HR: 0800h
AN: V51B-0573    [Abstracts]
TI: New insights on the Marquesas volcanic chain emplacement
AU: Adam, C
EM: adam@ipgp.jussieu.fr
AF: Institut de Physique du Globe - CNRS, 4,place Jussieu, Paris, 75252 France
AU: * Bonneville, A
EM: bonnevil@ipgp.jussieu.fr
AF: Institut de Physique du Globe - CNRS, 4,place Jussieu, Paris, 75252 France
AB: The Marquesas are one of a number of young hotspot volcanic chains in French Polynesia. The islands erupted onto 50-65 Ma old seafloor and radiometric ages of volcanism span from only a few hundred thousand years for a seamount at the southeast end of the chain to 5.75 Ma for Eiao atoll at the northwestern end. The Marquesas seem thus to be a classic hotspot chain however the main orientation of the chain (N140) does not correspond to the present direction of the absolute Pacific plate motion (N115). This observation has intrigued many researchers during the last decades and we propose here a new explanation based on a precise and complete mapping of the depth and geoid anomalies associated to the volcanic alignment. The analysis of the large scale features of these two datasets allow to characterize the seafloor swell and the corresponding geoid associated to the volcanic chain itself but it also evidences to the northeast a N150 elongated positive geoid anomaly not linked to any seafloor anomaly. This direction, that corresponds roughly to the direction of the crustal seafloor magnetic strips, corresponds to the trend shown by the volcanoes at their creation on the crust. We propose that the particular orientation of the Marquesas chain be due to the spreading of a mantle plume head under the control of the not yet known phenomenum at the origin of the N150 residual geoid anomaly.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8122 Dynamics, gravity and tectonics
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting