The effect of continents on mantle convective stirring

Samuel, Henri; Александров, В. П.; Deo, Bhaskar

doi:10.1029/2010gl046056

Cited by 10 publications

(11 citation statements)

References 24 publications

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“…Each diagram is divided in two domains according to the time of onset of convection in the simulations (early or late onset). As expected, the reference Rayleigh number has a clear monotonic influence on the onset of convection and on the degree of mixing [Samuel et al, 2011;Samuel and Tosi, 2012]. However, the dependence of the final value of the shrinking factor on the buoyancy ratio B and on the solidification time t MO is more complex.…”

Section: Early and Late Onset Of Convection And Mixingsupporting

confidence: 69%

“…Low values of σ − indicate stronger shortening of mantle parcels with larger aspect ratio, favoring mixing and homogenization with the surroundings via chemical diffusion [ Olson et al , ; Gurnis , ; Ottino , ]. Equivalently, this quantity expresses the amount by which the initial size of a mantle parcel has been reduced as a result of the deformation along its trajectory [ Samuel et al , ; Samuel and King , ]. In other words, for a mantle parcel of given initial size δ 0 , its dimension in the direction of maximum shrinking at time t is just δ = δ 0 σ − , implying that the smaller the σ − , the more efficient is mixing.…”

Section: Modelmentioning

confidence: 99%

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Onset of solid‐state mantle convection and mixing during magma ocean solidification

et al. 2017

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The energy sources involved in the early stages of the formation of terrestrial bodies can induce partial or even complete melting of the mantle, leading to the emergence of magma oceans. The fractional crystallization of a magma ocean can cause the formation of a compositional layering that can play a fundamental role for the subsequent long‐term dynamics of the interior and for the evolution of geochemical reservoirs. In order to assess to what extent primordial compositional heterogeneities generated by magma ocean solidification can be preserved, we investigate the solidification of a whole‐mantle Martian magma ocean, and in particular the conditions that allow solid‐state convection to start mixing the mantle before solidification is completed. To this end, we performed 2‐D numerical simulations in a cylindrical geometry. We treat the liquid magma ocean in a parameterized way while we self‐consistently solve the conservation equations of thermochemical convection in the growing solid cumulates accounting for pressure‐, temperature‐, and, where it applies, melt‐dependent viscosity. By testing the effects of different cooling rates and convective vigor, we show that for a lifetime of the liquid magma ocean of 1 Myr or longer, the onset of solid‐state convection prior to complete mantle crystallization is likely and that a significant part of the compositional heterogeneities generated by fractionation can be erased by efficient mantle mixing. We discuss the consequences of our findings in relation to the formation and evolution of compositional reservoirs on Mars and on the other terrestrial bodies of the solar system.

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Section: Early and Late Onset Of Convection And Mixingsupporting

confidence: 69%

Section: Modelmentioning

confidence: 99%

Onset of solid‐state mantle convection and mixing during magma ocean solidification

et al. 2017

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“…For instance, with

scriptB = 0

, the scaling we derived for constant viscosity predicts that a reduction of R a by one order of magnitude determines an increase of the mixing time by approximately a factor of 3.2. This result compares relatively well with the findings of Samuel et al [] who preformed a similar calculation (i.e., isoviscous fluid in 2‐D Cartesian geometry with aspect ratio of four assuming

scriptB = 0

) and estimated mixing times through a more sophisticated Lagrangian technique. They found that, independently of the wavelength of heterogeneity considered, the mixing time obtained with R a =10 6 is about four times larger than that obtained with R a =10 7 , which confirms the validity of our simple approach based on relative differences in the laterally averaged profile of the composition field.…”

Section: Discussionmentioning

confidence: 99%

“…Our description based on equation , however, was sufficient for our purposes. Indeed, a comparison of the effects of the Rayleigh number on mixing times with the results of Samuel et al [] confirmed the validity of our approach (see Figure and section 4.1).…”

Section: Model and Methodsmentioning

confidence: 99%

Overturn and evolution of a crystallized magma ocean: A numerical parameter study for Mars

2013

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Early in the history of terrestrial planets, the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core‐mantle boundary to the surface. Such a configuration is gravitationally unstable; it causes mantle overturn and the formation of a stable chemical layering. Using simulations of thermochemical convection, we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming Mars' scaling parameters. We found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio scriptB, which measures the relative importance of chemical to thermal buoyancy. In addition, when using a strongly temperature‐dependent viscosity, the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle. In order to obtain their subduction, a yielding mechanism must be invoked. In the context of Mars' evolution, our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet's age. Magma ocean freezing could thus be responsible for the long‐term preservation of compositional heterogeneities as required by meteoritic evidence. The inferred lack of a high density lid is difficult to reconcile with a stagnant‐lid regime operating throughout Mars' history. An episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that scriptB is large enough. Too large buoyancy ratios, however, tend to suppress convective heat transport, rendering it problematic to explain the late volcanic history of Mars.

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“…The underlying physics of those interactions can nevertheless be perceived by numerical investigations of the mechanical and thermal coupling between insulating lids and mantle flow. Various studies show that continents may create long wavelength patterns in the convective layer [ Phillips and Bunge , 2005; Grigné et al , 2007a, 2007b] while raising the temperature beneath supercontinents [ O'Neill et al , 2009; Phillips and Coltice , 2010] and in turn enhancing convective vigor for temperature‐dependent viscosity models [e.g., Lenardic et al , 2005; Samuel et al , 2011]. Furthermore, time‐dependent simulations show that continental insulation leads to mantle overheating and to aggregation and dispersal of supercontinents [ Gurnis , 1988].…”

Section: Introductionmentioning

confidence: 99%

Multiagent simulation of evolutive plate tectonics applied to the thermal evolution of the Earth

Combes¹,

Grigné²,

Husson³

et al. 2012

Geochem Geophys Geosyst

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[1] The feedback between plate tectonics and mantle convection controls the Earth's thermal evolution via the seafloor age distribution. We therefore designed the MACMA model to simulate time-dependent plate tectonics in a 2D cylindrical geometry with evolutive plate boundaries, based on multiagent systems that express thermal and mechanical interactions. We compute plate velocities using a local force balance and use explicit parameterizations to treat tectonic processes such as trench migration, subduction initiation, continental breakup and plate suturing. These implementations allow the model to update its geometry and thermal state at all times. Our approach has two goals: (1) to test how empirically-and analyticallydetermined rules for surface processes affect mantle and plate dynamics, and (2) to investigate how plate tectonics impact the thermal regime. Our predictions for driving forces, plate velocities and heat flux are in agreement with independent observations. Two time scales arise for the evolution of the heat flux: a linear long-term decrease and high-amplitude short-term fluctuations due to surface tectonics. We also obtain a plausible thermal history, with mantle temperature decreasing by less than 200 K over the last 3 Gyr. In addition, we show that on the long term, mantle viscosity is less thermally influential than tectonic processes such as continental breakup or subduction initiation, because Earth's cooling rate depends mainly on its ability to replace old insulating seafloor by young thin oceanic lithosphere. We infer that simple Copyright 2012 by the American Geophysical Union 1 of 24 convective considerations alone cannot account for the nature of mantle heat loss and that tectonic processes dictate the thermal evolution of the Earth.

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The effect of continents on mantle convective stirring

Cited by 10 publications

References 24 publications

Onset of solid‐state mantle convection and mixing during magma ocean solidification

Onset of solid‐state mantle convection and mixing during magma ocean solidification

Overturn and evolution of a crystallized magma ocean: A numerical parameter study for Mars

Multiagent simulation of evolutive plate tectonics applied to the thermal evolution of the Earth

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