TS9.1

Modelling studies show that subduction initiation requires failure of the load-bearing crustal and mantle layers and critically depends on the buoyancy and strength contrast within the lithosphere. Such findings suggest that the probability of subduction initiation must increases in the vicinity of continental margins. Yet, direct evidence for subduction initiation at passive margin is scarce and the mechanisms of subduction initiation in this particular setting remains a recurrent and long-standing unresolved question. Therefore, our study focuses on the kinematic and rheologic key parameter combinations relevant for the formation of a subduction zone, with the aim of identifying the feasibility of subduction initiation at a passive margin setting. To challenge the existing limits and discriminate processes that fit conditions for subduction nucleation, we compare and combine analogue and numerical modelling techniques. In this work, numerical modelling allows exploring temperature driven feedback mechanisms whereas analogue modelling allows for mapping characteristic length scales of deformation against the mode of subduction initiation. Overall, model results highlight that the convergence rate, the strength contrast at the margin as well as the degree of crust-mantle coupling control the development of a shear zone at the base of the crust, and the propagation of deformation into the mantle lithosphere. In addition, comparison between analogue and numerical modelling results infers that shear heating, weak sediments, magmatic heterogeneities or a serpentinite mantle wedge, are important parameters for the development of a self-sustaining subduction zone. The relevance of the modelling results is demonstrated by comparing length-scales of deformation with observations from inverted continental passive margins and orogenic systems, such as the Alps and Dinarides. Models predict that primary response of the lithosphere to compression is by folding and that tectonic structures and early-stage length-scales of deformation can be used to predict the likeliness of subduction initiation at a passive margin.

How to cite: Auzemery, A.: A comparison of numerical and analogue models of subduction initiation at passive margins., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-356, https://doi.org/10.5194/egusphere-egu22-356, 2022.

Analogue models are powerful tools for investigating extensional and convergent tectonic processes in 4D and at multiple scales. However, rarely do we introduce two successive phases of tectonism in a single analogue experiment to study the interaction between structures from two kinematically distinct tectonic events. Here we showcase a series of analogue experiments in which lithospheric-scale models are extended and subsequently shortened, simulating rifting followed by inversion and mountain building.

In our experiments, we simulate rifting by extending a multi-layer, brittle-ductile model lithosphere; this initial model is analogous to a hot, thickened lithosphere immediately after orogenesis. We demonstrate that the absence or presence of a narrow, pre-existing weakness in the lithospheric mantle results in end-member models of either wide or narrow rifting, respectively. Extension is immediately followed by shortening of the model, where we observe that contractional structures are localised along pre-existing rift basins. Analyses of particle imaging velocimetry (PIV) data reveal that shortening is accommodated by several mechanisms, including reverse reactivation of normal faults and buckling and/or inversion within pre-existing basins. We also show that these findings are consistent with field and geophysical observations from northern Australia as well as previous numerical experiments.

How to cite: Samsu, A., Betts, P., Amirpoorsaeed, F., Cruden, A., and Gorczyk, W.: Stretch and fold: Multistage analogue experiments of rifting, inversion, and orogenesis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10624, https://doi.org/10.5194/egusphere-egu22-10624, 2022.

The ribbon-like Altai accretionary sedimentary wedge, representing the SW exteriors of the the Tuva-Mongol Orocline, suffered important Devonian and Permian deformation, metamorphism and melting. The last Permian deformation was associated with massive lower crustal melting, granulitization and lateral lower crustal flow of anatectic material. This lateral transfer was controlled by upwelling of the mantle below the extended parts of the crust. The subsequent Permian shortening led to development of a series of crustal scale detachment folds cored by migmatite-magmatite complexes and surrounded by weakly metamorphosed rocks in marginal synforms.

The current study aims to understand the geometry, kinematics and dynamics of such large scale folding in the Chinese Altai during compression of thermally softened crust confined in the Tuva-Mongol Orocline. In such a setting, the angle of convergence is progressively increasing during collision, as the curvature of the orocline increases. To visualize and quantify this process, we employed analog modeling by using paraffin wax for ductile lower crust and sand-cenosphere mixture for brittle upper crust. The model domains (60cm×70cm×3cm) are preheated for 15 hours to attain a stable initial thermal and rheological gradient. The base of the models sustains the temperature at 51 °C (the melting point for the paraffin wax) while the top part of the model is heated to 48 °C by convective air. Strain in the models is quantified from the top view using the stereoscopic digital image correlation system from Lavision GmbH. The models are shortened by movement of indenter wall driven by a step-motor. Three series of experiments were designed to simulate the above detachment folds. In the first series of models, the indenter wall is perpendicular to the shortening direction. In the second scenario, the indenter wall is initially obliquely oriented to the shortening direction. As for last scenario, the angle of convergence α (defined as the angle between the plate motion vector and the plate boundary) is continuously increased from initial 60° to 90°. This last mode mimics the effect of the closing orocline confining the thermally softened crust. All models display progressive development of an array of folds with crestal grabens that are cored by molten and partially molten wax. We describe how the style of folding, degree of strain partitioning and distribution of transcurrent movements differ between the modes of convergence.

How to cite: Shu, T., Závada, P., Krýza, O., Jiang, Y., and Schulmann, K.: Large scale detachment folding of thermally softened crust within a closing orocline in the Chinese Altai - insights from analog modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11517, https://doi.org/10.5194/egusphere-egu22-11517, 2022.

 As normal faults accumulate displacement, smearing of weaker fine-grained materials, such as clays, along their fault plane can reduce fault permeability and thus affect fluid flow in subsurface reservoirs, making clay smear development relevant for groundwater, geothermal and CO₂ storage applications. Here we use analogue experiments to investigate the potential of smearing of weaker layers along fault planes in a multi-layer sequence of granular materials.  

The natural prototype is the interbedded limestone and marl sedimentary units of the Malm formation in a quarry in southern Germany. The normal faults in the quarry have small offset (usually < 50 cm) and dip between 40° – 65° predominantly trending NE – SW. We observe discontinuous marl smearing along the fault planes, which are surrounded by deformation zones with a dense tensile fracture population. Average limestone and marl bed thicknesses on both footwall and hanging wall is 32 cm and 4.5 cm, and 33 cm and 2.5 cm respectively.

Our analogue experiments are scaled to represent layers at quarry scale. We tested several sand and gypsum plaster mixtures using empirical and ring shear methods to find cohesive strength contrasts suitable for simulating the limestone-marl sequences. The material tests show that with increasing plaster content and confining pressure, cohesion increases, while the angle of internal friction shows a non-linear behaviour for plaster/sand mixtures. We here use sand for marl layers and gypsum for limestone. We sieve the materials in a 50 x 30 cm box of which half the base plate can drop down along a prescribed angle. We analyse deformation from 2D-timelapse and 3D-CT image data, using PIV and image analysis.

Models with sand (marl) layers within gypsum (limestone) without overburden show numerous mode I fractures at the free surface with localized fault planes. Shear zones are steep with dip angles in the range of 66° - 84°. Models with overburden form shear zones with dips ranging from 65° - 83°, forming less mode I fractures, but instead mainly shear fractures that cut across each cohesive layer. Sand smearing is observed to vary in models without overburden, while it is a consistent component of the fault zones at depth in models with overburden. We find that the quantity of sand smear is a function of the thickness of the embedded sand layers. The sand pours into large openings formed between cohesive gypsum powders with simultaneous mixing of the materials during fault displacement. This process causes an accumulation of sheared granular materials along the fault zone and in turn expands the shear zone width.

