Retrodictions of Mid Paleogene mantle flow and dynamic topography in the Atlantic region from compressible high resolution adjoint mantle convection models: Sensitivity to deep mantle viscosity and tomographic input model

2018 ◽  
Vol 53 ◽  
pp. 252-272 ◽  
Author(s):  
L. Colli ◽  
S. Ghelichkhan ◽  
H.-P. Bunge ◽  
J. Oeser
Keyword(s):  
High Resolution ◽  
Mantle Convection ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
Atlantic Region ◽  
Mantle Viscosity ◽  
Deep Mantle ◽  
Input Model

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 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.

scholarly journals The deep Earth origin of the Iceland plume and its effects on regional surface uplift and subsidence

2016 ◽  
Author(s):  
N. Barnett-Moore ◽  
R. Hassan ◽  
N. Flament ◽  
R. D. Müller
Keyword(s):  
North Atlantic ◽  
Flow Model ◽  
Mantle Flow ◽  
Seismic Structure ◽  
Dynamic Topography ◽  
The North ◽  
Deep Mantle ◽  
Deep Earth ◽  
The North Atlantic ◽  
Iceland Plume

Abstract. The present-day seismic structure of the mantle under the North Atlantic indicates that the Iceland hotspot represents the surface expression of a deep mantle plume, which is thought to have erupted in the North Atlantic during the Paleocene. The spatial and temporal evolution of the plume since its eruption is still highly debated, and little is known about its deep mantle history. Here, a paleogeographically constrained global mantle flow model is used to investigate the evolution of deep Earth flow and surface dynamic topography in the North Atlantic since the Jurassic. The model shows that over the last ~ 100 Myr a remarkably stable pattern of convergent flow has prevailed in the lowermost mantle near the tip of the African Large Low-Shear Velocity Province (LLSVP), making it an ideal plume nucleation site. The present-day location of the model plume is ~ 10° southeast from the inferred present-day location of the Iceland plume. We apply a constant surface rotation to the model through time, derived from correcting for this offset at present-day. A comparison between the rotated model dynamic topography evolution and available offshore geological and geophysical observations across the region confirms that a widespread episode of Paleocene transient uplift followed by early Eocene anomalous subsidence can be explained by the mantle-driven effects of a plume head ~ 2000 km in diameter, arriving beneath central western Greenland during the Paleocene. The rotated model plume eruption location beneath Western Greenland is compatible with previous models. The mantle flow model underestimates the magnitude of observed anomalous subsidence during the Paleocene in some parts of the North Atlantic by as much as several hundred meters, which we attribute to upper mantle convection processes, not captured by the model.

Subducting slab morphology and mantle transition zone upwelling in double-slab subduction models with inward-dipping directions

2019 ◽  
Vol 218 (3) ◽  
pp. 2089-2105 ◽  
Author(s):  
Tianyang Lyu ◽  
Zhiyuan Zhu ◽  
Benjun Wu
Keyword(s):  
Transition Zone ◽  
Lower Mantle ◽  
Numerical Models ◽  
Local Maximum ◽  
Substantial Effect ◽  
Mantle Flow ◽  
Slab Geometry ◽  
Mantle Transition Zone ◽  
Mantle Viscosity ◽  
Deep Mantle

SUMMARY Lithospheric plates on the Earth's surface interact with each other, producing distinctive structures comprising two descending slabs. Double-slab subduction with inward-dipping directions represents an important multiplate system that is not yet well understood. This paper presents 2-D numerical models that investigate the dynamic process of double-slab subduction with inward dipping, focussing on slab geometry and mantle transition zone upwelling flow. This unique double-slab configuration limits trench motion and causes steep downward slab movement, thus forming fold piles in the lower mantle and driving upward mantle flow between the slabs. The model results show the effects of lithospheric plate properties and lower-mantle viscosity on subducting plate kinematics, overriding plate stress and upward mantle flow beneath the overriding plate. Appropriate lower-mantle strength (such as an upper–lower mantle viscosity increase with a factor of 200) allows slabs to penetrate into the lower mantle with periodical buckling. While varying the length and thickness of a long overriding plate (≥2500) does not have a substantial effect on slab geometry, its viscosity has a marked impact on slab evolution and mantle flow pattern. When the overriding plate is strong, slabs exhibit an overturned geometry and hesitate to fold. Mantle transition zone upwelling velocity depends on the speed of descending slabs. The downward velocity of slabs with a large negative buoyancy (caused by thickness or density) is very fast, inducing a significant transition zone upwelling flow. A stiff slab slowly descends into the deep mantle, causing a small upward flow in the transition zone. In addition, the temporal variation of mantle upwelling velocity shows strong correlation with the evolution of slab folding geometry. In the double subduction system with inward-dipping directions, the mantle transition zone upwelling exhibits oscillatory rise with time. During the backward-folding stage, upwelling velocity reaches its local maximum. Our results provide new insights into the deep mantle source of intraplate volcanism in a three-plate interaction system such as the Southeast Asia region.

