Analogue Models Research Articles

Formation of mullions in two and three dimensions: Results from analogue modelling

Scale-model experiments, involving pure shear shortening of a single incompetent layer embedded in a competent matrix, were carried out to study the influence of the bulk strain geometry and an inclined layer on the growth rate and shape of mullions. The viscosity ratio between non-linear viscous layer and matrix varied from 1/4–1/35. If layer parallel shortening (eZ) is the same, the growth rate of mullions is highest under bulk constriction, moderate under bulk plane strain, and lowest under bulk flattening. Because of their low growth rate in a flattening strain field, formation of mullions is hardly possible. Initial layer inclination under bulk constriction led to antisymmetric mullions. Increasing the viscosity ratio between layer and matrix results in (1) faster rotation of the layer towards the main stretching axis, X, (2) earlier attainment of a stable mullion wavelength, and (3) earlier formation of flames. The style of deformation (coeval folding and boudinage vs. shearing) of a thin competent sheet, inserted into the incompetent layer, is controlled not only by the viscosity ratio, but also by the bonding between competent and incompetent material. The new results shed light on the deformation behavior of Sederholm-type dikes and sills at deep crustal levels.

Analog Schwarzschild black holes of Bose-Einstein condensates in a cavity: Quasinormal modes and quasibound states

Analog models of black holes have unequivocally proven to be extremely beneficial in providing critical information regarding black hole spectroscopy, superradiance, quantum phenomena and most importantly Hawking radiation and black hole evaporation; topics that have either recently begun to bloom through gravitational wave observations or have not yet been investigated in astrophysical setups. Black hole analog experiments have made astonishing steps toward the aforementioned directions and are paramount in understanding the quantum nature of the gravitational field. Recently, a tabletop analog Schwarzschild black hole has been proposed by placing Bose-Einstein condensates of photons inside a mirror's cavity, leading to a sink with a radial vortex that represents a velocity singularity. Here, we provide an extensive spectral analysis of both the tabletop acoustic black hole and its higher-dimensional gravitational analog. We find that quasinormal modes and quasibound states share qualitative similarities in both systems and show that the eikonal quasinormal modes of the analog acoustic black hole have a photon-sphere-like interpretation, which points to the existence of a phonon sphere in the analog black hole. Our results, complemented with the recently calculated graybody factors and Hawking radiation of the acoustic analog, can provide a theoretical test bed for future tabletop experiments with condensates of light in a mirror's cavity and provide significant insights regarding classical and quantum phenomena in higher-dimensional black holes.

An electrical analog permeability model assessing fluid flow in a decellularized organ

Background and objectiveIn recellularization, cell-seeding efficiency refers to the uniform distribution of cells across the decellularized organ, which should be enhanced to ensure effective functioning. During cell seeding, flow dynamics influence the distribution of cells because the driving force of cell movement is the fluid force. However, after decellularization, because of flow permeability through the vessel wall, the fluid pressure and velocity in the vessels of vascular trees are significantly reduced compared with those in the native organ, which might affect cell seeding efficiency. Therefore, it is necessary to assess the flow characteristics in the vessels of decellularized organs to select appropriate seeding conditions. Although electrical analog models have been widely used to investigate the flow distribution in organs, current models do not reflect the permeable conditions. This study proposes a model to extend the conventional electrical analog model to simulate the flow characteristics in decellularized organs. MethodsA resistor reflecting permeable flow was added to the original electrical analog model to describe the permeable conditions in the decellularized organs. Decellularization and pressure drop measurements of the kidney were also conducted for model development, calibration, and validation. The developed model was then applied to a decellularized kidney to reveal changes in flow characteristics. ResultsThe resistance calculation of permeable flow was determined for each generation of vascular trees. The coefficient of permeability can be indicated by the measured flow exiting through the outlet or the pressure drop across the decellularized organ. The developed permeability model had a qualitative and quantitative agreement with the experimental data without calibration. The results of the permeability model for the decellularized kidney indicated significant reductions of up to 70% in the flow rate and pressure of the organ compared to the native kidney. ConclusionsThe developed model can simulate the flow characteristics in each individual vessel of decellularized organs. The results from the model can be used to assess the optimal flow rate condition for the cell seeding process.

Seamount Subduction and Megathrust Seismicity: The Interplay Between Geometry and Friction

AbstractSubducting seamounts are recognized as one of the key features influencing megathrust earthquakes. However, whether they trigger or arrest ruptures remains debated. Here, we use analog models to study the influence of a single seamount on megathrust earthquakes, separating the effect of topography from that of friction. Four different model configurations have been developed (i.e., flat interface, high and low friction seamount, low friction patch). In our models, the seamount reduces recurrence time, interseismic coupling, and fault strength, suggesting that it acts as a barrier: 80% of the ruptures concentrate in flat regions that surround the seamount and only smaller magnitude earthquakes nucleate above it. The low‐friction zone, which mimics the fluid accumulation or the establishment of fracture systems in natural cases, seems to be the most efficient in arresting rupture propagation in our experimental setting.

Scaling CO2–brine mixing in permeable media via analogue models

Supercritical ${\rm CO}_2$ injection and dissolution into deep brine aquifers allow its sequestration within geological formations. After injection, ${\rm CO}_{2}$ gas phase is buoyancy-driven over the denser aqueous brine, reaching an apparent gravitational stable distribution. However, ${\rm CO}_2$ dissolution in brine propels convection since the mixture is even denser than the underlying brine. This process still needs to be characterised comprehensively. Here, we investigate the irreversible mixing of dissolved ${\rm CO}_2$ in brine through laboratory-scale numerical experiments utilising the Hele-Shaw model (Letelier et al., J. Fluid Mech., vol. 864, 2019, pp. 746–767) and a fully miscible two-fluid system. In this scenario, mixing the less dense fluid – mimicking ${\rm CO}_{2}$ gas phase – with the heavier fluid – representing aqueous brine – catalyses cabbeling-powered convection. Our numerical simulations recover the laboratory results in porous media by Neufeld et al. (Geophys. Res. Lett., vol. 37, issue 22, 2010, L22404) and may explain the scaling law obtained by Backhaus et al. (Phys. Rev. Lett., vol. 106, issue 10, 2011, 104501) in Hele-Shaw cells. More remarkably, we show that the mass flux between the two analogue fluids, characterised by the Sherwood number $ {{Sh}}$ , obeys the universal scaling law $ {{Sh}}\sim {{Ra}}\, \vartheta _{scalar}$ , with $ {{Ra}}$ the Rayleigh number and $\vartheta _{scalar}$ the mean scalar dissipation rate. This paper sheds light on the fluid dynamics and solubility trapping in geological carbon sequestration.

Damping of low-frequency oscillation using renewable generation units

Nowadays there is a significant increase the number of generation units based on renewable energy sources in electric power systems, the main goal of which is to ensure global access to affordable, reliable, sustainable and modern sources of energy. However, as the penetration level of renewable generation units increases, there are power oscillations easily occur, which create biggest challenges for the power system stability. In particular, the dominant modes of modern generation units, connected to the main grid via a voltage source converter, are in the range of higher frequencies than electromechanical oscillations. Consequently, the chance of occurrence of low-frequency oscillations increases, the parameters and the trajectory of which will differ from power oscillations in power system without renewables. The results of the analysis of low-frequency oscillation parameters in part of Eastern Siberia power system and evaluation of impact of renewable generation unit on power oscillations are presented in this article. The results were obtained by the Hybrid real time simulator based on the combination of analog, physical and digital modeling levels. The developed scheme of part of Eastern Siberia power system and simulation results were verified by SCADA system. The difference between the results of simulation and SCADA system did not exceed 1%. It indicates the adequacy of the Hybrid real time simulator and the developed scheme of power system. Based on the evaluation of the parameters of power oscillations and the calculation of the degree of damping of the transient process, it can be noted that the oscillatory stability of the power system is improved: damping time decreases, the damping ratio increases with increasing of renewables penetration level.

Drainage development on the northern Tibetan Plateau controlled by the Altyn Tagh Fault: Insights from analogue modelling

AbstractAlong the northern margin bounded by the Altyn Tagh Fault, the Tibetan Plateau has been uplifted relative to the Tarim Basin and horizontally extruded to the east for hundreds of kilometres. The Altyn Tagh Fault separates the western Kunlun Shan and Altyn Shan from the Tibetan Plateau, and these two mountain ranges form a topographic window through which river sources from the northern Tibetan Plateau flow into the Tarim Basin. In this study, we designed a specialized geomorphic sandbox to investigate major factors controlling the drainage development on the northern Tibetan Plateau. The modelling results revealed that the Altyn Tagh Fault and preexisting topography played dominant roles in reorganization and divide migration. This strike‐slip fault together with the topographic window has controlled the formation and frequent reorganization of two disproportional fault‐related drainage basins, with the eastern one much larger than the western one. Large‐scale horizontal slip along the fault has resulted in an asymmetric distribution of the drainage area, which showed eastward deviation relative to the topographic window. The modelling results are supported by the observed fluvial landforms as well as evidence of captured channels in nature. Rightward decreasing of the denudation and headward erosion rates in three‐step patterns in the model showed that the slip direction of the main plateau relative to the position of the topographic window influences the erosional dynamics. We conclude that the tectonic activity along the Altyn Tagh Fault, together with the preexisting topography, controlled the drainage development and dynamics in the northern Tibetan Plateau in the late Cenozoic.

Role of inheritance during tectonic inversion of a rift system in basement-involved to salt-decoupled transition: analogue modelling and application to the Pyrenean–Biscay system

Abstract. The reactivation of former rift systems and passive margins during tectonic inversion and their incorporation into fold-and-thrust belts result in significant structural differences not only between internal and external domains, but also along-strike. The Basque–Cantabrian and Asturian systems are among the best examples to address the role of along-strike changes in rift inheritance since they show a transition from salt to basement-inherited structures divided by a transition zone separating thick- from thin-skinned structural domains. While both domains have been widely described in the literature, the transfer system separating the two has not been sufficiently investigated due to poor seismic imaging and the lack of large-scale outcrops. This contribution aims to address the linkage between basement-controlled (i.e. thick-skinned) and salt-decoupled (i.e. thin-skinned) domains and to describe how deformation is accommodated in the transitional zone between these domains. An experimental programme based on analogue models has been designed that was inspired by the transition from the thin-skinned Basque–Cantabrian Pyrenees to the east to the thick-skinned Asturian Massif to the west. As observed in nature, experimental results show that oblique structures (at low angle with the shortening direction) form in the transitional domain, and their location depends on the linkage of the active structures occurring in both surrounding thick- and thin-skinned domains at different positions. Nevertheless, their orientation and evolution are controlled by the underlying decoupling horizon (i.e. salt). The deformation in the thick-skinned domain produces significant topography over a narrow deformation area due to the lack of effective decoupling levels. On the contrary, deformation in the thin-skinned domain is more distributed due to decoupling, resulting in a wider deformation area of less topography. As a result, syn-contractional sedimentation occurs mainly in the foreland basin in front of the thick-skinned domain, whereas it is observed in the foreland but also in piggyback basins in the thin-skinned domain.

Tectonic interactions during rift linkage: insights from analog and numerical experiments

Abstract. Continental rifts evolve by linkage and interaction of adjacent individual segments. As rift segments propagate, they can cause notable re-orientation of the local stress field so that stress orientations deviate from the regional trend. In return, this stress re-orientation can feed back on progressive deformation and may ultimately deflect propagating rift segments in an unexpected way. Here, we employ numerical and analog experiments of continental rifting to investigate the interaction between stress re-orientation and segment linkage. Both model types employ crustal-scale two-layer setups wherein pre-existing linear heterogeneities are introduced by mechanical weak seeds. We test various seed configurations to investigate the effect of (i) two competing rift segments that propagate unilaterally, (ii) linkage of two opposingly propagating rift segments, and (iii) the combination of these configurations on stress re-orientation and rift linkage. Both the analog and numerical models show counterintuitive rift deflection of two sub-parallel propagating rift segments competing for linkage with an opposingly propagating segment. The deflection pattern can be explained by means of stress analysis in numerical experiments wherein stress re-orientation occurs locally and propagates across the model domain as rift segments propagate. Major stress re-orientations may occur locally, which means that faults and rift segment trends do not necessarily align perpendicularly to far-field extension directions. Our results show that strain localization and stress re-orientation are closely linked, mutually influence each other, and may be an important factor for rift deflection among competing rift segments as observed in nature.

Mechanical characterisation of new Sand-Hemihydrate rock-analogue material: Implications for modelling of brittle crust processes

The analogue materials play a critical role in dynamically scaled experiments, defining the processes that can be simulated and the structures observable in the model. The dynamic scaling enables the direct comparison between the model and its natural counterpart. To obtain such a model the physical and mechanical properties of the analogue material must be scaled with respect to the rock prototype. A large variety of materials have been applied in analogue modelling studies to address the physical and mechanical requirements for the simulation of (i) upper crust, (ii) middle crust and (iii) lower crust and mantle processes. Nevertheless, the development of new model materials represents a continuous improvement of the analogue modelling techniques.We investigated the mechanical and physical properties of a new Granular Rock-Analogue Material (GRAM) (introduced in Massaro et al. (2022)) and its component materials. GRAM is an ultra-weak artificial sandstone composed of quartz sand cemented with gypsum, capable to deform by tensile and shear failure under variable stress conditions. GRAM aggregates in different mixing ratios (from 1% to 4% in weight of hemihydrate powder) were systematically tested with ring-shear tests and uniaxial compression tests. The relationships between the hemihydrate content and the mechanical properties of GRAM were examined. Additionally, the sample preparation procedure of GRAM was investigated, evaluating the impact of the residual water content on the mechanical properties of GRAM aggregates and defining a standard preparation procedure. Finally, GRAM was compared to natural rocks and to other granular materials applied in analogue modelling studies, in terms of physical and mechanical properties, application to physical modelling and dynamic scaling. It was underlined how the application of GRAM aggregates in dynamically scaled experiments can enhance the comprehension of the fault and fracture processes occurring at the scale of the damage zone.

PARAMETERS CONTROLLING THE GEOMETRY OF DETACHMENT AND FAULT‐BEND FOLDS: INSIGHTS FROM 3D FINITE‐ELEMENT MODELS APPLIED TO THE AHWAZ ANTICLINE IN THE DEZFUL EMBAYMENT, SW IRAN

Fault‐related folds are present in most tectonic settings and can serve as structural traps for hydrocarbons. These structures have therefore been widely studied by both structural and petroleum geologists using a range of techniques. Approaches include field‐ and seismic‐based methods, and numerical and analogue modelling. Geomechanical models attempt to examine the mechanical and geometric features of folds.This study investigates the effects of variations in a range of parameters, including detachment and ramp geometry, friction coefficient and internal friction angle, on the geometry and development of detachment folds and fault‐bend folds. For this purpose, we ran seven series of numerical, 3D elastic‐plastic finite element models using ABAQUS software (26 model runs in all). Each model set‐up consisted of five layers whose mechanical properties were based on those of stratigraphic units in the Zagros fold‐and‐thrust belt, SW Iran. The models were labelled series A to F and series H. Models in series A investigated the impact of concave, convex, wavy and oblique detachment surfaces on the development of detachment folds; those in series D examined the role of ramp dip and of listric, oblique and wavy ramps on the development of fault‐bend folds. Models in series B and E, and series C and F, examined the effects of variations in the friction coefficient and of the internal friction angle, respectively, on the development of these two classes of folds. Finally, hybrid models in series H were provided to evaluate the results.Major results were as follows. Firstly, the geometry of modelled detachment and fault‐bend folds was found to be influenced by the geometry of the associated ramps and detachment faults. Thus the crests of anticlines and the trough lines of synclines were located at points of maximum curvature and at inflexion points on a wavy detachment fault or wavy ramp, respectively. Second, two important additional factors controlling fold style were identified: the friction coefficient, and the presence of along‐strike geometric variations in the ramp or the detachment fault. Layers with low friction coefficients and high internal friction angles formed detachment folds with thick hinges and thin limbs; conversely, layers with high friction coefficients and low internal friction angles created detachment folds with thick limbs and thin hinges. Application of the results to modelling of the Ahwaz anticline in the Dezful Embayment, SW Iran, was successful, and in general the modelled structure was consistent with that observed in the field.

