Effects of a perovskite‐post perovskite phase change near core‐mantle boundary in compressible mantle convection

Nakagawa, Takashi; Tackley, P. J.

doi:10.1029/2004gl020648

Cited by 112 publications

(58 citation statements)

References 20 publications

(33 reference statements)

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“…Previous numerical studies suggested that this phase change may have important implications in terms of dynamics and evolution of the Earth's mantle (e.g. Nakagawa & Tackley 2004, 2006Zhang & Zhong 2011;Samuel & Tosi 2012). Experimental studies (Yoshino & Yamazaki 2007;Hunt et al 2009) and first principle calculations of atomic diffusion (Ammann et al 2010) indicate that postperovskite is less viscous than perovskite by a factor of O(10 −3 ) to O(10 −4 ).…”

Section: O N C L U D I N G Discussionmentioning

confidence: 97%

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

Deschamps

Tackley

2014

Geophysical Journal International

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S U M M A R YLarge-scale chemical lateral heterogeneities are inferred in the Earth's lowermost mantle by seismological studies. We explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time, by using similar analysis in 3-D spherical geometry. In this study, we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle, including the chemical density contrast between the primordial dense material and the regular mantle material (buoyancy ratio), thermal and chemical viscosity contrasts, volume fraction of primordial dense material and the Clapeyron slope of the phase transition at 660 km depth. We find that most of the findings from the 3-D Cartesian study still apply to 3-D spherical cases after slight modifications. Varying buoyancy ratio leads to different flow patterns, from rapid upwelling to stable layering; and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle. Chemical viscosity contrasts in a reasonable range have a second-order role in modifying the stability of the dense anomalies. The volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts, but has significant effects on calculations with intermediate and small thermal viscosity contrasts. The volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast. An endothermic phase transition at 660 km depth acts as a 'filter' allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle.

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Section: O N C L U D I N G Discussionmentioning

confidence: 97%

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

Deschamps

Tackley

2014

Geophysical Journal International

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“…Ever since the post-perovskite phase transition was discovered, the effect of post-perovskite to the CMB heat flux and the core-mantle coupling has widely been discussed (Nakagawa and Tackley, 2004;Buffett, 2004;van der Hilst et al, 2007;Lay et al, 2008;Nakagawa and Tackley, 2008). Tackley (2004, 2008) discuss the effects of post-perovskite phase transition on the CMB heat flux in the models of thermal and thermo-chemical convection and conclude, that the deep exothermic phase change enhances heat transport.…”

Section: Discussionmentioning

confidence: 99%

Implications of post-perovskite transport properties for core–mantle dynamics

Čı́žková

Čadek

Matyska

et al. 2010

Physics of the Earth and Planetary Interiors

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Recent evidence on perovskite to post-perovskite phase change in the lowermost mantle suggests that post-perovskite piles or lens should be present in the relatively cold downwelling areas, while the roots of the hot upwelling plumes consist of perovskite. Post-perovskite is often believed to be deformed predominantly by the dislocation creep and there are some hints that the activation parameters of the dislocation creep in post-perovskite induce lower viscosity than that of perovskite at the same pressure and temperature conditions. That can even result in a viscosity paradox in the lowermost mantle -viscosity in cold downwellings transformed to post-perovskite might be lower than the viscosity of warm perovskite plumes. Such a viscosity structure was indeed recently suggested by the geodynamical

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“…3 we include the ppv transition. We find a general increase of mantle temperature (Matyska and Yuen, 2006;Nakagawa and Tackley, 2004) which becomes particularly evident when both depthdependent thermal expansivity and conductivity are considered (Tosi et al, 2010). Such a temperature increase is caused by the presence of ppv which greatly enhances the instability of the bottom thermal boundary layer, promoting the formation of a larger number of upwellings (compare for instance Fig.…”

Section: Global Temperature Fieldsmentioning

confidence: 72%

Influences of lower-mantle properties on the formation of asthenosphere in oceanic upper mantle

2011

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Asthenosphere is a venerable concept based on geological intuition of Reginald Daly nearly 100 years ago. There have been various explanations for the existence of the asthenosphere. The concept of a plume-fed asthenosphere has been around for a few years due to the ideas put forth by Yamamoto et al.. Using a two-dimensional Cartesian code based on finite-volume method, we have investigated the influences of lower-mantle physical properties on the formation of a low-viscosity zone in the oceanic upper mantle in regions close to a large mantle upwelling. The rheological law is Newtonian and depends on both temperature and depth. An extended-Boussinesq model is assumed for the energetics and the olivine to spinel, the spinel to perovskite and perovskite to post-perovskite (ppv) phase transitions are considered. We have compared the differences in the behavior of hot upwellings passing through the transition zone in the mid-mantle for a variety of models, starting with constant physical properties in the lower-mantle and culminating with complex models which have the post-perovskite phase transition and depth-dependent coefficient of thermal expansion and thermal conductivity. We found that the formation of the asthenosphere in the upper mantle in the vicinity of large upwellings is facilitated in models where both depth-dependent thermal expansivity and conductivity are included. Models with constant thermal expansivity and thermal conductivity do not produce a hot low-viscosity zone, resembling the asthenosphere. We have also studied the influences of a cylindrical model and found similar results as the Cartesian model with the important difference that upper-mantle temperatures were much cooler than the Cartesian model by about 600 to 700 K. Our findings argue for the potentially important role played by lower-mantle material properties on

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Effects of a perovskite‐post perovskite phase change near core‐mantle boundary in compressible mantle convection

Cited by 112 publications

References 20 publications

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

Implications of post-perovskite transport properties for core–mantle dynamics

Influences of lower-mantle properties on the formation of asthenosphere in oceanic upper mantle

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