Plate Kinematics Research Articles

Embedded boundary conditions for shear-deformable plate bending

An efficient procedure for embedding kinematic boundary conditions of shear-deformable plate bending is based on stabilized variational formulations, obtained by Nitsche’s approach for enforcing surface constraints. Effective use of the plate thickness as scaling in the rotational constraint terms leads to a uniform problem statement with a single stabilization parameter. An alternative form of the plate kinematics precludes the vulnerability of computation based on the standard Reissner–Mindlin formulation to shear locking, yet raises other challenges in the form of higher-order regularity and unconventional boundary conditions. The embedded boundary Nitsche approach provides a framework that easily accommodates these features. The accuracy of the approach for both plate formulations is verified by representative computations with bicubic B-splines, exhibiting optimal rates of convergence, and robust performance with respect to values of the parameters.

Along-strike segmentation of the northeastern Brazilian margins controlled by geodynamics and lithospheric inheritance

Passive continental margins depict a wide range of crustal architectures. Such observation mainly come from wide-angle seismic that has proven to be a valuable tool to constrain margins’ onshore and offshore crustal structures. Yet, it is still unclear what are the main drivers of such diversity and whether some more general processes do also control their formation. Here, by analyzing coincident marine seismic reflection and refraction data acquired parallel to the coast of northeast Brazil we shed a unique view on the along-strike segmentation of its passive margins. Our two P-wave velocity models add up to 10 other wide-angle velocity models build in the scope of the SALSA (Sergipe ALagoas Seismic Acquisition) project to provide a coherent picture of the crustal and upper mantle architecture of the offshore domains of the Jequitinhonha, Almada, Camamu, Jacuípe, Sergipe and Alagoas margins. In the Camamu-Jacuípe segment, both crustal necking and the continent to ocean transition were shown to be sharp. Along strike, our models show extremely thin crust above a thick anomalous velocity layer and a relatively low density mantle. This architecture is interpreted as made of collapsed continental blocks above either highly intruded lower continental crust and/or serpentinized mantle that is locally exhumed. It greatly differs from the crustal structure imaged to the south, within the Jequitinhonha and Almada segments, where our models support the existence of a vast and homogeneous domain of exhumed lower continental crust. It also considerably contrasts with the offshore architecture of the Sergipe-Alagoas segment to the north. There, the necking and transition to normal oceanic crust was shown to be narrow but gradual and dominated by middle to lower continental crust. On our along-strike models, it is characterized by a thicker but also highly intruded continental crust. Crustal architecture evolves brutally at the frontiers of these segments which coincides precisely with the Camamu Triple Junction and the offshore prolongation of the Vaza Barris fault zone. The former is one of the major geodynamic features in the development of the Central Segment of the South-Atlantic Ocean while the later marks the suture between the São-Francisco Craton and the northeastern Brazilian Orogenic Belt. Therefore, we clearly evidence the first-order control of both geodynamics and lithospheric inheritance on the along-strike segmentation of the northeastern Brazilian passive margins. Our results emphasize the crucial role of plate kinematics and lithospheric strength in shaping their architectures and the exhumation of middle/lower continental crust as a more general process of their formation.

Machine learning assisted nonlinear deflection analysis of agglomerated carbon nanotube core smart sandwich plate with three-phase magneto-electro-elastic skin

This research focuses on evaluating the combined effects of the interphase of the three-phase magneto-electro-elastic (TPMEE) composites and carbon nanotubes (CNTs) agglomeration on the nonlinear deflection of the multifunctional sandwich plate, using an artificial neural network (ANN) assisted finite-element (FE) approach. The data points collected from the in-house developed FE computational tool are used to train the ANN model. To this end, a backpropagation-based Levenberg–Marquardt algorithm is used. The core of the plate is made of agglomerated CNTs, and the facesheets are made of TPMEE composites. Two different agglomeration states, partial and complete, are considered for evaluation. Also, three variations of CNTs arrangement are assumed. On the other hand, the interphase effects are incorporated through its volume fractions and compositions. The plate kinematics is based on the higher-order shear deformation theory, and the nonlinearity is assumed to follow von Karman's strain-displacement relation. The equations of motion are derived using the total potential energy principle. Finally, the direct iterative method is used to arrive at the solutions. The numerical examples are also provided to understand the influence of coupling fields associated with the parameters, such as agglomeration, interphase volume fraction, interphase compositions and CNTs arrangement.

Nonlinear harmonic vibrations of laminate plates with viscoelastic layers using refined zig-zag theory. Part 1 – Theoretical background

The paper is devoted to the theoretical formulation of the harmonic vibrations problem for laminate plates in the von Kàrmàn geometrically non-linear regime. The plate layers are modelled as viscoelastic using the fractional Zener material with the linear elastic material being a special case. The model of the material is formulated with the separation of the volumetric and deviatoric strain. The laminate plate kinematics is described using the refined zig-zag theory. The vibrations of the plate are formulated using the alternative exponential form with complex-conjugate amplitudes. The harmonic balance method and the time-averaging are applied to derive the amplitude equation of the problem in hand. The efficiency and correctness of the formulation is verified in the continuation paper Part 2 – numerical analysis.

Nonlinear harmonic vibrations of laminate plates with VE layers using refined zig-zag theory. Part 2 – Numerical solution

The paper is devoted to the numerical analysis of the harmonic vibrations of laminate plates with viscoelastic layers in the von Kàrmàn geometrically non-linear regime. The amplitude equation derived in the prequel paper Part 1 – theoretical background is discretized using the 8-noded bi-quadratic plate finite elements. The response curves are obtained using the continuation method to solve the discretised amplitude equation treated as the equation with the frequency of vibrations as a parameter. The proposed method of solution is verified by comparing the results with those from available literature. Furthermore, several numerical analyses are performed, including testing of FE mesh density, plate aspect ratio, various VE materials, support conditions and layers layout as well as the possibility of simplification of the complex-valued zig-zag function used in the description of plate kinematics. Several results of practical importance are found and discussed in the conclusions.

Ghost-arc geochemical anomaly at a spreading ridge caused by supersized flat subduction

The Southern Atlantic-Southwest Indian ridges (SASWIR) host mid-ocean ridge basalts with a residual subduction-related geochemical fingerprint (i.e., a ghost-arc signature) of unclear origin. Here, we show through an analysis of plate kinematic reconstructions and seismic tomography models that the SASWIR subduction-modified mantle source formed in the Jurassic close to the Georgia Islands slab (GI) and remained near-stationary in the mantle reference frame. In this analysis, the GI lies far inboard the Jurassic Patagonian-Antarctic Peninsula active margin. This was formerly attributed to a large-scale flat subduction event in the Late Triassic-Early Jurassic. We propose that during this flat slab stage, the subduction-modified mantle areas beneath the Mesozoic active margin and surrounding sutures zones may have been bulldozed inland by >2280 km. After the demise of the flat slab, this mantle anomaly remained near-stationary and was sampled by the Karoo mantle plume 183 Million years (Myr) ago and again since 55 Myr ago by the SASWIR. We refer to this process as asthenospheric anomaly telescoping. This study provides a hitherto unrecognized geodynamic effect of flat subduction, the viability of which we support through numerical modeling.

A Geodynamic Investigation of Plume‐Lithosphere Interactions Beneath the East African Rift

AbstractThe force balance that drives and maintains continental rifting to breakup is poorly understood. The East African Rift (EAR) provides an ideal natural laboratory to elucidate the relative role of plate driving forces as only lithospheric buoyancy forces and horizontal mantle tractions act on the system. Here, we employ high‐resolution 3D thermomechanical models to test whether: (a) the anomalous, rift‐parallel surface deformation observed by Global Navigation Satellite System (GNSS) data in the EAR are driven by viscous coupling to northward mantle flow associated with the African Superplume, and (b) the African Superplume is the dominant source mechanism of anomalous rift‐parallel seismic anisotropy beneath the EAR. We calculate Lattice Preferred Orientations (LPO) and surface deformation from two types of mantle flow: (a) a scenario with multiple plumes constrained by shear wave tomography and (b) a single superplume model with northward boundary condition to simulate large‐scale flow. Comparison of calculated LPO with observed seismic anisotropy, and surface velocities with GNSS and plate kinematics reveal that there is a better fit with the superplume mantle flow model, rather than the tomography‐based (multiple plumes) model. We also find a relatively better fit spatially between observed seismic anisotropy and calculated LPO with the superplume model beneath northern and central EAR, where the superplume is proposed to be shallowest. Our results suggest that the viscous coupling of the lithosphere to northward mantle flow associated with the African Superplume drives most of the rift‐parallel deformation and is the dominant source of the first‐order pattern of the observed seismic anisotropy in the EAR.

