Toward a Thermochemical Model of the Evolution of the Earth’s Mantle

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

doi:10.1007/3-540-26589-9_38

Cited by 3 publications

(3 citation statements)

References 74 publications

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“…We assume a homogeneous core in thermodynamic equilibrium similar to the approaches of Steinbach and Yuen [1994] and Honda and Iwase [1996]. Prior to this work, our modeling efforts relating to the problem of integrated convection -fractionation were restricted to two dimensions [Walzer and Hendel, 1999;Walzer et al, 2004b].…”

Section: Heating Initial and Boundary Conditions And Chemical Diffementioning

confidence: 99%

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: Heating Initial and Boundary Conditions And Chemical Diffementioning

confidence: 99%

Mantle convection and evolution with growing continents

Walzer

Hendel

2008

J. Geophys. Res.

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“…Viscosity ( It should be noted that the viscosity at the CMB employed by Walzer et al (2004) is a realistic value derived from the seismic model PREM. However, large temperature rise may induce very large viscosity contrast in the thermal boundary layer, so that the mantle viscosity is likely to be less than 10 23 Pa$s.…”

Section: Investigatorsmentioning

confidence: 99%

“…It is quite uncertain whether the extreme low velocity of mantle plume of w10 À10 m/s and its resultant extraordinary low Reynolds number, w10 À21 , is applicable in Stokes's analysis, which really applies to only very small particle without form drag, and not to gigantic mantle plume. Gubbins (2001) estimated the heat flux at the outer core to be about 25 mW/m 2 , while the model of Walzer et al (2004) for mantle convection is based on 20 mW/m 2 . The heat flux from the mantle heat flow of 10 TW is about 66 mW/m 2 , while Lay et al (2006) estimated 85 AE 25 W/m 2 from a heat conductivity of 10 W/(m K) that results in a CMB heat flow of 13 AE 4 TW.…”

Section: Investigatorsmentioning

confidence: 99%

On predicting mantle mushroom plumes

Tan

Thorpe

Zhao

2011

Geoscience Frontiers

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This study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction. The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers, while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics (CGD) models and simple small-scale laboratory analogue simulations. Our theory of transient instability shows that the formation of convection plumes is preceded by the onset of convection caused by unsteady-state heat conduction at the boundaries, from which filamentous plumes first appear. The plumes generated at the Core Mantle Boundary (CMB) and lithosphere rising and falling through the mantle have been predicted simply with our theory for various heat fluxes and viscosities, which still remain uncertain amongst geoscientists. The sizes of mushroom plumes in the sub-solidus mantle caused by heat fluxes of 20 and 120 mW/m 2 at the CMB are found to be 1842 km and 1173 km with critical times over 825 Myr and 334 Myr respectively. They are comparable to some large continental flood basalt provinces, and they number between 17 and 41. The thickness of the thermal boundary layers at the CMB from which convection plumes evolved are found to be 652 km and 415 km for 20 and 120 mW/m 2 respectively.Top cooling may produce plunging plumes of diameter of 585 km and at least 195 Myr old. The number of cold plumes is estimated to be 569, which has not been observed by seismic tomography

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Geodynamic Mantle Modeling and Its Relation to Origin and Preservation of Life

Walzer

Hendel

2013

High Performance Computing in Science and Engineering ‘13

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Toward a Thermochemical Model of the Evolution of the Earth’s Mantle

Cited by 3 publications

References 74 publications

Mantle convection and evolution with growing continents

Mantle convection and evolution with growing continents

On predicting mantle mushroom plumes

Geodynamic Mantle Modeling and Its Relation to Origin and Preservation of Life

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