HR: 1340h
AN: S43B-1004    [Abstracts]
TI: Crustal and Upper Mantle Structure Beneath the Cape Verde Islands From Teleseismic Receiver Functions.
AU: * Lodge, A
EM: alex.lodge@bris.ac.uk
AF: University of Bristol, Department of Earth Sciences, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ United Kingdom
AU: Helffrich, G
EM: george.helffrich@bris.ac.uk
AF: University of Bristol, Department of Earth Sciences, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ United Kingdom
AU: Fonseca, J F
EM: jfonseca@ist.utl.pt
AF: Instituto Superior Tecnico, Departamento de Fisica, Av. Rovisco Pais, Lisbon, 1049-001 Portugal
AU: Faria, B V
EM: vigil.isecmar@cvtelecom.cv
AF: Instituto Superior Tecnico, Departamento de Fisica, Av. Rovisco Pais, Lisbon, 1049-001 Portugal
AU: Kaneshima, S
EM: kane@geo.titech.ac.jp
AF: Tokyo Institute of Technology, Department of Earth and Planetary Sciences, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551 Japan
AB: Cape Verde is a hot spot island archipelago around 450 km west of the westernmost point of West Africa. The islands stand in 4 km of water on a roughly circular swell 2 km shallower than expected for crust of its age. The aim of this work is to provide seismic constraints on the nature of the swell, which may be attributed to thermally less dense, hot plume material or compositionally less dense, melting residue. We deployed a temporary network of broadband stations in Cape Verde to record teleseisms to study the shallow structure beneath the entire archipelago. Receiver function analysis indicates that a $\sim$20 km thick crust exists beneath all the islands, under which wavespeeds increase and density decreases in a layer extending to around 80 km depth. There does not appear to be any simple relationship between the layer thickness and the onset of volcanism, suggesting that the layer is not caused by simple flow of less dense material from a plume source. We explore a suite of models that can account for the receiver function profiles, the 2 km bathymetric anomaly, and the volume of material erupted to form the island edifices. We find that temperatures $>$300 degrees hotter than ambient mantle or melt depletion of $\sim$10% can explain them. The results suggest that the bathymetric anomaly is due to localized melting beneath the islands which uplifts them and spreads away from the individual volcanic centers, not a single source of buoyancy.
DE: 7220 Oceanic crust
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting