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| Titel |
A geodynamic model of plumes from the margins of Large Low Shear Velocity Provinces |
| VerfasserIn |
Bernhard Steinberger, Trond H. Torsvik  |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048287
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| Zusammenfassung |
| Eruption sites of most Large Igneous Provinces as well as kimberlites during the last few
hundred Myr lie - like many present-day hotspots - above the margins of the two Large Low
Shear Velocity Provinces (LLSVPs) of the lowermost mantle. Here a geodynamic
model that explains how plumes get created at these margins (and only there) is
presented. Time-dependent density distribution of the Earth’s mantle is modelled based
on 300 Myrs of subduction history, with a spherical harmonic code and a radial
viscosity structure constrained by mineral physics and surface observations. The initial
condition also features a heavy chemical layer at the base of the mantle. The sinking
subducted slabs form the chemical layer to two distinct large piles under Africa
and the Pacific whose location approximately coincides with the two LLSVPs,
as well as a smaller pile under Siberia, which may correspond to a smaller Low
Shear Velocity Province. They also push the thermal boundary layer towards the
chemical piles. Once this hot material reaches the steep edges of these piles, it is forced
upwards and begins to rise - in the lower part of the mantle as sheets, which then
split up into individual plumes in the upper mantle. Each pile is thus crowned by
4-5 plumes, like candles on a birthday cake, while a separate plume rises under
Siberia. Plume conduits become tilted with their bases moving towards the centers
of the piles, while their tops remain over the margins. Due to high viscosities in
the lower mantle up to about 1023 Pas, plumes in our model are rather massive
(diameters > 500 km) and entrain a substantial part of the chemical layer over
the time of the model run. Different approaches on how to reduce or avoid this
entrainment are discussed. Future models with lateral viscosity variations will aim at
maintaining the creation of plumes at the margin of piles, while additionally reducing
entrainment and thus enabling longer-term stability of chemically distinct piles. |
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