HR: 10:35h
AN: V22A-02    [Abstracts]
TI: Rare gas systematics in the Indian Ocean mantle: the DUPAL anomaly
AU: * Moreira, M A
EM: moreira@ipgp.jussieu.fr
AF: IPGP, 4 place jussieu, paris, 75005 France
AU: Raquin, A
EM: raquin@ipgp.jussieu.fr
AF: IPGP, 4 place jussieu, paris, 75005 France
AU: Gautheron, C
EM: gauteron@geol.u-psud.fr
AF: IPGP, 4 place jussieu, paris, 75005 France
AU: Allegre, C J
EM: allegre@ipgp.jussieu.fr
AF: IPGP, 4 place jussieu, paris, 75005 France
AB: The "DUPAL" anomaly, defined by S. Hart, located in the Indian Ocean and in a part of the South Atlantic is considered to result from the injection in a Atlantic-like mantle of a component with a low 206Pb/204Pb ratio, and relatively high 87Sr/86Sr, 207Pb/204Pb and 208Pb/204Pb ratios. This component has been associated to a plume (Kerguelen), to a thermally delaminated subcontinental lithosphere, to lower crust or to subduction of a mixture of sediments and old oceanic crust. In order to constrain the different hypothesis, we have performed a complete rare gas study (He, Ne, Ar, Kr and Xe) in basalts both from mid oceanic ridges and some oceanic islands from Indian ocean. The helium isotopic ratios of the most DUPAL-like samples are more radiogenic than in Pacific and Atlantic MORB (4He/3He >120,000). The 21Ne/22Ne ratio is also more nucleogenic and correlates with the helium. The significance of these characteristics is that the component injected in the Indian mantle is a material with high (U+Th)/3He and (U+Th)/22Ne and may be low 40Ar/36Ar. This kind of material is consistent with subcontinental mantle or lower crust, isolated from the mantle convection for more than 1.5Ga, previously enriched by fluids coming from dehydration of subducted slabs.
DE: 1025 Composition of the mantle
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005