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Depleted swell root beneath the Cape Verde Islands

¹ Earth Sciences Department, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, UK

The hotspot swell—an area of uplifted bathymetry or topography surrounding regional volcanism—is a defining hotspot characteristic, yet its origin is poorly understood. To test current ideas about swell formation, we studied the crust and shallow mantle structure of the Cape Verdes in a passive seismic experiment. The Cape Verde Islands are 450 km west of Senegal in the tropical Atlantic Ocean and are on the southwest flank of the Cape Verde Rise, the largest bathymetric anomaly in the oceans, rising 2 km above the surrounding seafloor (Crough, 1982). The archipelago occupies a unique position, an approximately stationary one in the hotspot frame of reference (Gripp and Gordon, 2002) and therefore with respect to the melting source believed to have produced it. Here we present an analysis of compressional to shear (P to S) converted seismic phases, recorded on a temporary network of seismograph stations on the Cape Verde Islands, that indicate a crust thickened to 22 km is underlain by a high-velocity, low-density layer, which overlies a zone of low shear-wave velocity starting at 80 km depth. We also measured shear-wave splitting delay times for teleseismic SKS phases, which are 0.81 s, compatible with an origin in this same layer. We interpret these observations as effects of hotspot melting, which produces a thickened crust and a depleted swell root that buoys the ocean floor and spreads laterally as it grows over time.

Key Words: hotspot • swell • Cape Verde • oceanic crust • ocean island basalt • receiver function • anisotropy

This article has been cited by other articles:

				A. K. Barker, P. M. Holm, D. W. Peate, and J. A. Baker Geochemical Stratigraphy of Submarine Lavas (3-5 Ma) from the Flamengos Valley, Santiago, Southern Cape Verde Islands J. Petrology, January 22, 2009; (2009) egn081v1. [Abstract] [Full Text] [PDF]