makran, and continental subduction zones, such as the Himalaya.

How to cite: Strak, V., Schellart, W. P., and Xue, K.: 3D mantle flow induced by retreating and advancing slabs: insights from analogue subduction models analysed with a tomographic Particle Image Velocimetry technique, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2074, https://doi.org/10.5194/egusphere-egu21-2074, 2021.

For a long time, the complexity of the lithosphere was ignored by numerical modelling because the inherited structural and compositional complexity of the “real” lithosphere is indeed mainly unknown to geologists so modeler preferred to understand first order parameters such as rate of extension, lithospheric thickness, mechanical coupling or decoupling at the Moho. These models were not representative of any particular region but they were helpful. As a wider community of geologist became interested in numerical modelling, a growing number of numerical models have attempted to account for a major player in structural geology: inheritance. However, the complexity of “real” Earth has been simplified and “idealized” where inherited “anomalies” (e.g. fault, pluton, craton) or a combination of them has been added without really knowing the exact initial conditions which are the unknown of the problem. Yet another approach has been to add a lot of them in a more or less random mater or to replace them by initial noise in the parameters. None of these approaches actually fulfil the need for end-users community to have predictive models.

Realizing that structural inheritance is some kind of kinematic forcing in the solution of the models but also that it is not possible to anticipate and identify all the geological structures that can be inherited in rifted margin lithospheres, we have developed a new approach, through the integration of a new kinematic module to pTatin2D thermomechanical code, permitting to understand the kinematics of deformation of the continental lithosphere and asthenosphere through time leading to the establishment of rifted margins. The method is settled and validated by fitting the architecture (i.e. basement, Moho, LAB, Tmax) and by solving the kinematics of a random unknow 2D cross section extracted from 3D thermomechanical rifted margin model.

This new tool aims to help geologists to better constrain and draw on their 2D geological cross sections the position of the Moho, the Lithosphere-Asthenosphere boundary (LAB), the temperature isotherms and the heat flux.

Key words: Kinematic thermomechanical modelling, asymmetric rifted margin architecture, modelling method.

How to cite: Perron, P., Le Pourhiet, L., Jourdon, A., Cornu, T., and Gout, C.: Role of kinematic thermomechanical modelling on constraining asymmetric continental break up, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15277, https://doi.org/10.5194/egusphere-egu21-15277, 2021.

The evolution of the Agulhas oceanic basin was influenced by the formation of the southern part of the Mid-Atlantic Ridge (MAR) as a result of the jump of the spreading axis. This sector of the South Atlantic began to open up as a result of the breakup of Gondwana about 135-140 million years ago. The process of opening was accompanied by kinematic rearrangements in the movement of the lithospheric plates. According to some evolutionary models, the jumps of the spreading axis in the area of the Agulhas basin occurred under the influence of hot spots. The hot spots of Shona, Bouvet, and Discovery played an important role in the evolutionary process of plate boundaries. 

The previously active Agulhas spreading ridge is located in the central part of basin. From the east, the basin is framed by the Agulhas plateau, from the west is the Meteor rise. On the north the basin is bounded by the Agulhas transform fault, and on the south by the Southwest Indian Ridge.

Using the method of physical modeling, the formation of volcanic provinces that influenced the formation of the Agulhas basin was modeled.

The first series of experiments is devoted to the jump of the spreading axis of the Agulhas Ridge and the formation of the MAR and the Meteor rise. The purpose of the experiments was to determine the conditions for the formation of Meteor rise, located on the western edge of the Agulhas basin. Experiments have shown that the formation of this block may be due to the action of a hot spot, and the block itself may have a complex structure and contain inclusions of continental crust, which could have separated during the break of the Falkland Plateau and the jump of the spreading axis.

The second series of experiments was devoted to modeling the Agulhas ridge, located on the northern rim of the Agulhas basin. The ridge has a linear structure extending along the Agulhas-Falkland transform fault. The purpose of the experiments was to test the hypothesis of the magmatic origin of this ridge in the conditions of a transform fault with transtension under the thermal influence of the Shona and Discovery hot spot. Experiments have shown that a linear magmatic ridge similar to the Agulhas ridge is formed in the transtension condition. It is also possible that the formation of the ridge may be associated with a change in the speed and direction of spreading.