The experiments with overburden show steep dipping fragmented fault zones, as well as the formation of tensile fractures that form in, and cut through cohesive beds, similar to what is observed in the quarry. Sand smearing processes of rolling and mixing in dilatant portions during displacement is however more brittle in nature than ductile smearing observed in the quarry.

How to cite: Izediunor, U., Buiter, S., and Schmatz, J.: Analogue experiments of normal fault formation in multi-layers of alternating strength, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8331, https://doi.org/10.5194/egusphere-egu22-8331, 2022.

When simulating lithosphere-scale rifting processes, analogue modellers have their model lithosphere float on top of a dense fluid representing the sub-lithospheric mantle (i.e. the asthenosphere). Such models provide crucial insights into rift evolution, but monitoring model-internal deformation has always been a major challenge. Here we present the results of new rifting experiments performed with a novel lithospheric-scale modelling machine that allows for X-ray CT-scanner, uniquely revealing the models’ internal evolution.

Our models involve a 4-layer lithosphere, with brittle layers for the competent upper crust and upper lithospheric mantel, and viscous layers for the ductile lower crust and lower lithospheric mantle. This model lithosphere is placed in a basin of glucose syrup simulating the asthenosphere and contained by mobile sidewalls. When stretching the model by moving these sidewalls apart (inducing either orthogonal or oblique extension), deformation is accompanied by syrup flow and isostatic compensation. A weakness within the upper mantle serves to localize deformation along the central axis of the model. We use photogrammetry and PIV techniques for detailed analysis of surface deformation, whereas CT imagery and PIV analysis of CT-sections provide unprecedented insights into internal model evolution.

We find that early on in orthogonal extension models, deformation initiates along the weakness in the upper mantle layer. This deformation is then transferred into the upper crust via shear zones in the lower crust, generating a dual graben structure there. In parts of the model, one of the grabens can become dominant and as extension progresses, so that a large shear zone cutting through the whole lithosphere forms (asymmetric, simple-shear rifting). In other parts of the model deformation may be more distributed so that both grabens are well-developed (symmetric, pure shear rifting). Meanwhile, the on-going stretching and thinning of the lithosphere splits the upper mantle layer, and the simulated lower mantle (and especially the asthenosphere) rises towards the model surface, bringing the lower mantle layer in contact with the lower crustal layer (i.e. necking of the lithosphere).

In oblique extension models initial deformation also localizes in the upper mantle layer, but no clear surface structures develops (except for a broad topographic depression along the central model axis). By increasing the extension velocity and thus the coupling between the upper mantle and upper crust, faulting initiated in the upper crust, creating two bands of en echelon grabens. Also in these models, we observe lithospheric necking.

Our (final stage) model results are similar to previous works. Yet the new CT-imagery provides the first-ever direct insights (both qualitative and quantitative) into the internal evolution of lithospheric-scale rift models. Furthermore, this new and versatile modelling machine in combination with our CT-scanning abilities provides a broad range of opportunities for advanced future lithospheric-scale modelling studies.

Figure: 3D CT image of an oblique extension model. UC: upper crust, LC: Lower crust, ULM: upper lithospheric mantle, LLM: lower lithospheric mantle, As: asthenosphere

How to cite: Zwaan, F. and Schreurs, G.: Lithospheric-scale experiments of continental rifting monitored in an X-Ray CT scanner, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6358, https://doi.org/10.5194/egusphere-egu22-6358, 2022.

Large offset detachment faults form with exhuming mantle-derived rocks into the seafloor at the slow and ultralow spreading ridges. However, their formation mechanism still remains partly elusive.  The thick axial lithosphere of ultraslow spreading ridges detected by seismic studies may prevent the formation of detachment faults. Previous studies have proposed that only the combination of both serpentinization and grain size reduction in the mantle lithosphere can result in detachment faults which are consistent with the natural cases. Here, through 3D self-consistent magmatic-thermomechanical numerical models with both brittle/plastic strain weakening and grain size evolution, we systematically investigate effects of these coupled brittle-ductile weakening processes on the formation of detachment faults at ultraslow spreading ridges. Numerical results show that ultraslow ridges spontaneously break into shorter and warmer magma-rich (10-20% of the ridge length) and longer and colder magma-starved segments (80-90% of the ridge length). Small grain size formed in the deep root of detachment faults near the brittle-ductile transition depth at the magma-starved amagmatic segments. Then with mantle rocks exhumation into the surface, the decreasing temperature leads to the growth of small grain size, consistent with the deformation process of detachment fault systems in the amagmatic segments of the eastern part of the Southwest Indian Ridge. Through quantitatively exploring effects of grain size reduction and strain weakening, we obtained that strain weakening may be the primary factor to control the formation of detachment faults at the ultra-slow spreading ridges, although grain size evolution can also influence the spreading pattern in case of small (<= 1 mm) initial grain size of the lithospheric mantle. Furthermore, we also found that the weak ductile domain induced by the very small initial grain size (<= 0.1 mm) promotes the formation of detachment faults in the models without grain size evolution.

How to cite: Liu, M., Rozel, A., and Gerya, T.: The effect of brittle-ductile weakening on the formation of detachment faults at ultraslow spreading ridges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2847, https://doi.org/10.5194/egusphere-egu22-2847, 2022.

The South Atlantic played a key role in the formulation of plate tectonic theory, and plate modelling has come a long way since the very first computer-assisted reconstructions of this ocean basin in the 1960s. This basin remains an active area of exploration interest as well as an excellent case study to discuss the past, present and future of plate modelling and to reflect on the reasons why discrepancies still remain, decades later, between alternative models reconstructing its geological history.

Today, high-resolution studies featuring multiple closely spaced static reconstructions give the opportunity to determine plate motions and their changes through time in more detail than ever before. They act as the foundation stones for many modern-day interpretations and simulations, providing context for regional geological and tectonic studies, and constraints for predictions of past climates, depositional environments, the evolution of stress regimes and, ultimately, the location of natural resources. Defining accurate sets of rotations that describe plate motion, as well as quantifying the uncertainties in them, is thus increasingly important.

As well as becoming more sophisticated, modelling techniques have also somewhat diversified in recent years. This is well illustrated by the fact that, for any one region on the planet, it is relatively easy to find alternative (and often irreconcilable) plate reconstructions built either on the basis of different data, different methodologies, or both. This prompts the question “how does one choose the right plate model” (and is there even such a thing as the “right” plate model). Focusing on the South Atlantic basin and using recently released version 6.0 of the Neftex plate model, I will discuss how unlocking the next generation of plate models requires implementing a global approach anchored on the principles of geodynamics.

How to cite: Perez Diaz, L.: From deep time to the future: unlocking the next generation of plate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9952, https://doi.org/10.5194/egusphere-egu22-9952, 2022.

EPOS, the European Plate Observing System, is a unique e-infrastructure and collaborative environment for the solid earth science community in Europe and beyond (https://www.epos-eu.org/). 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) (https://www.epos-eu.org/tcs/multi-scale-laboratories). Setting up mechanisms allowing for sharing metadata, data, and experimental facilities has been the main target achieved during the EPOS implementation phase. The TCS Multi-scale Laboratories offers coordination of the laboratories’ network, data services, and Trans-National access to laboratory facilities.

In the framework of data services, TCS Multi-Scale Laboratories promotes FAIR (Findable-Accessible-Interoperable-Re-Usable) (FAIR) sharing of experimental research data sets through Open Access data publications. Data sets are assigned with digital object identifiers (DOI) and are published under the CC BY license. Data publications are now conventionally citable in scientific journals and develop rapidly into a common bibliometric indicator and research metric. A dedicated metadata scheme (following international standards that are enriched with disciplinary controlled community vocabulary) facilitates ease exploration of the various data sets in a TCS catalogue (https://epos-msl.uu.nl/). Concerning analogue modelling, a growing number of data sets includes analogue material physical and mechanical properties and modelling results (raw data and processed products such as images, maps, graphs, animations, etc.) as well as software (for visualization, monitoring and analysis). The main geoscience data repository is currently GFZ Data Services, hosted at GFZ German Research Centre for Geosciences (https://dataservices.gfz-potsdam.de), but others are planned to be implemented within the next years.

In the framework of Trans-National access (TNA), TCS Multi-scale laboratories’ facilities are accessible to any researchers, creating new opportunities for synergy, collaboration and scientific innovation, according to TNAtrans-national access rules. TNA can be realized in the form of physical access (on-site experimenting and analysis), remote service (sample analysis) and virtual access (remotely operated processing). After three successful TNA calls, the pandemic has forced a moratorium on the TNA program.

The EPOS TCS Multiscale Laboratories framework is also providing the foundation for a comprehensive database of rock analogue materials, a dedicated bibliography, and facilitates the organization of community-wide activities (e.g., meetings, benchmarking) to stimulate collaboration among analogue laboratories and the exchange of know-how. Recent examples of these community efforts are also the contributions to the monthly MSL seminars, available on the MSL YouTube channel (https://www.youtube.com/channel/UCVNQFVql_TwcSBqgt3IR7mQ/featured), as well as the Special Issue on basin inversion in Solid Earth that is currently open for submissions  (https://www.solid-earth.net/articles_and_preprints/scheduled_sis.html#1160). 

How to cite: Funiciello, F., Rosenau, M., Dominguez, S., Willingshofer, E., ter Maat, G., Zwaan, F., Corbi, F., Eisermann, J. O., Guillaume, B., Souloumiac, P., Brizzi, S., Mastella, G., Reitano, R., Druguet, E., Schreurs, G., and Faccenna, C. and the EPOS Multi-Scale Laboratories Team: Sharing data and facilities in the analogue modelling community: the EPOS Multi-Scale Laboratories Thematic Core Service, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4212, https://doi.org/10.5194/egusphere-egu22-4212, 2022.

Inverted structures are some of the economically most important geological features worldwide. Besides their most common manifestation as traps for hydrocarbons, they are also interesting for the storage of CO₂ and extraction of other resources such as heat, minerals or hydrogen. Analogue modelling is frequently used to understand the long-term geological evolution of basins and basin inversion as an addition to numerical and mathematical models. Most analogue models use granular materials, like sands and glass beads, to simulate the brittle-plastic rheology of the crust. The main driving mechanism for basin inversion, both in nature and analogue models is the reactivation of pre-existing structures. This is due to strain-dependent weakening which leads to a reduced strength of a fault or shear zone in comparison with the surrounding bulk material. If the structure comes to a rest, several mechanisms lead to a time-dependent restrengthening of the structure. Therefore, older structures are usually more resistant to reactivation than younger ones, in the same material. In this study we use an annular shear tester to quantify the healing of granular materials commonly used for analogue models. We take advantage of a large collection of analogue material samples at the Helmholtz Laboratory for Tectonic Modelling, coming from many laboratories worldwide. To estimate granular healing, we employ slide-hold-slide tests with hold times comparable to typical analogue models of basin inversion. We show that all materials tested exhibit healing which follows a power-law relation quantified by with a healing rate. For example, fused glass microbeads showed a healing rate of 0.025 per decade in hold time. This means that for a tenfold increase in hold time the strength required to reactivate the given fault increases by 2.5%. Consequently, if a fault is inactive for a longer period of time, it is slightly stronger in comparison with a fault with shorter inactivity. Comparing the healing exponent for several materials reveals that some materials show a stronger healing than others. Glass beads have a stronger healing than sands, with quartz sands having lower healing rates than garnet or feldspar sands. Geomechanical tests on natural materials (quartz and gypsum fault gouges) and measurements of seismic velocities across fault zones suggest that healing obeys a similar power law. The healing rates in real rocks are roughly equal or higher depending on the temperature and water saturation of the fault. Albeit small, this change in reactivation strength for analogue materials might have a strong influence on the structural style of inversion if the models are run with different timespans between extensional phase and compressional phase. With a typical range of experimental time-spans of a view seconds to several hours this may result in up to 10% difference in reactivation strength similar to the difference between static and dynamic friction. This becomes especially relevant, if the angles of the formed pre-existing structures are close to the angle of internal friction of the bulk material which is the default in models where reactivated structures have been formed self-consistently in a pre-inversion phase.