Numerical modeling of caldera formation using Smoothed Particle Hydrodynamics (SPH)

SUMMARYCalderas are kilometer-scale basins formed when magma is rapidly removed from shallow magma storage zones. Despite extensive previous research, many questions remain about how host rock material properties influence the development of caldera structures. We employ a mesh-free, continuum numerical method, Smoothed Particle Hydrodynamics (SPH) to study caldera formation, with a focus on the role of host rock material properties. SPH provides several advantages over previous numerical approaches (finite element or discrete element methods), naturally accommodating strain localization and large deformations while employing well-known constitutive models. A continuum elastoplastic constitutive model with a simple Drucker–Prager yield condition can explain many observations from analogue sandbox models of caldera development. For this loading configuration, shear band orientation is primarily controlled by the angle of dilation. Evolving shear band orientation, as commonly observed in analogue experiments, requires a constitutive model where frictional strength and dilatancy decrease with strain, approaching a state of zero volumetric strain rate. This constitutive model also explains recorded loads on the down-going trapdoor in analogue experiments. Our results, combined with theoretical scaling arguments, raise questions about the use of analogue models to study caldera formation. Finally, we apply the model to the 2018 caldera collapse at Kīlauea volcano and conclude that the host rock at Kīlauea must exhibit relatively low dilatancy to explain the inferred near-vertical ring faults.

Structural evolution and mechanism of multi-phase rift basins: A case study of the Panyu 4 Sag in the Zhu Ⅰ Depression, Pearl River Mouth Basin, South China Sea

The study of changes in normal fault systems during different rift stages is important to understand the genesis and evolution of multi-phase rift basins, such as the Panyu 4 Sag in the Zhu Ⅰ Depression. Using 2D and 3D seismic data and analogue modelling, the Zhu Ⅰ Depression was characterized as a series of half-grabens bounded by NE-NEE-trending normal faults, it was found to have undergone two phases of the extension during the Paleogene. The Zhu Ⅰ Depression exhibited four fault sets with different strikes, including NNE, NE-NEE, EW, and NWW. The main controlling faults were NE-trending and EW-trending with high activity rates during Rift Phase 1 and Rift Phase 2, respectively. The average azimuths of the dominant strikes for type Ⅰa, type Ⅰb, and type Ⅱ faults were 75°, 85°, and 90°, which revealed that the minimum principal stress (σ3) directions during the rift phases 1 and 2 of the Zhu Ⅰ Depression were SSE (∼165°) and near-EW (∼180°), respectively. Two phases of structural-sedimentary evolution, with different directions and analogue modelling results, illustrated that the Panyu 4 Sag was formed as a superimposed basin under multi-phase anisotropic extension. The structural evolution of the Panyu 4 Sag since the Paleogene was mainly controlled by the combined effects of the Pacific, Eurasian, and Indian plates. Since the orientation of subduction of the Pacific plate changed from NNW to NWW, the stress field shifted from NW-SE-trending tension to S-N-trending tension, causing the superimposition of late near-E-W-oriented structural pattern on the early NE-oriented structural pattern.

Time-dependent frictional properties of granular materials used in analogue modelling: implications for mimicking fault healing during reactivation and inversion

Abstract. Analogue models are often used to model long-term geological processes such as mountain building or basin inversion. Most of these models use granular materials such as sand or glass beads to simulate the brittle behaviour of the crust. In granular material, deformation is localised in shear bands, which act as an analogue to natural fault zones and detachments. Shear bands, also known as faults, are permanent anomalies in the granular package and are often reactivated during a test run. This is due to their lower strength compared to the undeformed material. When the fault movement stops, time-dependent healing immediately begins to increase the strength of the fault. Faults that have been inactive for a long time therefore have a higher strength than younger faults. This time-dependent healing, also called time consolidation, can therefore affect the structure of an analogue model as the strength of the fault changes over time. Time consolidation is a well-known mechanism in granular mechanics, but it is poorly described for analogue materials and on the timescales of typical analogue models. In this study, we estimate the healing rate of different analogue materials and evaluate the impact on the reactivation potential of analogue faults. We find that healing rates are generally less than 3 % per 10-fold increase in holding time, which is comparable to natural fault zones. We qualitatively compare the frictional properties of the materials with grain characteristics and find a weak correlation of healing rates with sphericity and friction with an average quality score. Accordingly, in models where there are predefined faults or reactivation is forced by blocks, the stability range of the fault angles that can be reactivated can decrease by up to 7∘ over the duration of 12 h. The stress required to reactivate an existing fault can double in the same time, which can favour the development of new faults. In a basin inversion scenario, normal faults cannot be inverted because of the strong misorientation, so time consolidation plays little additional role for such models.