scholarly journals The impact of rheological uncertainty on dynamic topography predictions: Gearing up for dynamic topography models consistent with observations

2019 ◽  
Author(s):  
Ömer F. Bodur ◽  
Patrice F. Rey
Keyword(s):  
Mantle Convection ◽  
Numerical Models ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
Dynamic Component ◽  
Density Anomaly ◽  
Low Viscosity ◽  
Local Reduction ◽  
Non Linear ◽  
The Impact

Abstract. Much effort has been given on extracting the dynamic component of the Earth’s topography, which is 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 topographies generally larger by a factor of ∼2 compared to dynamic topographies estimated from residual topography after extraction of the isostatically compensated topography. Our 3D thermo-mechanical numerical experiments suggest that this discrepancy can be explained by the use of a viscosity model, which doesn’t account for non-linear viscosity behaviour. In this paper, we numerically model the dynamic topography induced by a spherical density anomaly embedded into the mantle. When we use non-linear viscosities, our numerical models predict dynamic topographies lesser by a factor of ∼2 than those derived from numerical models using isoviscous rheology. This reduction in dynamic topography is explained by either the formation of a low viscosity channel beneath the lithosphere, or a decrease in thickness of the mechanical lithosphere due to induced local reduction in viscosity. Furthermore, we show that uncertainties related to activation volume and fluid activity, lead to variations in dynamic topography of about 20 %.

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.

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Hernlund, J. W., &amp; Tackley, P. J. (2008). Modeling mantle convection in the spherical annulus. Physics of the Earth and Planetary Interiors, 171(1-4), 48-54.&lt;/p&gt;&lt;p&gt;Arnould, M., Coltice, N., Flament, N., Seigneur, V., &amp; M&amp;#252;ller, R. D. (2018). On the scales of dynamic topography in whole&amp;#8208;mantle convection models. Geochemistry, Geophysics, Geosystems, 19(9), 3140-3163.&lt;/p&gt;

scholarly journals Mantle plumes and mantle dynamics in the Wilson cycle

2019 ◽  
Vol 470 (1) ◽  
pp. 87-103 ◽  
Author(s):  
Philip J. Heron
Keyword(s):  
Mantle Convection ◽  
Large Scale ◽  
Thermal Evolution ◽  
Mantle Flow ◽  
Mantle Plumes ◽  
Mantle Dynamics ◽  
The Core ◽  
Deep Mantle ◽  
Igneous Provinces ◽  
Wilson Cycle

AbstractThis review discusses the thermal evolution of the mantle following large-scale tectonic activities such as continental collision and continental rifting. About 300 myr ago, continental material amalgamated through the large-scale subduction of oceanic seafloor, marking the termination of one or more oceanic basins (e.g. Wilson cycles) and the formation of the supercontinent Pangaea. The present day location of the continents is due to the rifting apart of Pangaea, with the dispersal of the supercontinent being characterized by increased volcanic activity linked to the generation of deep mantle plumes. The discussion presented here investigates theories regarding the thermal evolution of the mantle (e.g. mantle temperatures and sub-continental plumes) following the formation of a supercontinent. Rifting, orogenesis and mass eruptions from large igneous provinces change the landscape of the lithosphere, whereas processes related to the initiation and termination of oceanic subduction have a profound impact on deep mantle reservoirs and thermal upwelling through the modification of mantle flow. Upwelling and downwelling in mantle convection are dynamically linked and can influence processes from the crust to the core, placing the Wilson cycle and the evolution of oceans at the forefront of our dynamic Earth.

The adjoint equations for thermochemical compressible mantle convection: derivation and verification by twin experiments

2020 ◽  
Author(s):  
Sia Ghelichkhan ◽  
Hans-Peter Bunge
Keyword(s):  
Mantle Convection ◽  
Compressible Flows ◽  
Adjoint Method ◽  
Reference Model ◽  
Adjoint Equations ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
Final State ◽  
Flow Models ◽  
The Cost

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;The adjoint method is an efficient way to obtain gradient information in a mantle convection model relative to past flow structure, allowing one to retrodict mantle flow from observations of the present-day mantle state. While adjoint equations for isochemical mantle flow have been derived for both incompressible and compressible flows, here we extend the method to thermochemical mantle flow models, and present thermochemical adjoint equations in the elastic-liquid approximation. We verify the method with twin experiments, and retrodict the flow history of a thermochemical reference model (reference twin) assuming for the final state, either a consistent thermochemical interpretation, using the thermochemical adjoint equations, or an inconsistent purely thermal interpretation, using the isochemical adjoint equations. The consistent simulation correctly retrodicts the flow evolution of the reference twin. The inconsistent case, instead, restores a false flow history whereby internal buoyancy forces and convectively maintained topography are overestimated. Because the cost function is reduced in either case, our results suggest that the adjoint method can be used to link assumptions on the role of chemical mantle heterogeneity to geologic inferences of dynamic topography, thus providing additional means to test hypotheses on mantle composition and dynamics.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

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