Further constraints on the African superplume structure

Details Further constraints on the African superplume structure Further constraints on the African superplume structure

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003pepi..140..243n&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 140, Issue 1-3, p. 243-251.

Physics

14

Scientific paper

It is well established that there is a large-scale low velocity structure in the lowermost mantle beneath Africa, extending from the Southeastern Atlantic Ocean to the Southwestern Indian Ocean with a volume greater than 10billionkm3 (>7000km long, 1000km across and 1200km high) [Earth Planet. Sci. Lett. 206 (2003) 119]. This low velocity structure is often called the African superplume. Various studies also require sharp boundaries for the plume. However, as for its height and shear velocity reduction, there has been some controversy, especially concerning the velocities at the core-mantle-boundary (CMB). Here, we present an assortment of phases involving Sdiff, SKS, S and ScS with both vertical and horizontal paths sampling a 2D corridor through the structure. Travel time and waveform modeling of these seismic phases argues for a model with shear velocity reduction of approximately 3% within the superplume (which is basically a 200km thick layer low velocity layer beneath the Southern Atlantic Ocean, and a 1200km high structure beneath South Africa), and against a model of a substantially reduced low velocity layer (up to 10%, 300km) beneath the superplume. We also analyzed Pdiff and the differential times of PcP-P and compared them with Sdiff and ScS-S observations along the same great circle paths. The P-velocity is not very anomalous, at most -0.5%, much smaller than -1% as expected from a thermal anomaly with -3% lower S-velocity [Geophys. Res. Lett. 27 (2000) 421], thus again arguing for a chemical origin which was suggested from the modeling of African superplume sharp sides [Science 296 (2002) 1850].

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