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| Titel |
Evolution of the compositionally dense layer at the bottom of the mantle |
| VerfasserIn |
Márton Pál Farkas, Attila Galsa, Mátyás Herein, László Lenkey |
| 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 |
250077121
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| Zusammenfassung |
| Two-dimensional numerical models have been carried out in order to investigate how the
evolution of the compositionally dense D” layer influences the time series of the heat flux,
velocity, temperature and concentration of dense material. The initial density difference
between D” and the overlaying mantle, β was the single studied parameter which was varied
between 0.1–2%.
Based on the time series six stages of the D” evolution were separated from the surface
deformation of the dense layer to the totally homogenized mantle. In all studied cases the
final state got over the homogenization, even for β=2% when the traditional buoyancy ratio
was larger than 1. In order to investigate the evolution of the compositionally dense layer a
time-dependent buoyancy ratio, B was defined by the ratio of the chemical and thermal
density difference between D” and the overlaying mantle. The decrease in B was deduced
from three reasons: (1) the increase in temperature difference between the layers due to
the inhibited heat advection as well as the decrease in concentration difference
owing to (2) the pollution of the upper layer by surface erosion of the D” and (3)
the dilution of the dense layer with light material intermixed from the upper layer
facilitated by convection within D”. As the value of B approaches to 1, the mixing of
the dense material becomes more effective, it is the most vigorous phase of the
thermo-chemical convection. For B=0 the mantle is mixed, the homogenization continues
protractedly.
It was established that larger initial density difference, β has longer/stronger effect on the
monitored parameters. An exponential relation was found between the occurrences of
different stages characterizing the evolution of D” layer and β. The reduction in B during the
erosion/dilution phase ((2) and (3)) and the effective mixing of the dense layer (0-¤ B -¤1)
can be approximated by a linear function, thus the occurrences of single stages are
anticipated. The slope of the linear segments shows an exponential dependence on β, as
well.
This research has been supported by the Hungarian Scientific Research Fund (OTKA
K-72665). |
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