Agnes Kiraly

• Király, Ágnes; Wang, Yijun; Conrad, Clinton P; Hansen, Lars N & Mather, Ben (2026). CPO2Hill: An Efficient Parametrisation to Infer Anisotropic Viscous Behaviour Directly from Olivine Texture Parameters. Geodynamica. 1(1). doi: 10.5070/f3.49008. Full text in Research Archive Show summary

  Anisotropic viscosity is likely prevalent within the upper mantle, but is usually disregarded in geodynamics models. On a crystal scale, olivine’s intrinsic properties are such that dislocation creep occurs over an order of magnitude more easily along olivine’s [100] symmetry axis than along its [001] axis. However, deforming olivine aggregates generate crystallographic preferred orientations (CPO) with their own macroscopically effective anisotropic viscosities that have proven difficult to estimate from the microscopic anisotropies of individual olivine crystals. Here we present a simple method to derive anisotropic viscosity parameters directly from the CPO mean orientation tensors. To calibrate the method, we created a large database of textures likely to occur in geodynamic simulations. We tested our method within numerical simulations of simple shear with both constant and varying shear directions. Finally, we integrated our method into the geodynamic code ASPECT, where it can be used to explore the geodynamic importance of anisotropic viscosity.

• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips & Maupin, Valerie (2025). Mantle Flow and Anisotropy in Subduction Zones: Modeling and Clustering of Olivine Textures. Geochemistry Geophysics Geosystems. 26(7). doi: 10.1029/2025gc012160. Full text in Research Archive Show summary

  The mantle near Earth's subduction zones endures intense deformation that generates anisotropic rock textures. These textures can be observed seismically and modeled geodynamically, but the complexity of this deformation makes analyses of these textures difficult. In this study, we apply time‐series clustering analysis to tracers within subduction models, allowing for the identification of regions in the subduction zone with common deformation histories and olivine crystallographic‐preferred orientation development. We compare olivine texture evolution predicted using different methods in both retreating and stationary‐trench settings. Our results reveal distinct variations in olivine texture, indicating that both seismic and viscous anisotropy can exhibit substantial heterogeneity within the mantle wedge, sub‐slab, and subducting plate regions. For retreating trenches, olivine textures are strongest in the mid‐depth mantle wedge region about 200 km away from the trench between 100 and 300 km depth. Our study shows that trench‐normal olivine a ‐axis orientations dominate in the center of subduction zones. Toroidal flow around slab edges generates a mix of trench‐normal, trench‐parallel, and oblique fast seismic directions. Textures and anisotropy are stronger for the retreating trench model than for the stationary trench model since more deformation has been accumulated due to trench motion. These findings provide insights for interpreting seismic anisotropy in subduction zones and highlight the importance of considering texture heterogeneity, as characterized by clustering algorithms, when analyzing both geodynamic models and seismic observations of subduction zones.

• Tari, Gábor; Bada, Gábor; Kiraly, Agnes; Koroknai, Balázs; Kovács, Gábor & Lemberkovics, Viktor [Show all 7 contributors for this article] (2024). The Pannonian Basin: regional geology of a back-arc basin. In Chiarella, Domenico; Scarselli, Nicola & Adam, Jürgen (Ed.), Regional Geology and Tectonics Volume 2: Phanerozoic Rift Systems and Sedimentary Basins. Elsevier. ISSN 9780444641366. p. 1–25. doi: 10.1016/B978-0-444-64136-6.00005-1. Full text in Research Archive Show summary

  The Neogene Pannonian Basin has been described as the type example of a Mediterranean back-arc basin where extension did not advance to the opening of an oceanic basin. Due to the removal from the Alpine collision zone, the over thickened lithosphere of the Pannonian region collapsed during the Middle Miocene. The inherited Alpine contractional structural fabric frequently influenced the various styles of syn-rift extension by negative structural inversion. In some of the subbasins of this large basin complex, the geodynamic style of Neogene extensional deformation almost reached the stage of hyperextension but it stopped short of exhuming lower crustal or mantle units at the basin floor. Continental extension terminated due to the space constraints provided by the docking of the surrounding Carpathian thrust-fold belt onto various divergent and transform margin segments of the European plate. The Late Miocene to Pliocene postrift thermal subsidence saw the sedimentation of an unusually thick basin fill local

• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Fraters, Menno (2024). The Importance of Anisotropic Viscosity in Numerical Models, for Olivine Textures in Shear and Subduction Deformations. Tektonika. 2(1), p. 157–173. doi: 10.55575/tektonika2024.2.1.67. Full text in Research Archive Show summary

  Olivine lattice preferred orientation (LPO), or texture, forms in relation to deformation mechanisms such as dislocation creep and can be observed in the upper mantle as seismic anisotropy. Olivine is also mechanically anisotropic, meaning that it responds to stresses differently depending on the direction of the stress. Understanding the interplay between anisotropic viscosity (AV) and LPO, and their role in deformation, is necessary for relating seismic anisotropy to mantle flow patterns. In this study, we employ three methods to predict olivine texture (D-Rex, MDM, and MDM+AV) in a shear box model and a subduction model. D-Rex and MDM are two representative texture development methods that have been compared before, and our results are in line with previous studies showing that textures computed by D-Rex develop faster and are stronger and more point-like than textures calculated with MDM. MDM+AV uses the same isotropic mantle stresses and particle paths as D-Rex and MDM but includes the effect of AV for texture predictions. MDM+AV predicts a texture similar to MDM with a distinct girdle-like orientation for simple shear deformation or at low strain in the subduction model. At larger strains, MDM+AV’s textures are more point-like and stronger compared to the other two methods. The effective viscosity for MDM+AV drops by up to 60% in a shear box model and can be either strengthened or weakened relative to isotropic viscosity for different regions of the subduction model experiencing different patterns of deformation. Our results emphasize the significant role of AV in olivine texture development, which could substantially affect geodynamic processes in the upper mantle.

• Magni, Valentina; Kiraly, Agnes; Lynner, Colton; Avila, Pilar & Gill, James (2024). Mantle flow in subduction systems and its effects on surface tectonics and magmatism. Nature Reviews Earth & Environment. 6, p. 51–66. doi: 10.1038/s43017-024-00612-3. Full text in Research Archive Show summary

  Mantle flow triggered by subduction has a crucial role in the evolution of surface tectonics and volcanism. In this Review, we explore how patterns of mantle flow, particularly those in the upper mantle, evolve in response to subduction dynamics and cause surface topographic expressions. Poloidal flow in front of the slab (often called corner flow) is the main way new asthenospheric mantle is bought upwards into the mantle wedge. Toroidal flow around slab edges causes lateral mantle to flow from behind or adjacent to the slab edge towards the mantle wedge, for instance, at the Calabrian subduction zone under Etna. If accompanied by upwelling, toroidal flow can reach shallow depths and be traced in the geochemistry of volcanic rocks at the surface. Differential rates of trench retreat, the formation of slab windows and tears, and the switch from flat subduction to a steep dip angle can all cause increased asthenospheric input into the wedge, leading to distinct volcanism and topographic expressions at the surface. However, linking specific contributions of mantle flow to observed changes in dynamic topography is often difficult to distinguish from other crustal and lithospheric scale processes. To help distinguish the diverse expressions of mantle flow, future research should continue to iteratively update numerical and analogue models of mantle flow with emerging geological, geochemical and geophysical observations.

• Gallo, Leandro Cesar; Domeier, Mathew Michael; Sapienza, F.; Swanson-Hysell, N. L.; Vaes, B. & Zhang, Y. [Show all 14 contributors for this article] (2023). Embracing Uncertainty to Resolve Polar Wander: A Case Study of Cenozoic North America. Geophysical Research Letters. ISSN 0094-8276. 50(11). doi: 10.1029/2023GL103436. Full text in Research Archive Show summary

  Abstract Our understanding of Earth's paleogeography relies heavily on paleomagnetic apparent polar wander paths (APWPs), which represent the time‐dependent position of Earth's spin axis relative to a given block of lithosphere. However, conventional approaches to APWP construction have significant limitations. First, the paleomagnetic record contains substantial noise that is not integrated into APWPs. Second, parametric assumptions are adopted to represent spatial and temporal uncertainties even where the underlying data do not conform to the assumed distributions. The consequences of these limitations remain largely unknown. Here, we address these challenges with a bottom‐up Monte Carlo uncertainty propagation scheme that operates on site‐level paleomagnetic data. To demonstrate our methodology, we present an extensive compilation of site‐level Cenozoic paleomagnetic data from North America, which we use to generate a high‐resolution APWP. Our results demonstrate that even in the presence of substantial noise, polar wandering can be assessed with unprecedented temporal and spatial resolution.

• Kiraly, Agnes; Funiciello, Francesca; Capitanio, Fabio A. & Faccenna, Claudio (2021). Dynamic interactions between subduction zones. Global and Planetary Change. ISSN 0921-8181. 202. doi: 10.1016/j.gloplacha.2021.103501. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips & Hansen, Lars N. (2020). Evolving Viscous Anisotropy in the Upper Mantle and Its Geodynamic Implications. Geochemistry Geophysics Geosystems. 21(10). doi: 10.1029/2020GC009159. Full text in Research Archive Show summary

  Asthenospheric shear causes some minerals, particularly olivine, to develop anisotropic textures that can be detected seismically. In laboratory experiments, these textures are also associated with anisotropic viscous behavior, which should be important for geodynamic processes. To examine the role of anisotropic viscosity for asthenospheric deformation, we developed a numerical model of coupled anisotropic texture development and anisotropic viscosity, both calibrated with laboratory measurements of olivine aggregates. This model characterizes the time‐dependent coupling between large‐scale formation of lattice‐preferred orientation (i.e., texture) and changes in asthenospheric viscosity for a series of simple deformation paths that represent upper mantle geodynamic processes. We find that texture development beneath a moving surface plate tends to align the a axes of olivine into the plate motion direction, which weakens the effective viscosity in this direction and increases plate velocity for a given driving force. Our models indicate that the effective viscosity increases for shear in the horizontal direction perpendicular to the a axes. This increase should slow plate motions and new texture development in this perpendicular direction and could impede changes to the plate motion direction for tens of millions of years. However, the same well‐developed asthenospheric texture may foster subduction initiation perpendicular to the plate motion and deformations related to transform faults, as shearing on vertical planes seems to be favored across a sublithospheric olivine texture. These end‐member cases examining shear deformation in the presence of a well‐formed asthenospheric texture illustrate the importance of the mean olivine orientation, and its associated viscous anisotropy, for a variety of geodynamic processes.

