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| Titel |
Asymmetry of high-velocity lower crust on the South Atlantic rifted margins and implications for the interplay of magmatism and tectonics in continental breakup |
| VerfasserIn |
K. Becker, D. Franke, R. Trumbull, M. Schnabel, I. Heyde, B. Schreckenberger, H. Koopmann, K. Bauer, W. Jokat, C. M. Krawczyk |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 5, no. 2 ; Nr. 5, no. 2 (2014-10-02), S.1011-1026 |
| Datensatznummer |
250115342
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| Publikation (Nr.) |
 copernicus.org/se-5-1011-2014.pdf |
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| Zusammenfassung |
High-velocity lower crust (HVLC) and seaward-dipping reflector (SDR) sequences are typical features of volcanic rifted margins. However, the nature
and origin of HVLC is under discussion. Here we provide a comprehensive
analysis of deep crustal structures in the southern segment of the South
Atlantic and an assessment of HVLC along the margins. Two new seismic
refraction lines off South America fill a gap in the data coverage and
together with five existing velocity models allow for a detailed investigation
of the lower crustal properties on both margins. An important finding is the
major asymmetry in volumes of HVLC on the conjugate margins. The seismic
refraction lines across the South African margin reveal
cross-sectional areas of HVLC 4 times larger than at the South American margin, a finding
that is opposite to the asymmetric distribution of the flood basalts in the
Paraná–Etendeka Large Igneous Province. Also, the position of the
HVLC with respect to the SDR sequences varies
consistently along both margins. Close to the Falkland–Agulhas Fracture Zone
in the south, a small body of HVLC is not accompanied by SDRs. In the central portion of both margins, the HVLC is below the
inner SDR wedges while in the northern area, closer to
the Rio Grande Rise-Walvis Ridge, large volumes of HVLC extend far seaward
of the inner SDRs.
This challenges the concept of a simple extrusive/intrusive relationship
between SDR sequences and HVLC, and it provides
evidence for formation of the HVLC at different times during the rifting and
breakup process. We suggest that the drastically different HVLC volumes are
caused by asymmetric rifting in a simple-shear-dominated extension. |
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