Deep learning-based wave digital modeling of rate-dependent hysteretic nonlinearities for virtual analog applications

Electromagnetic components greatly contribute to the peculiar timbre of analog audio gear. Indeed, distortion effects due to the nonlinear behavior of magnetic materials are known to play an important role in enriching the harmonic content of an audio signal. However, despite the abundant research that has been devoted to the characterization of nonlinearities in the context of virtual analog modeling over the years, the discrete-time simulation of circuits exhibiting rate-dependent hysteretic phenomena remains an open challenge. In this article, we present a novel data-driven approach for the wave digital modeling of rate-dependent hysteresis using recurrent neural networks (RNNs). Thanks to the modularity of wave digital filters, we are able to locally characterize the wave scattering relations of a hysteretic reluctance by encapsulating an RNN-based model into a single one-port wave digital block. Hence, we successfully apply the proposed methodology to the emulation of the output stage of a vacuum-tube guitar amplifier featuring a nonlinear transformer.

How do inherited dip-slip faults affect the development of new extensional faults? Insights from wet clay analog models

The development of structurally controlled basins is frequently dominated by inherited geological and tectonic structures, especially when the affected region has undergone multiple tectonic phases. In this study we use physically scaled analog models to analyze the impact of inherited faults on the evolution of a new extensional fault system and its associated basin. In our experiments, we introduced inherited faults – bearing diverse geometries and orientations – cut through a homogeneous analog material (wet clay). After each experiment, we compare (a) how the inherited faults affected the inception and development of new faults and (b) the shape of the resulting basins, using a ‘reference model’ run without pre-existing faults. The results show that the orientation of pre-existing faults with respect to the extensional axis does affect the development of the new extensional structures. The main effects show up when the orientation of the pre-existing faults is closer to that expected for a fault that is optimally oriented (perpendicular) with respect to the direction of extension and has a dip close to an Andersonian extensional fault. Conversely, the impact on the resulting basin shape is more spatially complex, especially in the case of misoriented pre-existing faults. We also compare our experimental results with an analytical method based on the slip tendency theory. The application of our findings to selected natural cases demonstrates how one may interpret the occurrence, orientation, and activity of inherited faults by looking at the present-day geometry and wavelength of an extensional basin, particularly when newly formed extensional faults exhibit structurally unexpected trajectories.

Analogue modelling of the inversion of multiple extensional basins in foreland fold-and-thrust belts

Abstract. The presence of pre-existing rheological heterogeneities in the lithosphere plays a significant role during subsequent stages of deformation in essentially every geological process. Extensional basins located in foreland fold-and-thrust belts will alter the spatio-temporal evolution of its associated orogen. It remains unclear how far horizontal stresses can act and reactivate extensional structures due to their intrinsic irregular patterns of deformation deflection and localisation. Overprinting events and relative dating uncertainties in the geological record make it difficult to interpret how stresses were transferred across a heterogeneous crust. Here we examine the inversion of extensional basins in foreland fold-and-thrust belts by using three-dimensional analogue experiments that simulate first an extensional stage, followed by a shortening stage. Our results show how extensional basins proximal to the orogenic front effectively localise deformation in the shape of thrusts and prevent stress transfer beyond their location. Basins that are located at large distances from the orogenic front also show evidence of mild inversion at early stages but are characterised only by basin infill contraction and uplift. When multiple extensional basins are present, the degree and type of inversion will depend primarily on their relative location and distance to the orogenic front. Here we also prove that the presence of additional extensional features in the vicinity of a basin can be a first-order controlling factor in their overall reactivation history. We share additional insights of how a fold-and-thrust belt evolves once the extensional basins have been incorporated by the advancing wedge, and we provide comparisons with natural examples that shed light on some still unanswered questions related to the process of basin inversion in orogenic belts.

