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| Titel |
The deep structure of the South Atlantic rifted margins and the implications of the magmatic processes for the break-up |
| VerfasserIn |
Katharina Becker, Dieter Franke, Robert Trumbull, Michael Schnabel, Ingo Heyde, Bernd Schreckenberger, Hannes Koopmann, Klaus Bauer, Wilfried Jokat, Charlotte Krawczyk |
| 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 |
250089292
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| Publikation (Nr.) |
 EGU/EGU2014-3492.pdf |
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| Zusammenfassung |
| The high velocity lower crust HVLC (Vp > 7km/s) together with seaward dipping reflectors
(SDRs) and continental flood basalts are specific characteristics of volcanic rifted margins.
The nature and origin of the HVLC is still under discussion. Here we provide a
comprehensive study of the deep crustal structure of the South Atlantic rifted margins in
which we focus on variations in the distribution and size of HVLC bodies along and across
the margins.
Two new and five existing refraction lines complemented by gravity models
cover the area between the Rio Grande Rise - Walvis Ridge to the Falkland Agulhas
Fracture Zone. Three seismic lines on the South American margin outline the change
from a non-magmatic margin (lacking seaward dipping reflectors) in the south to a
well-developed volcanic rifted margin off Uruguay in the north. While the HVLC exhibit a
consistent increase in the cross-sectional area along both margins from South to North,
we observe a major asymmetry across the margins. The African margin has about
two-three times thicker and four times more voluminous HVLC than the South
American margin. Importantly, the erupted lavas in the Etendeka-Paraná Provinces
show the opposite asymmetry. Also the spatial position of the HVLC with regard
to the inner SDRs varies consistently along both margins. Close to the Falkland
Agulhas Fracture zone a small body of HVLC is not accompanied by seaward dipping
reflectors. In the central segment, HVLC is centered under the SDRs inner wedge but in
the north, HVLC also extends further seawards. These observations question a
simple extrusive/intrusive relationship between SDRs and HVLC, and they imply
differences in the timing of the HVLC formation during the rifting and break-up
process.
We conclude that the HVLC is predominantly a magmatic feature related mantle melting
during break-up. Melt generation models suggest that the greater thickness of HVLC on the
African margin is due to active upwelling combined with elevated temperatures whereas the
model predicts passive upwelling and a thick lithospheric lid for the South American
HVLC. The contrast in upwelling rate and lithospheric thickness can be explained
by a model of asymmetric rifting with a simple shear extension. Combining our
estimates for the total HVLC volumes with the SDRs and flood basalts implies a total
magma production about 6 x 106km3on the rifted margins of the South Atlantic. |
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