Inferring the viscosity and the 3-D density structure of the mantle from geoid, topography and plate velocities

Ricard, Yanick; Bai, Wangfeng

doi:10.1111/j.1365-246x.1991.tb00796.x

Cited by 157 publications

(74 citation statements)

References 38 publications

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“…1, which gives rise to the lower-mantle viscosity maximum at around 1800 km. Such a maximum is consistent with dynamic geoid and postglacial rebound modelling (Ricard and Wuming, 1991;Forte and Mitrovica, 2001;Mitrovica and Forte, 2004).…”

Section: Thermal Expansivity Viscosity and Radiative Heat Transfersupporting

confidence: 63%

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Lower-mantle material properties and convection models of multiscale plumes

Matyska

Yuen²

2007

Special Paper 430: Plates, Plumes and Planetary Processes

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We present the results of numerical mantle convection models demonstrating that dynamical effects induced by variable mantle viscosity, depth-dependent thermal expansivity, radiative thermal conductivity at the base of the mantle, the spinel to perovskite phase change and the perovskite to post-perovskite phase transition in the deep mantle can result in multiscale mantle plumes: stable lower-mantle superplumes are followed by groups of small upper-mantle plumes. Both radiative thermal conductivity at the base of the lower-mantle and a strongly decreasing thermal expansivity of perovskite in the lower-mantle can help to induce partially layered convection with intense shear heating under the transition zone, which creates a low viscosity zone and allow for the production of secondary mantle plumes emanating from this zone. Large-scale upwellings in the lower-mantle, which are induced mainly by both the style of lower-mantle viscosity stratification and decrease of thermal expansivity, control position of central upper-mantle plumes of each group as well as the upper-mantle plume-plume interactions.

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Section: Thermal Expansivity Viscosity and Radiative Heat Transfersupporting

confidence: 63%

“…The cold thermal boundary-layer at the top of the model is unstable and acts as a source of cold "lumps" which slowly fall to the "viscosity hill" (e.g. Ricard and Wuming, 1991;Mitrovica and Forte, 2004) in the mid lower-mantle.…”

Section: Basic Physics Of Simple Models-influence Of the Depth-dependmentioning

confidence: 99%

Lower-mantle material properties and convection models of multiscale plumes

Matyska

Yuen²

2007

Special Paper 430: Plates, Plumes and Planetary Processes

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“…The approach most commonly used in the past for both the top and bottom boundaries [e.g., Thoraval Ricard and Vigny [1989] and Ricard and Bai [1991] took into account the geometry of plates, and they attempted to predict the geoid and the plate motion driven by density heterogeneities in the mantle. The drawbacks of these models have been pointed out by Ribe [1992] solve this problem.)…”

mentioning

confidence: 99%

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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“…In general, viscous dissipation tends to be concentrated in the regions where the mantle's viscosity is lowest (Balachandar et al, 1995), since the heat production by viscous dissipation depends on the ratio of the square of the stress divided by viscosity, and stress-squared typically varies less rapidly than inverse-viscosity within a deforming medium. This continuity in stress is the reason why large-scale geoid anomalies are similar in shape to the large-scale apparent density structure of the lower mantle (Hager and Clayton, 1989;Forte et al, 1991;Ricard and Wuming, 1991). If mantle stresses were not reasonably continuous from top to bottom of the mantle, then the density anomalies in the lower mantle would be unable to produce spatially correlated but opposite sense anomalies in the low-order Geoid (Hager and Clayton, 1989).…”

Section: The Structure Of Viscous Dissipation Within the Mantlementioning

confidence: 99%

“…They commonly suggest that two mantle regions are likely to be of lower viscosity than the main central region of the mantle (Hager and Clayton, 1989;Forte et al, 1991;Ricard and Wuming, 1991). These regions, the ∼200-300 km thick asthenosphere that underlies the oceanic and continental lithosphere (Anderson, 1989, p. 51-53), and the ∼100-300 km thick D ′′ thermal boundary layer between the mantle and the outer core (Kendall and Shearer, 1994) (see Figure 6), are prime candidates for regions where the mantle's viscous dissipation is likely to be concentrated.…”

Section: The Structure Of Viscous Dissipation Within the Mantlementioning

confidence: 99%

The Current Energetics of Earth's Interior: A Gravitational Energy Perspective

2016

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The Earth's mantle convects to lose heat (Holmes, 1931); doing so drives plate tectonics (Turcotte and Oxburgh, 1967). Significant gravitational energy is created by the cooling of oceanic lithosphere atop hotter, less dense mantle. When slabs subduct, this gravitational energy is mostly (∼86% for whole mantle flow in a PREM-like mantle) transformed into heat by viscous dissipation. Using this perspective, we reassess the energetics of Earth's mantle. We also reconsider the terrestrial abundances of heat producing elements U, Th, and K, and argue they are lower than previously considered and that consequently the heat produced by radioactive decay within the mantle is comparable to the present-day potential gravitational energy release by subducting slabs-both are roughly ∼10-12 TW. We reassess possible core heat flow into the base of the mantle, and determine that the core may be still losing a significant amount of heat from its original formation, potentially more than the radioactive heat generation within the mantle. These factors are all likely to be important for Earth's current energetics, and argue that strong plume-driven upwelling is likely to exist within the convecting mantle.Keywords: mantle energetics, mantle evolution, Urey ratio, gravitational potential energy, mantle secular cooling, core energetics, core secular cooling INTRODUCTION Roles of Gravitational Energy Transformations in Mantle ConvectionA wonderful realization of the Plate Tectonics revolution was that the surface oceanic plates form the upper thermal boundary layer of a convecting mantle (Turcotte and Oxburgh, 1967). When oceanic plates cool near the Earth's surface, they become denser than underlying mantle. This density contrast provides the gravitational pull that causes plates to sink when they subduct. It is perhaps most familiar to think of convection in terms of cooling-or heating-linked buoyancy forces that cause hot regions to rise and cold regions to sink within a convecting fluid. While less familiar, an equivalent way to think about these phenomena is in terms of gravitational potential energy. Both rising low-density and sinking high-density regions release gravitational potential energy. In a highly viscous fluid like the Earth's mantle where inertial forces are negligible, the gravitational energy released from a sinking thermal density anomaly is completely transformed into viscous dissipation energy within the deforming fluid. For example, the Stokes problem of a sinking heavy ball in a highly viscous medium can be treated either as a force balance between the net buoyancy force on the ball and the viscous resisting force from the surrounding fluid's deformation, or as an energy balance between the gravitational energy released by the ball's sinking Morgan et al.Earth's Current Energetics and the viscous dissipation within the surrounding fluid. (In fluid dynamics, it is well-known that all slow viscous flow involves viscous friction-or viscous dissipation-that generates heat as the material strains. In this perspe...

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Inferring the viscosity and the 3-D density structure of the mantle from geoid, topography and plate velocities

Cited by 157 publications

References 38 publications

Lower-mantle material properties and convection models of multiscale plumes

Lower-mantle material properties and convection models of multiscale plumes

A global geoid model with imposed plate velocities and partial layering

The Current Energetics of Earth's Interior: A Gravitational Energy Perspective

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