Mantle anisotropy in NW Namibia from XKS splitting: asthenospheric flow,
magmatic underplating, and lithospheric shearing
Abstract
The presence of the Etendeka flood basalts in northwestern Namibia is
taken as evidence for the activity of the Tristan da Cunha mantle plume
during the breakup process between Africa and South America. We
investigate seismic anisotropy beneath NW Namibia by splitting analysis
of core-refracted teleseismic shear waves (XKS phases) to probe mantle
flow and lithospheric deformation related to the tectonic history of the
region. The waveform data were obtained from 34 onshore stations and 12
Ocean Bottom Seismometers. The results presented here are from joint
splitting analysis of multiple XKS phases. The majority of the fast
polarization directions (FPDs) exhibit an NE-SW orientation consistent
with a model of large-scale mantle flow due to the NE motion of the
African plate. No evidence for a direct effect of the mantle plume is
observed. In the northern part, we observe NNW-SSE-oriented FPDs that is
likely caused by shallow lithospheric structures.