South and East African fracture zones: a long lifespan since the breakup of Gondwana

Abstract Gondwana started to split up during the Early Jurassic ( c. 180 Ma) with the separation of Antarctica and Madagascar from Africa, followed by the separation of South America and Africa during the Early Cretaceous. Thanks to recent seismic profiles, the architecture of rifted margins and the transform fault zones, which developed as a result of the relative motion between tectonic plates, have been recently evidenced and studied along the whole eastern and southeastern Africa margins (i.e. in the Western Somali Basin, the Mozambique Basin, the Natal Basin and the Outeniqua Basin). But, the structure and overall kinematic evolution of the three major transform fault zones – such as the Agulhas, the Davie and the Limpopo fracture zones (FZ) – that together control the opening of major oceanic basins (Antarctic Ocean, Weddell Sea and Austral South Atlantic) remain poorly studied. The interpretation of an extensive regional multi-channel seismic dataset coupled with recent studies allows us to propose a detailed regional synthesis of the crustal domains and major structural elements of the rifted margins along the whole eastern and southeastern Africa. We provide new constraints on the structure and evolution of these three transform systems. Although our findings indicate common features in transform style (e.g. a right-lateral transform system, a wide sheared corridor), the deformation and magmatism along these systems appear quite different. In particular, our results show that the Davie and Agulhas transform faults postdate the development of the rift zone-controlling faults, whereas the Limpopo margin seems to be a simple intra-continental transform. Moreover, the Davie and Agulhas FZ recorded spectacular inversions during the transform stage, whereas transtensional deformation is developed along the Limpopo FZ. This different style of deformation may be explained by two main forcing parameters: (i) the far-field forces that may induce a rapid change of regional tectonic stress and (ii) the magmatic additions that modify mainly the crustal rheology. In the post-drift history, several reactivations of transform fault zones are recorded, implying that some transform margins are excellent recorders of large plate kinematic changes. Such reactivations can serve also as drains for magmatic fluids in the vicinity of hotspots emplacement.

Konenkov’s bending wave on an FGM plate supported by a semi-infinite viscoelastic Pasternak foundation

The analysis consists of the dynamic behaviour of a thin semi-infinite functionally graded plate under bending edge wave propagation. The plate is made of transversely isotropic materials supported by an elastic foundation. A quadratic variation of the properties of the materials is used to examine the behaviour of the FGM (Functionally Graded Materials) plate in the bending edge wave propagation. The Eringen differential form is employed to transition from non-local to local elasticity. The parameter entailed in the differential form is used to extrapolate the microstructure’s impact on the bending edge wave propagation in the functionally graded plate. Additionally, the surface elasticity theory is included to investigate the surface effects on the dispersion of edge wave. The viscosity effect of the plate and the foundation are taken into consideration while formulating the problem. To develop the kinematics of FGM plates, the Kirchhoff plate theory is considered. The motion of the plate is taken along the transverse direction of the plate. The viscoelastic theory proposed by Kelvin-Voigt is used to formulate the mathematical theory of the proposed model. A coupled equation corresponding to the moments and shear forces has been obtained while formulating the plate equation of motion. The rotatory inertia effect is neglected due to the small deflection of the plate. The numerical simulation presented in the paper shows the influence of the viscosity of the elastic foundation, surface effects, non-local elasticity, and the density of the materials on the natural frequency of bending edge wave propagation.

The role of the Ebro Block on the deformation experienced within the Pyrenean realm: Insights from deformable plate tectonic models

Plate kinematic models of the Pyrenees have been extensively debated due to discrepancies between plate kinematic constraints for the Iberian plate and Atlantic/Tethyan related plate motions. Recently, the morphology of the Iberian plate and its partitioning into several continental blocks has been proposed as a solution towards reconciling discrepancies between previously published reconstructions that treat Iberia as a single, rigid, tectonic plate. Herein, the first deformable plate tectonic modeling study of the Pyrenean realm is presented using previously published and newly presented reconstructions of Iberia. Special emphasis is given to the kinematics of the Ebro Block, a continental block situated between the Pyrenees and Iberian Ranges, whose kinematics are considered to play a key role in the extensional deformation experienced within the Pyrenean realm. Temporal variations in strain rate and crustal thickness calculated by deformable plate models provide insights regarding the pre-orogenic template of the Pyrenees and the variability in regional stress directions along the Iberia-Eurasia plate boundary from the Triassic to Cenomanian. Models that propose transtensional rift phases within the Pyrenean realm induced by the Landes High and Ebro Block kinematics since the Triassic are successful in deriving crustal thicknesses indicative of a pre-orogenic hyperextended rifted margin within the Pyrenean realm. The results of this study demonstrate the importance of continental block kinematics during rift-related deformation and their impact on the evolution and partitioning of rift domains. Furthermore, this study also highlights potential avenues to consider for improving future plate kinematic models of Iberia, and regions elsewhere.

Integrated effects of auxeticity and pyro-coupling on the nonlinear static behaviour of magneto-electro-elastic sandwich plates subjected to multi-field interactive loads

This work presents a detailed investigation of the effect of auxeticity synergised with the pyro-coupling behaviour of multiphase magneto-electro-elastic (M-MEE) composites using a finite element (FE) framework. The nonlinear deflection and bending problems of sandwich plates with auxetic core and M-MEE skins subjected to multi-physics load (electric, magnetic and thermal) are probed. The plate kinematics is governed by Reddy’s higher-order shear deformation theory (HSDT). The nonlinear relation between the strains and displacements is established through von-Karman’s nonlinear relations. The temperature profiles are considered linearly and nonlinearly varying across the thickness of the plate. Various parametric studies presented in this article highlight the influence of the auxetic cell inclination angle, rib-length ratio, rib thickness, the plate-to-core ratio etc., associated with the pyro-coupling on the nonlinear deflection and bending of sandwich plates. The results reveal that the plate deflection, bending behaviour and degree of pyro-coupling significantly depend on the auxetic unit cell dimensions and magnitude of electro-magnetic loads. The significant influence of temperature profiles on the pyro-coupling are witnessed at lower auxetic cell angle. The nonlinear deflections of the sandwich plate and hence the potentials developed tend to improve with the lower values of plate-to-core ratio and rib thickness. The prominent outcomes of this work related to integrated effects of auxeticity and pyro-coupling are not yet reported in the open literature and are deemed to be utilised as a future reference.

Breakup of Pangea and the Cretaceous Revolution

AbstractA 250 Ma, Pangea had just reached an equatorial position of dynamic equilibrium, after a 60° northward migration due to True Polar Wandering. It then began oscillating about itself for the next 150 Myr. The resulting extensional stresses triggered three successive phases of breakup, controlled by the mechanical resistance of a crescent of thick lithosphere, surrounding the Tethyan realm, which had adjusted the supercontinent to its hemispheric shape. The fracturing of the crescent was produced in three successive generations, each new generation corresponding to Coulomb fractures, conjugates of the preceding set. Flood basalts were associated with these deep fractures within the thick lithosphere crescent. We consider unlikely that this highly ordered pattern of fracturing was determined by the locations of the impacts of successive plumes. Between 260 and 180 Ma, thermal isolation was maximal and the asthenosphere of Pangea was about 150°C warmer than below Panthalassa. From 180 to 100 Ma, the breakup elongated Pangea by about 3,000 km in a north‐northwest–south‐southeast direction, producing gaps in the subduction girdle. Lateral mixing began, leading to a continuous rise in global sea level and progressive return to a globally homogeneous upper mantle with sea‐level at its maximum 100 Ma. This Cretaceous Revolution marked the end of the Pangea tectonics, radically different from our present plate tectonics. Neither post‐Cretaceous plate kinematic inferences, nor mantle dynamic and associated planetary cooling inferences are extendable to Pangea times.

Rate-dependent evolution of wrinkling films due to growth on semi-infinite planar viscoelastic substrates

A mechanistic understanding of morphogenesis in biology, the fabrication of advanced meta surfaces with specific functionalities and structures with enhanced energy dissipation often have in common that the combined effects of energy dissipation due to viscoelasticity and a loss of stability govern both their mechanical response and their final forms. In this paper we show that the interplay between viscoelasticity and multistability crucially influences the evolution of deformations in viscoelastic structures undergoing large deformations. The influence is studied on a prototypical system of a uniaxially growing film on a semi-infinite planar viscoelastic substrate, where it is shown that during the evolution of deformation the choice of multiple developing modes is greatly affected by this interplay. For the analysis of the underlying mechanics of the mode competition in the post-buckling regime, when the system undergoes large deformations, a 3D general finite-strain visco-hyperelastic theory is built. It includes kinematic and material nonlinearities in the film and in the substrate. For the case of ramp-loading time functions the phase space of the solutions is characterized and the evolution of a deformation pattern is analyzed. We find that the interaction between multistability and viscoelasticity greatly increases the evolution time of the system and that the growth rate and viscoelastic stress-relaxation rate influence the choice of the final equilibrium deformation state of the structure. This shows that viscoelastic structures can evolve into (meta)stable equilibrium states that are unattainable using purely elastic structures. The nonlinear problem is solved numerically with the use of the finite-element method. In parallel, we develop analytical solutions for a simplified problem that is based on Föppl–von Karman plate kinematics to describe the mechanics of the film and substrate that is modeled as a 2D linear-viscoelastic continuum. A remarkably good match between the analytical and the numerical results was obtained.

Quantification and Restoration of the Pre‐Drift Extension Across the NE Atlantic Conjugate Margins During the Mid‐Permian‐Early Cenozoic Multi‐Rifting Phases

AbstractThe formation of the NE Atlantic conjugate margins is the result of multiple rifting phases spanning from the Late Paleozoic and culminating in the early Eocene when breakup was accompanied with intense magmatic activity. The pre‐breakup configuration of the NE Atlantic continental margins is controlled by crustal extension, magmatism, and sub‐lithospheric processes, all of which need to be quantified for the pre‐breakup architecture to be restored. Key parameters that need to be extracted from the analysis of crustal structures and sediment record include stretching factors, timing of rifting phases, and nature of the deep crustal structures. The aim of this study is to quantify the pre‐drift extension of the NE Atlantic conjugate margins using interpreted crustal structure and forward basin modeling. We use a set of eight 2D conjugate crustal transects and corresponding stratigraphic models, constrained from an integrated analysis of 2D and 3D seismic and well data. The geometry and thickness of the present‐day crust is compared to a reference thickness which has experienced limited or no crustal extension since Permian time allowing the quantification of crustal stretching. Based on the eight conjugate crustal transects, the total pre‐drift extension is estimated to range between 181 and 390 km with an average of 270–295 km. These estimates are supported by the results of forward basin modeling, which predict total extension between 173 and 325 km, averaging 264 km. The cumulative pre‐drift extension estimates derived from basin modeling are in turn used to calculate the incremental crustal stretching factors at each of the three main rifting phases between the conjugate Greenland‐Norwegian margins. The mid‐Permian early Triassic rifting phase represents 32% of the total extension, while the equivalent values are 41% for the mid‐Jurassic to mid‐Cretaceous and 27% for the Late Cretaceous‐Paleocene rifting phases. These values are used to establish and present at first, a full‐fit palinspastic plate kinematic model for the NE Atlantic since the mid‐Permian and will be the base for future work on more elaborated models in order to build accurate paleogeographic and tectonic maps.

The origin of the depressions interrupting the eastern Sierra Pampeanas broken foreland, explained by localized crustal extension through the juan Fernández ridge path, using gravimetric data

The Salinas Grandes and Salina de Ambargasta salt pans are located in the Eastern Sierras Pampeanas in the Pampean broken foreland zone, a product of the Chilean-Pampean flat subduction zone. This region constitutes an anomalously flat morphology of 350 × 150 km and occupies an extensive area in a northeast-southwest direction.These flat depressions abruptly interrupt the eastern Sierras Pampeanas morphology, burying the structure beneath Late Cenozoic-Quaternary deposits of the Andean orogenic front. We obtained from a previous model in spherical harmonics, the geometry of the Moho observing a lower crustal attenuation below the salt pan areas, which is maximum towards the north of the Salina de Ambargasta. From the Bouguer anomaly, calculated by unifying data from different sources, and its residual anomaly, we calculated the analytical signal to adjust the gravimetric anomaly's wavelength, which shows that this flat morphology follows NE to NNE gravity minima. Werner deconvolution and localized Euler deconvolution calculated from the residual Bouguer anomaly indicate that the anomalous masses are located above 15 km depth, by the wavelengths of the anomalies, presumably indicating the differential uplift of high-density rocks placed in the lower and mid-crust, following the measured crustal attenuations. Additionally, these solutions show that this NE depression is segmented by NNW structures perpendicular to the main trough. Crustal thickness attenuation is interpreted as related to the track of the Juan Fernandez Ridge beneath the eastern Pampean broken foreland sector, based on plate kinematic reconstructions. As depicted in recently released tomographic data, its tearing and related asthenospheric upwelling could have promoted lithospheric localized extension, explaining the Salinas Grandes-Ambargasta depressions that are segmenting the eastern Sierras Pampeanas at the Andean orogenic front.

Reorganization of Northern Peri-Gondwanan Terranes at Cambrian–Ordovician Times: Insights from the Detrital Zircon Record of the Ossa-Morena Zone (SW Iberian Massif)

Abstract The Ossa-Morena Zone constitutes a fringe Gondwana-related terrane all along the Paleozoic. This continental block has been classically interpreted as being attached to a portion of the northern Gondwanan margin located close to the West African Craton. We report here the results of U-Pb dating on detrital zircon grains from 15 metasedimentary rocks collected in two well-exposed and well-dated Cambrian sections (Córdoba and Zafra) of the Ossa-Morena Zone. The studied samples show a dominant late Tonian-Ediacaran population peaked at c. 600 Ma. Secondary populations are Rhyacian-early Orosirian and late Orosirian-Statherian in age, with maxima at c. 2.1 and 1.9 Ga. Minor detrital zircon populations are Mesoarchean-early Siderian in age, with peaks between c. 3.05 and 2.45 Ga. Most of the studied samples lack a Stenian-early Tonian population, except for two of them with a minor peak at c. 1 Ga. Our results corroborate previous studies that locate the Ossa-Morena Zone close to the West African Craton and/or the Tuareg Shield (i.e., in a western position with respect to other Variscan zones of the Iberian Massif) at the onset of the rifting stage that opened the Rheic Ocean. Nevertheless, the absence of a significant Stenian-early Tonian population in the Cambrian Ossa-Morena rocks contrasts with the reported results on middle Ordovician-Lower Devonian rocks of this zone, which systematically contain an important population with a peak at c. 1 Ga. We relate this change to the latest Ediacaran-early Ordovician paleogeographic/paleotectonic evolution of the Ossa-Morena Zone, which might have recorded a significant eastward displacement, together with a reorganization of the drainage systems. Thus, the vanishing stages of the Cadomian orogeny could have translated eastward the Ossa-Morena Zone terrane at latest Ediacaran-earliest Cambrian time due to change in plate kinematics from subduction to right-lateral shearing. This translation would have shifted the Ossa-Morena Zone from an Ediacaran location close to the West African Craton to a Cambrian position close to the Tuareg Shield. Finally, the rift-to-drift transition occurred at late Cambrian-early Ordovician time along the northern Gondwanan margin would have reorganized the drainage systems, facilitating sediment supply from an eastern source with abundant Stenian-early Tonian detrital zircon grains, probably the Saharan Metacraton.

Evidence for regionally continuous Early Cretaceous sinistral shear zones along the western flank of the Coast Mountains, coastal British Columbia, Canada

Abstract The plate-boundary conditions of the Mesozoic North American Cordillera remain poorly constrained, but most studies support large (>800 km) southward motion of the Insular and Intermontane superterranes during Jurassic–Cretaceous time. An implicit feature in these models of large coastwise displacements is the presence of one or more continentalscale sinistral strike-slip faults that could have dismembered and displaced terrane fragments southward along the western margin of North America prior to the onset of mid-Cretaceous shortening and dextral strike-slip faulting. In this study, we documented a system of sinistral intra-arc shear zones within the Insular superterrane that may have accommodated large southward motion. Employment of a new large-n igneous zircon U-Pb method more than doubled the precision of measurements obtained by laser ablation–inductively coupled plasma–mass spectrometry (from ~1% to 0.5%) and allowed us to demonstrate the close temporal-spatial relationship between magmatism and deformation by dating comagmatic crosscutting phases. Crystallization ages of pre-, syn-, and postkinematic intrusions show that the intra-arc shear zones record an Early Cretaceous phase of sinistral oblique convergence that terminated between 107 and 101 Ma. Shear zone cessation coincided with: (1) collapse of the Gravina basin, (2) development of a single voluminous arc that stitched the Insular and Intermontane superterranes together, and (3) initiation of eastwest contractional deformation throughout the Coast Mountains. We interpret these concurrent tectono-magmatic events to mark a shift in plate kinematics from a sinistral-oblique system involving separate terranes and intervening ocean basins to a strongly convergent two-plate margin involving a single oceanic plate and the newly assembled western margin of North America.

