Plate Motions and Deep Mantle Convection

1972 ◽  
pp. 7-22 ◽  
Author(s):  
W. Jason Morgan
Keyword(s):  
Mantle Convection ◽  
Plate Motions ◽  
Deep Mantle

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 Radial 1‐D seismic structures in the deep mantle in mantle convection simulations with self‐consistently calculated mineralogy

2012 ◽  
Vol 13 (11) ◽  
Author(s):  
Takashi Nakagawa ◽  
Paul J. Tackley ◽  
Frédéric Deschamps ◽  
James A. D. Connolly
Keyword(s):  
Mantle Convection ◽  
Deep Mantle

scholarly journals Controlling thermal chaos in the mantle by positive feedback from radiative thermal conductivity

2002 ◽  
Vol 9 (3/4) ◽  
pp. 311-323 ◽  
Author(s):  
F. Dubuffet ◽  
D. A. Yuen ◽  
E. S. G. Rainey
Keyword(s):  
Thermal Conductivity ◽  
Boundary Layer ◽  
Mantle Convection ◽  
Variable Thermal Conductivity ◽  
Time Dependent ◽  
Internal Heating ◽  
Chaotic Flows ◽  
Deep Mantle ◽  
Radiative Conductivity ◽  
Radiative Thermal Conductivity

Abstract. The thermal conductivity of mantle materials has two components, the lattice component klat from phonons and the radiative component krad due to photons. These two contributions of variable thermal conductivity have a nonlinear dependence in the temperature, thus endowing the temperature equation in mantle convection with a strongly nonlinear character. The temperature derivatives of these two mechanisms have different signs, with ∂klat /∂T negative and dkrad /dT positive. This offers the possibility for the radiative conductivity to control the chaotic boundary layer instabilities developed in the deep mantle. We have parameterized the weight factor between krad and klat with a dimensionless parameter f , where f = 1 corresponds to the reference conductivity model. We have carried out two-dimensional, time-dependent calculations for variable thermal conductivity but constant viscosity in an aspect-ratio 6 box for surface Rayleigh numbers between 106 and 5 × 106. The averaged Péclet < Pe > numbers of these flows lie between 200 and 2000. Along the boundary in f separating the chaotic and steady-state solutions, the < Pe > number decreases and the Nusselt number increases with internal heating, illustrating the feedback between internal heating and radiative thermal conductivity. For purely basal heating situation, the time-dependent chaotic flows become stabilized for values of f of between 1.5 and 2. The bottom thermal boundary layer thickens and the surface heat flow increases with larger amounts of radiative conductivity. For magnitudes of internal heating characteristic of a chondritic mantle, much larger values of f , exceeding 10, are required to quench the bottom boundary layer instabilities. By isolating the individual conductive mechanisms, we have ascertained that the lattice conductivity is partly responsible for inducing boundary layer instabilities, while the radiative conductivity and purely depth-dependent conductivity exert a stabilizing influence and help to control thermal chaos developed in the deep mantle. These results have been verified to exist also in three-dimensional geometry and would argue for the need to consider the potentially important role played by radiative thermal conductivity in controlling chaotic flows in time-dependent mantle convection, the mantle heat transfer, the number of hotspots and the attendant mixing of geochemical anomalies.

Evidence for deep mantle convection and primordial heterogeneity from nitrogen and carbon stable isotopes in diamond

2012 ◽  
Vol 357-358 ◽  
pp. 179-193 ◽  
Author(s):  
M. Palot ◽  
P. Cartigny ◽  
J.W. Harris ◽  
F.V. Kaminsky ◽  
T. Stachel
Keyword(s):  
Stable Isotopes ◽  
Mantle Convection ◽  
Carbon Stable Isotopes ◽  
Deep Mantle

Adiabaticity and viscosity in deep mantle convection

1986 ◽  
Vol 13 (1) ◽  
pp. 38-41 ◽  
Author(s):  
Francesca Quareni ◽  
David A. Yuen ◽  
Marc R. Saari
Keyword(s):  
Mantle Convection ◽  
Deep Mantle
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