Publication Date:
2017-03-20
Description:
Northwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha
mantle plume during continental rupture between Africa and South America, as evidenced by the presence
of the Etendeka continental flood basalts. Here we use data from a passive-source seismological network to
investigate the upper mantle structure and to elucidate the Cretaceous mantle plume-lithosphere
interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the
lithosphere at an average depth of 80 km. We interpret this interface as the relic of the lithosphereasthenosphere
boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume
head with the pre-existing lithosphere. The velocity contrast might be explained by stagnated and ‘‘frozen’’
melts beneath an intensively depleted and dehydrated peridotitic mantle. The present-day LAB is poorly
visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area,
converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in
the landward plume-unaffected continental interior, suggesting high velocities in the upper mantle caused
by a thick lithosphere. This indicates that after lithospheric thinning during continental breakup, the lithosphere
has increased in thickness during the last 132 Myr. Thermal cooling of the continental lithosphere
alone cannot produce the lithospheric thickness required here. We propose that the remnant plume
material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration,
significantly contributed to the thickening of the mantle lithosphere.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
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