• Kiraly, Agnes; Portner, Daniel E.; Haynie, Kirstie L.; Chilson-Parks, Benjamin H.; Ghosh, Tithi & Jadamec, Margarete [Show all 10 contributors for this article] (2020). The effect of slab gaps on subduction dynamics and mantle upwelling. Tectonophysics. ISSN 0040-1951. 785. doi: 10.1016/j.tecto.2020.228458. Full text in Research Archive Show summary

  Gaps within a subducting plate can alter the surrounding mantle flow field and the overall subduction zone dynamics by allowing hot sub-slab mantle to flow through the gaps and into the mantle wedge. This through-slab flow can produce melting of the slab gap edges as well as significant upwelling that can lead to anomalous alkaline volcanism and/or dynamic uplift in the overriding plate, while the altered mantle flow patterns affect the trench evolution. Numerous geodynamic models have investigated the processes that form slab gaps, but few studies have examined the dynamics of slab gap-altered mantle flow, its effects on trench morphology and kinematics, or the controlling parameters on these processes. Here, laboratory subduction models with a pre-cut gap in a subducting silicone plate are used to explore how slab gap size, and slab gap depth influence the surrounding mantle flow field and trench dynamics. Results suggest that both the vertical extent and the depth of the top (trailing edge) of the slab gap are crucial parameters for modulating overall subduction dynamics. They show that a slab gap, which occurs near the surface and initially comprises 30% of the subducting plate width, can extend enough vertically in the slab to produce significant vertical flow through the gap. Changes to the trench geometry and kinematics are also evident in the models, such that double- and triple-arc geometries are formed during subduction of a shallow slab gap. All of these results are consistent with observations of slab gaps and their induced surface expressions, or the lack thereof, in Eastern Anatolia, East Java, Italy, and Argentina.

• Crameri, Fabio; Magni, Valentina; Domeier, Mathew; Shephard, Grace Elizabeth; Chotalia, Kiran & Cooper, George [Show all 14 contributors for this article] (2020). A transdisciplinary and community-driven database to unravel subduction zone initiation. Nature Communications. 11. doi: 10.1038/s41467-020-17522-9. Full text in Research Archive Show summary

  Subduction zones are pivotal for the recycling of Earth’s outer layer into its interior. However, the conditions under which new subduction zones initiate are enigmatic. Here, we constructed a transdisciplinary database featuring detailed analysis of more than a dozen documented subduction zone initiation events from the last hundred million years. Our initial findings reveal that horizontally forced subduction zone initiation is dominant over the last 100 Ma, and that most initiation events are proximal to pre-existing subduction zones. The SZI Database is expandable to facilitate access to the most current understanding of subduction zone initiation as research progresses, providing a community platform that establishes a common language to sharpen discussion across the Earth Science community.

• Magni, Valentina & Kiraly, Agnes (2019). Delamination, Encyclopedia of Ecology. Reference Module in Earth Systems and Environmental Sciences. Elsevier. ISSN 9780124095489. doi: 10.1016/B978-0-12-409548-9.09515-4. Full text in Research Archive
• Peral, Mireia; Kiraly, Agnes; Zlotnik, Sergio; Funiciello, Francesca; Fernandez, Manel & Faccenna, Claudio [Show all 7 contributors for this article] (2018). Opposite Subduction Polarity in Adjacent Plate Segments. Tectonics. ISSN 0278-7407. 37(9), p. 3285–3302. doi: 10.1029/2017TC004896. Full text in Research Archive Show summary

  Active and fossil subduction systems consisting of two adjacent plates with opposite retreating directions occur in several areas on Earth, as the Mediterranean or Western Pacific. The goal of this work is to better understand the first‐order plate dynamics of these systems using the results of experimental models. The laboratory model is composed of two separate plates made of silicon putty representing the lithosphere, on top of a tank filled with glucose syrup representing the mantle. The set of experiments is designed to test the influence of the width of plates and the initial separation between them on the resulting trench velocities, deformation of plates, and mantle flow. Results show that the mantle flow induced by both plates is asymmetric relative to the axis of each plate causing a progressive merging of the toroidal cells that prevents a steady state phase of the subduction process and generates a net outward drag perpendicular to the plates. Trench velocities increase when trenches approach each other and decrease when they separate after their intersection. The trench curvature of both plates increases linearly with time during the entire evolution of the process regardless their width and initial separation. The interaction between the return flows associated with each retreating plate, particularly in the interplate region, is stronger for near plate configurations and correlates with variations of rollback velocities. We propose that the inferred first‐order dynamics of the presented analog models can provide relevant clues to understand natural complex subduction systems.

• Kiraly, Agnes; Holt, Adam; Funiciello, Francesca; Faccenna, Claudio & Capitanio, Fabio A. (2018). Modeling Slab‐Slab Interactions: Dynamics of Outward Dipping Double‐Sided Subduction Systems. Geochemistry Geophysics Geosystems. 19(3), p. 693–714. doi: 10.1002/2017GC007199. Full text in Research Archive Show summary

  Slab‐slab interaction is a characteristic feature of tectonically complex areas. Outward dipping double‐sided subduction is one of these complex cases, which has several examples on Earth, most notably the Molucca Sea and Adriatic Sea. This study focuses on developing a framework for linking plate kinematics and slab interactions in an outward dipping subduction geometry. We used analog and numerical models to better understand the underlying subduction dynamics. Compared to a single subduction model, double‐sided subduction exhibits more time‐dependent and vigorous toroidal flow cells that are elongated (i.e., not circular). Because both the Molucca and Adriatic Sea exhibit an asymmetric subduction configuration, we also examine the role that asymmetry plays in the dynamics of outward dipping double‐sided subduction. We introduce asymmetry in two ways; with variable initial depths for the two slabs (“geometric” asymmetry), and with variable buoyancy within the subducting plate (“mechanical” asymmetry). Relative to the symmetric case, we probe how asymmetry affects the overall slab kinematics, whether asymmetric behavior intensifies or equilibrates as subduction proceeds. While initial geometric asymmetry disappears once the slabs are anchored to the 660 km discontinuity, the mechanical asymmetry can cause more permanent differences between the two subduction zones. In the most extreme case, the partly continental slab stops subducting due to the unequal slab pull force. The results show that the slab‐slab interaction is most effective when the two trenches are closer than 10–8 cm in the laboratory, which is 600–480 km when scaled to the Earth.

