HR: 0800h
AN: T11C-0737    [Abstracts]
TI: 80-Myr history of buoyancy and volcanic fluxes along the trails of the Walvis and St. Helena hotspots (South Atlantic)
AU: * Vidal, V
EM: Valerie.Vidal@ens-lyon.fr
AF: Laboratoire de Physique, ENS Lyon - CNRS, 46 Allee d'Italie, Lyon, 69364, France
AU: Adam, C
EM: adam@jamstec.go.jp
AF: Institute for Research on Earth Evolution, JAMSTEC, 2-15 Natsushima, Yokosuka, 237- 0061, Japan
AU: Escartin, J
EM: escartin@ipgp.jussieu.fr
AF: Laboratoire de Geosciences Marines, IPGP - CNRS, 4 place Jussieu, Paris, 75252, France
AB: Walvis and St.~Helena are the only long-lived hotspot chains in the South Atlantic. Therefore, their characterization is important to constrain the processes associated with mantle plume formation, their temporal evolution, and the interaction with plate and mantle dynamics in the region. We study the temporal evolution of plume buoyancy and magma production rate along both hotspot chains, which are constrained from the swell and volume of volcanic materials emplaced along the chain. The regional depth anomaly is calculated by correcting the 2' bathymetry grid of Smith & Sandwell (1997) for thermal subsidence and sediment loading. We separate the topography associated with volcanism and the swell surrounding the hotspot chains using the MiFil filtering method (Adam et al., 2005). We then estimate the temporal variations associated with both parameters by computing volumes along the hotspot tracks. Neither Walvis nor St.~Helena show a 'classical' hotspot behavior. We find that two plumes are at the origin of the St.~Helena chain. This study also shows a swell associated with the Circe seamount, supporting the existence of a hotspot NW of the St.~Helena trail. The variation in swell and volcanic fluxes suggests temporal variability in the plume behavior at time scales of 10-20~m.y. and 5~m.y., which may be related to oscillations and instabilities of the plume conduit, respectively. Cumulative fluxes in the area are largest for Walvis and weakest for Circe, and all are significantly lower than that reported for the Hawai'i hotspot.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting