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| Titel |
The influence of post-perovskite strength on mantle thermo-chemical evolution |
| VerfasserIn |
H. Samuel, N. Tosi |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061335
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| Zusammenfassung |
| A range of geophysical and mineral physics considerations strongly support the presence of
the post-perovskite phase in the lowermost mantle. Recent studies point to the possibility of
strong viscosity differences between the perovskite and the post-perovskite phases. The
magnitude and sign however of such a viscosity contrast remains debated, with studies
supporting the idea of a weaker post-perovskite, while other suggest a stronger
post-perovskite is also possible.
We have therefore investigated the influence of post-perovskite strength on Earth’s mantle
convective dynamics and stirring efficiency, using numerical experiments and simple
analytical theory. We show that the viscosity of the post-perovskite phase can have a dramatic
influence on mantle convective dynamics: weak post-perovskite enhances the destabilization
of the bottom thermal boundary layer, increasing significantly the heat flux. This yields an
increase in mantle temperatures that can be predicted using simple energy scalings.
This increase in mantle temperature lowers viscosity, and enhances the convective
vigor.
The stirring efficiencies measured in our numerical experiments show a significant
increase with decreasing the post-perovskite strength. This observed influence is well
reproduced by a simple chaotic mixing model.
By coupling this mixing model with a parameterized convection evolution, we find that
the presence of weak post-perovskite can increase mantle convective stirring efficiency by at
least one order of magnitude.
Our results suggest that the effect of post-perovskite strength on the thermal and chemical
evolution of the Earth’s mantle must be accounted for when interpreting surface observations
such as heat flow data and the geochemical record. |
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