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The evolution of faults within the same stress field is frequently influenced by numerous factors, involving the reactivation of pre-existing structures, stress transmission through ductile detachment layers, and the growth, interaction, as well as linkage of new fault segments. This study analyses a complex multi-phase oblique extension fault system in the Nanpu Sag (NPS) of the Bohai Bay Basin (BBB), China. High-resolution three-dimensional (3D) seismic data and analogue modelling indicate that the oblique extensional reactivation of pre-existing structures governs the sequential arrangement of fault segments in the caprock, and they dip synthetically to the reactivated fault at depth. During the NW-SE extension in the Eocene, the predominant movement of the pre-existing fault is strike-slip. Subsequently, during the N-S extension since the Oligocene, inclined at 20° to the pre-existing fault, forming splay fault segments and ultimately creating large en-échelon arcuate faults linked by relay ramps. Using fault throw-distance (T-D) and laser scanning, we reconstructed the fault evolution model of oblique extension reactivation in the presence of a ductile detachment basement. Our study illustrates that the arcuate faults can be categorized into linear master fault segments controlled by pre-existing structures, bending splay faults in the termination zone, and normal fault segments responding to the regional stress field. The interaction between faults occurs among normal faults and strike-slip faults, and the kinematic unification of the two fault systems is accomplished in the intersection zone. As the faults continue to evolve, the new fault segments tend to relinquish the control of pre-existing structures and concentrate more on the development of planar and continuous major faults. The ductile detachment layer significantly contributes to the uniform distribution of strain, resulting in narrow shear zones and discontinuous normal faults in its absence. [ABSTRACT FROM AUTHOR]

Subduction initiation (SI) is crucial for understanding the driving mechanisms of plate tectonics, the strength, and heterogeneity of the lithosphere, as well as the interaction of various driving/resisting forces. However, where and how subduction zones form remains confusing and contentious because of limited observational data. Geodynamic modelling provides a data-independent, reproducible way to test different hypotheses of SI. Most numerical models of SI have been reviewed by the geodynamic community in the past; however, little attention was paid to analogue modelling works. In this study, we have reviewed analogue models of SI according to the driving mechanisms (induced or spontaneous), then to whether or not SI occurs near pre-existing subduction zones, and finally to the tectonic settings of SI, which are usually different-typed lithospheric weak zones, including lithospheric-scale inclined faults, locally thinned zones, transform boundaries, passive margins, island arcs, back-arc basins/spreading centres, and plume head margins. Induced SI and strain localization cannot occur within the intact plate unless some weak zones exist, whose strengths are largely affected by their tectonic styles. The lithospheric-scale inclined fault is the weakest tectonic setting; the locally thinned zone also has relatively low strength; the transform boundary and the passive margin are strong. Spontaneous SI of oceanic lithosphere is usually triggered by extra loads, such as collapsed continental crust and flooding plume materials. The negative buoyancy of oceanic lithosphere will then take over and drive self-sustaining subduction. Modelling results may explain why a young oceanic plate sometimes underthrusts beneath an old one and why transference SI still does not happen after long-lasting India-Asia collision (~55 Ma). According to the experiences and deficiencies of the past works, future analogue modelling works should focus on transform collapse, subduction transference, case studies modelling, non-cylindrical modelling, realistic model setups of weak zones, and quantitative evaluation/analyses of SI. [ABSTRACT FROM AUTHOR]

Abstract We present a kinematic model developed from geodetic observations, topography analysis and analogue tectonic modelling results, which reveals a striking similarity between the rotational tectonic settings of the Gakkel Ridge-Chersky Range system in the Arctic, and the Central Indian Tectonic Zone within the Indian subcontinent. A crucial aspect of large-scale extensional rift systems is the gradual variation of extension along the rift axis, due to plate rotation about a Euler pole, which may lead to contraction on the opposite side of the Euler pole to form a rotational tectonic system. Our geodetic and topographic analysis, combined with the reanalysis of analogue tectonic modelling results demonstrates such rotational tectonic plate motion in both the Arctic and Indian case. However, the plate boundary between the North American and Eurasian Plates as represented by the Arctic Gakkel Ridge-Chersky Range system is strongly localized, whereas the Central Indian Tectonic Zone that separates the North and South India Plates involves diffuse deformation instead. Furthermore, in both the Arctic and Central Indian we find that the relative Euler rotation pole is located near an indenter-like feature, which possibly controls the present-day rotational tectonics and contrasting topography on opposite sides of the Euler pole.

This study investigates the dynamics of magmatic intrusions based on the joint analysis of analog and numerical models. By injecting different fluids from the bottom of a solidified gelatin block, we simulate the propagation of magmatic intrusions through the crust and record their shapes, trajectories, and velocity as they rise towards the surface. Additionally, we make use of a 2D fluid-filled crack propagation model constrained by our experimental observations. The numerical simulations demonstrate that our viscous fluid-filled crack experiments, conducted with silicon-oil injections, propagate in the same regime as typical basaltic intrusions. The comparison between analog and numerical results allow us to define the domain of validity of the numerical model and its limit of applicability. This study provides new insights into the processes that control the propagation of magmatic intrusions and our ability to reproduce them using analog and numerical models.

Improving the efficiency of photosynthesis has important theoretical and practical value, and the application of pulsed light is an effective strategy for this goal. This study explored the theoretical temporal model of photosynthesis. In the experiment, the mean rate of oxygen evolution was measured under different photosynthetic photon flux densities and cycle durations with incremental pulse width modulation. The results revealed that the instantaneous oxygen evolution rate calculated using the differential method is an exponential curve, and a mathematical model was fitted. A photosynthetic capacitance model was proposed by referencing the capacitor charge circuit. The model suggests that a particular substance, which is stored in the photosynthetic capacitor, is consumed during the light period and accumulated during the dark period. This model could be used to explain the impact of the pulse parameters on the photosynthetic rate and provide new avenues for the study of photosynthesis under pulsed light to increase the photosynthetic rate. Oxygen evolution rate was measured using a new differential method. Temporal curve of photosynthetic rate was achieved by calculation. A capacitance model was proposed for photosynthesis under pulsed light. [ABSTRACT FROM AUTHOR]

