Publication Date:
2022-09-04
Description:
The Walvis Ridge (WR) is the most prominent hotspot track related to the opening in the South
Atlantic Ocean. Several hypotheses have been developed to explain its origin and evolution.
The presence of a massive magmatic structure at the landfall of the WR in Northwest Namibia
raised speculation about the role of a hotspot during the opening of the South Atlantic ocean. To
investigate its deeper velocity structure at the junction of the WR with the African continent
was the focus of the amphibious seismological WALPASS experiment. In total 12 oceanbottom
seismometers and 28 broad-band land stations were installed between 2010 and 2012
to acquire seismological data. Here,we present the results of seismic ambient noise tomography
to investigate to which extent the Tristan hotspot modified the crustal structure in the landward
prolongation of the ridge and in the adjacent oceanic basins. For the tomography, vertical and
hydrophone component cross correlations for 〉300 d for OBS stations and between 1 and 2 yr
for land stations data were analysed. More than 49 000 velocity measurements (742 dispersion
curves) were inverted for group velocity maps at 75 individual signal periods, which then had
been inverted for a regional 3-D shear wave velocity model. The resulting 3-D model reveals
structural features of the crust related to the continent–ocean transition and its disturbance
caused by the initial formation of the WR ∼130 Ma. We found relatively thick continental
crust below Northwest Namibia and below the near-shore part of the WR, a strong asymmetry
offshore with typical, thin oceanic crust in the Namibe Basin (crossing over into the Angola
Basin further offshore) to the North and a wide zone of transitional crust towards the Walvis
Basin south of the WR.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
NonPeerReviewed
Format:
application/pdf