The Antarctic sector of the South Atlantic, and in particular the Agulhas Basin, has a complex history of evolution. This is due to the displacement of the three major Gondwanan continents, and the activity of hot spots in this region and kinematic rearrangements, and the spatiotemporal migration of the Bouve triple junction with a complex stress field, the existence of the continental Falkland Plateau, and other factors.

The geological environment of the Agulhas basin is characterized by objects and structures that allow us to approach the history of the evolution of this complex area.

How to cite: Tolstova, A., Dubinin, E., and Groholsky, A.: Physical modelling of structural features of the Agulhas Basin and its evolution (South Atlantic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15906, https://doi.org/10.5194/egusphere-egu21-15906, 2021.

Rift systems worldwide are influenced by pre-existing crustal or lithospheric structures. Here, we use brittle-viscous analogue models to examine the role of tectonic inheritance on fault evolution during two non-coaxial rift phases. In our experiments the tectonic inheritance is a linear crustal weakness zone consisting of two offset and parallel linear segments connected by a central oblique linear segment. The first phase of rifting is either orthogonal and followed by a second phase of oblique rifting or vice versa.

The experiments reveal that the tectonic inheritance localizes initial faulting during early rifting, with faults in the domains away from it forming later. The nature and orientation of early faults depends on first-phase rift obliquity, with a progressive switch from dip-slip dominated faulting to strike-slip dominated faulting with increasing obliquity, even resulting in local transpressional structures at very high rift obliquities. First-phase rift structures, in particular those above the tectonic inheritance, exert an important control on the overall fault geometry during the second phase of rifting. Our experiments show that two-phase rifting results in fault patterns evolving by the formation of second-phase new faults and the reactivation of first-phase faults.  Irrespective of the order of the applied two phases of non-coaxial rifting and the difference in rift obliquity angle between the two phases, a major rift (master rift) forms above the tectonic inheritance, underlining its strong control on fault evolution despite markedly different multiphase rift histories.

Nevertheless, close inspection of the master rift reveals differences related to the relative order of the two rift phases: (i) Oblique rifting superseding orthogonal rifting results in a major master rift, whose rift-boundary faults are not reactivated during second-phase rifting. Instead, first-phase intra-rift normal faults are being reactivated with an important strike-slip component of displacement.

Above the oblique segment of the tectonic inheritance, first-phase en echelon intra-rift normal faults are mostly reactivated and propagate along strike reorienting their tips into high angles to the local principal stretching direction (ii) Orthogonal rifting overprinting oblique rifting, on the other hand, produces first-phase strike-slip faults that link up and trend (sub)-parallel to later formed rift-boundary faults and intra-rift normal faults.

Away from the tectonic inheritance faults have more freedom to evolve in response to the regional rift obliquity, and although they may reactivate, propagate sideways and slightly reorient their fault tips during the second phase of rifting, their trend at the end of the second-phase of rifting with respect to the orientation of the master rift reflects whether first-phase rifting was orthogonal or oblique. Our model results can be used to assess the influence of tectonic inheritance on faulting, the relative order of rifting and the relative difference in obliquity in natural settings that have undergone two phases of rifting.

How to cite: Schreurs, G. and Bühler, M.: The role of tectonic inheritance during multiphase rifting: insights from analogue model experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2907, https://doi.org/10.5194/egusphere-egu21-2907, 2021.

Augmented Reality Sandboxes are a valuable tool for science outreach and teaching due to their intuitive and haptic interaction-enhancing operation. Most of the common AR-Sandboxes are limited to the visualization of topography with contour lines and colours, as well as water simulations on the digital terrain surface. However, many geologists will intuitively want to use this system to visualize geology and literally “dig deeper”, to see how geological units change below the surface. In fact, if we consider the AR-Sandbox in its bare essential, as a 2.5-D haptic dynamic interface to a 3-D or 4-D system, then many more potential applications come to mind: from geological education and outreach, over the representation of geophysical fields, to dynamic simulations. 