• Kiraly, Agnes; Faccenna, Claudio & Funiciello, Francesca (2018). Subduction zones interaction around the Adria microplate and the origin of the Apenninic arc. Tectonics. ISSN 0278-7407. 37(10), p. 3941–3953. doi: 10.1029/2018TC005211. Full text in Research Archive

View all works in NVA

• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips & Maupin, Valerie (2025). Subduction dynamics and mantle anisotropy: modeling and clustering of olivine textures. Full text in Research Archive Show summary

  The mantle near Earth's subduction zones experiences significant deformation, forming anisotropic rock textures. These textures can be detected using seismic methods and simulated in geodynamic models. This study employs time-series clustering to examine tracers in subduction models, identifying regions with similar deformation histories, olivine crystallographic-preferred orientation (CPO) development, and CPO-induced anisotropic viscosity. We compare the evolution of olivine textures predicted by various numerical methods (e.g. D-Rex, MDM, and MDM+AV) for both retreating and stationary trench subduction settings. Our modeling shows notable variations in olivine texture around the slab and as a function of subduction dynamics. These variations, which are illuminated by the clustering analysis, show that texture, seismic, and viscous anisotropy can vary greatly within the mantle wedge, sub-slab, and subducting plate regions of the upper mantle. In the retreating-trench model, the strongest textures are observed in the mid-depth mantle wedge region and beneath the slab at the 660 km transition zone. Trench-normal olivine a-axis orientations are predominant in the center of subduction zones, while toroidal flow around slab edges produces a mix of trench-normal, trench-parallel, and oblique fast seismic directions. On the other hand, in the stationary-trench model, the trench-normal signal in front of the slab is weaker while there are stronger trench-normal signals behind the slab at shallow depths between 100 and 300 km. At the edge of the slab, weak toroidal flow produces trench-oblique orientations while trench-parallel and trench-normal orientations are missing. In general, the retreating trench model exhibits stronger textures and anisotropy due to increased deformation from trench motion. These results provide valuable insights into seismic anisotropy in subduction zones and underscore the importance of considering texture heterogeneity when interpreting geodynamic models and seismic data. The use of time-series clustering algorithms highlights the intricate pattern of evolution and the relationship between deformation history, CPO, and CPO-induced viscous anisotropy occurring within subduction zones.

• Menichelli, Irene; Funiciello, Francesca; Faccenna, Claudio; Kiraly, Agnes & Chiarabba, Claudio (2025). A New Perspective on Circum-Mediterranean Orogens: Insights from Seismic Imaging and Analog Models. Full text in Research Archive Show summary

  The central Mediterranean serves as a natural laboratory for studying various geodynamic processes, including continental collision and oceanic subduction (Dewey et al., 1989; Royden and Faccenna, 2018). The orogenic belts in this unique region are exceptional examples of subduction-related systems, shaped by different processes, such as continental underplating, delamination, trench retreat, among others. Despite extensive research on the Alps-Apennines-Dinarides-Hellenides orogenic systems, several scientific debates remain unresolved, highlighting the complexity of this area. Previous studies using tomographic imaging have revealed the presence of high-velocity anomalies beneath these orogenic belts, which suggest the occurrence of a subduction process (e.g., Piromallo and Morelli, 2003; Giacomuzzi et al., 2012; Paffrath et al., 2021). However, these findings often differ, leading to varying interpretations of slab dip directions, geometry and extension as resolved by tomographs. Additionally, features such as slab windows, gaps, and tears, imaged as low-velocity anomalies in various models, add further complexity to the geodynamic picture. In this study, we integrate seismic imaging (Menichelli et al., 2023) with analogue modelling (Funiciello et al., 2003; Kiraly et al., 2018, 2020) to showcase the strengths of this combined approach. While tomographic models provide valuable insights into the lithospheric and mantle velocity structures, they only offer a static snapshot without revealing the deep dynamics—something that analogue modelling addresses. This approach has been specifically applied to the central Mediterranean to target ongoing questions about the subduction processes that have shaped the region. This method offers valuable insights into subduction, mantle dynamics, and plate interactions, providing a comprehensive understanding of the connections between shallow and deep geodynamic processes. This presentation will provide a brief overview of the results obtained from the computation of the 3D tomographic model of the central Mediterranean (Menichelli et al., 2023), with a specific focus on the Alps and the Apennines-Dinarides system. The tomographic images and related findings show how lithospheric composition, rheology and fluid content influence the geometry and kinematics of the slabs, including the Adriatic slab, that lie beneath these mountain ranges. Additionally, these aspects have been investigated through experimental models conducted at Roma Tre University (Laboratory of Experimental Tectonics), which offer critical insights into their role in shaping current deformation processes.

