TS9.1

EDI
Analogue and numerical modelling of tectonic processes

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.

Public information:
Special issue announcement:

Are you an analogue modeller and working on basin inversion? Please consider submitting your work to the upcoming special issue on analogue modelling of basin inversion in Solid Earth, edited by Frank Zwaan, Michael Rudolf, Riccardo Reitano, Susanne Buiter, Ernst Willingshofer and Guido Schreurs.

The call for submission will open on the 1st of October 2021
More info: https://www.solid-earth.net/articles_and_preprints/scheduled_sis.html
Co-organized by GD8/GM9
Convener: Frank ZwaanECSECS | Co-conveners: Fabio Corbi, Ágnes KirályECSECS, Valentina Magni, Michael Rudolf
vPICO presentations
| Mon, 26 Apr, 15:30–17:00 (CEST)
Public information:
Special issue announcement:

Are you an analogue modeller and working on basin inversion? Please consider submitting your work to the upcoming special issue on analogue modelling of basin inversion in Solid Earth, edited by Frank Zwaan, Michael Rudolf, Riccardo Reitano, Susanne Buiter, Ernst Willingshofer and Guido Schreurs.

The call for submission will open on the 1st of October 2021
More info: https://www.solid-earth.net/articles_and_preprints/scheduled_sis.html

Session assets

Session materials

vPICO presentations: Mon, 26 Apr

Chairpersons: Frank Zwaan, Ágnes Király, Valentina Magni
15:30–15:40
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EGU21-14923
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solicited
Laetitia Le Pourhiet

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.

Methods and rheology
15:40–15:42
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EGU21-2268
Fanny Garel, Catherine Thoraval, Andrea Tommasi, Sylvie Demouchy, and D. Rhodri Davies

Deformed plate boundaries, rigid lithospheric plates, and the more deformable asthenospheric mantle underneath, are for the most part made of homogeneous peridotite, which most abundant mineral is olivine. The key ingredient explaining such contrasted mechanical properties is the rheology, with deformation mechanisms depend on physical conditions and on intrinsic, possibly inherited, material properties such as grain size or crystal orientation. Here, we investigate plate break-up using thermo-mechanical models of subduction with a deforming upper plate. Our models feature cutting-edge low-temperature dislocation creep ensuring a continuity in rheology from asthenosphere to lithosphere. We discuss the dynamical transition from lithosphere to asthenosphere at the base of the plates, and how this transitions shallows during plate extension. The potential of deformation to localize from the base of the lithospheric plate is evaluated through the partitioning between diffusion and dislocation creep and its evolution resulting from a feedback related to strain-rate dependent viscosity. We analyze the evolution of physical fields to understand why deformation sometimes (but not always) localize to form a new plate boundary.

How to cite: Garel, F., Thoraval, C., Tommasi, A., Demouchy, S., and Davies, D. R.:  Self-weakening feedbacks in the ductile lithospheric mantle: looking for a realistic mantle rheology enabling plate boundary formation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2268, https://doi.org/10.5194/egusphere-egu21-2268, 2021.

15:42–15:44
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EGU21-9746
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ECS
Lucy (Xi) Lu, Dazhi Jiang, Adam Beall, and Ake Fagereng

The Earth’s lithosphere has abundant structures and fabrics generated by various tectonic processes. These geological features span a wide range of characteristic lengths, from crystal lattice spacing to the dimensions of lithospheric plates. Using field observations of exhumed geological features, we aim to understand the rheological behaviour of Earth’s lithosphere. However, our direct field and laboratory observations are limited to the most accessible scales, typically from outcrops to microscopes. There is therefore a significant intrinsic scale gap between direct observations and the tectonic processes operating along plate boundaries. A micromechanics-based Multi-order Power-Law Approach (MOPLA) has been developed to bridge this scale gap. MOPLA treats the heterogeneous rock mass as a continuum of rheologically distinct elements. The rheological properties and the strain rate and stress fields of the constituent elements and the composite material are computed by solving partitioning and homogenization equations self-consistently. The partitioned ‘local’ fields in individual elements are related to small-scale geological features. The ‘bulk’ fields and the homogenized rheological properties are associated with tectonic processes and the macroscopic behaviour of the heterogeneous rock mass. The algorithm of MOPLA is implemented in a MATLAB package and has been successfully applied to various studies on multiscale deformation in the lithosphere. In this work, we will introduce this multiscale approach and also briefly introduce our ongoing work on characterising the rheological behaviour of a heterogeneous subduction shear zone using MOPLA.

How to cite: Lu, L. (., Jiang, D., Beall, A., and Fagereng, A.: A Micromechanics-based Multiscale Approach toward Continental Deformation and Tectonic Processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9746, https://doi.org/10.5194/egusphere-egu21-9746, 2021.

15:44–15:46
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EGU21-6046
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ECS
Taco Broerse, Nemanja Krstekanic, Cor Kasbergen, and Ernst Willingshofer

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.

15:46–15:48
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EGU21-13590
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ECS
Luigi Massaro, Jürgen Adam, Elham Jonade, and Yasuhiro Yamada

Strike-slip fault zones commonly display complex 3D geometries, with high structural variability along strike and with depth and their architecture and evolution are difficult to analyse. In this regard, analogue modelling represents a powerful tool to investigate the structural, kinematic and mechanical processes in strike-slip fault systems with variable scales. In detail, dynamically scaled experiments allow the direct comparison between model and nature. The geometrical scale factor defines the model resolution, in terms of model/prototype length equivalence, and depends on the physical properties of prototype and model material. Therefore, the choice of the analogue material is critical in scaled analogue experiments.
Granular materials like dry silica sand are ideal for the simulation of upper crustal deformation processes due to similar non-linear strain-dependent deformation behaviour of granular flow and brittle rock deformation. Comparing the geometrical scaling factor of the common analogue materials applied in tectonic models, we identified a model resolution gap for the simulation of fault-fracture processes corresponding to the structural scale (1 m – 100 m) observed in fault zones and damage zones in outcrops, field studies or subsurface well data. We developed a new Granular Rock-Analogue Material (GRAM) for the simulation of fault-fracture processes at the structural scale. GRAM is an ultra-weak sand aggregate composed of silica sand and hemihydrate powder capable to deform by tensile and shear failure under variable stress conditions. Based on dynamical shear tests, the new GRAM is characterised by a similar stress-strain curve as dry silica sand and has a geometrical scaling factor L*= Lmodel/Lnature = 10-3 (1 cm in model = 20 m in nature).
We performed strike-slip experiments at two different length scales, applying as model material dry silica sand and the new GRAM. Digital Image Correlation (DIC) time-series stereo images of the experiments surface allowed the comparison of the developed structures at different stages of dextral displacement above a single planar basement fault. The analysis of fractures localisation and growth in the strike-slip zone with displacement and strain components enabled the comparison of the different structural styles characterising dry silica sand and GRAM models. The application of the developed GRAM in scaled experiments can provide new insights to the multi-scale investigation of complex deformation processes with analogue models. 

How to cite: Massaro, L., Adam, J., Jonade, E., and Yamada, Y.: Analogue modelling of strike-slip tectonics from basin to structural-scale comparing silica sand and new rock-analogue materials, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13590, https://doi.org/10.5194/egusphere-egu21-13590, 2021.

