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| Titel |
Probing the age and temperature of rifting in Afar |
| VerfasserIn |
John Armitage, Saskia Goes, David Ferguson, James Hammond, Eric Calais |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093024
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| Publikation (Nr.) |
 EGU/EGU2014-7394.pdf |
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| Zusammenfassung |
| Rifting along the southern part of the Red Sea margin in NE Africa (leading to formation of
Afar) has been closely associated with magmatic activity since the initiation of extension at
around ~ 25Ma. Numerous active volcanoes are currently found along rift zones here and
magma intrusion into the crust has potentially accommodated significant amounts of
extension. This extensive present-day volcanism has been linked to elevated mantle
temperature, perhaps due to a thermal plume, or as a consequence of passive flow in the
mantle beneath the extending lithosphere. Geochemical evidence for basaltic lavas erupted in
Afar have been used to suggest that mantle temperatures are in the range 1370 to 1490°C,
and that the region is currently experiencing late stage rifting. Analysis of changes in shear
wave seismic velocities and relative travel time tomography suggests mantle temperatures are
within a similar range, yet the region has greater similarities to a young spreading
centre. The range in potential temperature estimates is however very large, with
different implications for the volcanic history of the region and hence timing of
break-up.
Rather than focusing a single observable, we use a relatively straight forward model of
extension and decompression melting to predict the seismic-velocity and attenuation structure
of the asthenosphere and lithosphere, synthetic receiver functions as a result of this seismic
structure, crustal thickness as a result of decompression and finally the melt composition.
From this combined study we find that melt composition and seismic structure
are dependent on both temperature and time. If mantle potential temperature is
1350°C then both the seismic structure and melt composition can be matched
if the duration of extension is more than 30 Myr. However this is longer than the
estimated duration of extension from plate reconstructions, and given the low rate of
extension in Afar, this cold model only generates up to 5 km of igneous crust. If
mantle potential temperature is 1450°C then both the seismic structure and melt
composition can be matched after 22 Myr of extension. Furthermore, igneous crustal
thickness is in excess of 10 km. Therefore, the most simple explanation is that Afar is a
developing continental rift zone where melting is enhanced by a warm mantle. |
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