• Kiraly, Agnes; Wang, Yijun; Conrad, Clinton Phillips; Dannberg, Juliane; Fraters, Menno & Gassmoeller, Rene [Show all 7 contributors for this article] (2025). ANIMA the journey: how we model olivine CPO-related anisotropic viscosity. Full text in Research Archive Show summary

  The long-term fluid-like movements in the Earth’s mantle largely depend on the rheological behaviour of olivine, the main rock-forming mineral in the upper mantle. Although the average viscosity of the mantle can be estimated from post-glacial rebound or geoid anomalies, the micromechanical mechanisms that facilitate the deformation of the solid mantle have been identified from rock mechanics experiments. Dislocation creep emerges as the predominant deformation mechanism in the uppermost mantle, aligning olivine crystals into a crystallographic preferred orientation (CPO) parallel to the flow, while this alignment of crystals also results in anisotropic viscous behaviour. Thus, anisotropic viscosity and CPO evolve hand in hand, and this interaction may impact many geodynamic processes. For example, beneath tectonic plates CPO evolves parallel to the plate motion direction, weakening the asthenosphere in that direction. However, if the plate motion direction changes, the asthenosphere will resist this change, leading to smaller velocities, less deformation and therefore a slow evolution of the CPO towards the new plate motion direction. In the ANIMA project, we aimed to find an efficient way of modelling CPO evolution and the related anisotropic viscosity in a fully coupled way within a geodynamic simulation. We developed a method that tracks CPO evolution on advected particles based on the D-REX method and utilizes the eigenvalues of the mean CPO orientation matrices to predict the anisotropic viscous parameters. These parameters allow us to calculate a tensor form of the viscosity, which we then feed back into our model solution. This method can be applied in combination with other rheologies, although with a cost of having to represent the viscosity as a tensor in the entire model domain, regardless of the dominant deformation mechanism. Despite an estimated increase in computational cost by up to an order of magnitude, incorporating anisotropic viscosity coupled to CPO evolution stands feasible for regional geodynamic models. This development will facilitate the study of a broad new range of geodynamics problems that involve olivine texture and anisotropic viscosity.

• Crosetto, Silvia; Kiraly, Agnes; Brizzi, Silvia; Funiciello, Francesca & Faccenna, Claudio (2025). To tear or not to tear? A comparison between analogue modelling and field observations along the Kefalonia Transform Fault System. Full text in Research Archive Show summary

  The Central Mediterranean is a great natural laboratory for many processes related to subduction. Along the Dinaric-Hellenic margin, the rigid Adria microplate indents the Eastern Alps and Dinarides in the north, while the southern part subducts beneath the advancing Hellenides. The Kefalonia Transform Fault System (KTFS) marks the current position of this unique transition between subduction of more buoyant continental lithosphere and less buoyant oceanic lithosphere. The resulting differential convergence is thought to have caused vertical tearing or bending of the subducting slab, although the lack of detailed seismological investigations leaves an open question concerning this geometry. Slab tears have a significant role in surface evolution around subduction zones. They affect mantle flow, stress propagation within the subducting plate, as well as dynamic topography and volcanism on the surface. However, most models of slab tears investigate their evolution by pre-cutting the subducting lithosphere. We investigated the mechanisms underlying the dynamic formation of a vertical slab tear to interpret geodetic, tomographic, and tectonic observations from around the KTFS. To achieve this, we built a setup with a geometry inspired by the natural subduction system, varied the continental domain's rheology, and introduced an ocean-continent transition zone composed of non-Newtonian analogue materials that allow for strain localisation and slab detachment. In particular, we wanted to: i) explore how the subducting plate deforms when a tear is forming; ii) observe how the mantle flow reacts to such changes in subduction dynamics; iii) estimate what are the resulting effects on the stress distribution and surface strain on the overriding plate. We analysed two experimental end-members (i.e., model (A) ocean and continent in lateral contact Vs model (B) separated by non-Newtonian, transitional material) and compared them with the natural observations and the geometry of the subduction system. In both models the rigidity of the continental segment has a critical role in the type of deformation we observe during continental subduction, and controls the amount of stretching, rotation, and continental subduction. The transition zone in model (B) localises deformation, minimising shear and extensional deformation of the continent. At the end of the experiment, the subduction front geometry of model (B) better reproduces the actual eastern Adriatic margin in correspondence of the KTFS, and the deformation observed on the continental plate is consistent with the structures observed on the field, indicating a certain level of coupling between slab and overriding plate. This similarity without achieving slab tearing suggests that a slab bend may be sufficient to reach the present natural configuration. Consequently, a slab tear may be absent or its extent be limited to a deeper section of the slab.