Compression
15:48–15:50
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EGU21-13914
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ECS
Camilo Andrés Conde Carvajal, Cristhian Bolívar Riascos Rodríguez, Michael Andres Avila Paez, and Andreas Kammer

Among the foreland belts of the Andean mountain system, the Eastern Cordillera of Colombia (EC) represents a unique example of an isolated, bi-vergent mountain belt. In contrast, to block tectonics of broken foreland basins, it displays a ductile deformation style which involves two mountain fronts with a structural relief of the order of 10 km. Internal parts of the EC have been shortened by buckling at high and a homogeneously strained basement at deeper structural levels. These deformation patterns likely attest to conditions of a thermally weakened backarc setting. Two opposed scenarios have been postulated for its surface uplift and consequent exhumation: 1) an E-migrating deformation front and the formation of progressively forward breaking faults; and 2) the pop-up of a weak crustal welt enclosed by strong foreland blocks. In this latter setting, a synchronous early formation of marginal mountain fronts and a late-stage surface uplift of a central domain may be anticipated. These two constellations compare, in terms of a contrasting model setup, to a foreland migrating orogenic wedge or a relatively stable, doubly vergent wedge formed above a structural discontinuity or rheologic boundaries that acted as sites for the nucleation of the marginal faults.

In this contribution, we opt to examine the “boundary” conditions for the development of a doubly vergent wedge formed at the tip line of a rigid tapering backstop, that simulates a rigid foreland block. With respect to the shape of this backstop, we examine the effects of tip angles less than the angle of internal friction (<30°) and find, that at a low tip angle of 10° the pop-up evolves above a forward-breaking principal kink-band with the synchronous formation of a sequence of conjugate back-kinks that cut into the sand pack, as it is pushed toward the backstop. At a moderate tip angle of 20o the forward-breaking kink-band is slightly steeper than the backstop and gives rise to a frontal fold with an overturned limb. This latter geometrical configuration loosely compares to the structural relations of a structural section through the high plains of Bogotá, where the eastern mountain front defines a strongly deformed antiform, that is juxtaposed against an undeformed margin of the adjacent Guyana shield.

How to cite: Conde Carvajal, C. A., Riascos Rodríguez, C. B., Avila Paez, M. A., and Kammer, A.: The influence of backstop geometry in the structural style of the Eastern Cordillera of Colombia: A sandbox modeling approach , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13914, https://doi.org/10.5194/egusphere-egu21-13914, 2021.

15:50–15:52
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EGU21-11205
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ECS
Paul Pitard, Anne Replumaz, Marie-Pierre Doin, Cédric Thieulot, Marie-Luce Chevalier, Philippe Hervé Leloup, Julia de Sigoyer, Mingkun Bai, Li Haibing, and Mélanie Balvay

Decoding the Tibetan plateau and its structural evolution has been a thorny issue for decades, triggering many controversial discussions between the proponents of the numerous key models. Numerical simulations of buoyancy forces associated with a thick crust and a low viscosity channel in the Tibetan crust predict continuous deformation, crustal uplift and thickening through an outward flow of partially molten middle/lower crust. Surface geological observations of fault systems, however, favor a model of localized deformation through the interaction between strike-slip and thrust faults. Here, we investigate the role of thrusting mechanisms involved in the plateau formation, which is essential in order to discuss these end-members competing models. We focus on the Muli thrust, a major Miocene thrust fault located at the eastern edge of the Tibetan Plateau, characterized by a pronounced topographic step of ~2000 m. We provide here an innovative quantitative approach combining thermo-kinematic modelling based on low-temperature thermochronology data, with conceptual 2-dimensional (2D) simulations of the crust’s mechanical behavior. Using the code PECUBE, we test different scenarios of rock cooling by forward modelling and inversion method in order to constrain the amount and timing of exhumation, as well as its simplified first-order crustal geometry. Given that low-temperature thermochronology data only provides the thermal history of the upper part of the crust (< 10 km), such thermo-kinematic modelling does not reveal any direct evidence of the potential implication of the lower crust. To overcome such limitations, we performed 2D mechanical modelling of the Muli thrust to constrain its mechanical behavior at the crustal scale to decipher its importance in the thickening of the plateau margin. We present here, how complementary numerical simulations based on in-situ geological observations on thrust faults, combined with thermochronology data, can be used to have a better understanding of the geological processes involved in the thickening of the Tibetan crust, and discuss both the strengths and weaknesses of such modelling.

