The effect of composite rheology on mantle convection models with plate-like behavior

2020 ◽  
Author(s):  
Maelis Arnould ◽  
Tobias Rolf
Keyword(s):  
Deformation Mechanism ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
Lattice Preferred Orientation

<p>The coupling between mantle convection and plate tectonics results in mantle flow patterns and properties which can be characterized with different seismic methods. In particular, the presence of mantle seismic anisotropy in the uppermost mantle suggests the existence of mineral Lattice-Preferred Orientation (LPO) caused by asthenospheric flow. Dislocation creep, which implies non-Newtonian mantle rheology, has been identified as a deformation mechanism responsible for such LPO leading to seismic anisotropy. While it has been proposed that the use of a composite rheology (with both diffusion and dislocation creep) significantly impacts the planform of convection and thus the resulting tectonic behavior at the surface, large-scale mantle convection studies have typically assumed diffusion creep (Newtonian rheology) as the only deformation mechanism, due to computational limitations.</p><p>Here, we investigate the role of composite rheology on mantle convection with self-consistent plate-like behavior using the code StagYY in 2D annulus (Hernlund and Tackley, 2008). We quantify the spatial distribution of dislocation creep in the mantle in models characterized by different transitional stresses between Newtonian and non-Newtonian rheology. Such models are built on previous viscoplastic cases featuring Earth-like plate velocities, surface heat flow and topography with Newtonian rheology (Arnould et al., 2018). We then investigate how composite rheology impacts the planform of convection and the style of plate-like behavior.</p><p> </p><p><strong>References:</strong></p><p>Hernlund, J. W., & Tackley, P. J. (2008). Modeling mantle convection in the spherical annulus. Physics of the Earth and Planetary Interiors, 171(1-4), 48-54.</p><p>Arnould, M., Coltice, N., Flament, N., Seigneur, V., & Müller, R. D. (2018). On the scales of dynamic topography in whole‐mantle convection models. Geochemistry, Geophysics, Geosystems, 19(9), 3140-3163.</p>

On the generation of plate-like surface tectonics in whole-mantle convection models employing composite rheology 

2021 ◽  
Author(s):  
Maelis Arnould ◽  
Tobias Rolf ◽  
Antonio Manjón-Cabeza Córdoba
Keyword(s):  
Deformation Mechanism ◽  
Upper Mantle ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Seismic Anisotropy ◽  
Temporal Distribution ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Mantle Flow ◽  
Uppermost Mantle

<p>Earth’s lithospheric behavior is tied to the properties and dynamics of mantle flow. In particular, upper mantle rheology controls the coupling between the lithosphere and the asthenosphere, and therefore partly dictates Earth’s tectonic behavior. It is thus important to gain insight into how Earth’s upper mantle deforms in order to understand the evolution of plate tectonics. The presence of seismic anisotropy in the uppermost mantle suggests the existence of mineral lattice-preferred orientation (LPO) caused by the asthenospheric flow. Together with laboratory experiments of mantle rock deformation, this indicates that Earth’s uppermost mantle can deform in a non-Newtonian way, through dislocation creep. Although such a deformation mechanism can significantly impact both mantle flow and the surface tectonic behavior, most numerical studies of whole-mantle convection use a viscoplastic rheology involving diffusion creep as the only deformation mechanism in the mantle.</p><p>Here, we investigate the effects of using a composite rheology (with both diffusion and dislocation creep) on the surface tectonic behavior in 2D-cartesian whole-mantle convection models that self-consistently generate plate-like tectonics. We vary the proportion of dislocation creep in the mantle by imposing different temperature- and depth-dependent transitional stresses between diffusion and dislocation creep. Using different yield stresses, we investigate how the amount of dislocation creep affects the planform of convection and promotes surface plate-like or stagnant-lid behavior. In particular, we show that for a given yield stress promoting plate-like behavior in diffusion-creep-only models, a progressive increase in the amount of dislocation creep affects the shape and dynamics of slabs, eventually leading to stagnant-lid convection. We discuss the spatio-temporal distribution of dislocation creep in the mantle in light of the observed geometry of slabs and the spatial distribution of seismic anisotropy in Earth’s upper-mantle.</p>

MAVEPROS: a new open source software to predict mantle elastic properties and build realistic tomographic models

2020 ◽  
Author(s):  
Manuele Faccenda
Keyword(s):  
Single Crystal ◽  
Open Source ◽  
Elastic Properties ◽  
Open Source Software ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Volume Fraction ◽  
Dislocation Creep ◽  
Mantle Flow ◽  
Polycrystalline Aggregates

<p>Coupling large-scale geodynamic and seismological modelling appears a promising methodology for the understanding of the Earth’s recent dynamics and present-day structure. So far, the two types of modelling have been mainly conducted separately, and a code capable of linking these two methodologies of investigation is still lacking.</p><p>In this contribution I present MAVEPROS, a new open source software that allows both for the modelling of strain-induced mantle fabrics and seismic anisotropy, and for the generation of realistic synthetic tomographic models.</p><p>As an input, the software requires the velocity, pressure, temperature (and additionally the fraction of deformation accommodated by dislocation creep) fields (averaged each 100 kyr for typical mantle strain rates) outputted by the large-scale mantle flow models.</p><p>The strain-induced mantle fabrics are then modelled with D-Rex (Kaminski et al., 2004, GJI), an open source code that has been parallelized and modified to account for fast computation, combined diffusion-dislocation creep (Faccenda and Capitanio, 2012a, GRL; 2013, Gcubed), LPO of transition zone and lower mantle polycrystalline aggregates, P-T dependence of single crystal elastic tensors (Faccenda, 2014, PEPI), advection and non-steady-state deformation of crystal aggregates in 2D/3D cartesian/spherical grids with basic/staggered velocity nodes (Hu et al., 2017, EPSL), homogeneous sampling of the mantle by implementation of the Deformable PIC method (Samuel, 2018, GJI), apparent anisotropy in layered or crack-bearing rocks estimated with the Differential Effective Medium (DEM) (Sturgeon et al., Gcubed, 2019). The new version of D-Rex can solve for the LPO evolution of 100.000s polycrystalline aggregates of the whole mantle in a few hours, outputting the full elastic tensor of poly-crystalline aggregates as a function of each single crystal orientation, volume fraction and P-T scaled elastic moduli.</p><p>The crystal aggregates can then be interpolated in a tomographic grid for either visual inspection of the mantle elastic properties  (such as Vp and Vs isotropic anomalies; radial, azimuthal, Vp and Vs anisotropies; reflected/refracted energy at discontinuities for different incidence angles as imaged by receiver function studies; ), or to generate input files for large-scale synthetic waveform modelling (e.g., SPECFEM3D format; FSTRACK format to calculate SKS splitting (Becker et al., 2006, GJI)).</p>

scholarly journals Mantle Convection and Possible Mantle Plumes beneath Antarctica - Insights from Geodynamic Models and Implications for Topography

2021 ◽  
pp. M56-2020-2
Author(s):  
Eva Bredow ◽  
Bernhard Steinberger
Keyword(s):  
Mantle Plume ◽  
Seismic Tomography ◽  
Mantle Convection ◽  
Large Scale ◽  
Shear Velocity ◽  
Mantle Flow ◽  
Mantle Plumes ◽  
Dynamic Topography ◽  
West Antarctica ◽  
Geodynamic Models

AbstractThis chapter describes the large-scale mantle flow structures beneath Antarctica as derived from global seismic tomography models of the present-day state. In combination with plate reconstructions, the time-dependent pattern of paleosubduction can be simulated and is also shown from the rarely seen Antarctic perspective. Furthermore, a dynamic topography model demonstrates which kind and scales of surface manifestations can be expected as a direct and observable result of mantle convection. The last section of the chapter features an overview of the classical concept of deep-mantle plumes from a geodynamic point of view and how recent insights, mostly from seismic tomography, have changed the understanding of plume structures and dynamics over the past decades. The long-standing and controversial hypothesis of a mantle plume beneath West Antarctica is summarised and addressed with geodynamic models, which estimate the excess heat flow of a potential plume at the bedrock surface. However, the predicted heatflow is small while differences in surface heat flux estimates are large, therefore the results are not conclusive with regard to the existence of a West Antarctic mantle plume. Finally, it is shown that global mantle flow would cause tilting of whole-mantle plume conduits beneath West Antarctica such that their base is predicted to be displaced about northward relative to the surface position, closer to the southern margin of the Pacific Large Low Shear Velocity Province.

scholarly journals The impact of rheological uncertainty on dynamic topography predictions

Solid Earth ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 2167-2178 ◽  
Author(s):  
Ömer F. Bodur ◽  
Patrice F. Rey
Keyword(s):  
Mantle Convection ◽  
Numerical Experiments ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
Density Anomaly ◽  
Low Viscosity ◽  
Local Reduction ◽  
Dynamic Components ◽  
Mantle Rheology ◽  
The Impact

Abstract. Much effort is being made to extract the dynamic components of the Earth's topography driven by density heterogeneities in the mantle. Seismically mapped density anomalies have been used as an input into mantle convection models to predict the present-day mantle flow and stresses applied on the Earth's surface, resulting in dynamic topography. However, mantle convection models give dynamic topography amplitudes generally larger by a factor of ∼2, depending on the flow wavelength, compared to dynamic topography amplitudes obtained by removing the isostatically compensated topography from the Earth's topography. In this paper, we use 3-D numerical experiments to evaluate the extent to which the dynamic topography depends on mantle rheology. We calculate the amplitude of instantaneous dynamic topography induced by the motion of a small spherical density anomaly (∼100 km radius) embedded into the mantle. Our experiments show that, at relatively short wavelengths (<1000 km), the amplitude of dynamic topography, in the case of non-Newtonian mantle rheology, is reduced by a factor of ∼2 compared to isoviscous rheology. This is explained by the formation of a low-viscosity channel beneath the lithosphere and a decrease in thickness of the mechanical lithosphere due to induced local reduction in viscosity. The latter is often neglected in global mantle convection models. Although our results are strictly valid for flow wavelengths less than 1000 km, we note that in non-Newtonian rheology all wavelengths are coupled, and the dynamic topography at long wavelengths will be influenced.

Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean

Geology ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 8-12 ◽  
Author(s):  
Vadim Levin ◽  
Stephen Elkington ◽  
James Bourke ◽  
Ivonne Arroyo ◽  
Lepolt Linkimer
Keyword(s):  
Costa Rica ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Volcanic Eruptions ◽  
Central American ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
The Pacific ◽  
The Caribbean ◽  
Surrounding Areas

Abstract Surrounded by subducting slabs and continental keels, the upper mantle of the Pacific is largely prevented from mixing with surrounding areas. One possible outlet is beneath the southern part of the Central American isthmus, where regional observations of seismic anisotropy, temporal changes in isotopic composition of volcanic eruptions, and considerations of dynamic topography all suggest upper mantle flow from the Pacific to the Caribbean. We derive new constraints on the nature of seismic anisotropy in the upper mantle of southern Costa Rica from observations of birefringence in teleseismic shear waves. Fast and slow components separate by ∼1 s, with faster waves polarized along the 40°–50° (northeast) direction, near-orthogonally to the Central American convergent margin. Our results are consistent with upper mantle flow from the Pacific to the Caribbean and require an opening in the lithosphere subducting under the region.

scholarly journals What drives tectonic plates?