• Wang, Yijun; Kiraly, Agnes & Conrad, Clinton Phillips (2024). Implementation of anisotropic viscosity in ASPECT. Full text in Research Archive
• Torgersen, Eivind & Kiraly, Agnes (2024). Isen i Antarktis og de flytende bergartene inne i jorda har et overraskende fellestrekk. [Journal]. https://www.titan.uio.no/naturvitenskap/2024/isen-i-antarkti. Full text in Research Archive
• Kiraly, Agnes (2024). DYNAMICE: An ERC Starting grant project to bridge the gap between geodynamics and ice modelling. EGU Geodynamics Blog. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars; Wang, Yijun & Mather, Ben (2024). Direct estimation of anisotropic viscosity parameters using texture scores of olivine polycrystals. Full text in Research Archive
• Jaah, Ilyas; Kiraly, Agnes; Shephard, Grace; Conrad, Clinton Phillips & Domeier, Mathew Michael (2024). On the Role of Anisotropic Viscosity on the Motion of the Pacific Plate. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Wang, Yijun (2023). Deriving anisotropic viscosity parameters directly from texture scores of olivine polycrystals. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Fraters, Menno & Hansen, Lars (2023). Anisotropic Viscosity in Subduction Models. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Fraters, Menno (2023). Effect of olivine anisotropic viscosity in advancing and retreating subduction settings. Full text in Research Archive Show summary

  Lattice preferred orientation (LPO) of olivine crystals occurs due to deformation in the mantle. Different parts of the upper mantle can undergo a large variety of deformation paths. During simple processes, such as simple shearing below oceans due to the movement of tectonic plates, the LPO will reflect the direction of the movement of tectonic plates. On the other hand, in areas, such as around subduction zones, the mantle undergoes more complex deformation paths, resulting in a less easily predictable LPO. Seismic anisotropy has been used as a proxy for mantle flows and the LPO formed in the mantle. To interpret the seismic anisotropy observations more accurately, we need to understand how LPO forms in different regions of subduction. LPO has been implemented in many numerical modelling tools to predict seismic anisotropy, which places constraints on mantle dynamics. However, a few recent studies have linked olivine texture development to viscous anisotropy, resulted from the summed effect of individual crystals that are deforming anisotropically. Anisotropic viscosity can affect deformation and in turn the resulting LPO. To study the effect of anisotropic viscosity (AV) and LPO evolution in geodynamics processes, it is important to know the role of AV on LPO and the differences between the numerical methods that calculate them. We choose three methods of olivine texture development to examine in this study. D-Rex is a polycrystal LPO model that is relatively balanced in computational efficiency and accuracy. From previous studies, D-Rex has been shown to produce faster texture development and stronger texture compared to other methods, including our second choice, the modified director method (MDM). The MDM parameterizes the olivine LPO formation as relative rotation rates along the slip systems that participate in the rotation of olivine grains due to finite deformation. We also couple the MDM with a micromechanical model for olivine AV (which makes our third choice MDM+AV), to allow the anisotropic texture to modify the viscosity and in turn affect the formation of LPO. Here we compare the LPO evolution under subduction settings with a slowly advancing trench and a retreating trench, with and without the effect of AV. Since the mantle flow pattern in subduction zones is not homogeneous, different particles experience a variety of deformation paths. We place 60 particles in each subduction model around the slab to track the deformation and resulting olivine texture. We compute olivine texture using the above-mentioned three different methods (D-Rex, MDM, MDM+AV). With the particles, we can identify characteristic textures developed in key regions such as the mantle wedge, sub-slab area, and lateral slab edge. We then run a statistical analysis on the texture parameter and anisotropic properties of the particles from both retreating and advancing subduction models, to study where anisotropic viscosity has the largest effect on the mantle flow. We expect AV to have a larger effect in a retreating slab setting since the mantle flows feeding material to the sub-slab region is more intensive.

• Kiraly, Agnes; Wang, Yijun; Conrad, Clinton Phillips; Hansen, Lars N. & Mather, Ben (2023). Modelling anisotropic viscosity. Full text in Research Archive Show summary

  Many of Earth’s layers – from the crust to the inner core – are mechanically anisotropic. Anisotropic (i.e. direction-dependent) behaviour of rocks can derive from intrinsic properties of rock forming minerals or from microscopic or macroscopic layering of rocks and/or melts with different composition (extrinsic anisotropy). The Earth Science community often discusses the phenomena of seismic anisotropy, which results from the direction dependent propagation of seismic waves. However, materials that are characterized by elastic (seismic) anisotropy often exhibit viscous anisotropy as well, which is less explored. In geodynamics we are primarily interested in anisotropic viscosity in the crust and the mantle, where both intrinsic and extrinsic anisotropy are present. To model anisotropic viscous behaviour, we have to handle the viscosity as a 4th order tensor while also thinking about the re-orientation of anisotropy (or evolution of texture) in time. In the upper mantle the main source of anisotropy derives from the lattice preferred orientation (LPO) of olivine. Under deformation olivine grains rotate into the deformation direction (we often refer to this as texture evolution), resulting in a texture where some – or many – olivine grains are aligned with each other. Furthermore, because single olivine crystals are mechanically anisotropic – which means they deform more easily along some slip systems than others – then LPO that is developed in the upper mantle will yield anisotropic viscosity on a macroscopic scale. The foundation of our modelling approach is the Modified Director Method, which includes texture evolution and micromechanical models, both deriving from rock mechanic laboratory experiments on olivine aggregates (Hansen et al., 2016a, 2016b). The micromechanical model allows us to calculate the stress needed to achieve a certain strain rate on an aggregate, while the texture evolution model calculates the rotation of grains under a given deformation. To integrate these models into a geodynamic code, or use it to model the evolution of texture and anisotropic viscosity under specific deformation paths, we have to characterize our texture with a rank 4 viscosity or fluidity tensor (Király et al., 2020). It has been shown that the anisotropy related to olivine textures can be characterized by the Hill coefficients (Hill, 1948; Signorelli et al., 2021). Here we show that by building a large database of different textures derived from geodynamic models, we can define a linear model between simple texture parameters and the Hill coefficients with a reasonable cost. This is advantageous for integrating anisotropic viscosity into 4D geodynamic models because it allows for a direct determination of the viscosity tensor from the evolving rock texture, saving a large amount of computational time.

• Kiraly, Agnes (2023). Mantle flow around subduction zones. Full text in Research Archive
• Kiraly, Agnes; Fraters, Menno & Gassmoeller, Rene (2022). Implementing 3D anisotropic viscosity calculations into ASPECT. Full text in Research Archive Show summary

  Olivine, the main rock-forming mineral of Earth's mantle, responds to tectonic stress by deforming viscously over millions of years. This deformation creates an anisotropic (direction-dependent) texture that typically aligns with the mantle flow direction. According to laboratory experiments on olivine, we expect this texture to also exhibit anisotropic viscosity (AV), with deformation occurring more easily when it is parallel to, rather than across, the texture. However, the direction dependency of lithospheric and asthenospheric viscosity is rarely addressed in geodynamic models. The open-source modeling package ASPECT can address AV in a 2D setting using the director method, where AV is present due to shape preferred orientation created by dike intrusions (Perry-Houts and Karlstrom, 2019). We have adapted this implementation for current versions of ASPECT and benchmarked it against similar Rayleigh-Taylor instability models by Lev and Hager (2008). Unfortunately, a 2D method is inappropriate to address AV related to olivine crystallographic preferred orientation (CPO or texture), as, by default, olivine has three independent slip systems on which deformation can occur. Integrating anisotropic viscosity into 3D models would also allow us to use the actual laboratory-based parametrizations of the olivine slip system activities and texture parameters when describing the evolution of CPO and AV. One of the biggest challenges in addressing AV in a 3D setting is to find the full, rank 4, viscosity tensor, which can be done with a method similar to the one for the fluidity tensor in Király et al., (2021). Here, we present the initial results of simple geodynamic setups (shear box, corner flow), where 3D olivine CPO develops, based on the D-Rex method (Fraters and Billen, 2021), and this CPO creates AV based on the micromechanical model described in Hansen et al., (2016). Our goal is to create a tool within ASPECT that allows for CPO to develop and affect the asthenospheric or lithospheric mantle’s viscosity to improve modeling a wide range of geodynamic problems.

• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars N. & Fraters, Menno (2022). Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity. Full text in Research Archive Show summary

  The development of olivine texture, or lattice preferred orientation (LPO), has been implemented in many numerical modelling tools to predict seismic anisotropy, which places constraints on mantle dynamics. However, a few recent studies have linked olivine texture development to its mechanical anisotropy, which in turn can affect deformation rates and also the resulting texture. To study the effect of anisotropic viscosity (AV) and LPO evolution in geodynamics processes, it is important to know the role of AV and LPO and the differences between the numerical methods that calculate them. The modified director method parameterizes the olivine LPO formation as relative rotation rates along the slip systems that participate in the rotation of olivine grains due to finite deformation. When it is coupled with a micromechanical model for olivine AV, it allows the anisotropic texture to modify the viscosity. We compare the olivine textures predicted by the modified director method both with and without a coupled micromechanical model and textures predicted by the D-Rex LPO evolution model. To do this, we recalculate the texture observed in simple 3D models such as a shear box model and two other well-understood models: a corner flow model and a subduction model. In general, we observed that the D-Rex models predict a stronger anisotropic texture compared to the texture predicted by the modified director method both with and without the micromechanical model, in agreement with previous studies. When including the micromechanical model, the anisotropic texture changes the observed strain rates, which allows for a slightly faster texture evolution that is more similar to the D-Rex predictions than it is to those produced by the modified director method alone. We found that even for the simplest settings there is an increase of 10~15% in strain rate during deformation until a strain of 2.5. When shearing the asthenosphere over ~10 Myr, such anisotropy could modify the effective viscosity of the mantle,causing an up to 40% increase in plate velocity for the same applied stress. The anisotropy can also induce deformation in planes other than the initial shear plane, which can change the direction of the primary deformation. Our ultimate goal is to understand the role of AV and LPO evolution in geodynamic processes by looking at deformation paths predicted by geodynamic models in ASPECTWith this initial test, we will gain a basic understanding of olivine AV behavior and LPO evolution under different deformation settings calculated with different numerical methods, which we will carry onto our next step of implementing anisotropic viscosity of olivine in 3D into ASPECT. How to cite: Wang, Y., Király, Á., Conrad, C. P., Hansen, L., and Fraters, M.: Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7201, https://doi.org/10.5194/egusphere-egu22-7201, 2022.

• Wang, Yijun; Kiraly, Agnes; Fraters, Menno; Gassmoeller, Rene; Dannberg, Juliane & Hansen, Lars [Show all 7 contributors for this article] (2022). Olivine texture evolution under a simple deformation scheme: Comparing different numerical methods of LPO calculations. Full text in Research Archive
• Kiraly, Agnes; Wang, Yijun; Fraters, Menno; Gassmoeller, Rene; Dannberg, Juliane & Hansen, Lars [Show all 7 contributors for this article] (2022). Incorporating olivine CPO-related anisotropic viscosity into 3D geodynamics simulations. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes; Conrad, Clinton Phillips; Fraters, Menno & Hansen, Lars (2022). Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity. Full text in Research Archive
• Kiraly, Agnes (2021). Slabs, edges, and gaps. Full text in Research Archive
• Kiraly, Agnes (2021). Dynamic interactions between subduction zones. Full text in Research Archive Show summary

