Plate Motion Research Articles

Partial melt in mesoscale upper mantle upwellings beneath ocean basins

How tectonic plate motions are coupled with mantle flows remains an open question. Quasi-periodic 2000 km wavelength undulations aligned with absolute plate motion in the Pacific and Indian Ocean basins, observed in gravity and seafloor topography and coinciding with seismically imaged low shear velocity fingers in the upper mantle, suggest the presence of meso‑scale convection below the lithosphere. However, the correspondence of sub-lithospheric mantle mass excess, seafloor lows and slow upper mantle seismic velocities cannot be explained by temperature variations alone. Here we introduce a simplified system of bi-dimensional convective cells of width ∼1000 km, extending from the base of the lithosphere through the extended mantle transition zone (down to 1000 km depth), at least partly driven from below. From mass balance considerations in a viscous Earth, we show that the density excess required in the hot upwelling limbs may reflect the formation of stable dense lenses of dehydration-induced partial melt atop the 410 km discontinuity, and upward entrainment of a small fraction of quasi-buoyant partially molten and recrystallized material across the upper mantle. Our model provides an explanation for the thin low shear velocity layer detected intermittently above the 410 km discontinuity in some parts of ocean basins away from subducted slabs, and supports the presence of water in the transition zone.

The Davis Strait proto-microcontinent: The role of plate tectonic reorganization in continental cleaving

A prolonged period of rifting and seafloor spreading between Greenland and North America formed the Labrador Sea and Baffin Bay oceanic basins, connected by the Davis Strait. However, disagreement exists regarding the exact plate motions between Greenland and Canada, as well as the tectonic evolution of the Davis Strait, with previous models unable to explain the origin of anomalously thick continental crust within the seaway. Here, we present a new plate tectonic reconstruction of Greenland’s separation from Canada, constrained by a new comprehensive set of mid-ocean ridge (MOR) and transform fault lineaments identified using free-air, vertical gradient, and filtered directional gradient maps from the Sandwell and Smith gravity data. Furthermore, the reinterpretation of seismic reflection data offshore West Greenland, along with a newly compiled crustal thickness model, identifies an isolated terrane of relatively thick (19–24 km) continental crust that was separated from Greenland during a newly recognised phase of E-W extension along West Greenland’s margin. We interpret this continental block as an incompletely rifted microcontinent, which we term the Davis Strait proto-microcontinent. Our reconstruction suggests release of the proto-microcontinent coincided with a change in the spreading orientation from ∼ 58 to 49 Myr during the alignment of Canada and Greenland's rifted margins, indicating a fundamental control of lithospheric structure on plate motions. Proto-microcontinent separation was induced by transpression along a newly recognised NE-SW trending transform margin that joined the Labrador Sea and Baffin Bay, prior to development of the Ungava Fracture Zone (UFZ). The location of this transform margin is constrained using our crustal thickness model, which demonstrates a sharp NE-SW trending continent-ocean transition across the northern Saglek basin. We term this newly identified first-order tectonic feature the Pre-Ungava Transform Margin (Pre-UTM), which accommodated early NE-SW motion between Greenland and Canada. Our identified mechanism of microcontinent formation may be widely applicable to other microcontinents around the globe, and further study is merited to understand the role of plate motion changes and transpression in microcontinent calving.

East European sedimentary basins long heated by a fading mantle upwelling

A strong negative anomaly of seismic wave velocities at the core-mantle boundary (the Perm Anomaly) beneath the East European platform is attributed to the remnant of a deep mantle upwelling. The interaction between the upwelling and the East European lithosphere in the geological past and its resulting surface manifestations are still poorly understood. Using mantle plume modelling and global plate motion reconstructions, we show here that the East European lithosphere is likely to have been situated over the weakening Perm Anomaly upwelling for about 150–200 million years. As the East European platform moved above the Perm Anomaly in post-Jurassic times, the vertical tectonic movements recorded in sedimentary hydrocarbon-rich basins show either hiatus/uplift or insignificant subsidence. Analytical modelling of heat conduction through the lithosphere demonstrates that the basins have been slowly heated for a long time by the Perm Anomaly upwelling, creating suitable conditions for hydrocarbon maturation. This suggests a profound relationship between mantle plume dynamics, basin evolution, and hydrocarbon generation.

Did plate tectonic changes lead to the emergence of hominid bipedalism?

When early hominids began walking upright around 6 Ma, their evolutionary course took a sharp turn. The new posture enabled physical and mental developments that had not been possible before. The factors driving the transition from quadrupedalism to bipedalism remain open. Most studies have linked this fundamental transition to environmental, topographical, geomorphological, and climatic changes that progressively transformed jungle- and forest-dominated areas of southern and eastern Africa into vast savannas, thus partitioning ecological niches. During the same timeframe, major tectonic events occurred worldwide within a relatively short geological period, due to a significant and sudden shift in the motion of the Pacific plate. In our previous work, we coined the term ripple tectonics to link a major tectonic impact to the short-term local events it caused worldwide. The ripple tectonic cascade in the Pacific around 6 Ma instigated significant environmental transformations in Africa, which ultimately catalyzed the biological evolution of early hominids towards a bipedal posture.

Dynamics of seaweed-inspired piezoelectric plates for energy harvesting from oscillatory cross flow

Inspired by the vibrations of aquatic plants such as seaweed in the unsteady flow fields generated by free-surface waves, we investigate a novel device based on piezoelectric plates to harvest energy from oscillatory cross flows. Towards this end, numerical studies are conducted using a flow-structure-electric interaction model to understand the underlying physical mechanisms involved in the dynamics and energy harvesting performance of one or a pair of piezoelectric plates in an oscillatory cross flow. In a single-plate configuration, both periodic and irregular responses have been observed depending on parameters such as normalized plate stiffness and Keulegan–Carpenter number. Large power harvesting is achieved with the excitation of natural modes. Besides, when the time scale of the motion and the intrinsic time scale of the circuit are close to each other the power extraction is enhanced. In a two-plate configuration with tandem formation, the hydrodynamic interaction between the two plates can induce irregularity in the response. In terms of energy harvesting, two counteracting mechanisms have been identified, shielding and energy recovery. The shielding effect reduces plate motion and energy harvesting, whereas with the energy recovery effect one plate is able to recovery energy from the wake of another for performance enhancement. The competition between these mechanisms leads to constructive or destructive interactions between the two plates. These results suggest that for better performance the system should be excited at its natural period, which should be close to the intrinsic time scale of the circuit. Moreover, using a pair of plates in a tandem formation can further improve the energy harvesting capacity when conditions for constructive interaction are satisfied.

Dynamic response of H-FGS plates integrated with Pasternak foundation subjected to harmonic loading in the thermal environment using Chebyshev-FEM

The main goal of this article is to introduce a finite element method (FEM) based on Chebyshev polynomials, referred to as Chebyshev-FEM, to investigate the dynamic response of functionally graded sandwich (FGS) plates with a honeycomb core and two functionally graded (FG) skin layers, denoted as H-FGS plates integrated with Pasternak foundation (PF) subjected to harmonic loading (HL) within a thermal environment. Chebyshev polynomials are a series of orthogonal polynomials defined recursively. The value of the polynomials belongs to the range [–1] and vanishes at Gauss points. The equation of motion for H-FGS plates is derived using Hamilton’s principle. Comparative examples are implemented to validate the accuracy and performance of the proposed method. Additionally, the effect of input parameters on both free and forced vibrations of H-FGS plates integrated with PF subjected to HL within a thermal environment is studied in detail.

Onset of Plate Motion in the Presence of Chemical Heterogeneities in the Mantle and the Effect of Mantle Temperature

AbstractChemical heterogeneities of various origins have been observed in the Earth's mantle. Their assumed higher density acts on the style of mantle convection and therefore, as tectonic plates form the highly viscous upper boundary layer of mantle convection, the onset of surface motion is also affected by chemical heterogeneities. We perform 2D basally heated thermochemical mantle convection models which initially include layers of dense material at different mantle depths. In comparison to purely thermal convection models, the onset of first plate motion is delayed. This delay is even more pronounced, the deeper the location of dense material, the larger its volume and the higher its density. Additionally, we varied the starting temperature of our models. In an initially hot mantle, a strong temperature‐dependent viscosity contrast between the mantle and cold surface leads to a cold, highly viscous plate (stagnant lid). For an initially cold mantle, rising plumes first need to transport basal heat upwards to create a sufficient viscosity contrast. Consequently, the formation and subsequent breaking of the stagnant lid is delayed. Considering a hotter mantle after Earth's magma ocean phase, we find that plate motion can occur within approximately the first 0.5 Gyr of solid‐state convection if no chemical structures are present or for dense material situated at the surface. Deep chemical heterogeneities delay the onset by at least one order of magnitude. Furthermore, the early surface motion will have been more erratic than todays stable plate motion, probably with a few single subduction events.

Fairweather transform boundary Oligocene to present orogenesis: Fairweather Range vertical extrusion and rotation of the Yakutat microplate at ca. 3 Ma

Oblique-slip along transform fault boundaries is often partitioned between a strike-slip system and thrust faults that accommodate contraction. However, topography along the Yakutat-North American transform (Fairweather fault), is asymmetric with low-terrain above active thrusts on the western, Yakutat side of the transform and high topography on the continental side with peaks >4500 m (Mount Fairweather: 4671 m) to the west of the Border Ranges fault, limited recorded earthquakes >M4, and no apparent reverse faults to generate the highest terrain. In this study we compile, for the first time, published U-Pb zircon, 40Ar/39Ar and K-Ar (hornblende, muscovite, and biotite) and U-Th/He and fission-track (zircon and apatite) bedrock ages (109) from 75 samples to investigate the exhumation history of the Fairweather Range region, complemented by a published detrital sample (ZFT and AFT) and 13 new 40Ar/39Ar (hornblende, biotite, and K-feldspar) ages on 9 bedrock samples from both sides of the Fairweather fault. Additionally, we examined published seismicity and geodetic data of the Fairweather region and assessed if plate paleo-vectors correlate with the cooling history of the Fairweather Range. Cooling age, seismic, and block-motion patterns indicate the Fairweather Range has been vertically extruded between the Fairweather and the Border Ranges faults as a coherent block since ca. 25 Ma. The pre-6 Ma Pacific plate motion (N30°W) aligns with the N33°W strike of the Fairweather Fault whereas a hypothetical pre-6 Ma Yakutat microplate paleo-vector of (N39°W) does not: indicating a post-6 Ma timing for Yakutat microplate counter-clockwise rotation (9°). We infer that rotation and impingement of the Yakutat microplate along the Fairweather fault at ca. 3 Ma led to the development of the Fairweather restraining bend and increased cooling rates. The resultant thickened Fairweather welt and the ∼30 km thick southeast end of the Yakutat microplate compounded double-indenter tectonics into Alaska's southeast convergent corner

Study of the dynamic behavior of plates in gradient properties with logarithmic and exponential porosity

In this paper, we are interested in the dynamic behavior of porous plates in property gradient, the property gradient material is a new generation of composite material, which is characterized by a gradual and continuous variation of physical properties, in order to attenuate the major singularity of laminar materials, which is the direct transition from one material to another. The proposed theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components, in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments.In order to model our plate as well as possible, we will use a high-order theory with four variables only, by injecting the exact position of the neutral surface. The originality of this work lies in the consideration of two types of porosity distribution “logarithmic and exponential” in the calculation of the position of the neutral surface.The plate is subjected to a vertical load of sinusoidal distribution expressed in double series of Fourier. The equation of motion for FG rectangular plates is obtained through Hamilton’s principle. The closed form solutions are obtained by using Navier technique, and then fundamental frequencies are found by solving the results of eigen value problems.The object of this work is to study the influence of the variation of the volume fraction, the power index and The dimension ratio on the response of the frequency , and ,the constraints , and and the dimensionless deflection and the dimensionless displacement obtained in the presence of porosity with logarithmic and exponential distribution compared to those uniformly distributed.

An Ellipsoidal Plate Motion Model of the Indo‐Australian Tectonic Plate

AbstractWe present a class of “ellipsoidal rotation matrices” which can be used to characterize tectonic plate motion; where geocentric Cartesian coordinates travel along paths tangential to the ellipsoid. We contrast them with conventional Euler pole plate motion models which are more closely aligned with spherical coordinate systems and inherently induce a change in geodetic ellipsoidal height. We demonstrate the use of each in the Indo‐Australian tectonic plate setting, which is known to move approximately 7 cm/year in a north‐northeast direction. Geocentric Datum of Australia 2020 (GDA2020) coordinates are “plate‐fixed” static coordinates obtained using a conventional Euler pole plate motion model to align time dependent coordinates with the 2014 realization of the International Terrestrial Reference Frame at the epoch 2020.0. We show that this Euler pole plate motion model can introduce ellipsoidal height velocities of up to −0.2 mm/year. This is small but systematic, so pertinent for consideration with high accuracy vertical land motion studies using GDA2020 coordinates and velocities. We further investigate the comparative statistical accuracy of conventional Euler pole and the ellipsoidal models with respect to characterizing plate motion captured in high quality Global Navigation Satellite System data.

The last gasp of the Rogaland Igneous Complex, Norway: a palaeopole for the 920 Ma Tellnes intrusion

SUMMARY The Rogaland Igneous Complex (RIC) in southern Norway intruded into Sveconorwegian granulite crust beginning ∼930 Ma. Three massif anorthosite bodies, Egersund–Ogna, Helleren and Åna-Sira, were intruded some 10 Myr later by the Bjerkreim–Sokndal layered intrusion. The Garsaknatt leuconorite and the ilmenite-rich Tellnes norite, one of the youngest rock in the complex at ∼920 Ma, intrude the anorthosite or nearby country rock. Magnetic mineralogy and palaeomagnetic studies carried out on the Tellnes norite, the Garsaknatt leuconorite and the surrounding Åna-Sira anorthosite, indicate the magnetization of all three bodies are dominated by hemo-ilmenite carrying the remanence as a thermochemical remanent magnetization, although magnetite is present in some samples. The three bodies yield steep negative inclinations with northwesterly declinations (Tellnes, I = −71.9°, D = 305.0°, α95 = 10.6°; Garsaknatt, I = −73.1°, D = 312.7°, α95 = 4.7°; and Åna-Sira, I = −81.2°, D = 326.3°, α95 = 6.7°). When combined with data from other bodies in the RIC, the older anorthosites have steeper inclinations, and higher palaeolatitudes, while the younger units have less steep inclinations and shallower palaeolatitudes by nearly 10°, indicating northward plate motion during cooling of the intrusions. Age of the remanence is difficult to determine precisely, however, best estimates are ∼910 Ma for the older anorthosites and ∼900 Ma for the younger intrusions. Although these differences are significant, a unified pole position (35.6° N, 215.1° E), combining all the 111 sites from the RIC, strongly supports the assumed position of southern Baltica in Rodinia at ∼900 MA.

Unfolding rotational tectonics and topographic evolution from localized verses diffuse plate boundary counterparts

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.

Numerical Analysis of Unsteady Vibrations of a Plate Resting on an Elastic Isotropic Half-Space

The paper is devoted to the numerical solution of the problem of vibrations of an infinite elastic plate resting on an elastic isotropic half-space using the analytical method based on the ray method with its numerical realization via the Maplesoft package. Unsteady oscillations are caused by the action of instantaneous loads on the plate, resulting in the appearance of two plane wave surfaces of strong discontinuity in the elastic half-space, behind the fronts of which, up to the contact boundary, the solution is constructed using ray series. The unknown functions entering the coefficients of the ray series and the equation of plate motion are determined from the boundary conditions of the contact interaction between the plate and the half-space. Previously, the approximate solution of this problem was obtained analytically without using mathematical packages, and the dynamic deflection of the plate involving only the first three terms of the ray series was written down. In this work, a two-layer medium with different properties was investigated using an algorithm developed to solve contact dynamic problems related to the occurrence and propagation of strong and weak discontinuity surfaces.

