Global surface heat flux anomalies from seismic tomography‐based models of mantle flow: Implications for mantle convection

Pari, Giovanni; Peltier, W. R.

doi:10.1029/98jb01668

Cited by 26 publications

(35 citation statements)

References 114 publications

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“…As has been shown in several previous studies [King, 1995;Thoraval and Richards, 1997;Pari and Peltier, 1998], the robustness of models inferred from the geoid strongly decreases with the number of free parameters. Our six model parameters, discussed in section 3.1, obviously compose a minimum set necessary to characterize the physical system under consideration.…”

Section: Appendix: Robustness Of the Modelsmentioning

confidence: 52%

A global geoid model with imposed plate velocities and partial layering

Čadek¹,

Fleitout²

1999

J. Geophys. Res.

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Abstract. Most inversions of the long-wavelength geoid in conjunction with the seismic tomographic information have so far been carried out under the assumption of either purely whole mantle or perfectly layered circulation. Moreover, modeling the lithosphere as a spherical shell with a uniform low viscosity was found to yield the best fit to the observed geoid. We have tested whether a good prediction of the geoid can also be achieved by including two constraints: a semipermeable behavior of the 660-kin discontinuity and surface plate velocities equal to the observed ones. The mass transfer between upper and lower mantle has been changed by imposing a surface density anomaly at a depth of 660 kin, which is proportional to the mass anomaly needed to achieve perfectly layered circulation. On the top of the mantle we assume a stiff lithosphere that moves with a velocity corresponding to the observed plate motion. The viscosity only varies with depth. Considering a simple three-layer viscosity structure and changing the permeability of the 660-kin interface, we have obtained a satisfactory variance reduction of the geoid data (--75% for degrees 2-12). The best fit to the geoid is obtained if the mass transfer across the 660-kin boundary is reduced to one third in comparison with the purely whole mantle model. The best fitting viscosity profile is characterized by a clearly defined asthenosphere and a viscosity increase by at least 2 orders of magnitude in the lower mantle. The amplitudes of dynamic topography predicted by our model are remarkably small (--100 m), thus fully compatible with the observation. In section 2 we shall discuss the various ingredients of the model that we propose and discuss further the notions of "partial layering" and imposed surface plate velocities. In section 3 the results of a systematic exploration of the effect of the viscosity profiles and of the layering coefficient on the predicted geoid will be presented. The associated surface topography, the stresses at the base of the lithosphere and the flow at 660-km depth will be discussed. In section 4 we shall address the origin of the differences between the proposed models and the classic whole mantle, free-slip models. Potential existence of a semipermeable interface located deeper than 660 km will be examined in section 5. In section 6we shall summarize weaknesses brought by some over-

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Section: Appendix: Robustness Of the Modelsmentioning

confidence: 52%

A global geoid model with imposed plate velocities and partial layering

Čadek¹,

Fleitout²

1999

J. Geophys. Res.

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“…The existence of two different groups of viscosity models, predicting the same portion of the geoid, confirms the non-unique nature of the geoid inversion, first discussed by King [12] and recently corroborated by Pari and Peltier [26]. A thorough discussion of different viscosity profiles from the viewpoint of mineral physics can be found in [1,6] where similar viscosity models as presented in this paper are proposed.…”

Section: Viscosity Profilesmentioning

confidence: 56%

“…The preliminary results presented here can be understood as an attempt to contribute to the formation of a general model of the Earth which would be consistent with the thermal processes governing its evolution (cf. [26,42]). …”

Section: Discussionmentioning

confidence: 99%

Radial profiles of temperature and viscosity in the Earth's mantle inferred from the geoid and lateral seismic structure

