Connecting mantle flow below passive margins and intraplate melt generation: an application to the Cameroon Volcanic Line.

2021 ◽  
Author(s):  
Matthew Likely ◽  
Jeroen van Hunen ◽  
Linda Kirstein ◽  
Godfrey Fitton ◽  
Lara Kalnins ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Numerical Models ◽  
Source Region ◽  
Linear Chain ◽  
Small Scale ◽  
Mantle Flow ◽  
Cameroon Volcanic Line ◽  
Intraplate Volcanism ◽  
Lithospheric Thickness ◽  
Melt Generation

<p>Approximately 90% of all magmatism on Earth can be explained through plate tectonics; the remainder is associated with intraplate volcanism. In large part, this intraplate volcanism can be attributed to mantle plumes, yet this does not represent all known examples. A number of hypotheses have been proposed to explain non-plume related intraplate volcanism. One geodynamically viable theory through the process of small-scale convection associated with lithospheric instabilities evolving into edge driven convection (EDC) in regions which possess large variations in lithospheric thickness. One such intraplate volcanic example that may be explained by this process is the Cameroon Volcanic Line, which forms a linear chain of non-age progressive volcanoes that straddle the African continental lithosphere and the Atlantic oceanic lithosphere.</p><p>In this study we compute numerical models utilising mantle convection modelling software ‘ASPECT’, to investigate the initiation, evolution and potential of melt generation as a result of EDC through geological time, applying these models to the Cameroon Volcanic Line. Our preliminary modelling results suggest that episodic intraplate melting events can indeed be generated through edge-driven convection. But in order to do so, mantle temperatures need to be higher than average to produce sufficient melt from a typical upper mantle source. We therefore investigate the possibility that more enriched mantle lithosphere, destabilised by the assembly and breakup of Pangaea, could flow into the source region of the Cameroon volcanism, allowing the production of similar quantities of melt with less elevated mantle temperatures. We present results on how lithospheric development, evolution and stability, as well as supercontinent cycles can influence intraplate volcanism.</p>

scholarly journals Numerical models of slab migration in continental collision zones

Solid Earth ◽  
2012 ◽  
Vol 3 (2) ◽  
pp. 293-306 ◽  
Author(s):  
V. Magni ◽  
J. van Hunen ◽  
F. Funiciello ◽  
C. Faccenna
Keyword(s):  
Subduction Zone ◽  
Plate Tectonics ◽  
Numerical Models ◽  
Continental Collision ◽  
Force Balance ◽  
Small Scale ◽  
Dip Angle ◽  
External Forces ◽  
Stress Dependent ◽  
Subduction System

Abstract. Continental collision is an intrinsic feature of plate tectonics. The closure of an oceanic basin leads to the onset of subduction of buoyant continental material, which slows down and eventually stops the subduction process. In natural cases, evidence of advancing margins has been recognized in continental collision zones such as India-Eurasia and Arabia-Eurasia. We perform a parametric study of the geometrical and rheological influence on subduction dynamics during the subduction of continental lithosphere. In our 2-D numerical models of a free subduction system with temperature and stress-dependent rheology, the trench and the overriding plate move self-consistently as a function of the dynamics of the system (i.e. no external forces are imposed). This setup enables to study how continental subduction influences the trench migration. We found that in all models the slab starts to advance once the continent enters the subduction zone and continues to migrate until few million years after the ultimate slab detachment. Our results support the idea that the advancing mode is favoured and, in part, provided by the intrinsic force balance of continental collision. We suggest that the advance is first induced by the locking of the subduction zone and the subsequent steepening of the slab, and next by the sinking of the deepest oceanic part of the slab, during stretching and break-off of the slab. These processes are responsible for the migration of the subduction zone by triggering small-scale convection cells in the mantle that, in turn, drag the plates. The amount of advance ranges from 40 to 220 km and depends on the dip angle of the slab before the onset of collision.

Numerical simulation of asthenospheric flow around cratonic keels

2020 ◽  
Author(s):  
Edgar Santos ◽  
Victor Sacek
Keyword(s):  
Upper Mantle ◽  
Numerical Models ◽  
Relative Displacement ◽  
Planetary Science ◽  
Small Scale ◽  
Time Interval ◽  
Mantle Flow ◽  
Continental Margins ◽  
Thermochemical Convection ◽  
Synthetic Models

<p>In this work, we studied the mantle flow around cratonic keels using numerical models to simulate the thermochemical convection in the terrestrial mantle taking into account the relative displacement between the lithosphere and asthenosphere. The numerical simulations were performed using the finite element code developed by Sacek (2017) to solve the Stokes Flow for an incompressible Newtonian fluid. Several synthetic models in 2D and 3D were constructed considering different keel geometries and different regimes of relative displacement between the lithosphere and asthenosphere. In the present numerical experiments, we adopted a rheology in which the viscosity of the mantle is controlled by temperature, pressure and composition, assuming that the cratonic keel is compositionally more viscous than the surrounding asthenosphere, using a factor f to rescale the lithospheric viscosity compared to the asthenospheric one. We tested different f values, reference viscosity for the asthenosphere, and relative velocity between the lithosphere and the base of the upper mantle, quantifying the amount of deformation of the cratonic keel in each scenario. In general, we conclude that for a relatively low compositional factor (f < 20), the lithospheric keel can be significantly deformed in a time interval of few tens of million years when the lithosphere is moving horizontally relative to the base of the upper mantle, does not preserving its initial geometry. The synthetic models can be helpful for a better understanding of the interaction in the lithosphere-asthenosphere interface such as the deformation and flow patterns in the mantle around the keels, the rate of erosion of the root of the continental lithosphere due to the convection in the upper mantle and how it affects the thermal flow to the surface.</p><p>Sacek, V. (2017). Post-rift influence of small-scale convection on the landscape evolution at divergent continental margins. Earth and Planetary Science Letters, 459, 48-57.</p>

scholarly journals Velocity structure and radial anisotropy of the lithosphere in southern Madagascar from surface wave dispersion

2020 ◽  
Vol 224 (3) ◽  
pp. 1930-1944 ◽  
Author(s):  
E J Rindraharisaona ◽  
F Tilmann ◽  
X Yuan ◽  
J Dreiling ◽  
J Giese ◽  
...  
Keyword(s):  
Receiver Functions ◽  
Dispersion Curves ◽  
Eastern Coast ◽  
Small Scale ◽  
Seismic Structure ◽  
Lithospheric Thickness ◽  
Velocity Models ◽  
Phase Velocities ◽  
Maximum Value ◽  
Radial Anisotropy

SUMMARY We investigate the upper mantle seismic structure beneath southern Madagascar and infer the imprint of geodynamic events since Madagascar’s break-up from Africa and India and earlier rifting episodes. Rayleigh and Love wave phase velocities along a profile across southern Madagascar were determined by application of the two-station method to teleseismic earthquake data. For shorter periods (<20 s), these data were supplemented by previously published dispersion curves determined from ambient noise correlation. First, tomographic models of the phase velocities were determined. In a second step, 1-D models of SV and SH wave velocities were inverted based on the dispersion curves extracted from the tomographic models. As the lithospheric mantle is represented by high velocities we identify the lithosphere–asthenosphere boundary by the strongest negative velocity gradient. Finally, the radial anisotropy (RA) is derived from the difference between the SV and SH velocity models. An additional constraint on the lithospheric thickness is provided by the presence of a negative conversion seen in S receiver functions, which results in comparable estimates under most of Madagascar. We infer a lithospheric thickness of 110−150 km beneath southern Madagascar, significantly thinner than beneath the mobile belts in East Africa (150−200 km), where the crust is of comparable age and which were located close to Madagascar in Gondwanaland. The lithospheric thickness is correlated with the geological domains. The thinnest lithosphere (∼110 km) is found beneath the Morondava basin. The pre-breakup Karoo failed rifting, the rifting and breakup of Gondwanaland have likely thinned the lithosphere there. The thickness of the lithosphere in the Proterozoic terranes (Androyen and Anosyen domains) ranges from 125 to 140 km, which is still ∼30 km thinner than in the Mozambique belt in Tanzania. The lithosphere is the thickest beneath Ikalamavony domain (Proterozoic) and the west part of the Antananarivo domain (Archean) with a thickness of ∼150 km. Below the eastern part of Archean domain the lithosphere thickness reduces to ∼130 km. The lithosphere below the entire profile is characterized by positive RA. The strongest RA is observed in the uppermost mantle beneath the Morondava basin (maximum value of ∼9 per cent), which is understandable from the strong stretching that the basin was exposed to during the Karoo and subsequent rifting episode. Anisotropy is still significantly positive below the Proterozoic (maximum value of ∼5 per cent) and Archean (maximum value of ∼6 per cent) domains, which may result from lithospheric extension during the Mesozoic and/or thereafter. In the asthenosphere, a positive RA is observed beneath the eastern part Morondava sedimentary basin and the Proterozoic domain, indicating a horizontal asthenospheric flow pattern. Negative RA is found beneath the Archean in the east, suggesting a small-scale asthenospheric upwelling, consistent with previous studies. Alternatively, the relatively high shear wave velocity in the asthenosphere in this region indicate that the negative RA could be associated to the Réunion mantle plume, at least beneath the volcanic formation, along the eastern coast.

scholarly journals The Effectiveness of Ensemble-Neural Network Techniques to Predict Peak Uplift Resistance of Buried Pipes in Reinforced Sand

2021 ◽  
Vol 11 (3) ◽  
pp. 908
Author(s):  
Jie Zeng ◽  
Panagiotis G. Asteris ◽  
Anna P. Mamou ◽  
Ahmed Salih Mohammed ◽  
Emmanuil A. Golias ◽  
...  
Keyword(s):  
Neural Network ◽  
Numerical Models ◽  
Correlation Coefficients ◽  
Network Models ◽  
Small Scale ◽  
Offshore Platforms ◽  
Neural Network Models ◽  
Buried Pipes ◽  
Ensemble Techniques ◽  
Uplift Resistance

Buried pipes are extensively used for oil transportation from offshore platforms. Under unfavorable loading combinations, the pipe’s uplift resistance may be exceeded, which may result in excessive deformations and significant disruptions. This paper presents findings from a series of small-scale tests performed on pipes buried in geogrid-reinforced sands, with the measured peak uplift resistance being used to calibrate advanced numerical models employing neural networks. Multilayer perceptron (MLP) and Radial Basis Function (RBF) primary structure types have been used to train two neural network models, which were then further developed using bagging and boosting ensemble techniques. Correlation coefficients in excess of 0.954 between the measured and predicted peak uplift resistance have been achieved. The results show that the design of pipelines can be significantly improved using the proposed novel, reliable and robust soft computing models.

scholarly journals Observational aspects of prominence oscillations

2007 ◽  
Vol 3 (S247) ◽  
pp. 152-157 ◽  
Author(s):  
Oddbjørn Engvold
Keyword(s):  
Magnetic Structure ◽  
Numerical Models ◽  
Small Scale ◽  
Solar Prominences ◽  
Scale Structures ◽  
Oscillations And Waves ◽  
Available Information ◽  
Small Scale Structures

AbstractSeismology has become a powerful tool in studies of the magnetic structure of solar prominences and filaments. Reversely, analytical and numerical models are guided by available information about the spatial and thermodynamical structure of these enigmatic structures. The present invited paper reviews recent observational results on oscillations and waves as well as details about small-scale structures and dynamics of prominences and filaments.

Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project

2000 ◽  
Vol 663 ◽  
Author(s):  
J. Samper ◽  
R. Juncosa ◽  
V. Navarro ◽  
J. Delgado ◽  
L. Montenegro ◽  
...  
Keyword(s):  
Large Scale ◽  
Reference Model ◽  
Numerical Models ◽  
Full Scale ◽  
Small Scale ◽  
Model Parameters ◽  
In Situ Test ◽  
Wide Range ◽  
Engineered Barrier

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.

Precambrian tectonic evolution of Earth: an outline

2021 ◽  
Vol 124 (1) ◽  
pp. 141-162 ◽  
Author(s):  
J.F. Dewey ◽  
E.S. Kiseeva ◽  
J.A. Pearce ◽  
L.J. Robb
Keyword(s):  
Tectonic Evolution ◽  
Plate Tectonics ◽  
Global Scale ◽  
Sensu Stricto ◽  
Strike Slip ◽  
Small Scale ◽  
Data Sets ◽  
Crustal Material ◽  
Plate Tectonic ◽  
Single Plate

Abstract Space probes in our solar system have examined all bodies larger than about 400 km in diameter and shown that Earth is the only silicate planet with extant plate tectonics sensu stricto. Venus and Earth are about the same size at 12 000 km diameter, and close in density at 5 200 and 5 500 kg.m-3 respectively. Venus and Mars are stagnant lid planets; Mars may have had plate tectonics and Venus may have had alternating ca. 0.5 Ga periods of stagnant lid punctuated by short periods of plate turnover. In this paper, we contend that Earth has seen five, distinct, tectonic periods characterized by mainly different rock associations and patterns with rapid transitions between them; the Hadean to ca. 4.0 Ga, the Eo- and Palaeoarchaean to ca. 3.1 Ga, the Neoarchaean to ca. 2.5 Ga, the Proterozoic to ca. 0.8 Ga, and the Neoproterozoic and Phanerozoic. Plate tectonics sensu stricto, as we know it for present-day Earth, was operating during the Neoproterozoic and Phanerozoic, as witnessed by features such as obducted supra-subduction zone ophiolites, blueschists, jadeite, ruby, continental thin sediment sheets, continental shelf, edge, and rise assemblages, collisional sutures, and long strike-slip faults with large displacements. From rock associations and structures, nothing resembling plate tectonics operated prior to ca. 2.5 Ga. Archaean geology is almost wholly dissimilar from Proterozoic-Phanerozoic geology. Most of the Proterozoic operated in a plate tectonic milieu but, during the Archaean, Earth behaved in a non-plate tectonic way and was probably characterised by a stagnant lid with heat-loss by pluming and volcanism, together with diapiric inversion of tonalite-trondjemite-granodiorite (TTG) basement diapirs through sinking keels of greenstone supracrustals, and very minor mobilism. The Palaeoarchaean differed from the Neoarchaean in having a more blobby appearance whereas a crude linearity is typical of the Neoarchaean. The Hadean was probably a dry stagnant lid Earth with the bulk of its water delivered during the late heavy bombardment, when that thin mafic lithosphere was fragmented to sink into the asthenosphere and generate the copious TTG Ancient Grey Gneisses (AGG). During the Archaean, a stagnant unsegmented, lithospheric lid characterised Earth, although a case can be made for some form of mobilism with “block jostling”, rifting, compression and strike-slip faulting on a small scale. We conclude, following Burke and Dewey (1973), that there is no evidence for subduction on a global scale before about 2.5 Ga, although there is geochemical evidence for some form of local recycling of crustal material into the mantle during that period. After 2.5 Ga, linear/curvilinear deformation belts were developed, which “weld” cratons together and palaeomagnetism indicates that large, lateral, relative motions among continents had begun by at least 1.88 Ga. The “boring billion”, from about 1.8 to 0.8 Ga, was a period of two super-continents (Nuna, also known as Columbia, and Rodinia) characterised by substantial magmatism of intraplate type leading to the hypothesis that Earth had reverted to a single plate planet over this period; however, orogens with marginal accretionary tectonics and related magmatism and ore genesis indicate that plate tectonics was still taking place at and beyond the bounds of these supercontinents. The break-up of Rodinia heralded modern plate tectonics from about 0.8 Ga. Our conclusions are based, almost wholly, upon geological data sets, including petrology, ore geology and geochemistry, with minor input from modelling and theory.

scholarly journals Radiation in the neighbourhood of a double layer

2014 ◽  
Vol 32 (6) ◽  
pp. 677-687 ◽  
Author(s):  
R. Pottelette ◽  
M. Berthomier ◽  
J. Pickett
Keyword(s):  
Phase Space ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
Source Region ◽  
Double Layers ◽  
Small Scale ◽  
High Time Resolution ◽  
Local Electron ◽  
Nonlinear Phase ◽  
Electron Holes