Analog Models of Lithospheric‐Scale Rifting Monitored in an X‐Ray CT Scanner

AbstractRifting and continental break‐up are fundamental tectonic processes, the understanding of which is of prime importance. However, the vast temporal and spatial scales involved pose major limitations to researchers. Analog tectonic modeling represents a great means to mitigate these limitations, but studying the complex internal deformation of lithospheric‐scale models remains a challenge. We therefore present a novel method for lithospheric‐scale rifting models that are uniquely monitored in an X‐ray CT scanner, which combined with digital image correlation (DIC) techniques, provides unparalleled insights into model deformation. Our first models illustrate how the degree of coupling between competent lithospheric layers, which are separated by a weak lower crustal layer, strongly impacts rift system development. Low coupling isolates the upper crust from the upper lithospheric mantle layer below, preventing an efficient transfer of deformation between both layers. By contrast, fast rifting increases coupling, so that deformation in the mantle is efficiently transferred to the upper crust, inducing either a symmetric or asymmetric (double) rift system. Furthermore, oblique divergence may lead to en echelon graben arrangements and delayed exhumation of the lower crustal layer. The successful application of our novel modeling approach, yielding these first‐order insights, provides a clear incentive to continue running lithospheric‐scale rifting models, and to apply advanced monitoring techniques to extract as much information from models as possible. There is indeed a broad range of opportunities for follow‐up studies within (and beyond) the field of rift tectonics.

Morpho-structural criteria for the identification of spreading-induced deformation processes potentially compromising stratovolcano stability

Characterisation of surface deformation at stratovolcanoes is essential for a better understanding of the processes that can compromise edifice structural stability and potential for flank collapse. Spreading produced by the presence of a hydrothermal system or intrusion of a viscous magma body can produce similar deformation signatures, and both processes have implications for flank instability. In this work, we perform analogue models and consider examples from real volcanoes (Damavand, Ubinas, Semeru and Casita) so as to characterise and recognise surface deformation patterns produced by spreading due to the presence of a hydrothermal system and in response to magma intrusion. The experiments show that there are differences in the resulting surface deformation associated with each process. Magma intrusion results in a sharp transition between areas of subsidence and uplift, and is associated with faults with oblique strikes in the upper part of the edifice. Instead, asymmetric flank spreading is associated with hydrothermal system and results in flank bulging close to the base of the edifice. Although laboratory analogue models show different deformation responses that could be diagnostic of the associated processes, application in the field is difficult as often these diagnostic features are not preserved during evolution. However, basal bulging represents a potential diagnostic for the identification of asymmetric volcano flank spreading associated with hydrothermal activity, and the potential for instability. Remote sensing techniques can allow identification of such surface deformation features, providing a useful tool for hazard assessment and design of monitoring strategies at potentially unstable volcanoes.

Analogue modelling of a Tabberabberan fold-thrust belt in the Cobar region and implications for the origin of Cobar-type mineral deposits

The Cobar Supergroup is a package of Siluro-Devonian sedimentary, volcanic and volcaniclastic rocks in central New South Wales that underwent significant deformation during the Middle Devonian Tabberabberan Orogeny. The Cobar Supergroup, particularly within the Cobar Basin, constitutes one of the most mineral-rich rock packages in New South Wales, being endowed with Au, Cu, Pb, Zn and Ag, mainly in what are commonly referred to as Cobar-type deposits. Inconsistencies in the traditional stratigraphic interpretation of the area have led to a re-evaluation of its structural history, in particular the role of the Rookery Fault, which bounds the eastern side of the basin. Evidence suggests that that structure may dip to the east, rather than the west, as is traditionally assumed, leading to the possibility that Tabberabberan deformation in the area took the form of a west-verging fold-thrust belt. Analogue modelling is employed to examine the consequences of that scenario. Such a mechanism explains the known distribution of stratigraphic units of the Cobar Supergroup and its basement, as well as observed structures, in particular a high strain zone immediately west of the Rookery Fault. The modelling indicates that deeper parts of the crust were thrust up along the Rookery Fault, which, along with substantial burial, led to perturbation of the geotherm and heating of the footwall. This accounts for the higher metamorphic grade immediately west of the Rookery Fault. Furthermore, heating and overpressuring of basement rocks in the footwall led to mobilisation of metal-bearing fluids and transport of them along the high strain zone and subsequent deposition of those metals within favourable structural traps, with variable interaction with basinal fluids, to form Cobar-type deposits. A fold-thrust mechanism with ongoing erosion of the thrust wedge can also explain the distribution of Middle to Upper Devonian rock sequences in the region. KEY POINTS A west-verging fold-thrust model is proposed to explain Tabberabberan deformation of the Cobar Supergroup and its basement. Analogue modelling is employed to demonstrate the fold-thrust model. A fold-thrust model explains the distribution of Ordovician to Upper Devonian stratigraphic units in the Cobar region, as well as associated structures, metamorphic grade distribution and the origin of syn-deformational Au, Cu, Pb, Zn, Ag mineral deposits.