Helium isotopes on the Macdonald seamount (Austral chain): constraints on the origin of the superswell |
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Authors: | Manuel Moreira Claude Allègre |
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Institution: | Laboratoire de géochimie et cosmochimie, UMR CNRS 7578, Institut de physique du Globe de Paris, université Denis-Diderot, Paris-7, 4, place Jussieu, 75252 Paris cedex 05, France |
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Abstract: | We present new helium isotope data from the Macdonald seamount (Austral chain). The helium isotopic ratio varies from 4He/3He=45 000 (R/Ra=16.0) to 200 170 (R/Ra=3.6). The helium content is between 1.5×10?8 and 1.1×10?5 ccSTP/g. These helium results show clearly the presence of primitive mantle material in the source of the Austral chain. Macdonald has the lowest 4He/3He ratio among the Polynesian submarine volcanoes, except Hawaii (Loihi). The simplest explanation for the primitive helium signature is the presence under Macdonald of a mantle plume that derives either from the 670 km or 2900 km boundary layers, or, eventually, from the top of a large mantle dome resulting from a stratified two-layer convection. This plume contains less-degassed material with low 4He/3He ratio. To cite this article: M. Moreira, C. Allègre, C. R. Geoscience 336 (2004). |
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Keywords: | helium Macdonald mantle plumes superswell Polynesia hélium Macdonald panaches superbombement Polynésie |
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