Along 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. [ABSTRACT FROM AUTHOR]

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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. 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. [ABSTRACT FROM AUTHOR]

Volcanic eruptions are often preceded by episodes of in ation and emplacement of magma along tensile fractures. Here we study the 2021 Tajogaite-Cumbre Vieja eruption on La Palma, Canary Islands, and present evidence for tensile fractures dissecting the new cone during the terminal stage of the eruption. We use synthetic aperture radar (SAR) observations, together with drone images and time-lapse camera data, to determine the timing, scale and complexities associated with a fracturing event, which is diverging at a topographic ridge. By comparing the field dataset with analogue models, we further explore the details of lens-shaped fractures that are characteristic for faults diverging at topographic highs and converging at topographic lows. The observations made at Cumbre Vieja and in our models are transferrable to other volcanoes and add further evidence that topography is substantially affecting the geometry and complexity of fractures and magma pathways, and the locations of eruptions.

Sedimentary breccias deposited on a talus slope during extension at the front of a normal fault or at the base of a slope are related to the creation of substantial topography. The architecture of talus slopes resulting from exhumation during extension is different from that of rock cliffs without deformation. In this work, we run several analogue models, with or without extension, in order to analyse the external geometry and internal organization of sedimentary breccias and their evolution in time and space. This temporal organization of the sand layers in the experiments shows that normal unroofing sequences are characteristic of progressive exhumation and continuous deformation during extension, whereas reverse unroofing is related to cliff destruction without vertical movement. In the experiment with wet layers of sand, the blocks that resulted from the aggregates of sand grains are generally deposited farther away than single sand grains and are located at the base of the slope; this is one of the main characteristics of rockfalls. The analogue results are compared to natural examples.

Abstract We present a series of analogue models inspired by the geology of the Zürcher Weinland region in the Northern Alpine Foreland Basin of Switzerland to explore the influence of rheological weak, i.e. (partially) ductile layers on the 3D evolution of tectonic deformation. Our model series test the impact of varying weak layer thickness and rheology, as well as different kinematics of an underlying “basal fault”. Model analysis focuses on deformation in the weak layer overburden and, uniquely, within the weak layer itself. We find that for low to moderate basal fault displacements, the above-mentioned parameters strongly influence the degree of coupling between the basal fault and the weak layer overburden. Coupling between the basal fault and overburden decreases by reducing the strength of the weak layer, or by increasing the weak layer’s thickness. As a result, basal fault displacement is less readily transferred through the weak layer, leading to a different structural style in the overburden. By contrast, increasing the amount, or rate, of basal fault slip enhances coupling and leads to a more similar structural style between basal fault and overburden. Moreover, dip-slip displacement on the basal fault is more readily transferred to the overburden than strike-slip displacement of the same magnitude. Our model results compare fairly well to natural examples in the Northern Alpine Foreland Basin, explaining various structural features. These comparisons suggest that rheological weak layers such as the Jurassic Opalinus Clay have exerted a stronger control on fault zone architecture than is commonly inferred, potentially resulting in vertical fault segmentation and variations in structural style. Furthermore, the novel addition of internal marker intervals to the weak layer in our models reveals how complex viscous flow within these layers can accommodate basal fault slip. Our model results demonstrate the complex links between fault kinematics, mechanics and 3D geometries, and can be used for interpreting structures in the Alpine Foreland, as well as in other settings with similar weak layers and basal faults driving deformation in the system.

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.

The East African Rift System (EARS) represents a major tectonic feature splitting the African continent apart into the Nubian Plate situated to the west, and the Somalian Plate to the east. The EARS comprises various rift segments and two microplates (the Victoria and Rovuma plates) and represents a key location for studying rift evolution. Researchers have proposed various scenarios for the evolution of the EARS, but the impact of continental-scale rotational rifting, caused by the rotation of the Somalian Plate, has received only limited attention. In this study we apply analogue models to explore the dynamic evolution of the EARS within the broader rotational rifting framework. Our models show that rotational rifting leads to the lateral propagation of deformation towards the rotation axis, but we must distinguish between the propagation of distributed deformation, which can move very rapidly, and localized deformation, which can significantly lag behind. The various structural weakness arrangements in our models (representing pre-existing structural heterogeneities) lead to a variety of different structures. Laterally overlapping weaknesses are required for localizing parallel rift basins to create rift pass structures, possibly leading to the rotation and segregation of micro-plates, as is the case for the Victoria Plate in the EARS. Additional model observations concern the development of early pairs of rift-bounding faults flanking the rift basins, followed by the localization of deformation along the axes of the most advanced rift basins. Furthermore, the orientation of rift segments with respect to the regional (rotational) plate divergence affects deformation along these segments: oblique rift segments are 30 less wide due to a strike-slip deformation component. Overall, our model results are a good fit with the large-scale features of the EARS, providing constraints on the timing of rift development and on the segregation and rotation of the Victoria plate within the broader rotational rifting framework of the EARS. [ABSTRACT FROM AUTHOR]

We present a series of analogue models inspired by the geology of the Zürcher Weinland region in the Northern Alpine Foreland Basin of Switzerland to explore the influence of rheological weak, i.e. (partially) ductile layers on the 3D evolution of tectonic deformation. Our model series test the impact of varying weak layer thickness and rheology, as well as different kinematics of an underlying "basal fault". Model analysis focuses on deformation in the weak layer overburden and, uniquely, within the weak layer itself. We find that for low to moderate basal fault displacements, the above-mentioned parameters strongly influence the degree of coupling between the basal fault and the weak layer overburden. Coupling between the basal fault and overburden decreases by reducing the strength of the weak layer, or by increasing the weak layer's thickness. As a result, basal fault displacement is less readily transferred through the weak layer, leading to a different structural style in the overburden. By contrast, increasing the amount, or rate, of basal fault slip enhances coupling and leads to a more similar structural style between basal fault and overburden. Moreover, dip-slip displacement on the basal fault is more readily transferred to the overburden than strike-slip displacement of the same magnitude. Our model results compare fairly well to natural examples in the Northern Alpine Foreland Basin, explaining various structural features. These comparisons suggest that rheological weak layers such as the Jurassic Opalinus Clay have exerted a stronger control on fault zone architecture than is commonly inferred, potentially resulting in vertical fault segmentation and variations in structural style. Furthermore, the novel addition of internal marker intervals to the weak layer in our models reveals how complex viscous flow within these layers can accommodate basal fault slip. Our model results demonstrate the complex links between fault kinematics, mechanics and 3D geometries, and can be used for interpreting structures in the Alpine Foreland, as well as in other settings with similar weak layers and basal faults driving deformation in the system. [ABSTRACT FROM AUTHOR]

