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| Titel |
Effect of the temperature- and depth-dependent viscosity on mantle convection |
| VerfasserIn |
Lukács Benedek Kuslits, Márton Pál Farkas, Attila Galsa |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080000
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| Zusammenfassung |
| Finite element numerical modeling has been carried out in order to investigate the effect of
the depth- and temperature-dependent viscosity on the thermal convection occurring in the
Earth’s mantle. Calculations were made in a 2D spherical shell domain applying Boussinesq
approximation.
It was established by systematic model calculations that the stronger depth-dependence of
the viscosity (higher γ) hinders the convection rather in the deeper zone of the mantle that
retards the heat from the core and cools the mantle. The less vigorous convection results in
slower flow and increases the mobility of the surface (the ratio of the average surface
and mantle velocity). Stronger temperature-dependence of the viscosity (higher
δ) has qualitatively the opposite effect. Above the core mantle boundary, which
is the hottest part of the mantle, the viscosity decreases that facilitates the heat
transport from the core. Whereas the cold, more viscous surface retards the heat. It
warms up the mantle, decreases its average viscosity and accelerates the creep flow.
Due to the cold and more viscous surface layer the mobility reduces. The observed
velocity, temperate, heat flux and viscosity parameters show a power law function of
δ.
Two additional numerical model calculations were made with more realistic γ and δ
parameters scaling the depth- and temperature-dependence of the mantle convection. In
model 1 the viscosity increased exponentially 100 times (γ=100) and decreased 7 orders of
magnitude (δ=107) as the depth and temperature grew from the surface to the core,
respectively. Owing to the strong temperature-dependence of the viscosity a rigid lid formed
around the mantle that reduced the heat outcome effectively and resulted in a hot
mantle. Model 2 had the viscosity scaling factors of γ=10 and δ=106, and a 30 times
viscosity jump was built in model at the depth of 660 km to reflect the effect of the
olivine - perovskite + magnesiowustite mineralogical phase transition. Rigid lid did
not evolved in model 2 because of the stronger depth-dependence (300) and the
weaker temperature-dependence (106) of the viscosity. As a consequence, lower
temperature, higher viscosity and less vigorous flow system characterized the mantle
convection.
This research has been supported by the Hungarian Scientific Research Fund (OTKA
K-72665) and it was implemented thanks to the scholarship in the framework of the TÁMOP
4.2.4.A-1 priority project, it has been supported by the Hungarian Government and the
European Union and co-financed by the European Social Fund. |
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