  Fundamental properties of subducting slabs, such as their buoyancy, the dip direction and the rheology of the slab and the surrounding mantle, determine the first order motions and geometries of subduction zones. Due to the horizontal migration of slabs n the mantle, subduction zones often “approach” each other, altering the dynamics of single subductions. In this presentation, I will summarize the dynamics of subduction zone interactions in four simple geometries, that are most commonly used to describe the geodynamic history of tectonically complex areas. Using data from geological and geophysical observations and the results of many geodynamics models, we can conclude some common features of subduction zones interactions, such as: changing slab dips, reduced trench migration rates, complex flow patterns in the mantle, and strong rotations of lithospheric blocks. These features are resulted from the stress transfer between neighboring slabs which ultimately changes the force balance of individual subduction zones. Understanding the dynamics of such complex systems can help to interpret geological and geophysical data, and to reconstruct the tectonic history of areas, where multiple subduction zones are/were active simultaneously. A great example for such a tectonically complex area is the Central Mediterranean, which I will discuss in the light of the conclusions we make about the dynamics of subduction zones interactions.

• Kiraly, Agnes; Conrad, Clinton Phillips; Hansen, Lars & Fraters, Menno RT (2020). The formation of viscous anisotropy in the asthenosphere and its effect on plate tectonics. Full text in Research Archive
• Chotalia, Kiran; Cooper, George; Crameri, Fabio; Domeier, Mathew; Eakin, Caroline & Grima, Antoniette Greta [Show all 14 contributors for this article] (2020). The trans-disciplinary and community-driven subduction zone initiation (SZI) database. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips & Hansen, Lars (2020). Evolving viscous anisotropy in the upper mantle and its geodynamic implications. Full text in Research Archive
• Crameri, Fabio; Magni, Valentina; Domeier, Mathew; Shephard, Grace; Cooper, George & Chotalia, Kiran [Show all 14 contributors for this article] (2019). Subduction zone initiation (SZI) database 1.0: Ready, set, model! Full text in Research Archive
• Crameri, Fabio; Chotalia, Kiran; Cooper, George; Domeier, Mathew; Eakin, Caroline & Grima, Antoinette [Show all 14 contributors for this article] (2019). Subduction Zone Initiation Database 1.0. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips; Domeier, Mathew & Hansen, Lars (2019). Does anisotropic mantle viscosity impede changes in plate motion? Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips & Hansen, Lars (2019). Anisotropic viscosity of olivine: The relationship between texture parameters and rheological behavior. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips; Domeier, Mathew & Hansen, Lars (2019). Does anisotropic mantle viscosity impede changes in plate motions. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips & Hansen, L. (2018). Geodynamic consequences of anisotropic mantle viscosity. Full text in Research Archive
• Kiraly, Agnes; Conrad, Clinton Phillips & Hansen, L. (2018). Geodynamic consequences of anisotropic mantle viscosity. Full text in Research Archive
• Wang, Yijun; Kiraly, Agnes & Conrad, Clinton Phillips (2025). Texture evolution in subduction models, influenced by anisotropic viscosity. Simple tests, cluster analysis, and numerical implementation. Universitetet i Oslo. Full text in Research Archive Show summary

  The anisotropic viscosity of olivine plays a crucial role in mantle dynamics, influencing both large-scale geodynamic processes and texture evolution, and thus the resulting seismic anisotropy. While experimental studies have characterized the directional dependence in the viscosity of olivine, its integration into numerical geodynamic models remains limited. This thesis systematically investigates the effects of anisotropic viscosity during simple shear and during complex deformations in subduction zones, using a series of numerical methods implemented outside and within the geodynamic modeling software, ASPECT. As an initial step to estimate the effect of anisotropic viscosity, we compute olivine textures and texture-induced anisotropic viscosity as postprocessors based on deformation paths obtained from geodynamic models run in ASPECT. In these models, textures and Associated anisotropic viscosity do not modify deformations directly. We demonstrate that anisotropic viscosity has a limited impact during simple shear with a constant imposed velocity but can significantly alter texture development and the effective viscosity in a more dynamic subduction model. This is particularly the case in regions where accumulated strain is large, for example, in the mantle wedge region. Using time-series cluster analysis, we expand the analysis in subduction models to include more than 1000 particles located throughout the subduction zone covering the mantle wedge, sub-slab, and slab areas. We identify the spatial variability of mantle deformation, olivine texture, and anisotropic direction and strength, which are particularly pronounced in the retreating-trench model with large deformation. The clusters characterize the trench-normal orientations above and beneath the slab, as well as the trench-parallel orientations between 300 and 400 km depth behind the slab. These directions have also also observed in seismic anisotropy studies near subduction systems. To describe texture-induced anisotropic viscosity, we establish a quantitative relationship between olivine texture and anisotropic viscosity parameters, expressed as the Hill coefficients. This relationship is validated with textures both from experiments and numerical models. We then integrate this relationship into ASPECT, representing anisotropic viscosity with a tensor composed of the Hill coefficients and a stress-dependent scalar component. This implementation is tested under simple shear deformation, providing a framework for incorporating anisotropic viscosity into large-scale geodynamic simulations. Collectively, this research advances our understanding of how anisotropic viscosity influences olivine textures and mantle Dynamics and provides a computational methodology for integrating anisotropic viscosity into geodynamic models. The results emphasize the necessity of considering anisotropic viscosity in subduction zone modeling and offer new insights into the interpretation of seismic anisotropy in complex mantle flow environments.

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