The effects of a variation of the radial viscosity profile on mantle evolution

Walzer, Uwe; Hendel, Roland; Baumgardner, John R.

doi:10.1016/j.tecto.2004.02.012

Cited by 43 publications

(20 citation statements)

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“…Two typical viscosity profiles from our model are given by Figure 9. The derivation of it is to be found in Walzer et al [2004a] where we also show that the existence of a prominent asthenosphere and a viscoplastic yield stress, s y , generates plate-like movements of pieces of oceanic lithosphere and elongated, narrow zones of subduction at the surface.…”

Section: General Discussion and Conclusionmentioning

confidence: 70%

“…Therefore we should anticipate viscosity discontinuities at these boundaries that influence convection. According to our derivation [Walzer et al, 2004a], the transition zone is highly viscous, at least between 520 and 660 km depth. The likelihood of a high-viscosity transition layer, that is embedded between two low-viscosity layers, is consistent with the proposition that the transition zone is composed mostly of garnet and spinel [Meade and Jeanloz, 1990;Karato et al, 1995;Karato, 1997;Allègre, 2002].…”

Section: Balance Equationsmentioning

confidence: 81%

“…Therefore the viscosity profile will decrease dramatically in that depth interval. For that reason we expect that our derivation of the viscosity profile [Walzer et al, 2004a] is justified at least in broad outline. That is, why we have partly imposed the radius-dependent factor of lithospheric viscosity (cf.…”

Section: Episodic Growth Of the Continental Crustmentioning

confidence: 98%

“…That is, h 3 (r) describes the dependence of viscosity on pressure and mineral phase. The derivation of h 3 (r) is provided in Walzer et al [2004a]. In that paper, we start from a self-consistent theory using the Helmholtz free energy, the Birch -Murnaghan equation of state, the free-volume Grüneisen parameter and Gilvarry's [1956] formulation of Lindemann's law.…”

Section: Balance Equationsmentioning

confidence: 99%

“…Also, Richards et al [2001] used this code to investigate surface mobility as a function of viscosity variation and yield stress. However, the viscosity profile derived in Walzer et al [2004a] with three high-viscosity and three low-viscosity zones and steep gradients is very challenging to be represented properly on coarser grids [Müller, 2008]. Here we are going to improve the matrixdependent transfer technique to transfer these high and low peaks to the coarsest grid possible.…”

Section: Appendix B: Limitations Of Terra and Future Improvementsmentioning

confidence: 99%

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Mantle convection and evolution with growing continents

Walzer

Hendel

2008

J. Geophys. Res.

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[1] We present a three-dimensional spherical shell numerical model for chemical differentiation and redistribution of incompatible elements in a convective Earth's mantle heated mostly from within by U, Th, and K and slightly from below. The evolution-model equations guarantee conservation of mass, momentum, energy, angular momentum, and four sums of the number of atoms of the pairs 238 U-206 Pb, 235 U-207 Pb, 232 Th-208 Pb, and 40 K-40 Ar. The pressure-and temperature-dependent viscosity is supplemented by a viscoplastic yield stress, s y . The lithospheric viscosity is partly imposed to mimic its increase by dehydration of oceanic lithosphere and other effects. Also, the asthenosphere is generated not only by the distribution of temperature and melting temperature, but essentially by the profiles of water solubility and water abundance. Therefore we introduced a radial viscosity profile factor describing that behavior. However, the focus of this paper is the episodic growth of continents and oceanic plateaus. As a complement, the differentiation generates the depleted MORB mantle (DMM) which predominates immediately beneath the lithosphere. Our continents are not artificially imposed on the surface of the spherical shell, but instead they evolve by the interplay between chemical differentiation and convection/mixing. No restrictions are imposed regarding number, size, form, and distribution of continents. However, oceanic plateaus that impinge upon a continent have to be united with it. This mimics the accretion of terranes. The numerical results show an episodic growth of the total mass of the continents and display a plausible time history for the laterally averaged surface heat flow, qob, and the Rayleigh number, Ra. We use our model to explore a moderate region of Ra-s y parameter space. We find Earth-like continent distributions in a central part of the Ra-s y space we explored. We identified a Ra-s y region where the calculated total continental volume is very close to the observed value; another Ra-s y region where the Urey number, Ur, is close to the accepted value; a third Ra-s y area where surface heat flow is very close to the present-day observed mean global heat flow using typical abundances of the heat-producing elements. It is remarkable that these different acceptable Ra-s y regions share a common overlap area, where Earth-like behavior is simultaneously fulfilled.Although the convective flow patterns and the chemical differentiation of oceanic plateaus are coupled, the evolution of time-dependent Rayleigh number, Ra t , is relatively well predictable and the stochastic parts of the Ra t (t) curves are small. Regarding the time distribution of juvenile growth rates of the total mass of the continents, predictions are possible only in the first epoch of the evolution, presumed that the initial conditions are given. Later on, the distribution of the continental growth episodes is increasingly stochastic. Independent of the varying individual runs, our model shows that the total mass of the presen...

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Section: General Discussion and Conclusionmentioning

confidence: 70%