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| Titel |
Revealing the magnetic mineralogy of thick lava flows |
| VerfasserIn |
H. P. Gunnlaugsson, L. Kristjánsson, P. Nørnberg, S. Steinthorsson |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028082
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| Zusammenfassung |
| The remanent magnetization of basaltic rocks is complicated, depending on factors including
the chemistry of the magma, its cooling rate, external magnetic field and oxygen
fugacity. In thick lava flows, some of the affecting parameters are constant while others
vary in a systematic way, allowing detailed study of the magnetic properties of the
rocks.
Here we present the results of a combined remanence/Mössbauer study of a 5.5
m thick basalt flow from Hrútagjárdyngja (HD) in SE Iceland. The findings are
compared to similar findings from the Roza flow field (Columbia River Basalt)
[1].
Mössbauer spectroscopy is an ideal method for characterizing the magnetic mineralogy in
basalt [2], and here it is illustrated how the method can yield quantitative information
on the iron-oxide mineralogy, oxidation processes, and indirectly the magnetic
properties.
In the Roza samples, the Mössbauer spectra reveal the magnetic phase as titanomagnetite
(Ti-Mt; Fe3-xTixO4). In the bottom part of the flow, the value of x is determined to be ~ 0.6,
gradually increasing toward the top due to higher oxidation state and slower cooling
rate.
In the HD samples, this picture is slightly different due to oxidation of the iron in olivine
to pure magnetite and hematite both in the bottom part and the top part. It is discussed how
this has affected the remanence.
[1] Audunsson, H., Levi, S., Hodges, F.: Magnetic property zonation in a thick lava flow.
J. Geophys. Res. 97, 4349–4360 (1992)
[2] H. P. Gunnlaugsson, H. Rasmussen, L. Kristjánsson, S. Steinthorsson, Ö.
Helgason, P. Nørnberg, M. B. Madsen and S. Mørup, Mössbauer spectroscopy
of magnetic minerals in basalt on Earth and Mars, Hyp. Int. 182 (2008) 87-101. |
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