Constraints on mantle viscosity structure from continental drift histories in spherical mantle convection models

2018 ◽  
Vol 746 ◽  
pp. 339-351 ◽  
Author(s):  
T. Rolf ◽  
F.A. Capitanio ◽  
P.J. Tackley
Keyword(s):  
Mantle Convection ◽  
Continental Drift ◽  
Mantle Viscosity

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.

Effects of strain weakening in self-consistent models of mantle convection with plate-like behavior and continental drift

2020 ◽  
Author(s):  
Tobias Rolf ◽  
Maëlis Arnould
Keyword(s):  
Mantle Convection ◽  
Previous History ◽  
Plate Boundary ◽  
Continental Drift ◽  
Rheological Parameters ◽  
Plate Boundaries ◽  
The Earth ◽  
Cumulative Strain ◽  
First Results ◽  
Long Time

<p>It is now well-established that the Earth’s mantle and lithosphere form an integrated, dynamically self-regulating system. Numerical convection models that self-consistently generate plate-like behavior are a powerful tool to investigate this system, but have only recently reached a level at which they can be linked to the geodynamics of the Earth. Strongly temperature-dependent and viscoplastic rheology is known to be a key ingredient for these models to be successful. Such rheologies, however, are typically time-independent and lack a memory on the previous history of deformation. Yet, it is known that the Earth’s geodynamic evolution is somewhat guided by structures of pre-existing weakness, which was initiated a potentially long time before.</p><p>As a step forward we implement a simple form of rheological memory in the mantle convection code <em>StagYY</em>: strain weakening [<em>Fuchs & Becker, 2019,</em> <em>Role of strain-dependent weakening memory on the style of mantle convection and plate boundary stability</em>, <em>Geophys. J. Int., 218, 601-618</em>]. We present calculations in 2D cases with and without continents, and also selected 3D cases. By varying the governing parameters for plate-like behavior as well as the rates of rheological damage and healing, we examine how strain weakening modifies the generation of plate-like behavior and its time dependence as well as the drift of continents.</p><p>First results indicate the importance of the balance of weakening (via the critical strain) and thermal healing. The averaged cumulative strain (effectively the degree of lithospheric weakening) is lower when healing is more effective, so that plastic failure of the lithospheric and the formation of new plate boundaries is complicated, as expected. In initial models with strong, long-living continents, accumulated strain is very small within the continents and seems insufficient to induce substantial weakening, even if the memory on previous deformation is infinite (i.e. no healing with continents). Further models with weaker continents and different rheological parameters will be presented.</p>

scholarly journals THEORIES OF CONTINENTAL DRIFT

2020 ◽  
Vol 17 (3) ◽  
pp. 1513-1518
Author(s):  
Vishvantha D Veeraiyan ◽  
Dr. Deepak Nallasamy V
Keyword(s):  
Mantle Convection ◽  
Continental Drift ◽  
The Earth ◽  
Plate Formation ◽  
The Impact ◽  
The Way

Continental drift is the process of continental plates moving. The movement is very slow, and it might take even years to show the impact on the Earth. The movement depends on gravity, convection drift, and plate formation. Gravity impacts the movements as the mantle (The layer below the crust) is always spinning because of gravity and the plates are located on the mantle. Convection drift impacts on the movement because convection drift is a cycle of melting and cooling of rocks in the mantle which can slowly impact the movement of the plate. Plate formation also affects the way the plates move as the new plates formed pushes the nearby plates causing movement.

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