In this contribution, we present an open-source implementation of an AR-Sandbox system with an interface in Python, which enables simple access to this tool. This implementation allows for creative and novel applications in geosciences education and outreach in general. With a link to a 3-D geomodelling system, we show how we can display geologic subsurface information such as the outcropping lithology, creating an interactive geological map for structural geology classes. The relations of subsurface structures, topography and outcrop, can be explored in a playful and comprehensible way. Additional examples are geoelectric fields and the propagation of seismic waves, as well as simulations of landslides at the surface. We further extended the functionality with an implementation of ArUco marker detection to enable interactive cross-section generation, among other examples. Many other implementations can be envisaged for the use of this system, and we look forward to creative contributions to geoscience education.

How to cite: Wellmann, F., Virgo, S., Escallon, D., de la Varga, M., Jüstel, A., Wagner, F., Kowalski, J., and Fehling, R.: Open AR-Sandbox: a Haptic Interface for Geoscience Education and Outreach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15031, https://doi.org/10.5194/egusphere-egu21-15031, 2021.

EPOS, the European Plate Observing System, is a unique e-infrastructure and collaborative environment for the solid earth science community in Europe and beyond. A wide range of world-class experimental (analogue modelling and rock and melt physics) and analytical (paleomagnetic, geochemistry, microscopy) laboratory infrastructures are concerted in a “Thematic Core Service” (TCS) labelled “Multi-scale Laboratories” (MSL). Sharing experimental facilities and data on analogue modelling of tectonic processes as well as on properties and applicability of different rock analogue materials are among the thematic areas that have been achieved during the current implementation phase of EPOS. The TCS Multi-scale Laboratories offers coordination of the laboratories’ network, data services, and trans-national access to laboratory facilities.

In the framework of Transnational Access (TNA), TCS Multi-scale laboratories’ facilities are accessible to researchers across the world, creating new opportunities for synergy, collaboration and scientific innovation, according to trans-national access rules. TNA can be realized in the form of physical access (in-situ experimenting and analysis), remote service (sample analysis) and virtual access (remote processing). After three successful TNA calls, the 2020 and 2021 TNA calls have been suspended due to Covid-19 pandemic restrictions. A TNA call is now foreseen for 2022 offering access to a variety of experimental facilities and complementary expertise.

In the framework of data services, TCS Multi Scale Laboratories promotes FAIR (Findable-Accessible-Interoperable-Re-Usable) sharing of experimental research data sets through Open Access data publications. Data sets are assigned with digital object identifiers (DOI) and are published under open CC BY licences. They are thus citable in all relevant scientific journals. A dedicated metadata schema (following international standards that are enrichiched with disciplinary controlled community vocabulary) eases exploration of the various data sets in a TCS catalogue. With respect to analogue modelling, a growing number of analogue modelling data sets include analogue material properties (friction and rheology data) and modelling results (images, maps, graphs, animations) as well as software (visualization and analysis). The main repository for data sets is currently GFZ Data Services, a domain repository for Geosciences, hosted at GFZ German Research Centre for Geosciences, but others are planned to be implemented within the next years.

The EPOS TCS Multiscale Laboratories framework will lay the foundation for a comprehensive database of rock analogue materials, a dedicated bibliography, and will facilitate the organization of community wide activities (eg. meetings, benchmarking, etc.) to stimulate collaboration among analogue laboratories and the exchange of know-how.

How to cite: Willingshofer, E., Funiciello, F., Rosenau, M., Schreurs, G., Zwaan, F., Buiter, S., ter Maat, G., Lange, O., Elger, K., Faccenna, C., Acocella, V., Reitano, R., Mastella, G., Guillaume, B., and Corbi, F. and the EPOS TCS MSL analogue modelling team: Sharing experimental data and facilities in EPOS: Updates on services for the analogue modelling community in the TCS Multi-scale Laboratories, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16301, https://doi.org/10.5194/egusphere-egu21-16301, 2021.