Flexural waves at the edge of nonlocal elastic plate associated with the Pasternak foundation

In this article, an elastic foundation is used to study the characteristics of flexural edge waves propagating on a piezoelectric structure. The nonlocal elasticity theory is introduced to investigate the microscale effect on edge wave propagation. The traditional Kirchhoff plate hypothesis is used to determine the kinematics of the piezoelectric plate. By considering the sinusoidal waveform, a closed-form dispersion relation can be obtained. In the context of a flexural edge wave on a piezoelectric plate, an analytical and graphical comparison between the two boundary conditions (i.e. short circuit and open circuit) is discussed. In the presence of nonlocal elasticity, the dispersion relation is implied as an implicit function of frequency and wave number. A significant difference occurred between the dispersion curves for piezoelectric plates with different foundations and nonlocal parameters. Due to the Pasternak elastic foundation, an increasing rate of the fundamental mode of frequency is observed at the traction-free edge of a thin, semi-infinite piezoelectric plate. In contrast, the nonlocal elasticity tends to decrease this fundamental frequency mode for a particular wave number value. The corresponding phase velocity decreases rapidly within a short range of wave numbers.

Subduction and Slab Detachment Under Moving Trenches During Ongoing India‐Asia Convergence

AbstractThe dynamics of slab detachment and associated geological fingerprints have been inferred from various numerical and analog models. These invariably use a setup with slab‐pull‐driven convergence in which a slab detaches below a mantle‐stationary trench after the arrest of plate convergence due to arrival of continental lithosphere. In contrast, geological reconstructions show that post‐detachment plate convergence is common and that trenches and sutures are rarely mantle‐stationary during detachment. Here, we identify the more realistic kinematic context of slab detachment using the example of the India‐Asia convergent system. We first show that only the India and Himalayas slabs (from India's northern margin) and the Carlsberg slab (from the western margin) unequivocally detached from Indian lithosphere. Several other slabs below the Indian Ocean do not require a Neotethyan origin and may be of Mesotethys and Paleotethys origin. Additionally, the still‐connected slabs are being dragged together with the Indian plate forward (Hindu Kush) or sideways (Burma, Chaman) through the mantle. We show that Indian slab detachment occurred at moving trenches during ongoing plate convergence, providing more realistic geodynamic conditions for use in future numerical and analog experiments. We identify that the actively detaching Hindu Kush slab is a type‐example of this setting, whilst a 25–13 Ma phase of shallow detachment of the Himalayas slab, here reconstructed from plate kinematics and tomography, agrees well with independent, published geological estimates from the Himalayas orogen of slab detachment. The Sulaiman Ranges of Pakistan may hold the geological signatures of detachment of the laterally dragged Carlsberg slab.

The interplay between basement fabric, rifting, syn‐rift folding, and inversion in the Rio do Peixe Basin, NE Brazil

AbstractThe Rio do Peixe Basin is part of a series of aborted Cretaceous rifts formed within the Proterozoic Borborema Province, onshore NE Brazil in response to rifting between Africa and South America. The basin is remarkably well‐imaged and comprises fault‐bounded depocentres, the main ones being the NE‐oriented Brejo das Freiras and the E–W‐oriented Sousa half‐grabens. These grabens and their bounding faults are influenced by Neoproterozoic basement shear zones and present a complex framework of secondary normal faults and folds. Recent workers also interpret large reverse faults and regional post‐rift shortening driven by far‐field stresses from the Andes. For those reasons, the basin represents an ideal setting to investigate the multiphase history of rift basins. We thus combine borehole‐calibrated 2D and 3D seismic and magnetic data with section restoration and numerical modelling to investigate the architecture and evolution of this basin. We aim to understand: (i) the controls of the basement fabric in 3D fault architecture and kinematics and (ii) how syn‐rift faults controlled the geometry and development of fault‐related folds. By doing this, we also investigate the timing, kinematics, and magnitude of inversion in the basin to explore its multiphase history. We demonstrate that (i) the basement fabric controlled not only the strike of faults but also their geometry and polarity at depth, (ii) folds in the syn‐rift sequence are attributed simply to syn‐rift extension along stepped and/or curved faults, and (iii) inverted and/or reverse faults occur within the basin, but these are minor and appear to have formed during rifting. We explain this minor inversion by a change in plate kinematics related to the onset of the nearby transform margin to the north. These results have implications for understanding the 3D evolution of oblique grabens, the role of structural inheritance, and the recognition of inversion‐ versus extension‐related folds in rift basins worldwide.