Structure of the Crust and Mantle Lithosphere underneath NW Namibia Revealed by the WALPASS Seismic Experiment

shantanu.pandey [ at ]


The amphibian Walvis Ridge Passive-Source Seismic Experiment (WALPASS) have been operated for a period of two years from 2010 to 2012 in the area where the Walvis Ridge intersects the continental margin of northwestern Namibia. The deployment was intended to study the lithospheric and upper mantle structure in the ocean-continent transition area beneath the passive continental margin. The main idea is to find seismic anomalies related to the postulated hotspot track from the continent to the ocean along the Walvis Ridge that links the Etendeka continental flood-basalt province to the Tristan da Cunha hotspot in the mid Atlantic ocean. This could provide clues of the role of plume-lithosphere interaction during the continental break-up. We present here seismic structures of the crustal and mantle lithosphere in this geophysically little studied region using seismic methods including P and S receiver functions and shear wave splitting. The average crustal thickness in the continental Namibia is ~35 km with a relatively low Vp/Vs ratio of 1.7. Underneath the NE extension of the Walvis Ridge the crust is the thickest (45 km) with a high Vp/Vs ratio (>1.80). The thick crust and high Vp/Vs ratio beneath the Walvis Ridge are consistent with high Vp derived by controlled source seismics, implying a magmatic underplating. A low velocity zone in the mantle is observed at depths of 60-120 km, possibly representing the base of the lithosphere. The P-to-S converted phases at the 410 and 660 km discontinuities arrive 2-3 s earlier, indicating higher upper mantle velocities (+5%). Seismic anisotropy in the mantle derived by the SKS splitting exhibits a pattern of the plume and plate interaction.

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Conference (Poster)
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American Geophysical Union, Fall Meeting 2013, 09 Dec 2013 - 13 Dec 2013.
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Yuan, X. , Jokat, W. , Weber, M. , Geissler, W. , Heit, B. , Eken, T. , Pandey, S. , Lushetile, B. and Hoffmann, K. (2013): Structure of the Crust and Mantle Lithosphere underneath NW Namibia Revealed by the WALPASS Seismic Experiment , American Geophysical Union, Fall Meeting 2013, 9 December 2013 - 13 December 2013 .

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