Abstract. In the auroral kilometric radiation (AKR) source region, acceleration layers narrow in altitude and associated with parallel field-aligned potential drops of several kV can be identified by using both particles and wave-field high time-resolution measurements from the Fast Auroral SnapshoT explorer spacecraft (FAST). These so-called double layers (DLs) are recorded around density enhancements in the auroral cavity, where the enhancement can be at the edge of the cavity or even within the cavity at a small scale. Once immersed in the plasma, DLs necessarily accelerate particles along the magnetic field lines, thereby generating locally strong turbulent processes leading to the formation of nonlinear phase space holes. The FAST data reveal the asymmetric character of the turbulence: the regions located on the high-potential side of the DLs are characterized by the presence of electron holes, while on the low-potential side, ion holes are recorded. The existence of these nonlinear phase space holes may affect the AKR radiation pattern in the neighbourhood of a DL where the electron distribution function is drastically different from a horseshoe shape. We present some observations which illustrate the systematic generation of elementary radiation events occurring significantly above the local electron gyrofrequency in the presence of electron holes. These fine-scale AKR radiators are associated with a local electron distribution which presents a pronounced beam-like shape.

scholarly journals Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics

2013 ◽  
Vol 10 (3) ◽  
pp. 1529-1541 ◽  
Author(s):  
N. Wright ◽  
S. Zahirovic ◽  
R. D. Müller ◽  
M. Seton
Keyword(s):  
Ocean Circulation ◽  
Plate Tectonics ◽  
Numerical Models ◽  
Plate Motion ◽  
Temporal Data Mining ◽  
Dynamic Topography ◽  
Southeastern Australia ◽  
Eastern Australia ◽  
Spatio Temporal ◽  
Fossil Data

Abstract. A variety of paleogeographic reconstructions have been published, with applications ranging from paleoclimate, ocean circulation and faunal radiation models to resource exploration; yet their uncertainties remain difficult to assess as they are generally presented as low-resolution static maps. We present a methodology for ground-truthing the digital Palaeogeographic Atlas of Australia by linking the GPlates plate reconstruction tool to the global Paleobiology Database and a Phanerozoic plate motion model. We develop a spatio-temporal data mining workflow to validate the Phanerozoic Palaeogeographic Atlas of Australia with paleoenvironments derived from fossil data. While there is general agreement between fossil data and the paleogeographic model, the methodology highlights key inconsistencies. The Early Devonian paleogeographic model of southeastern Australia insufficiently describes the Emsian inundation that may be refined using biofacies distributions. Additionally, the paleogeographic model and fossil data can be used to strengthen numerical models, such as the dynamic topography and the associated inundation of eastern Australia during the Cretaceous. Although paleobiology data provide constraints only for paleoenvironments with high preservation potential of organisms, our approach enables the use of additional proxy data to generate improved paleogeographic reconstructions.

scholarly journals The South Georgia Wave Experiment: A Means for Improved Analysis of Gravity Waves and Low-Level Wind Impacts Generated from Mountainous Islands

2018 ◽  
Vol 99 (5) ◽  
pp. 1027-1040 ◽  
Author(s):  
D. R. Jackson ◽  
A. Gadian ◽  
N. P. Hindley ◽  
L. Hoffmann ◽  
J. Hughes ◽  
...  
Keyword(s):  
High Resolution ◽  
Gravity Waves ◽  
Numerical Models ◽  
Small Island ◽  
Small Scale ◽  
The South ◽  
South Georgia ◽  
Low Level ◽  
Wave Experiment ◽  
Realistic Representation

AbstractGravity waves (GWs) play an important role in many atmospheric processes. However, the observation-based understanding of GWs is limited, and representing them in numerical models is difficult. Recent studies show that small islands can be intense sources of GWs, with climatologically significant effects on the atmospheric circulation. South Georgia, in the South Atlantic, is a notable source of such “small island” waves. GWs are usually too small scale to be resolved by current models, so their effects are represented approximately using resolved model fields (parameterization). However, the small-island waves are not well represented by such parameterizations, and the explicit representation of GWs in very-high-resolution models is still in its infancy. Steep islands such as South Georgia are also known to generate low-level wakes, affecting the flow hundreds of kilometers downwind. These wakes are also poorly represented in models.We present results from the South Georgia Wave Experiment (SG-WEX) for 5 July 2015. Analysis of GWs from satellite observations is augmented by radiosonde observations made from South Georgia. Simulations were also made using high-resolution configurations of the Met Office Unified Model (UM). Comparison with observations indicates that the UM performs well for this case, with realistic representation of GW patterns and low-level wakes. Examination of a longer simulation period suggests that the wakes generally are well represented by the model. The realism of these simulations suggests they can be used to develop parameterizations for use at coarser model resolutions.

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