HR: 0800h
AN: V51B-0562    [Abstracts]
TI: New Age and Geochemical Data From Seamounts in the Canary and Madeira Volcanic Provinces: A Contribution to the "Great Plume Debate"
AU: * Geldmacher, J
EM: jgeldmacher@ifm-geomar.de
AF: IFM-GEOMAR, Geb. Ostufer, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Hoernle, K
EM: khoernle@ifm-geomar.de
AF: IFM-GEOMAR, Geb. Ostufer, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: van den Bogaard, P
EM: pbogaard@ifm-geomar.de
AF: IFM-GEOMAR, Geb. Ostufer, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Duggen, S
EM: sd@dlc.ku.dk
AF: Danish Lithosphere Centre, Oster Voldgade 10, Copenhagen, 1350 Denmark
AU: Werner, R
EM: rwerner@tethys-geoconsulting.de
AF: TETHYS Geoconsulting Gmbh, Wischhofstr. 1-3, Kiel, 24148 Germany
AB: The role of hotspots (mantle plumes) in the formation of intraplate volcanic island and seamount groups is being increasingly questioned, in particular concerning the abundant and somewhat irregularly distributed island and seamount volcanoes off the coast of northwest Africa. However, new $^{40}$Ar/$^{39}$Ar ages and Sr-Nd-Pb isotope geochemistry of volcanic rocks from two seamounts northeast of the Canary Islands and two northeast of the Madeira Islands provide new support for the plume hypothesis. The oldest ages of shield stage volcanism from seamounts and islands northeast of the Canary and Madeira Islands confirm progressions of increasing age to the northeast for both island/seamount chains consistent with northeast directed plate motion. Calculated angular velocities for the average movement of the African plate in both regions gave similar values of about 0.45\deg plus/minus 0.05\deg/Ma around a rotation pole located north of the Azores Islands. Furthermore, the curvature of the chains clearly deviates from the E-W orientation of fracture zones in the East Atlantic. A local control of surface volcanism by lithospheric zones of weakness, however, is likely for some E-W elongated seamounts and islands. The isotope geochemistry additionally confirms that the two volcanic provinces are derived from distinct sources, consistent with distinct mantle plumes having formed both volcanic groups. Conventional hotspot models, however, cannot easily explain the wide distribution of seamounts in the Canary region and the long history of volcanic activity at single volcanic centers (e.g. Dacia seamount, 47-4 Ma; Selvagen Islands, 30-3 Ma). A possible explanation could involve interaction of a Canary mantle plume with small-scale upper mantle processes such as edge driven convection at the edge of the NW African craton (e.g. King and Ritsema, 2000, Science 290, 1137-1140).
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8157 Plate motions--past (3040)
DE: 1025 Composition of the mantle
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting