HR: 0800h
AN: V41B-1397    [Abstracts]
TI: Radiometric Dating of Large Volume Flank Collapses in The Lesser Antilles Arc.
AU: QUIDELLEUR, X
AF: Geochronologie UPS-IPGP, Sciences de la Terre, Universite Paris-Sud, batiment 504, Orsay, 91405 France
AU: QUIDELLEUR, X
AF: Paleomagnetisme IPGP, Tour 14, Paris, 75252 France
AU: * SAMPER, A
EM: samper@geol.u-psud.fr
AF: Geochronologie UPS-IPGP, Sciences de la Terre, Universite Paris-Sud, batiment 504, Orsay, 91405 France
AU: BOUDON, G
AF: Geochimie et Volcanologie et Observatoires Volcanologiques, IPGP, Tour 46, Paris, 75252 France
AU: LE FRIANT, A
AF: Geochimie et Volcanologie et Observatoires Volcanologiques, IPGP, Tour 46, Paris, 75252 France
AU: KOMOROWSKI, J
AF: Geochimie et Volcanologie et Observatoires Volcanologiques, IPGP, Tour 46, Paris, 75252 France
AB: It is now admitted that flank collapses, probably triggered by magmatic inflation and/or gravitational collapses, is a recurrent process of the evolution of the Lesser Antilles Arc volcanoes. Large magnitude debris avalanche deposits have been identified offshore, in the Grenada basin (Deplus et al., 2001; Le Friant et al., 2001). The widest extensions have been observed off the coast of Dominica and St Lucia, with associated volumes up to 20 km3. Another large-scale event, with marine evidences probably covered by sediments and latter flank collapses, has been inferred onland from morphological evidences and characteristic deposits of the Carbets structure in Martinique. We present radiometric dating of these three major events using the K-Ar Cassignol-Gillot technique performed on selected groundmass. Both volcanic formations preceding flank collapses (remnants of the horseshoe shaped structures or basal lava flows) and following landslides (lava domes) have been dated. In the Qualibou depression of St. Lucia, the former structure has been dated at 1096+-16 ka and the collapse constrained by dome emplacement prior to 97+-2 ka (Petit Piton). In Dominica, several structures have been associated with repetitive flank collapse events inferred from marine data (Le Friant et al., 2002). The Plat-Pays event probably occurred after 96+-2 ka. Inside the inherited depression, Scotts Head, which is interpreted as a proximal pluri-kilometric megabloc from the Soufriere avalanche, has been dated at 14+-1 ka, providing an older bound for this event. In Martinique Island, three different domes within the Carbets structure have been dated at 335+-5 ka. Assuming a rapid magma emplacement following pressure release due to deloading, this constrains the age of this high magnitude event. Finally, these results obtained from three of the most voluminous flank collapses provide constraints to estimate the recurrence of these events, which represent one of the major hazards associated with volcanoes of the Lesser Antilles Arc.
DE: 1749 Volcanology, geochemistry, and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting