The wide-angle seismic image of a complex rifted margin, offshore North Namibia: Implications for the tectonics of continental breakup.

Planert, Lars, Behrmann, Jan , Jokat, Wilfried, Fromm, Tanja, Ryberg, Trond, Weber, Michael and Haberland, Christian (2017) The wide-angle seismic image of a complex rifted margin, offshore North Namibia: Implications for the tectonics of continental breakup. Tectonophysics, 716 . pp. 130-148. DOI 10.1016/j.tecto.2016.06.024.

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Supplementary data:

Abstract

Highlights

• Up to 33 km thick dominantly gabbroic crust beneath Walvis Ridge
• Massive gabbro addition with subjacent cumulates to the COB south of Walvis Ridge.
• Slow upper mantle at ~ 35 km depth beneath Etendeka Plateau
• 4–6 km thick oceanic crust in the Angola Basin north of Florianopolis Transform
• Velocity models suggest a dominant tectonic control on the location of magmatism.

Abstract

Voluminous magmatism during the South Atlantic opening has been considered as a classical example for plume related continental breakup. We present a study of the crustal structure around Walvis Ridge, near the intersection with the African margin. Two wide-angle seismic profiles were acquired. One is oriented NNW–SSE, following the continent–ocean transition and crossing Walvis Ridge. A second amphibious profile runs NW–SE from the Angola Basin into continental Namibia. At the continent–ocean boundary (COB) the mafic crust beneath Walvis Ridge is up to 33 km thick, with a pronounced high-velocity lower crustal body. Towards the south there is a smooth transition to 20–25 km thick crust underlying the COB in the Walvis Basin, with a similar velocity structure, indicating a gabbroic lower crust with associated cumulates at the base. The northern boundary of Walvis Ridge towards the Angola Basin shows a sudden change to oceanic crust only 4–6 km thick, coincident with the projection of the Florianopolis Fracture Zone, one of the most prominent tectonic features of the South Atlantic ocean basin. In the amphibious profile the COB is defined by a sharp transition from oceanic to rifted continental crust, with a magmatic overprint landward of the intersection of Walvis Ridge with the Namibian margin. The continental crust beneath the Congo Craton is 40 km thick, shoaling to 35 km further SE. The velocity models show that massive high-velocity gabbroic intrusives are restricted to a narrow zone directly underneath Walvis Ridge and the COB in the south. This distribution of rift-related magmatism is not easily reconciled with models of continental breakup following the establishment of a large, axially symmetric plume in the Earth's mantle. Rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magma-dominated southern and an essentially amagmatic northern segment.

Document Type: Article
Additional Information: Data presented in this paper are available through the GIPP Experiment and Data Archive (Ryberg et al., 2014).
Keywords: Wide-angle seismic; Crustal structure; Walvis Ridge; Hotspot; Rifted continental margin; South Atlantic; RV Maria S. Merian, MSM17
Research affiliation: GFZ
AWI
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.tecto.2016.06.024
ISSN: 0040-1951
Related URLs:
Projects: SAMPLE (SPP 1375)
Expeditions/Models/Experiments:
Date Deposited: 27 Jun 2016 09:35
Last Modified: 01 Feb 2019 15:03
URI: http://oceanrep.geomar.de/id/eprint/33262

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