How to cite: Pitard, P., Replumaz, A., Doin, M.-P., Thieulot, C., Chevalier, M.-L., Leloup, P. H., de Sigoyer, J., Bai, M., Haibing, L., and Balvay, M.: Combining thermo-kinematic and mechanical modelling on thrust faults - a quantitative approach to crustal deformation history: Case study from SE Tibet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11205, https://doi.org/10.5194/egusphere-egu21-11205, 2021.

15:52–15:54
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EGU21-433
Yossi Mart, Liran Goren, and Einat Aharonov

The post-Triassic age of all oceanic lithospheres indicates the efficiency and the sustainability of lithospheric subduction, which consumes the basaltic seafloor and recirculates it in the upper mantle. Since at present the initiation of subduction is very rare, comprehension of this cardinal process should be carried through modeling – numeric or analog. While deciphering processes through numeric modeling is commonly comprehensive, the analog models can determine major factor that constrain a tectonic procedure. Analog centrifuge experiments were applied to initiate self-sustained modelled subduction, trying to determine the critical factors that trigger its early stages.

Analytically we presumed that where densities of two lithospheric plates, juxtaposed across a weakness zone, exceed a critical value, then the denser lithosphere eventually will drive underneath the lighter one, provided the friction across the interface is not too high. Consequently, analog experiments were carried out in a centrifuge at acceleration of ca. 1000 g., deforming miniaturized models of three layers representing the asthenosphere, the ductile and the brittle lithosphere. The lithospheres were modeled to include lighter and denser components, juxtaposed along a slightly lubricated contact plane, where the density difference between these components was ca. 200 kg/m3. No mechanism of lateral force was applied in the experiment (even though such a vector exists in nature due to the seafloor spreading at the oceanic ridges), to test the possibility of subduction in domains where such a force is minor or non-existent.

The analog experiments showed that the penetration of the denser modeled lithosphere under the lighter one led to extension and subsequent break-up of the over-riding plate. That break-up generated seawards trench rollback, normal faulting, rifting, and formed proto-back-arc basins. Lateral differential reduction of the friction between the juxtaposed plates led to the development of arcuate subduction zones. The experimental miniaturization, and subsequent numerical and analytical modeling, suggest that the observed deformation in the analog models could be meaningful to the planet as well.

Constraints of the analog experimentation setting did not enable the modeling of the subduction beyond the initial stages, but there is ground to presume that at depths of 40-50 km, metamorphic processes of the generation of eclogites would change the initial mineralogy on the subducting plate. Reactions with water would convert basalts into metamorphic serpentinites and schists. Higher temperatures and pressures would melt parts of the subducted slab to generate felsic magmas, which would ascend towards the surface diapirically due to their lighter density. Alternately, low availability of H2O would gradually alter the oceanic basalt and gabbro into eclogite, which would sink into the mantle due to its increased density.

How to cite: Mart, Y., Goren, L., and Aharonov, E.: Centrifuge Experiments of the Initiation of Self-Sustaining Subduction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-433, https://doi.org/10.5194/egusphere-egu21-433, 2021.

15:54–15:56
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EGU21-13393
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ECS
István Bozsó, Ylona van Dinther, Liviu Matenco, Attila Balázs, and István Kovács

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.

15:56–15:58
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EGU21-10396
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ECS
Paraskevi Io Ioannidi, Laetitia Le Pourhiet, Philippe Agard, Samuel Angiboust, and Onno Oncken

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.

15:58–16:00
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EGU21-2074
Vincent Strak, Wouter Pieter Schellart, and Kai Xue

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.

