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| Titel |
Electrical conductivity of silicate liquids and a magma ocean dynamo |
| VerfasserIn |
Lars Stixrude, Roberto Scipioni |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152277
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| Publikation (Nr.) |
 EGU/EGU2017-17096.pdf |
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| Zusammenfassung |
| Are silicate dynamos possible? So far planetary dynamos seated in silicate material are
unknown. Several lines of evidence motivate the consideration of a silicate dynamo in the
early Earth: 1) Paleomagnetic evidence of a very early dynamo-generated field 2) models of
the early thermal state of Earth in which the mantle may have been too hot to permit a
core-generated magnetic field, and 3) the possibility of a deep and thick basal magma ocean.
The key requirement is that the electrical conductivity σ of silicate liquids be sufficiently
large at the relevant high pressure-temperature conditions (σ > 1000 S/m). Despite its
importance, σ of silicate liquids is unknown above a few GPa in pressure, and measured
values at low pressure are far too small to support a dynamo. However, observations of
reflectivity from oxide liquids in shock wave experiments suggest a different mechanism of
conductivity at high pressure (electrons, rather than ions). We have used ab initio
molecular dynamics simulations to compute from first principles the value of σ at
extreme conditions in systems with compositions that are simple (SiO2) and rich
(MgO-FeO-CaO-Al2O3-Na2O-SiO2). We use DFT+U with and without spin polarization
combined with the Kubo-Greenwood formula. We find that the value of σ exceeds the
minimum requirements and that a silicate dynamo seated in a basal magma ocean is viable. |
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