HR: 08:00h
AN: V41G-01 INVITED    [Abstracts]
TI: Dynamics and internal structure of a mantle plume conduit
AU: * Farnetani, C
EM: cinzia@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, PARIS cedex 05, 75 252, France
AU: Hofmann, A W
EM: hofmann@mpch-mainz.mpg.de
AF: Max-Planck-Institut für Chemie, Postfach 3060, Mainz, 3060, Germany
AB: Plumes are often thought of as thermal structures, the key parameter being their excess temperature with respect to the surrounding mantle, while the associated velocity field is frequently neglected. However, in order to understand the structure of a plume conduit and the internal distribution of geochemical heterogeneities we change perspective and focus on velocities and strain rates. Like the hands of an invisible sculptor, velocity gradients constantly modify the shape of heterogeneities rising in the plume conduit. Numerical simulations of a vigorous thermal plume provide a high resolution velocity field that is used to advect deep-seated passive heterogeneities. Our first objective is to investigate the relation between initial length-scales of heterogeneities across D" and the length- and time-scale of geochemical variations induced in the plume conduit. We also explore dynamical differences between the central and peripheral part of the plume conduit, and calculate the strain rate, the buoyancy flux and the elongation as a function of radial distance from the plume axis. Our results clearly show that most of the plume buoyancy flux occurs in highly sheared parts of the conduit. We then concentrate on a 'Hawaiian' plume sheared by a fast moving oceanic plate. Our fully three-dimensional numerical model allows us to study the flow trajectories inside a sheared plume conduit and the deformations undergone by passive heterogeneities. Although our approach is simplistic, we consider the lifetime of a volcano carried by the plate over different parts of the plume conduit and we investigate the relation between heterogeneous structures in the mantle and the spatio-temporal geochemical variability registered by the volcano.
DE: 3619 Magma genesis and partial melting (1037)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8410 Geochemical modeling (1009, 3610)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting