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>

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>

scholarly journals Feedbacks between a non-Newtonian upper mantle, mantle viscosity structure and mantle dynamics

2020 ◽  
Vol 224 (2) ◽  
pp. 961-972
Author(s):  
A G Semple ◽  
A Lenardic
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Mantle Convection ◽  
Mantle Flow ◽  
Mantle Dynamics ◽  
Plate Motions ◽  
Low Viscosity ◽  
Mantle Viscosity ◽  
Flow Feature ◽  
Mantle Rheology

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

scholarly journals Supplemental Material: Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean

2020 ◽  
Author(s):  
Vadim Levin ◽  
et al.
Keyword(s):  
Data Analysis ◽  
Costa Rica ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Data Sources ◽  
Mantle Flow ◽  
Analysis Methodology ◽  
The Pacific ◽  
Wave Splitting ◽  
The Caribbean

Data sources, details of data analysis methodology, and additional diagrams and maps of shear wave splitting measurements.<br>

scholarly journals Seismic anisotropy reveals crustal flow driven by mantle vertical loading in the Pacific NW

2020 ◽  
Vol 6 (28) ◽  
pp. eabb0476
Author(s):  
Jorge C. Castellanos ◽  
Jonathan Perry-Houts ◽  
Robert W. Clayton ◽  
YoungHee Kim ◽  
A. Christian Stanciu ◽  
...  
Keyword(s):  
Pacific Northwest ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Azimuthal Anisotropy ◽  
Mantle Flow ◽  
Near Surface ◽  
Vertical Loading ◽  
The Pacific ◽  
Anisotropy Model ◽  
Lithosphere Dynamics

Buoyancy anomalies within Earth’s mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.

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.

Seismic anisotropy and mantle deformation in NW Iran through splitting measurements of SKS and direct S phases

2020 ◽  
Author(s):  
Shiva Arvin ◽  
Farhad Sobouti ◽  
Keith Priestley ◽  
Abdolreza Ghods ◽  
Seyed Khalil Motaghi ◽  
...  
Keyword(s):  
Flow Field ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Central Iran ◽  
Plate Motion ◽  
Propagation Path ◽  
Mantle Flow ◽  
South Caspian Basin ◽  
Nw Iran ◽  
S Waves

&lt;p&gt;&lt;span&gt;The present tectonics of Iran has resulted from the continental convergence of the Arabian and Eurasian plates. Our study area, in NW Iran comprises a part of this collision zone and consists of an assemblage of distinct lithospheric blocks including the central Iranian Plateau, the South Caspian Basin, and the Talesh western Alborz Mountains. A proper knowledge of mantle flow field is required to bettwer constrain mantle kinematics in relation to the dynamics of continental deformation in NW Iran. To achieve this aim, we examined splitting of teleseismic shear waves (e.g. SKS and S) arriving with steep arrival angles beneath the receiver, which provide excellent lateral resolution in the upper mantle. We used data from 68 temporary broadband stations with varying operation periods (4 to 31 months) along 3 linear profiles. We perfomed splitting analyses on SK(K)S and direct S waves. &lt;/span&gt;Resultant splitting parameters obtained from both shear phases exhibit broad similarities. Relatively large time delays observed for direct S-waves, however, are anticipated since these waves travel longer than SKS along a non-vertical propagation path in an anisotropic layer. Overall, the fast polarization directions (FPDs) in the Alborz, Talesh, Tarom Mountain and in NW Iran indicate a strong consistency with NE-SW anisotropic orientations. Besides, we observe a good accordance between S and SKS results. A comparison of splitting parameters with the absolute plate motion (APM) vector and structural trends in Iran and eastern Turkey suggests asthenospheric flow field as the dominant source for observed seismic anisotropy. The lithospheric layer beneath these regions is relatively thin (compared to the adjacent Zagros region), explaining why it appears to only make a partial contribution to the observed anisotropy. The stations located in central Iran just southwest of the Alborz yield angular deviations from the general NE-SW trend as this may be explained by changing style of deformation across the different tectonic blocks. These stations indicate significant misfit between SK(K)S and direct S-waves that could be caused by local heterogeneities developed due to a diffuse boundary from the flow organization in the upper mantle of central Iran. Another possibility for large differences between two types of waves might be reflect the anisotropic structure of a remnant slab segment or a foundered lithospheric root beneath central Iran with a volume small enough to be detected by SKS phases, but not by the direct S waves.&lt;/p&gt;

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

&lt;p&gt;Coupling large-scale geodynamic and seismological modelling appears a promising methodology for the understanding of the Earth&amp;#8217;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;The crystal aggregates can then be interpolated in a tomographic grid for either visual inspection of the mantle elastic properties &amp;#160;(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)).&lt;/p&gt;

Mantle flow under the Central Alps: Constraints from non-vertical-ray SKS shear-wave splittting

2020 ◽  
Author(s):  
Eric Löberich ◽  
Götz Bokelmann
Keyword(s):  
Shear Wave ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Single Layer ◽  
Depth Resolution ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Central Alps ◽  
Upper Mantle Anisotropy ◽  
Wave Splitting

&lt;p&gt;The association of seismic anisotropy and deformation, as e.g. exploited by shear-wave splitting measurements, provides a unique opportunity to map the orientation of geodynamic processes in the upper mantle and to constraint their nature. However, due to the limited depth-resolution of steeply arriving core-phases, used for shear-wave splitting investigations, it appears difficult to differentiate between asthenospheric and lithospheric origins of observed seismic anisotropy. To change that, we take advantage of the different backazimuthal variations of fast orientation &lt;em&gt;&amp;#966;&lt;/em&gt; and delay time &lt;em&gt;&amp;#916;t&lt;/em&gt;, when considering the non-vertical incidence of phases passing through an olivine block with vertical b-axis as opposed to one with vertical c-axis. Both these alignments can occur depending on the type of deformation, e.g. a sub-horizontal foliation orientation in the case of a simple asthenospheric flow and a sub-vertical foliation when considering vertically-coherent deformation in the lithosphere. In this study we investigate the cause of seismic anisotropy in the Central Alps. Combining high-quality manual shear-wave splitting measurements of three datasets leads to a dense station coverage. Fast orientations &lt;em&gt;&amp;#966;&lt;/em&gt; show a spatially coherent and relatively simple mountain-chain-parallel pattern, likely related to a single-layer case of upper mantle anisotropy. Considering the measurements of the whole study area together, our non-vertical-ray shear-wave splitting procedure points towards a b-up olivine situation and thus favors an asthenospheric anisotropy source, with a horizontal flow plane of deformation. We also test the influence of position relative to the European slab, distinguishing a northern and southern subarea based on vertically-integrated travel times through a tomographic model. Differences in the statistical distribution of splitting parameters &lt;em&gt;&amp;#966;&lt;/em&gt; and &lt;em&gt;&amp;#916;t&lt;/em&gt;, and in the backazimuthal variation of &lt;em&gt;&amp;#948;&amp;#966;&lt;/em&gt; and &lt;em&gt;&amp;#948;&amp;#916;t&lt;/em&gt;, become apparent. While the observed seismic anisotropy in the northern subarea shows indications of asthenospheric flow, likely a depth-dependent plane Couette-Poiseuille flow around the Alps, the origin in the southern subarea remains more difficult to determine and may also contain effects from the slab itself.&lt;/p&gt;

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