Mantle Anisotropy in NW Namibia From XKS Splitting: Effects of Asthenospheric Flow, Lithospheric Structures, and Magmatic Underplating

Abstract

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 continental breakup 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. We present the results of the joint splitting analysis of XKS data collected from 34 onshore stations and 12 ocean‐bottom seismometers. The fast polarization directions (FPDs) are consistent with a model that combines the effects of lithospheric deformation and large‐scale mantle flow due to the NE motion of the African plate. The dominantly NNW‐SSE‐oriented FPDs in the northern part are likely caused by shallow lithospheric structures. Our observations do not show any strong evidence of a pervasive effect of the Tristan da Cunha mantle plume.

Keywords

• seismic anisotropy
• Tristan da Cunha mantle plume
• Namibia
• lithospheric shearing
• continental breakup
• shear wave splitting