Čadek¹,

Berg²

1998

Earth and Planetary Science Letters

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In the framework of dynamical modelling of the geoid, we have estimated basic features of the radial profile of temperature in the mantle. The applied parameterization of the geotherm directly characterizes thermal boundary layers and values of the thermal gradient in the upper and lower mantle. In the inverse modelling scheme these parameters are related to the observables (geoid and seismic structure of the mantle) through the viscosity profile which is parameterized as an exponential function of pressure and temperature. We have tested ¾10 4 model geotherms. For each of them we have found proper rheological parameters by fitting the geoid with the aid of a genetic algorithm. The geotherms which best fit the geoid show a significant increase of temperature (¾600-800ºC) close to the 660-km discontinuity. The value of the thermal gradient in the mid-mantle is found to be sub-adiabatic. Both a narrow thermal core-mantle boundary layer and a broad region with a superadiabatic regime can produce a satisfactory fit of the geoid. The corresponding viscosity profiles show similarities to previously presented models, in particular in the viscosity maximum occurring in the deep lower mantle. The best-fitting model predicts the values of activation volume V Ł and energy E Ł which are in a good agreement with the data from mineral physics, except for V Ł in the lower mantle which is found somewhat lower than the estimate based on melting temperature analysis. An interesting feature of the viscosity profiles is a local decrease of viscosity somewhere between 500 and 1000 km depth which results from the steep increase of temperature in the vicinity of the 660-km discontinuity.

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“…More importantly, we believe, and as has already been discussed, that it is possible that a "soft zone" exists at 660 km depth, and this may lead to stronger layering for a given value of the Clapeyton slope. It will also be noted that the high degree of layering that is necessary to reduce the surface heat flow, while not as strong as some geochemical studies [Pari and Peltier, 1998]. The results of the present paper compel us to further explore the extent to which radial heat transfer might provide an even stronger constraint on layering when a priori models of the convection process are brought into play.…”

Section: Discussionmentioning

confidence: 97%

On scaling relations in time‐dependent mantle convection and the heat transfer constraint on layering

Butler¹,

Peltier²

2000

J. Geophys. Res.

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Abstract. We present a series of simulations of the mantle convection process based upon an axisymmetric numerical model and highlight a wide range of results in which scaling emerges. For the more challenging simulations it was found necessary to employ a finite difference mesh with uneven grid spacing in the radial coordinate, and we present the appropriate transformed field equations that are required to implement a model of this kind. The statistics of mass flux events transiting the 660-km phase transition are calculated for a large number of high-resolution calculations, and some of these are shown to display scale invariance properties in the high Rayleigh number regime. We also present a new parameterized model of convection and demonstrate its success in predicting the manner in which many of the bulk properties of the convection process scale with convection control parameters. Results are also presented which demonstrate that quantities such as heat flow, characteristic velocity, and thermal boundary layer thickness scale with the mean viscosity even in time-dependent simulations in which the effects of phase transitions, depth-varying viscosity, and internal heating are active. The heat flow scaling exponent is seen to decrease in magnitude with increasing internal heating rate and Clapeyron slope of the 660-km phase transition, but it is shown to be insensitive to depth variation of viscosity. Heat flow is seen to be reduced only modestly as the degree of layering increases unless layering is extreme. These calculations clearly demonstrate that in order for the surface heat flow predicted by the model to equal that characteristic of Earth, the mean viscosity of the mantle that controls the convection process must be considerably higher than the viscosity inferred on the basis of postglacial rebound and/or the flow must be significantly layered by the endothermic phase transition at 660 km depth. If mantle viscosity may be assumed to be Newtonian, in which case the creep resistance that controls rebound and convection must be the same, this constitutes a strong argument for the importance of layering. The force of this argument depends upon the existence of an accurate estimate of the temperature at the core-mantle boundary which has only recently become available.

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Global surface heat flux anomalies from seismic tomography‐based models of mantle flow: Implications for mantle convection

Cited by 26 publications

References 114 publications

A global geoid model with imposed plate velocities and partial layering

A global geoid model with imposed plate velocities and partial layering

Radial profiles of temperature and viscosity in the Earth's mantle inferred from the geoid and lateral seismic structure

On scaling relations in time‐dependent mantle convection and the heat transfer constraint on layering

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