TY  - JOUR
A1  - Planert, Lars
A1  - Behrmann, Jan H.
A1  - Jokat, Wilfried
A1  - Fromm, Tanja
A1  - Ryberg, Trond
A1  - Weber, Michael
A1  - Haberland, Christian
T1  - The wide-angle seismic image of a complex rifted margin, offshore North Namibia: Implications for the tectonics of continental breakup
JF  - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth
N2  - 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.
KW  - Wide-angle seismic
KW  - Crustal structure
KW  - Walvis Ridge
KW  - Hotspot
KW  - Rifted continental margin
KW  - South Atlantic
Y1  - 2017
U6  - https://doi.org/10.1016/j.tecto.2016.06.024
SN  - 0040-1951
SN  - 1879-3266
VL  - 716
SP  - 130
EP  - 148
PB  - Elsevier
CY  - Amsterdam
ER  -