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. 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 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). The proposed GRAM is composed of quartz 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 quartz 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. [ABSTRACT FROM AUTHOR]

• Analogue experiments confirm the effect of isostacy on crater floor fracture formation by upward flexing of crater floors. • Long-term relaxation of crust below craters and their periphery is caused by lower crustal flow toward crater centres. • The geometry of floor fractures caused by relaxation depends on crater diameters and crustal strength. Crater floor fractures are prominent post-cratering structural vestiges that are known from large impact craters on rocky celestial bodies. Two mechanisms have been proposed to explain the formation of crater floor fractures: emplacement of horizontal igneous sheets below crater floors and isostatic re-equilibration of crust underlying target rocks, i.e., crustal relaxation. Here, we use two-layer analogue experiments to model the deformation of lower and upper crust following crater formation, scaled to the physical conditions on Earth, to explore the structural and kinematic consequences of crustal relaxation. Specifically, the structural evolution of model upper crust was systematically analysed for various initial depths and diameters of crater floors, gleaned from previous numerical models for average continental crust. The analogue modelling results provide quantitative estimates of the duration, geometry and distribution of deformation zones in the upper crust and, for the first time, a quantitative relationship between the diameter, depth and fracture geometry of crater floors. The experiments also show that crater floor uplift is accomplished by long-wavelength subsidence of the crater periphery, which may operate on time scales of hundreds of thousands of years in nature. We conclude that patterns of natural crater floor fractures, including impact melt rock dikes known from the Sudbury and Vredefort impact structures, can be caused by long-term uplift of the crater floor, compensated by lateral crustal flow toward the crater centre. [Display omitted] [ABSTRACT FROM AUTHOR]

Analogue modelling of wrench tectonics typically utilizes a rigid basement with a velocity discontinuity under a brittle or brittle-viscous cover, such as in Riedel experiments, which confines fault localization in the overlaying model. However, such a set-up is hardly compatible with modeling brittle-ductile systems such as the upper and lower crust or a brittle sedimentary cover overlying a viscous evaporitic layer. To achieve a more realistic experimental approach, Bruno Vendeville designed an alternative experimental set-up decoupling the basement from the brittle overburden with a viscous layer in which the basement is not involved. In this configuration, strike-slip movement is driven laterally rather than from the base up, facilitated by "weak zones" that preferentially localize the deformation during shortening and enable sliding between compartments. This original approach provides greater flexibility for modeling complex strike-slip settings, allowing for more freedom for strike-slip structures to form and evolve through time. Although the experiments described in this work were conducted in the late 1990s, the co-authors have chosen to revisit and adapt this earlier work for this Special Issue to underscore Bruno's influence on another aspect of salt tectonics and his pioneering foresight in the field of analogue modelling. • Wrench zones have traditionally been modeled using basal discontinuities. • An alternative brittle-viscous set-up utilizing weak zones is presented. • Wrenching is triggered by shortening without to involve the rigid basement. • This set-up provides greater freedom for the formation and evolution of strike-slip structures. • The style of the wrench zone varies according to the degree of lateral confinement. [ABSTRACT FROM AUTHOR]

Megaflaps comprise steeply dipping to overturned panels of the oldest suprasalt strata flanking steep diapirs, and represent the roofs of early inflated salt. These large-scale structures result from salt-sediment interaction at minibasin scales and entail multiple kilometres of folding and vertical relief. They are divided into two end-member types (halokinetic and contractional) and form by some combination of limb rotation and kink-band migration. They can be difficult to image and interpret adjacent to flaring diapirs and beneath allochthonous salt due to steep bedding dips and suboptimal illumination. Using physical models, we investigate halokinetic megaflaps driven by differential loading. Models with vertically-stacked vs. laterally-shifting loading above a prekinematic layer have been run to determine the main processes and mechanisms controlling the growth and kinematic evolution of megaflaps. Parameters such as the thickness of the prekinematic cover, the width of the proto-salt wall, the synkinematic sedimentation rate, and variations in the mechanical properties of the prekinematic cover have been tested to evaluate their role in megaflap generation. The experimental results demonstrate that in absence of tectonic forces, halokinetic megaflaps are generated by a combination of 1) an early increase of pressure-head gradient between two adjacent minibasins with different rates of sedimentation and subsidence, and 2) the disappearance of this gradient that occurs when welding occurs beneath the more quickly subsiding minibasin. The geometry, kinematic evolution, and degree of small-scale deformation of the megaflaps in our analogue models are consistent with both exposed (e.g., Paradox Basin) and seismically imaged halokinetic megaflaps (e.g., deepwater northern Gulf of Mexico). • We investigate halokinetic megaflaps driven by differential loading using analogue models. • Modelled megaflaps stretch and thin upward when they are made by sand, and have a constant thickness when are more cohesive. • They formed by rapid subsidence of a minibasin once the adjacent one was welded and pressure-head gradient disappears. • Halokinetic megaflap folding was dominantly by bed rotation early, but mostly by kinkband migration late in the history. • Megaflap's development ended when allochthonous salt broke out and overrode them. [ABSTRACT FROM AUTHOR]

We conducted scaled analogue modelling to show the influence of varying single layer initial orientation on the geometry of folds and boudins in a bulk constrictional strain field. The initial angle between the plane of shortening and the competent layer (θ Z(i)) was incrementally increased from 0° to 90° by multiples of 11.25°. While the amount of layer thickening decreased with increasing θ Z(i) , the deformation structures produced range from pure dome-and-basin folds to coeval folds and boudins. Based on the attitude of fold axes, there are extension-parallel (F EPR) and extension-perpendicular (F EPP) folds, with axes subparallel and subperpendicular to the principal stretching axis (X), respectively. Coeval growth of F EPR folds and boudins occurred when θ Z(i) > ca. 25°. The F EPP folds can be subdivided into a first type which affect the entire layer (if θ Z(i) ranges between 11.25 and 78.75°) and a second type, referred to as FB EPP folds, which are affecting pre-existing boudins if θ Z(i) > 45°. The interlimb angle of all types of folds increases with increasing θ Z(i). Folds and boudins similar to the ones produced in this study can be found in salt domes and in tectonites of subduction zones. • Constrictional structures range from dome-and-basin folds to coeval folds and boudins. • Under bulk constriction, the competent layer rotates slower than a passive plane. • Extension-parallel and –perpendicular folds grow simultaneously. • Extension-perpendicular folds affect previous boudins. [ABSTRACT FROM AUTHOR]

Tunisia, located in the Northern African margin, was subjected to Late Permian-Early Cretaceous N–S extension subsequent to Pangea breakup and leading to the Tethyan opening and widening. During the Mid- and Late Cretaceous, the NE–SW crustal extension that established the Pantelleria-Malta-Sirt grabens system underlining the eastern margin stretched also the Tunisian Atlassic domain, creating and/or reactivating many NW-SE extensional structures as much as the grabens in central Tunisia and leading to volcanism and halokinesis along several weak zones. Neogene compressional tectonics inverted the earlier extensional structures and impacted most of the halokinetic features established within the post-Triassic cover. The M'Rhila-Labaied-Trozza fault relay zone, located in the middle of central Tunisia, shows both extensional and compressional structures with Triassic extrusive features and seems to be a key feature for understanding the geodynamic development of the area. In this work, we combined field and geophysical data together with analogue models to decipher the structure and the kinematic evolution of the study area. The results showed that the studied structures are associated with reactive Mesozoic salt ridges established along an extensional fault relay zone that utilized NW-SE, E-W and NE-SW inherited fractures. These initially created extensional corridors allowing Triassic evaporite extrusion and accumulation, then influenced the deformation of the area in transpressional and local pure compressional regimes depending on the fractures and stress orientations during tectonic inversion. Analogue guided interpretation of the successive deformational stages of the study area from salt ridge growth to its tectonic inversion. • Triassic salts occupy an abnormal stratigraphy positions in central Tunisia. • Analogue modelling is a suitable method to explain halokinetic movements in Central Tunisia. • Halokinetic movements highly affect structural evolution of the study area. [ABSTRACT FROM AUTHOR]

• Elongated calderas were often considered proxy for the regional extension. • We run circular caldera collapse analogue models afterward elongated by extension. • We prove that extension justifies only 13% of elongation for calderas in the MER. • Only specific sectors of caldera faults are capable of reactivation under extension. • Caldera structures influence the architecture of newly forming regional faults. Caldera collapses are paramount volcano-tectonic features because they form during hazardous explosive volcanic eruptions, they are ideal sites for geothermal development and mineral resources exploitation, and also because they preserve the evidence of the interaction between caldera magmatism and the regional tectonic processes. Despite this, many aspects of the caldera collapse process remain unclear, particularly concerning the interaction between caldera and tectonic related fault systems. We therefore used analogue models 1) to quantify the effect of regional strain on caldera elongation in extensional settings, such as the Main Ethiopian and the Kenya rifts, 2) to describe the effect of regional strain on caldera structures and, vice-versa 3) to document, for the first time, "the other side of the coin", that is how caldera structures affect the formation of newly forming regional extensional faults. Our models showed that tectonic extension only explains a small proportion (e.g. 13% for the Main Ethiopian Rift) of the elongation of most rift calderas. Furthermore, we showed how specific segments of caldera faults may accommodate regional extension by reactivating, therefore precluding caldera elongation. Finally, we showed how the presence of caldera structures may influence the geometry of newly forming regional normal faults, that display a marked curvature, "faking" caldera ring faults. We have suggested that these "fake" curved caldera ring faults may lead to incorrect estimations of caldera elongation in nature. In addition, such faults may also mislead geothermal fluid exploration, as they are likely disconnected from the caldera structures or the caldera plumbing system, and less likely the locus of hydrothermal fluid flow. [Display omitted] [ABSTRACT FROM AUTHOR]

Basement inherited structures represent a significant factor affecting thrust propagation dynamics during the growth of fold-and-thrust belts. In this study inspirited from seismic data analysis of Gaoquan anticline in the Northern Tianshan foreland basin, we devised an experimental approach to investigate the structural and kinematical evolution of deformation from preexisting basement restraining bend to subsequent contractional deformation. Tested parameters included reactivation of the basement restraining bend and erosion. Results indicated that when preexisting basement restraining bend was reactivated and folded an overlying décollement , subsequent thrust nucleated preferentially at the top of the folded décollement. Erosion helped localize deformation, thereby reducing the width of the deformation zone and promoting "out-of-sequence" thrusting during compression. Finally, as we employed silicone polymer to simulate overpressured mudstone layer in the major décollement , our experiments also provide insights into a better understanding of the relationship between shallow salt-detached thrusting and deep inherited basement structures, such as in the Jura Mountains structures. • Experimental models with wrench and compressional tectonics are presented. • asement restraining bends are reactivated or not during subsequent compression. • Restraining bend reactivation affects the mode of fold and thrust propagation. • Erosion during restraining bend reactivation affects sequence of thrusting. [ABSTRACT FROM AUTHOR]

The competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these 'internal' and 'external' factors remain poorly understood, especially in 3D. In this study, we used brittle‐viscous analogue models to assess how multiphase rifting, that is changes in plate divergence rate or direction, and the presence and orientation of weaknesses in the competent mantle and crust, influences rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without any kinematic changes already creates complex rift structures. Divergence rates affect the strength of the weak lower crustal layer and hence the degree of mantle‐crustal coupling; slow rifting decreases coupling, so that crustal weaknesses can dominate deformation localisation and surface structures, whereas fast rifting increases coupling and deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle‐related deformation can overprint structures that previously formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle‐controlled towards crust‐controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are sufficiently well developed. We furthermore place our results in a larger framework of brittle‐viscous rift modelling results from previous experimental studies, showing the importance of general lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can produce a variety of deformation styles that may, however, lead to comparable end products. Therefore, careful investigation of the distribution of strain localisation, and to an equal extent of basin depocenter locations over time is required to properly determine the evolution of complex rift systems, providing an incentive to revisit various natural examples. [ABSTRACT FROM AUTHOR]

The Linhe Depression is the largest tectonic unit in the Hetao Basin. The recently discovered commercial oil flow in the structural trap of wells JH2X and S5 has proved that the Meso-Cenozoic strata in the Linhe Depression have great exploration potential. Research on the kinematic model for the Mesozoic–Cenozoic Linhe Depression is important for analysing the geological conditions of hydrocarbon accumulation. In this study, field observations, seismic interpretation and scaled analogue modelling are performed. The results prove that the Linhe Depression experienced different stages of tectonic evolution, such as compressional depression (K1l), conversion from contraction to uniform subsidence (K1g), extensional rifting (E2–N2) and strike-slip deformation (Q), during the Mesozoic–Cenozoic eras. The kinematic model of negative inverted basins was first established with the early differential compression superimposed by the late extension. The seismic interpretation and analogue modelling results show that Jilantai Sag in the southern part of the Linhe Depression was subjected to compression from the Bayanwulashan fold–thrust belt on the NW side and the Helanshan fold–thrust belt on the SE side during Early Cretaceous time. Meanwhile, the Hanghou Sag in the northern part of the Linhe Depression was only compressed by the Langshan fold–thrust belt from the NW direction. The rifted structure generated by the extension from the SE direction during the Cenozoic Era resulted in the negative inversion of the pre-existing thrusts in different patterns. The intensity of negative inversion is controlled by several key factors, such as dip angle and the patterns of thrust faults, along with different basement textures. The morphological changes in the forebulge zone developed during Early Cretaceous time are responsible for the development of the segmented Central fault zones in the Hanghou Sag. [ABSTRACT FROM AUTHOR]

Mountain building (orogeny) has a strong causal relationship with compression induced by plate drifting. It is generally accepted that orogenic belts are distributed perpendicular to the direction of plate movement. Extensive Late Mesozoic intra-continental deformations occurred around the North China Craton (NCC) in three different directions (i.e. EW-, WNW- and NNE-striking), which were previously attributed to three different geodynamic processes; the closure of the Mongolia-Okhotsk Ocean, convergence of the NCC and the South China block, and subduction of the paleo-Pacific plate. Remarkably, all these tectonic events were synchronised. Analogue modelling experiments were used to constrain far-field stress and basement shapes, to reconsider tectonic evolution around the NCC during this period. Results showed that all of these tectonic deformations could be plausibly interpreted as a unitary geodynamic regime governed by the westward indentation of the wedge-shaped NCC, driven by subduction of the paleo-Pacific plate. Mountain chains were formed along the edges of the wedge, indicating that the distribution of orogenic belts is not necessarily correlated with the direction of plate movement.

Inspired by the structural evolution of the South-Central Pyrenean Thrust Salient we have designed an experimental program to investigate the role of the geometry of viscous detachments on the formation of thrust salients. The precontractional wedge geometry of the salt overburden facilitates propagation of the deformation front to the forward edge of the viscous detachment. As deformation progresses, interaction between structures formed above the viscous detachment and the adjacent frictional detachment mostly depends on the angles of the lateral edges of the weak layer with respect to the shortening direction. The orientation of the oblique structures defining thrust salients does not generally mimic the edges of the viscous detachment. They can even form at a high angle to the shortening direction if active structures in the frictional and viscous detachments connect along-strike. Thrust wedges above frictional and viscous detachments show different kinematic evolution. During the late stages of deformation frictional wedges propagate forward whereas viscous wedges deform internally by break-back thrust sequences. Both wedges show along-strike differences of the surface taper that have an impact on the evolution of the topography and related synorogenic sediment dispersal. Experimental results are consistent with the structural evolution and tectono-sedimentary relationships observed in the South-Central Pyrenees. [ABSTRACT FROM AUTHOR]

The European Alps result from the closure of a former Triassic to Cretaceous rifting system in which significative accumulation of Upper Triassic salt deposited. The thickness and spatial distribution of these salts had a major impact on the morphology and dynamic of the Alpine orogen all over the Western Alps. Following a bibliographical review, four regional cross-sections are revisited over the External Western Alps to emphasise along-strike variations of the orogenic wedge influenced by the presence or absence of Triassic salts. Each section is then compared with analogue models to examine the controlling factors explaining the structural styles variations. In the Northern Subalpine Chains, the absence of salt favoured a frictional decollement which promoted a narrow and thick orogenic wedge in the Bornes, Chartreuse, and Vercors massifs. Discrepancies in the spacing between the thrusts and the number of folds were however influenced by the thickness of incompetent layers in the sedimentary column. In the Jura and the SW Alps, the occurrence of Triassic salts promoted a viscous decollement and thus a wide and relatively thin orogenic wedge. However, in the SW Alps, thicker salt deposits allowed the development of pre-orogenic salt structures. These later constituted vertical heterogeneities having exerted a strong structural inheritance during the following compression, by accommodating a substantial part of the Alpine shortening, in squeezed diapirs especially. Triassic salt remobilization during the orogeny also locally promoted the development of syn-orogenic minibasins. This review highlights the significant role played by Triassic salt in shaping the Western Alps, and paves the way for possible new interpretations of the dynamics of the Alps regarding the exhumation of crystalline basement blocks, or new structural interpretations of Alpine domains, such as the Vocontian Domain. [ABSTRACT FROM AUTHOR]

This work includes, first, a synthesis of experimental analogue modelling programs assessing the influence of along-strike thickness variations in the development of oblique structures in fold-and-thrust belts. As a second part, we present a new experimental program testing, systematically, the influence of tapered décollement-cover thrust wedges. Previous experiments show that frictional, brittle models feature numerous, short-wavelength structures where the cover is thinner. Deformation fronts are totally or locally oblique to the backstop when the cover thinning is progressive or sharp, respectively. Low (<30°) or higher structural obliquities occur when thickness variations are progressive or sharp, respectively. The addition of a basal or intermediate décollement, commonly entails the transference of deformation towards its external pinch-out. Consequently salients occur and transfer zones and oblique structures form over décollement boundaries. Their location and orientation strongly depend on the pre-compressional shape of the décollements. Furthermore, as demonstrated by our modelling results, tapered brittle covers over viscous décollements result in asymmetric thrust wedges formed by structures that end or change their vergence laterally, resulting in obliquities generally <30°. Two natural case studies, showing strong (South Pyrenean Central Salient) or moderately oblique (Keping Shan fold-and-thrust belt) structures are revisited and compared to the described analogue models. • We study structural obliquities related to along-strike thickness changes. • We synthesized series of analogue models focused on the origin of oblique structures. • Previous models are completed with new ones involving tapered salt-detached systems. • New results and synthesized models are compared to three different natural examples. [ABSTRACT FROM AUTHOR]

The role of pre-existing structures during the building of the Zagros fold-and-thrust belt is a matter of debate. The orientation of the pre-existing basement faults varies in different parts of the Zagros belt. Major directions of the basement faulting in the Arabian plate and Zagros are N–S, NE–SW, NW–SE and E–W. Reactivation of these inherited pre-existing faults occurred at the Cretaceous. In this study, analogue modelling was constructed to test the effect of various orientations of the pre-existing basement faults on the deformation style in the northern boundary of Dezful Embayment. The model consisted of sand layers that partly overlay a viscous layer of silicon above wooden plates. Model results explain the development of deflection in the deformation front and the incompatibility location of faults in the basement and surface. The presence of the basal décollement horizon between the basement and overlying sedimentary sequences separated faulting geometry in the basement from sedimentary cover. Model results suggest that the flexure of the Zagros Mountain Front Faults (ZMFF) in the north part of Dezful Embayment is resulted by reactivation of pre-existing Bala Rud fault (BRF) which is an oblique ramp. The close similarity between the major structures produced during the analogue experiments and those observed in nature, suggests that BRF as a pre-existing basement fault has a major role in the deformation of the structures in the study area. [ABSTRACT FROM AUTHOR]

A variety of tool shoulder designs comprising three families i.e. blade, spiral and circular shaped scrolls, were produced to improve the material flow and restrictions to avoid the tunnel void. The bobbin tools were manufactured by 3D printing additive manufacturing technology using solid filament. The butt weld joint was produced by each tool using plasticine as the workpiece material. The apparent surface features and bi-colour cross-sections provided a physical flow comparison among the shoulder designs. For the bobbin friction stir welding (BFSW), the tool shoulder with a three-spiral design produced the most stability with the best combination of the flow patterns on surface and cross-sections. The circular family tools showed a suitable intermixing on the surface pattern, while the blade scrolls showed better flow features within the cross-sections. The flow-driven effect of the shoulder features of the bobbin-tool design (inscribed grooves) was replicated by the 3D-printed tools and the analogue modelling of the weld samples. Similar flow patterns were achieved by dissimilar aluminium-copper weld, validating the accuracy of the analogue plasticine for the flow visualization of the bobbin friction stir welding. [ABSTRACT FROM AUTHOR]

This study introduces a fused filament fabrication (FFF) process for manufacturing complex-structured asteroid analogue objects to be applied in tomographic microwave radar measurements and inversion studies. We describe an approach to control the volume fraction of the plastic and, thereby, the effective relative permittivity within a tetrahedral wireframe which serves as metamaterial representing the actual asteroid composition. To determine the effective permittivity of the plastic–air mixture, we use an exponential model. In this study, two analogue objects based on the shape of the asteroids 1998 KY26 and (25143) Itokawa were 3D-printed in a scale suitable for microwave laboratory measurements using ABS filament with a controlled constant relative electric permittivity. The results obtained suggest that the permittivity of solid and powdery asteroid minerals can be modelled with the proposed technique and, in particular, that the numerical structural permittivity models of the earlier numerical studies can be approximated by 3D-printed analogues.

Many orogens on the planet result from plate convergence involving subduction of a continental margin. The lithosphere is strongly deformed during mountain building involving subduction of a plate composed generally of accreted continental margin units and some fragments of downgoing oceanic crust and mantle. A complex deformation involving strong partitioning of deformation modes and kinematics produces crustal shortening, accompanied by crustal thickening. Partitioning depends on three main factors: (1) rheologic layering of the lithosphere; (2) interaction between tectonics and surface processes; (3) subduction kinematics and 3D geometry of continental margins (oblique convergence, shape of indenters). Here we present an original view and discussion on the impact of deformation partitioning on the structure and evolution of orogens by examining the Taiwan mountain belt as a case study. Major unsolved questions are addressed through geological observations from the Taiwan orogen and insights from analogue models integrating surface processes. Some of these questions include: What is the role played by décollements or weak zones in crustal deformation and what is the impact of structural heterogeneities inherited from the early extensional history of a rifted passive continental margin? What is the relationship between deep underplating, induced uplift and flow of crustal material during erosion (finite strain evolution during wedge growth)? Are syn-convergent normal faults an effect of deformation partitioning and erosion? What is the role of strain partitioning on the location of major seismogenic faults in active mountain belts? What can be learned about the long-term and the present-day evolution of Taiwan? [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of a new approach based on sandbox models to the understanding of the tectonic evolution of the Volta Redonda Basin, southeastern Brazil. Those models were designed to replicate the overlapping process of two of the four superimposed tectonic events identified in the Volta Redonda Basin: the first one, a rifting event with NW-SE extension direction that created the basin, and the subsequent E-W sinistral transcurrent tectonics. The boundary conditions for the models were set from the geological premises described in previous works, which resulted in the current conceptual geological models of the study area. The sandbox models were composed of alternating layers of colored sand, deposited on two pieces of acetate or cardboard sheets, which acted as pre-existing basement structures. Once completed, the models were cut and photographed to allow observation and interpretation of the resulting internal structures. Moreover, the interpretations maintain similarities with adopted conceptual models and permit conclusions about structures previously identified in other works. Finally, the consequent structural framework exposes the effects of structural reactivation and Basin geometry changes due to the superposition of deformational events and matches with the general structural aspects identified in field studies.

This paper presents the results of a new approach based on sandbox models to the understanding of the tectonic evolution of the Volta Redonda Basin, southeastern Brazil. Those models were designed to replicate the overlapping process of two of the four superimposed tectonic events identified in the Volta Redonda Basin: the first one, a rifting event with NW-SE extension direction that created the basin, and the subsequent E-W sinistral transcurrent tectonics. The boundary conditions for the models were set from the geological premises described in previous works, which resulted in the current conceptual geological models of the study area. The sandbox models were composed of alternating layers of colored sand, deposited on two pieces of acetate or cardboard sheets, which acted as pre-existing basement structures. Once completed, the models were cut and photographed to allow observation and interpretation of the resulting internal structures. Moreover, the interpretations maintain similarities with adopted conceptual models and permit conclusions about structures previously identified in other works. Finally, the consequent structural framework exposes the effects of structural reactivation and Basin geometry changes due to the superposition of deformational events and matches with the general structural aspects identified in field studies. [ABSTRACT FROM AUTHOR]

Cohesion and friction coefficients are fundamental parameters of granular materials used in analogue experiments. Our six models, comprising two sets of quartz sand with a 0–3 mm thickness of basal glass beads, illustrate that accretionary wedges with high basal friction have relatively larger slope angles and heights, shorter wedge lengths, and larger numbers of faults with smaller spacings and displacements than wedges with low basal friction. It should be noted that the differences in the geometry and evolution of the two sets of homogeneous quartz sands are not distinct; however, the differences are substantial when the models have low basal friction of the glass beads. In particular, there are two different tendencies of growth in wedge height with progressive shortening, that is, progressive growth of wedge height with high basal friction and steady‐state growth of wedge height with basal glass beads. We thus infer that the wedge geometries in our experiments are preferentially controlled by the low basal friction achieved with glass beads. In particular, the basal décollement (even when thin) has a significant influence on the location and development of accretionary wedges, in contrast to the physical properties of brittle materials (e.g., friction coefficient and cohesion). [ABSTRACT FROM AUTHOR]

The flow-inducing effect of the bobbin-tool features (tri-flat pin and scrolled shoulder) were replicated by a simple analogue model for aluminium welds by layered plasticine samples. Flow patterns of the weld zone were clarified by a typical stereomicroscopy instrument assisted by dark-field/bright-field illumination. The effects of the pin features, specifically threads and flats in centre of bond zone and scrolled shoulder in sides of stirred zone, were identified. This study shows that internal flow features for BFSW welds is transferable from the friction stir welding process to the functional metal forming processes such where the shearing can extensively affect the microstructure. The similarity between the flow pattern of the provided aluminium samples and the plasticine analogue can validate the accuracy of the flow model presented in this work. [ABSTRACT FROM AUTHOR]

The Pyrenees are a collisional orogen striking WNW-ESE. However, in the Ainsa oblique zone in the south-central part of the Pyrenees, faults and folds rotate to ∼N–S over a westward thinning evaporitic layer. The influence of lateral change in basal friction due to declining evaporitic layer thickness in a fold-and-thrust belt is studied by analogue modelling simulating the Ainsa oblique zone. In the experiments the transition zone is simulated by a viscous silicone mixture sheet that laterally changes in thickness adjacent to frictional-plastic quartz-sand. The models confirm that a transition between weak and strong basal friction causes oblique structures to develop. Weak detachment zones are prone to fault propagation whereas strong detachment zones are prone to imbrication. At the transition zone those structural styles are combined, resulting in a complex domain. The differences in deformation style cause dextral shear and clockwise rotation in the transition zone and larger horizontal deformation propagation in the weak basal friction zone. Structures produced in the analogue models are compared to structures in the Ainsa oblique zone and found to be representative. Therefore, this study shows that transition between weak and strong detachment layers can explain the regional structural deformation style in the Ainsa oblique zone. • The Ainsa oblique zone has oblique fold and fault structures likely due to an unevenly distributed basal viscous salt layer. • A new analogue set-up simulates lateral progressive thinning of a viscous silicone sheet representing the Ainsa oblique zone. • Experimentally obtained oblique fold and fault angles over a thinning viscous sheet match the Ainsa zone structural angles. • Transition between high and low basal friction combines two deformation styles causing dextral shear and clockwise rotation. [ABSTRACT FROM AUTHOR]

Better understanding of stress perturbations, strain propagation and fluid flow in the upper crust require characterisation of fault damage zone evolution. Outcrop studies help understand the different processes operating during fault movement; but capture little about the evolution through time. In this study, we investigate damage zone evolution using high-resolution analogue modelling; simulating the growth of a normal fault population. The incremental strain reveals that early deformation stages occur by strain localisation into corridors of distributed deformation. Active deformation within these corridors becomes narrower as segment linkage occurs, leading to the formation of master faults, encouraging further localisation of incremental strain. This results in wide zones of cumulative strain around the fault, accommodated by different types of fault damage geometry, which formed at very different stages of the fault system growth. We also highlight the new concept of "fault system damage", that shows similarities with observations in nature. These first descriptions of the fault damage evolution allow an understanding of the composite content of damage zones. This gives support to assess zones of permeability enhancement in naturally fractured reservoirs, and proposes a view of damage distribution for targeting fluid flow, geothermal resources, leaks, micro/macro seismicity and mechanical properties of fault zones. • Fault damage zones evolution is described and grow by fault segment linkage. • Damage zone types are described in out-of-plane dimension. • Damage at fault system scale occurs by the interaction of several master faults. • A new concept of fault system damages is described and compared to nature. [ABSTRACT FROM AUTHOR]

In contractional (subduction/collisional) settings, convergence is accommodated by the formation of thin- and thick-skinned thrust and fold belts. The transmission of such deformation over larger distances into orogenic foreland areas is influenced by the inherited rheological characteristics of continental lithosphere. Lateral rheological variations parallel to the strike of continental foreland areas creates contrasting geometries and sequences of deformation that interact during orogenic build-up. We investigate the far-field transmission of strain within a continental lithosphere characterized by a laterally variable rheology through physical analogue modelling. Rheological weak crustal zones were introduced at distance from an advancing backstop to study the progressive along strike linkage and interference of structures during contraction. The results reveal that rheologically weak crustal zones localise far-field contractional deformation. When the size of weak zones, by means of their horizontal extend to depth ratio, is large, deformation localises at the boundaries of the weak zone where they lead to the formation of large-offset faults. Subsequently the faults migrate along-strike into areas that are rheologically stronger. When the size of the weak zone is reduced, a large-scale contractional step-over forms in orogenic forelands, where rheologically contrasting domains transmit out-of-sequence deformation by a gradual migration of thrust offsets and fold amplitudes along their strike. These results show that crustal scale orogenic step-overs do not always reflect variations in the geometry of the plate boundary (indenter) or along-strike gradients in shortening rates. Such features may also form in response to variations in rheology, as the ones created by inherited extensional basins situated at large distances from plate boundaries in the orogenic foreland. • Crustal weak zone(−s) localise strain at far distance from the indenter. • Contractional step over might reveal the presence of crustal weak zone. • Crustal deformation at weak zone will be associated with lithospheric folding. • The symmetry of lithosphere fold can reveal the lithosphere strength. [ABSTRACT FROM AUTHOR]

Fractures formed when igneous rocks cool below the surface of the Earth are of considerable current interest in studies of hydrology, mineral systems and radioactive waste disposal. However, little is known about the geometry and kinematics of such fractures. Conceptual models suggest that early fractures result from emplacement forces (the Cloos model) while two-dimensional numerical modelling suggests that fractures may result from the contraction of cooling bodies. We use analogue modelling to investigate the geometry of fractures formed in a cylindrical static contracting body. Our experiments show that dehydration of buried starch flour is a workable analogue. Fractures in the analogue material result from drying and contraction of a cylindrical volume which differs from previous experiments in which drying was from a single planar surface and resulted in the formation of columnar joints. In buried analogue models two key fracture sets form internally, producing sub-vertical radial fractures, and concentric fractures that curve downwards with depth. Fracture density decreases towards the centre and bottom of the samples. Samples that were buried more deeply have fewer and less curved concentric fractures than those with shallow burials. Radial fractures have similar orientations to those predicted from numerical models, and concentric fractures are comparable to marginal fissure orientations of the Cloos model. The analogue models suggest that both radial and concentric fractures may result from the contraction of plutonic bodies. • Analogue models to understand fracturing of plutons during cooling. • Radial and concentric, steepening downwards, fractures are formed in contracting cylindrical volumes. • Results depend on rate of contraction and burial depth. [ABSTRACT FROM AUTHOR]

Crustal shearing of pre-tectonic weak bodies (e.g. salt pillows, igneous pockets) associated with basement strike-slip fault systems is common in nature. Yet the structural pattern arising from the interference between a brittle shear zone and such weak rheological heterogeneities is still not fully explained. In the present work, different sand-box analogue modelling experiments were carried out to better understand, not only the shear zone perturbation effect caused by a strictly rheologic (viscous-weak) anomaly, but also the one arising from a combined morphological perturbation (i.e. traverse topographic crest). Obtained results show that the development of different shear zone deformation patterns is in each case essentially determined by the interplay between: (i) ductile wrenching strain accommodation in the (viscous) weak body; and (ii) coincidence vs. mismatch between main brittle-viscous rheological boundaries and (crest-related) topographic steps. Comparison of the experimentally obtained results with complying natural examples is further discussed, and essentially focused on the NE Atlantic tectono-magmatic interference between the Gloria transform fault and the Tore-Madeira submarine ridge. • Analogue modelling of strike-slip brittle shear propagation across a pre-tectonic weak (viscous) anomaly. • Combined (morpho-rheologic) effect exerted by the viscous anomaly and by a (90° or 120°) trasverse topographic crest. • Coincidence vs. mismatch between rheological and morphological boundaries and its influence on the resulting structural pattern. • Control on the distribution of different structures around opposite quarters of the viscous anomaly. • The natural example of the transform Gloria fault - Tore Madeira rise tectono-magmatic interference in NE Atlantic. [ABSTRACT FROM AUTHOR]

The PIV (particle image velocimetry) method became a standard tool for the calculation of displacement fields in physical geodynamic models. For understanding the deformation dynamics of geodynamic models, in our study, we implemented several post-processing algorithms on the derived displacement field and calculated the velocity and strain(-rate) components, such as the divergence of the velocity field, vorticity and shear strain-rate. In the model of oroclinal buckling, we focused on strain analysis of the upper crust and correlated the shear strain-rate, vorticity and divergence anomalies with visual deformation patterns in the upper crust. The divergence of velocity fields in these models correspond to the pop-up and pop-down belts oriented along the axial trace of the oroclinal bends. High shear strain-rate domains correlate with horizontal, isovolumic shear zones alongside these belts, while vorticity shows rotational trend of fold axial traces of the pop-up and pop-down belts, around orocline inflection. In another series of models, we simulated the development of melt-cored crustal scale detachment folds and employed the same set of parameters to investigate the ductile deformation visible in side-view of the model domain. We developed a method that allows tracing the divergence in subcells locked on target subdomains. We tracked and quantified melt flow between the melt source area at the bottom of the model and progressively developing folds. This mass transfer analysis revealed polyphase fold evolution, where initial fold perturbations quickly amplify as the melt accumulates in the triangular hinge sector below and between the rotating fold limbs. While the early amplification leads to decompression driving the melt into the hinge zone area between the limbs, the fold lock-up stage and continued attenuation of the vertical limbs is associated with melt expulsion from the fold interlimb domain back into the source layer, where it can be transferred laterally to the foreland. • Models of oroclinal buckling and detachment folding were investigated by the PIV method. • Several model parameters related to the velocity and strain were used to analyze the deformation features in both models. • The divergence of the velocity field reflects distortion of the model surface. • Analysis of the divergence reflects mass transfer budget in detachment folds. • The fold growth rate is driven by the degree of melt flux into the axial zone. [ABSTRACT FROM AUTHOR]