2019 ◽  
Vol 5 (10) ◽  
pp. eaax4295 ◽  
Author(s):  
Nicolas Coltice ◽  
Laurent Husson ◽  
Claudio Faccenna ◽  
Maëlis Arnould
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Dynamic Models ◽  
Dynamic Balance ◽  
Mantle Flow ◽  
Consistent System ◽  
Tectonic Plates ◽  
Slowing Down ◽  
Ill Posed

Does Earth’s mantle drive plates, or do plates drive mantle flow? This long-standing question may be ill posed, however, as both the lithosphere and mantle belong to a single self-organizing system. Alternatively, this question is better recast as follows: Does the dynamic balance between plates and mantle change over long-term tectonic reorganizations, and at what spatial wavelengths are those processes operating? A hurdle in answering this question is in designing dynamic models of mantle convection with realistic tectonic behavior evolving over supercontinent cycles. By devising these models, we find that slabs pull plates at rapid rates and tear continents apart, with keels of continents only slowing down their drift when they are not attached to a subducting plate. Our models show that the tectonic tessellation varies at a higher degree than mantle flow, which partly unlocks the conceptualization of plate tectonics and mantle convection as a unique, self-consistent system.

Combining tomographic images and geodynamic modeling of past mantle flow: from simple analytical solutions to numerical inverse methods

2020 ◽  
Author(s):  
Lorenzo Colli
Keyword(s):  
Analytical Solutions ◽  
Mantle Convection ◽  
Large Scale ◽  
Thermal Evolution ◽  
Past History ◽  
Tomographic Imaging ◽  
Mantle Flow ◽  
The South ◽  
Future Evolution ◽  
Trade Offs

&lt;p&gt;&lt;span&gt;Physics-based geodynamic modeling of mantle convection provide a unifying framework for solid-Earth sciences, explicitly linking together disparate fields such as tectonophysics, tomographic imaging, basin analysis, mantle mineralogy, geomorphology, global geodesy and the long-term chemical and thermal evolution of the mantle. Studying the evolution of mantle convection in time is particularly powerful as it reduces trade-offs, increase the possible linkages and the opportunities to cross-test hypotheses. But since mantle convection evolves over geologic timescales, its future evolution is precluded from us and we must focus on its past history.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Here I will show how geodynamic modeling of past mantle flow can be combined with tomographic imaging and geologic observations, highlighting the strengths of this approach and some of its potential pitfalls. I will use a series of case studies, starting from simple analytical solutions for channelized flow in the South Atlantic and Caribbean regions. I will move on to an application of sequential assimilation to the South China Sea, ending with computationally demanding large-scale numerical optimizations of past mantle flow.&lt;/span&gt;&lt;/p&gt;

scholarly journals Landscape responses to dynamic topography and climate change on the South African source-to-sink system since the Oligocene

2021 ◽  
Author(s):  
Claire A. Mallard ◽  
Tristan Salles
Keyword(s):  
South African ◽  
Large Scale ◽  
Sedimentary Basin ◽  
Drainage System ◽  
Sediment Flux ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
The South ◽  
Source To Sink ◽  
Underlying Mechanisms

Abstract. The South African landscape displays important lithological and topographical heterogeneities between the eastern, western margins and the plateau. Yet the underlying mechanisms and timings responsible for this peculiar layout remain unclear. While studies have proposed a post-Gondwana uplift driver, others have related these heterogeneities to a more recent evolution induced by deep mantle flow dynamics during the last 30 million years. This theory seems supported by the rapid increase of sediment flux in the Orange basin since the Oligocene. However, the triggers and responses of the South African landscape to dynamic topography are still debated. Here we use a series of numerical simulations forced with Earth data to evaluate the contribution of dynamic topography and precipitation on the Orange river source-to-sink system since the Oligocene. We show that, if the tested uplift histories influence deposits distribution and thicknesses in the Orange sedimentary basin, they poorly affect the large-scale drainage system organisation and only strongly impact the erosion across the catchment for two of the four tested dynamic topography cases. Conversely, it appears that paleo-rainfall regimes are the major forcing mechanism that drives the recent increase of sediment flux in the Orange basin. From our simulations, we find that climate strongly smoothed the dynamic topography signal in the South African landscape and that none of the currently proposed dynamic topography scenarios produce an uplift high enough to drive the pulse of erosion and associated sedimentation observed during the Palaeocene. These findings support the hypothesis of a pre-Oligocene uplift. Our results are crucial to improve our understanding of the recent evolution of the South African landscape.

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