Strike-slip
16:00–16:02
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EGU21-4553
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ECS
Tuo Shen, Xiwei Xu, Shiyong Zhou, Shaogang Wei, and Xiaoqiong Lei

In recent decades, plateau margins have attracted attention because the understanding of their dynamics and history provides insights into the modes of crustal deformation responsible for the plateau structure and morphology and more widely into the deformation of continental lithosphere. The slip transformation and strain partitioning mechanism at the eastern termination of the Kunlun fault system remain unclear. Geophysics investigations revealed the Ruoergai Basin as a rigid block; however, insufficient information is available on the role of this block in tectonic transformation zone at east Tibet. We employed the finite element method in our simulations to delimitate the presence of the Ruoergai block and determine how it affects the surrounding area. We found that the Ruoergai block moves independently to the east or northeast, and its motion differs from that of the Bayan Har block in the eastward escape process of this last-named block. The formation and behavior of Awancang fault and Longriba fault seems to impact by the Ruoergai block. The influence of the Ruoergai block in the east margin should not be ignored. The Awancang fault and Ruoergai block absorbed the north vector velocity of the Bayan Har block, after which the Bayan Har block started moving southeast. The strain partitioning at the eastern margin of the Tibet Plateau is progressively complete[A1]  from the Awancang fault, Ruoergai block, and Longriba fault area to the Longmenshan block. The presence of the Ruoergai block could decrease the strike-slip rate of the Maqin–Maqu section of the Kunlun fault. Given its influence in the region, the Ruoergai block should be incorporated in future studies on regional deformation and in deformation and tectonic transformation models. Then we compared the deformation and tectonic transformation models in the northern margin of the Tibet Plateau. Proposed a rigid block compression pattern unite the tectonic transformation and deformation issue, further explain most of the fault behaviors in the northern margin and eastern margin of Tibet.

 

How to cite: Shen, T., Xu, X., Zhou, S., Wei, S., and Lei, X.: Role of rigid block in tectonic transformation zone at east Tibet , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4553, https://doi.org/10.5194/egusphere-egu21-4553, 2021.

16:02–16:04
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EGU21-13297
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ECS
Sarah Visage, Pauline Souloumiac, Nadaya Cubas, Bertrand Maillot, Arthur Delorme, and Yann Klinger

During large strike-slip earthquakes, the displacement at the ground surface, only partially measured, is often under-estimated in comparison with the amount of slip inferred at depth. The resulting concept of shallow slip deficit is challenged by the precise measurements of surface deformation of on- and off-fault deformation by space imaging techniques, showing that a significant amount of deformation might be accommodated through distributed damage in a zone several hundred meters to kilometers wide around the fault. In this study, analogue modeling is used to quantify the distribution of on/off-fault surface deformation along strike-slip faults over the long term and to understand how it relates to the deep structure of the fault.

To do so, we used a 1.5 m x 1.34 m PVC box, and studied the deformation of a homogeneous sand pack deposited above a straight basal fault, with sand thicknesses varying from 2 to 8 cm. During strike-slip fault experiments, the first structures to appear are the Riedel shears (R-shears) followed by the synthetic shears (S-shears). These structures eventually coalesce to form an anastomosed fault zone, made of a succession of segments separated by geometrical complexities of variable size. Optical imagery is used, at every stage of the strike-slip fault formation, to (1) describe the 3D surface displacement and (2) precisely quantify on/off-fault deformation. 

At the initiation of the fault before the formation of the Riedels, a zone of diffuse deformation is highlighted by a positive divergence of the displacement. This diffuse zone is also characterized by a vertical deformation that forms a bulge.

When the displacement Ux parallel to the basal fault has a gradient dUx/dy >= 0.1, we consider that it is "on-fault" deformation, and it is "off-fault, when that gradient is between 0.02 and 0.1.

At the Riedel shear stage, we find 40% of off-fault deformation over a unique Riedel fault and about 60% if deformation is distributed over two Riedels.

Once the strike-slip fault is formed, the ratio drops between 0 to 5 % of off-fault deformation over a fault segment, but the ratio increases to 20% along geometrical complexities.

Moreover, we also show that off-fault deformation around the early Riedel structures partly control the long-lived segmentation and morphology of the strike-slip fault.

