Crustal structure of the eastern Walvis Ridge

Tanja.Fromm [ at ]


Walvis Ridge is an aseismic oceanic ridge stretching from the African continent to the Mid Atlantic Ridge, representing the trail of the Tristan da Cunha hotspot. To estimate the influence of the plume, a large-scale geophysical experiment was conducted in 2011 and the P-wave velocity models derived from seismic refraction data are presented here. A 480 km long profile consisting of 27 ocean bottom stations crosses the ridge approximately 600 km west of the coast, while another profile is located parallel to the ridge along the crest with an extension on the continent. 28 ocean bottom stations, 50 land receiver and 8 dynamite shots are distributed along the total length of 730 km. Crustal velocities beneath Walvis Ridge range between 5.5 km/s and 7.0 km/s, which are typical velocities for oceanic crust. The thickness, however, is approximately three times larger than normal: 17 km in the western part increasing to 22 km towards the continent. The continent ocean transition is characterized by 30 km thick crust with a high velocity body (HVB) in the lower crust and seismic velocities up to 7.5 km/s. The western boundary of the HVB is at a similar longitude as HVBs found more south. But different from those, the eastern boundary lies well within the continental domain, at the ~40 km thick crust of the Kaoko fold belt. Here, the variation of seismic velocities indicates that hot material intruded the continental crust during the initial rifting stage. However, beyond this relatively sharp boundary (40 km wide), the remaining continental crust seems not to be affected. The cross-profile indicates that Walvis Ridge might be broader than its topographic expression and that the northward lying seamounts are part of the ridge. A HVB can only be found at the northern flank of the ridge, but not at its base.

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Conference (Talk)
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SAMPLE Colloquium 2014, 03 Jun 2014 - 06 Jun 2014, Bremerhaven.
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Fromm, T. , Jokat, W. , Behrmann, J. H. , Ryberg, T. and Weber, M. (2014): Crustal structure of the eastern Walvis Ridge , SAMPLE Colloquium 2014, Bremerhaven, 3 June 2014 - 6 June 2014 .

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