HR: 0800h
AN: U41A-0707    [Abstracts]
TI: Convective Patterns in the Indo-Atlantic Mantle over the last 260 Myr
AU: * Stutzmann, E
EM: stutz@ipgp.jussieu.fr
AF: IPG, 4 place Jussieu, PARIS cedex05, 75252 France
AU: Davaille, A
EM: davaille@ipgp.jussieu.fr
AF: IPG, 4 place Jussieu, PARIS cedex05, 75252 France
AU: Silveira, G
EM: mdsilveira@fc.ul.pt
AF: Centro de Geofˇsica da Universidade de Lisboa, Edifˇcio C8, Campo Grande, LISBOA, 1749-016 Portugal
AU: Besse, J
EM: besse@ipgp.jussieu.fr
AF: IPG, 4 place Jussieu, PARIS cedex05, 75252 France
AU: Courtillot, V
EM: courtil@ipgp.jussieu.fr
AF: IPG, 4 place Jussieu, PARIS cedex05, 75252 France
AB: Using recent fluid mechanics results as a framework, we reinterpret the images of the Indo-Atlantic mantle obtained from global tomography studies together with geochemical, geological and paleomagnetic observations to unravel the pattern of convection in the Indo-Atlantic "box" and its temporal evolution over the last 260 Myr. Seismic tomography sections at different depths show that the Earth's mantle seems to be divided in two "boxes" by the subducted plates, the Pacific and the Indo-Atlantic boxes. The latter presently contains a) a broad slow seismic anomaly at the CMB, which divides into several branches higher in the lower mantle, b) one "superswell" centered on the western edge of South Africa, c) at least 5 "primary hotspots" with long tracks related to trapps, and d) numerous smaller hotspots. Moreover, in the last 260 Myr, this mantle box has undergone 10 traps events, 7 of them related to continental break up. Several of these past events are spatially correlated with present-day seismic anomalies and/or upwellings, suggesting episodicity. Laboratory experiments show that superswells, long-lived hot spot tracks and traps probably represent three stages of a same phenomenon: the episodic destabilization of a hot thermal boundary layer lying close to the bottom of the mantle and containing chemical heterogeneities. This could produce thermochemical plumes, either with large heads (trapps) and thin tails (tracks) if less viscous than the ambient mantle, or fingerlike domes if more viscous than the ambient mantle. The recurrence of such phenomenon in the mantle would be 100-200 Myr with a wavelength of 2000-4000 km at the CMB, which is in agreement with the observations.
DE: 8180 Tomography
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8125 Evolution of the Earth
DE: 1734 Seismology
DE: 1213 Earth's interior--dynamics (8115, 8120)
SC: Union [U]
MN: 2004 AGU Fall Meeting