How to cite: Rudolf, M., Rosenau, M., and Oncken, O.: Influence of Time-dependent Healing on Reactivation of Granular Shear Zones in analogue models: A Community Benchmark, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1670, https://doi.org/10.5194/egusphere-egu22-1670, 2022.

Dynamically scaled experiments allow the direct comparison of geometrical, kinematical and mechanical processes between model and nature. The geometrical scaling factor defines the model resolution, which depends mainly on the density and cohesive strength ratios of model material and natural rocks. Granular materials such as quartz sands are ideal for the simulation of upper crustal deformation processes as a result of similar nonlinear deformation behaviour of granular flow and brittle rock deformation. We compared the geometrical scaling factor of common analogue materials applied in tectonic models and identified a gap in model resolution corresponding to the outcrop and structural scale (1–100 m).

In this study, we present a new granular rock-analogue material (GRAM) with a dynamic scaling suitable for the simulation of fault and fracture processes in analogue experiments. The proposed material is composed of silica sand and hemihydrate powder and is suitable to form cohesive aggregates capable of deforming by tensile and shear failure under variable stress conditions. Based on dynamical shear tests, GRAM is characterized by a similar stress-strain curve as dry silica sand, has a cohesive strength of 7.88 kPa and an average density of 1.36 g cm⁻³. The derived geometrical scaling factor is 1 cm in model = 10.65 m in nature. For a large-scale test, GRAM material was applied in strike-slip analogue experiments. Early results demonstrate the potential of GRAM to simulate fault and fracture processes, and their interaction in fault zones and damage zones during different stages of fault evolution in dynamically scaled analogue experiments.

How to cite: Massaro, L., Adam, J., Jonade, E., and Yamada, Y.: New granular rock-analogue materials for simulation of multi-scale fault and fracture processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10156, https://doi.org/10.5194/egusphere-egu22-10156, 2022.

Crustal deformation occurs both as localized slip along faults and distributed deformation off faults; however, we have few robust geologic estimates of off-fault deformation over multiple earthquake cycles. Scaled physical experiments simulate crustal strike-slip faulting and allow direct measurement of the ratio of fault slip to regional deformation, quantified as Kinematic Efficiency (KE). We offer an approach for KE prediction using a 2D Convolutional Neural Network (CNN) trained directly on images of fault maps produced by physical experiments of strike-slip loading of wet kaolin. A suite of experiments with different loading rate and basal boundary conditions, contribute over 13,000 fault maps throughout strike-slip fault evolution. Strain maps allow us to directly calculate KE and its uncertainty, utilized in the loss function and performance metric. The trained CNN achieves 91% accuracy in KE prediction of an unseen dataset. We then apply this CNN trained on wet kaolin experiments to strike-slip experiments in dry sand. The different rheology of sand and kaolin may lead to different relationships between fault geometry and off-fault deformation, which can be detected by differences in the predictive power of the CNN trained only on kaolin.  We also apply the trained CNN to crustal maps of off-fault deformation over coseismic, 10ka and 1 Ma time scales. The CNN predicted off-fault deformation overlap available geologic estimates.

How to cite: Cooke, M., Elston, H., Chaipornkaew, L., Visage, S., Souloumniac, P., and Mukerji, T.: Prediction of Off-Fault Deformation from Strike-slip Fault Structures in clay and sand experiments using Convolutional Neural Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3265, https://doi.org/10.5194/egusphere-egu22-3265, 2022.

Transform faults and non-transform offsets define the bounds of mid-ocean ridge spreading segments, but tectonic and magmatic controls on the length of segments and the morphology of intervening offsets are poorly understood. A general observation at intermediate and slow-spreading oceanic environments is that localized strike-slip motion along transform faults tends to occur on larger offsets in space or crustal age, whereas more diffuse deformation at non-transform zones occurs at shorter offsets distances. In addition, variables such as lithospheric thickness, the size and spacing of faults, and the fraction (M) of extension accommodated by magmatic accretion (rather than faulting) are known to influence the overall morphology of the ridge segment and its vicinity. We hypothesize that the decrease in the amount of magmatic extension along the ridge segment towards the discontinuity along with the ridge segment offset play a role in defining the transition between transform and non-transform offsets.

In this study, we employ a 3D-numerical model to investigate how the relative amounts of fault- or magma-accommodated spreading and distance offset (D) between ridge segments control the development of transform versus non-transform offsets. Our model employs a ridge-like initial temperature structure, with magma intrusion simulated by adding a divergence to the right-hand-side of the continuity equation within a magmatic accretion zone at the ridge axis. M, the fraction of magmatically compensated spreading inside the magmatic accretion zone, can be varied along strike. By using a visco-elasto-plastic formulation the model can simulate the spontaneous formation and evolution of normal faults that accommodate part of the spreading. The temperature field is allowed to evolve and the model accounts for an increased, temperature-dependent conductivity around each ridge segment. We vary both the offset distance D separating two axes of magmatic accretion as well as the length L over which M decreases along the ridge axes towards the discontinuity. We find that increasing L leads to non-transform offsets, particularly for small offset distances D. As D increases, the occurrence of the offset zone is less prominently dominated by L. Depending on M, the style of faulting differs along the magmatic segments. While for M>0.5 we observe migrating faults creating topography similar to abyssal hills, values for M that are smaller or equal to 0.5 lead to stationary faults which are located closer to the ridge axis. 

How to cite: Schierjott, J., Ito, G., Behn, M., Morrow, T., Tian, X., and Kaus, B.: Transform versus non-transform offsets controlled by offset length and the variation in magmatic accretion within the offset zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8822, https://doi.org/10.5194/egusphere-egu22-8822, 2022.

Primary inclusions in natural diamonds provide unique information about deep-seated mantle minerals and fluids. Findings of the VI and VII modifications of H₂O-ice as inclusions in diamonds show the presence of aqueous fluids at different depths in the diamond-bearing mantle (Kagi et al., 2000; Tschauner et al., 2018). In this work, we apply various experimental techniques for the investigation of mineral associations and H₂O phases, captured as inclusions in diamonds, in the pressure range from 4 to 8 GPa and at temperatures from 500 °C to 1250 °C. In situ observations using diamond anvil cell (DAC) technique revealed crystallization of ice VII in association with ilmenite and olivine minerals upon cooling from 890 °C at 4 GPa, in agreement with the data, obtained from natural samples by Tschauner et al. (2018). Heating of this assemblage to 1200 °C at 6 GPa results in the formation of another mineral association, which includes ilmenite, pyroxene and clinohumite. Obtained experimental results can be used to reconstruct the pressure and temperature conditions of mineral and fluid inclusions capturing upon diamond growth and transfer in the lithosphere.  

This work was supported by grant No. 20-77-00079 from the Russian Science Foundation.

How to cite: Chertkova, N., Spivak, A., Burova, A., Zakharchenko, E., Litvin, Y., Safonov, O., and Bobrov, A.: Experimental study on the conditions of inclusions capturing during diamond growth in the upper mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10849, https://doi.org/10.5194/egusphere-egu22-10849, 2022.