Geophysical and geochemical models of mantle convection: Successes and future challenges

Ricard, Yanick; Coltice, Nicolas

doi:10.1029/150gm06

Cited by 5 publications

(3 citation statements)

References 58 publications

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“…It proves the high accuracy of the available thermo-chemical data and gives the exciting indication that these data will be soon integrated into complex geodynamical models. Understanding the dynamics of mantle reservoirs with different composition/petrology is indeed necessary to explain the complexities of geochemical observations [van Keken and Ballentine, 1998;Ricard and Coltice, 2004;Tackley, 2000]. Figure 7 however, illustrate the fact that this integration must be done on the basis of thermodynamical principle, not by assuming an a priori depth dependent mineralogy.…”

Section: Discussionmentioning

confidence: 99%

Synthetic tomographic images of slabs from mineral physics

Ricard

Mattern

Matas

2005

Earth's Deep Mantle: Structure, Composition, and Evolution

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Section: Discussionmentioning

confidence: 99%

Synthetic tomographic images of slabs from mineral physics

Ricard

Mattern

Matas

2005

Earth's Deep Mantle: Structure, Composition, and Evolution

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“…[4] A simple 1-D model can be proposed for the evolution of a scalar field C with strain and diffusion [Kellogg and Turcotte, 1987]. As in by Ricard and Coltice [2005], we consider a homogeneous stripe of thickness a(t), experiencing pure shear, which initial concentration differs from the background. In the direction of pure shear z, perpendicular to the stripe, the conservation of C across the deforming heterogeneity writes:…”

Section: Mixing Timementioning

confidence: 99%

Mixing times in the mantle of the early Earth derived from 2‐D and 3‐D numerical simulations of convection

Coltice¹,

Schmalzl²

2006

Geophysical Research Letters

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The Earth's mantle is chemically heterogeneous at all scales, as shown by elemental and isotopic analysis of oceanic basalts. This heterogeneity is continuously destroyed by convective stirring and slow diffusion. It has been argued that 3‐D time‐dependent convection is less efficient than 2‐D convection, except in the presence of a toroidal component. In this study we question this conclusion with numerical simulations and show that mixing in 3‐D time‐dependent convection is as efficient as in 2‐D, and only depends on convective vigor. We compute mixing times of thermal and chemical heterogeneities in the early Earth of 10 and 100 Myrs respectively.

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“…A large number of geodynamic studies favour only a phase transition at 660 km in a homogeneous mantle (e.g. Richards & Hager 1984; Ricard et al 1984; see Ricard & Coltice 2004 for a review), whereas some geochemical studies tend to support a chemical discontinuity at 660‐km depth (see e.g. Hofmann 1997).…”

Section: Introductionmentioning

confidence: 99%

On the bulk composition of the lower mantle: predictions and limitations from generalized inversion of radial seismic profiles

Matas¹,

Bass²,

Ricard³

et al. 2007

Geophysical Journal International

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S U M M A R YWe examine the problem of obtaining the thermal structure and bulk chemical composition of the lower mantle from its seismologically determined velocity and density profiles, and the most recent results on the elastic properties of the relevant phases (including, of particular importance, shear moduli). A novel aspect of this paper is the application of an iterative technique solving generalized non-linear inverse problem, which allows us to simultaneously consider a complex chemical system (the MgO-FeO-SiO 2 -Al 2 O 3 -CaO system, which includes all major components in the lower mantle), and to rigorously evaluate the full covariance and resolution matrices. The effects of experimental uncertainties in the shear moduli are carefully accounted for. We show that although the a posteriori uncertainties in the results for lower-mantle compositions are relatively large, the averaged lower-mantle Mg/Si ratio should be lower than 1.3 in order to satisfactorily fit the 1-D seismic profiles. Two distinct families of best-fitting models are determined. The first is based upon a value for the pressure derivative of the perovskite shear modulus that is representative of various existing experimental measurements (µ 0 = 1.8). Under this assumption, it is not possible to match the lower mantle seismic properties with an adiabatic geotherm and uniform chemical composition. Instead, this family of solutions is characterized by a geotherm with large temperature gradients (dT/dz increases from 0.5 to 0.9 K km −1 between 800 and 2700 km and the temperature reaches 3400 K at the depth of 2700 km), and a depth dependent bulk composition with an Mg/Si ratio decreasing from 1.18 ± 0.14 to 1.03 ± 0.16 between 800 and 2700 km. The second family of solutions is obtained when we attempt to fit the lower mantle with a simpler compositional and thermal structure. This can only be done when the pressure derivative of the shear modulus for perovskite is close to the most recent values obtained by Brillouin spectroscopy, that is, with a µ 0 close to 1.6 instead of 1.8. The resulting temperature gradient is 0.25 K km −1 in the upper part of the lower mantle and 0.5 K km −1 below 1700 km depth; the geotherm reaches 2800 K at a depth of 2700 km. Corresponding Mg/Si ratio remains rather constant and close to 1.16 throughout the lower mantle. We show that the temperature gradient is strongly correlated with the pressure derivative µ 0 of the shear modulus of perovskite: lower values of µ 0 imply lower thermal gradients. We also discuss the importance of the Bullen parameter as an additional constraint. In order to refine conclusions on the lower-mantle structure, additional independent observables, such as accurate observations on electrical conductivity and 1-D Q profiles, are necessary.

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Geophysical and geochemical models of mantle convection: Successes and future challenges

Cited by 5 publications

References 58 publications

Synthetic tomographic images of slabs from mineral physics

Synthetic tomographic images of slabs from mineral physics

Mixing times in the mantle of the early Earth derived from 2‐D and 3‐D numerical simulations of convection

On the bulk composition of the lower mantle: predictions and limitations from generalized inversion of radial seismic profiles

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