Experimental results are then compared to observations and measurements of near-field and far-field deformation obtained along the 2013 Mw 7.7 Balochistan earthquake by Vallage et al. (2015) and Gold et al. (2015). Azimuthal displacements measured in a relay zone  (Vallage et al. 2015) are consistent with those observed along our experimental relay zones. Although our experiments were only run with sand, we found a similar distribution of the deformation at the surface. These observations suggest that the distribution of the surface deformation of strike-slip fault earthquakes is inherent to the fault structure, possibly inherited from the Riedel shear stage, and not induced by earthquakes dynamics.

How to cite: Visage, S., Souloumiac, P., Cubas, N., Maillot, B., Delorme, A., and Klinger, Y.: Strike-slip fault in a sandbox: insight of on- and off-fault deformation from analogue modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13297, https://doi.org/10.5194/egusphere-egu21-13297, 2021.

Extension
16:04–16:06
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EGU21-15277
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ECS
Paul Perron, Laetitia Le Pourhiet, Anthony Jourdon, Tristan Cornu, and Claude Gout

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.

16:06–16:08
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EGU21-15906
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ECS
Anastasiia Tolstova, Eugene Dubinin, and Andrey Groholsky

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.

16:08–16:10
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EGU21-2907
Guido Schreurs and Mario Bühler

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.

16:10–16:12
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EGU21-8014
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ECS
João Pedro Macedo Silva, Victor Sacek, and Rafael Monteiro da Silva

The evolution of escarpments bordering the coast during the post-rift phase is numerically simulated mostly by landscape surface processes models. However, there are few thermomechanical models that were applied to study the post-rift evolution of these escarpments. In the present work, we used a finite element thermomechanical model to simulate lithospheric extension and evaluate the sensitivity of escarpment amplitude over time under different geological and rheological conditions from the onset of lithospheric extension to the post-rift phase. The results showed that the evolution of escarpment amplitude and its preservation for tens of millions of years are sensitive to crustal and lithospheric thicknesses. We observed that escarpment preservation is higher for scenarios with a thinner crust with a strong lower crust and a thicker lithospheric mantle. This behavior is related to the degree of coupling between the crust and lithospheric mantle that affect the vertical displacement of the lithosphere due to flexural and isostatic response. Additionally, even without surface processes of erosion and sedimentation, the amplitude of the escarpment can monotonically decrease with time due to the lateral flow of the lower crust. This effect is expressive in the scenarios where the effective viscosity of the lower crust is relatively low and the upper crust is rheologically decoupled from the lithospheric mantle. In these cases, the amplitude of the escarpment can decrease from 2-3 km during the rifting phase to less 1 km after 40 Myr after the onset of lithospheric extension. On the other hand, in scenarios where the crust is rheologically coupled, the amplitude of the escarpment after 100 Myr since the lithospheric stretching is only ~25% smaller than maximum amplitude observed during the rifting phase. We conclude that the rheological structure of the lithosphere can play an important role in the formation and preservation of escarpments at divergent margins simultaneously with surface process.

How to cite: Macedo Silva, J. P., Sacek, V., and Monteiro da Silva, R.: The influence of lithospheric rheology on escarpment evolution at divergent margins: a numerical approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8014, https://doi.org/10.5194/egusphere-egu21-8014, 2021.

Education & Outreach
16:12–16:14
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EGU21-15031
Florian Wellmann, Simon Virgo, Daniel Escallon, Miguel de la Varga, Alexander Jüstel, Florian Wagner, Julia Kowalski, and Robin Fehling

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.

16:14–16:16
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EGU21-16301
Ernst Willingshofer, Francesca Funiciello, Matthias Rosenau, Guido Schreurs, Frank Zwaan, Susanne Buiter, Geertje ter Maat, Otto Lange, Kirsten Elger, Claudio Faccenna, Valerio Acocella, Riccardo Reitano, Giacomo Mastella, Benjamin Guillaume, and Fabio Corbi and the EPOS TCS MSL analogue modelling team

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.

16:16–17:00