Linking Pacific Plate Motions to Metamorphism and Magmatism in Japan During Cretaceous to Paleogene Times

Plate reconstructions of oceanic domains are generally based on paleo-magnetic and seafloor spreading records. However, uncertainties associated with such reconstructions grow rapidly with increasing geological age because the original oceanic plates have been subducted. Here we synthesize advances in seismic tomographic mapping of subducted plates now lying within the mantle that assist plate reconstructions. Our proposed Japan–NW Pacific subduction histories incorporate tomography results and show three distinct stages comparable to those revealed by geochronology, petrology, and geochemistry. We propose major revisions to previously accepted ideas about the age, kinematics, and identity of the plates outboard of Japan during the Cretaceous–Paleogene Sanbagawa-Ryoke paired metamorphism. These revisions require updates to relevant plate convergence boundary conditions and thermo-dynamic models.

Joint Resonance Analysis in Multiple Modes of Soft Ferromagnetic Rectangular Thin Plate

In this article, the nonlinear principal and internal resonance properties of a soft ferromagnetic rectangular thin plate are investigated in a magnetic field environment. The nonlinear partial differential equation of motion of a soft ferromagnetic rectangular thin plate is derived under the effect of homogeneous simple harmonic excitation. The system of nonlinear differential equations with multiple degrees of freedom is established by the assumed one-sided fixed trilateral simply support condition using the Galerkin’s method. The system of nonlinear differential equations is solved by the multiscale method to obtain the response of two modes under the simple harmonic force at the principal and internal resonance. The numerical results of the system response show that when the frequency of the simple harmonic force is close to one of the modes (first-order or second-order mode) causing it to resonate, the other mode will also resonate internally. The magnetic field can have an inhibiting effect on the resonant response of the system and also affect the kinematic state of the system. The internal resonance provides a mechanism for transferring energy from a high mode to a lower mode.

Variable plate kinematics promotes changes in back-arc deformation regime along the north-eastern Eurasia plate boundary

The stretching of the lithosphere leading to back-arc basins formation generally develops behind arc-trench systems and is considered the consequence of slab retreat relative to the upper plate. Here, we examine the deformation regime evolution within the overriding plate due to subduction processes, using thermo-mechanical numerical simulations. We explore the north-eastern Eurasia plate boundary and the mechanisms of subducting Pacific plate since 57 Ma. During this time interval, several extensional basins formed along the Eurasia margin, such as the East China Sea, the Japan Sea, and the Kuril basin. Here, we increased the simulation complexity, with the inclusion of (i) the kinematic variability of the Pacific plate over the geological past with respect to a fixed Eurasia, incorporating time-dependent (i.e., temporally evolving) velocities computed from plate motion reconstructions; (ii) a Low-Velocity Zone within the asthenosphere, and (iii) a horizontal eastward mantle flow. Our results show a crucial role of the mantle flow for the development of lithospheric extension and back-arc basin opening, and a main kinematic control of the subduction trench position, which advances and retreats, into distance intervals in the order of ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} 100 km, and providing stages of compression and extension in a back-arc basin.

Deciphering the crustal anisotropy and mantle flow beneath the Indo-Burma ranges from the harmonic decomposition of the receiver functions

The hyper-oblique indentation of the Indian plate beneath the Burmese sliver gives rise to the Indo-Burma Ranges (IBR) in the eastern part of the Indian subcontinent. This geological formation encompasses one of the enigmatic hotspots and includes the densely populated regions of India and Myanmar. Harmonic Decomposition (HD) of the receiver functions, derived from the Multi-Taper Correlation (MTC) technique, is used to model seismic anisotropy and morphological crustal deformation caused by subduction underneath IBR. We used teleseismic earthquake data from eleven broadband seismic stations installed within the IBR and its foredeep region. The findings indicate that the attitude of the fast symmetry axis or dipping direction of the interface is influenced by the trend of regional geological features and absolute plate motion, with the IBR exhibiting NNE-SSW and N-S directions and the Himalayan region showing NE-SW and E-W directions. Our results reveal that the coupling of the Indian plate with the Burmese and Eurasian plates induces lithospheric fabrics that align perpendicular to the coupling direction, resulting in anisotropy in the brittle upper crust. Directional analysis of the HD model for the interfaces at the middle or lower crust reveals the strike of the fast symmetry axis in the NNE-SSW direction, which suggests the alignment of minerals and partial melt in the direction of the major shear stress. The interface across the Moho reflects four-lobed periodicity, that is, 90o ambiguity in the strike direction of the fast symmetry axis, varying from the E-W to the N-S directions. The ambiguity indicates the possibility of the 2D-induced entrained mantle flow along the subducting Indian plate and the 3D toroidal flow parallel to the trend of the IBR.

Auxetic honeycomb core layer effect on vibrations of annular plates based on shear deformation theory

Light composite materials such as auxetic honeycomb structures offer a unique combination of strength, lightweight, and durability, making them ideal for a wide range of industrial and structural applications. Consequently, it is crucial to study the effect of these materials on the dynamic behavior of structures. In this study, an analytical solution based on the multiple-scale method has been proposed to solve equations of motion of a multilayer axisymmetric annular plate. The plate includes two top and bottom isotropic layers and one auxetic honeycomb core layer. By considering both radial and transverse deflections, the governing equations are derived based on the first-order shear deformation theory. The radial and transverse frequencies of the plate are determined from the order zero of equations and a correction coefficient for each frequency has been extracted from the order one and solvability conditions. The response of the plate under harmonic transverse excitation has been determined analytically and by conducting a parametric study, the effect of different geometrical and mechanical parameters on the free and forced vibration responses has been studied. It is observed that employing a honeycomb core in the multilayer plate allows us to significantly decrease the plate weight while the dynamic response and the frequencies remain nearly the same or vary slightly. The results are validated by comparing them with the finite element method and some other references.

Subduction transforms azimuthal anisotropy in the Juan de Fuca plate

To clarify the internal structure of the oceanic lithosphere-asthenosphere system, here we determine a new 3-D model of azimuthal anisotropic shear-wave velocity (Vs) down to ∼200 km depth from the Juan de Fuca (JdF) mid-ocean ridge to the Cascadia subduction zone, by inverting newly measured teleseismic fundamental mode Rayleigh-wave phase and amplitude data at periods of 25–100 s. The JdF lithosphere is clearly imaged as a high-velocity anomaly from the ridge to the subduction zone. Distinct azimuthal anisotropies are revealed in the JdF lithosphere before and after its subduction. Obvious trench-normal fast-velocity directions (FVDs) exist in the JdF plate beneath the Pacific Ocean, whereas the subducting JdF slab beneath the Cascadia margin generally exhibits trench-parallel FVDs. We propose that the subduction-induced structure and mineral alignment in the JdF slab transform the fossil fabrics in the JdF plate formed at the mid-ocean ridge and altered during the plate motion and cooling.

The Esquinzo Ultra-Alkaline Rock Suite of Fuerteventura Basal Complex (Canary Islands): Evidence for Origin of Carbonatites by Fractional Crystallization

The origin of the carbonatites that appear on Earth is one of the most controversial current topics in the petrogenesis of igneous rocks. Situated in the northern sector of the Basal Complex of Fuerteventura (Canary Islands), the Miocene Esquinzo ultra-alkaline plutonic rock complex is composed of pyroxenites, melteigites-ijolites-urtites, malignites-nepheline syenites, carbonatites, silicocarbonatites, nephelinites and nepheline phonolites. This work tries to establish the genesis of this massif of ultra-alkaline rocks with associated carbonatites from Fuerteventura (which are very rare in the oceans). The geochemical characteristics of these rocks and the minerals that are included in them have allowed us to establish their origin. This complex was generated by three successive magmatic events associated with differentiation of melanephelinite magmas emplaced in the oceanic crust. Silicocarbonatite and calciocarbonatite (sövites) dykes are related to the first magmatic event and were formed by fractional crystallization of H2O- and CO2-rich ijolite magmas. The melanephelinite magmas that formed these plutonic ultra-alkaline rocks were apparently generated as partial melts of asthenospheric mantle, which assimilated enriched lithospheric mantle material as they ascended. The upwelling of this large body of anomalous asthenospheric Miocene material exceeded the deformation associated with plate motions and led to an oceanic rifting event in Fuerteventura.