HR: 1330h
AN: V32A-1003    [PDF]
TI: Helium and Neon Isotopic Systematics in Kerguelen Archipelago High-MgO Basalts and Picrites
AU: * Doucet, S
EM: doucet@ipgp.jussieu.fr
AF: Laboratoire de G\'{e}ochimie et Cosmochimie, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: * Doucet, S
EM: doucet@ipgp.jussieu.fr
AF: D\'{e}partement des Sciences de la Terre et de l'Environnement, Universit\'{e} Libre de Bruxelles, Av. Roosevelt, 50, Brussels, 1050 Belgium
AU: Moreira, M
AF: Laboratoire de G\'{e}ochimie et Cosmochimie, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: Weis, D
AF: D\'{e}partement des Sciences de la Terre et de l'Environnement, Universit\'{e} Libre de Bruxelles, Av. Roosevelt, 50, Brussels, 1050 Belgium
AU: Weis, D
AF: Department of Earth and Ocean Sciences, University of British Columbia, 2329 West Mall, Vancouver, V6T 1Z4 Canada
AU: Scoates, J
AF: D\'{e}partement des Sciences de la Terre et de l'Environnement, Universit\'{e} Libre de Bruxelles, Av. Roosevelt, 50, Brussels, 1050 Belgium
AU: Scoates, J
AF: Department of Earth and Ocean Sciences, University of British Columbia, 2329 West Mall, Vancouver, V6T 1Z4 Canada
AB: The Pb-Hf-Nd-Sr compositions of the mildly alkalic basalts ($<$ 25 Ma) erupted in the southeastern Kerguelen Archipelago are inferred to represent the enriched Kerguelen plume end-member (Weis et al. G3 2002). We present new helium (He) and neon (Ne) isotopic compositions for olivines of eight high-MgO basalts and picrites (6-17 wt.$%$ MgO) from this part of the archipelago to better characterize the mantle sources involved in the genesis of Kerguelen plume-related basalts. Crushing experiments were performed on a ARESIBO mass spectrometer, which is connected to a new fully automated extraction/purification line. The studied olivines have extremely variable $^4$He/$^3$He compositions ($\sim$ 90000 to 40000). This covers a range from the limited field of radiogenic MORB to primitive values observed in OIB ($^4$He/$^3$He $\sim$ 90000, and down to $\sim$ 15000, respectively). These olivines are characterized by primitive Ne isotopic compositions (lower $^{21}$Ne/$^{22}$Ne for a given $^{20}$Ne/$^{22}$Ne relative to MORB). Ne and He isotopic results are apparently decoupled, which could be related to He loss during magmatic evolution or secondary processes occurring during exposure time. The $^{20}$Ne/$^{22}$Ne-$^{21}$Ne/$^{22}$Ne compositions define a linear trend, which completes the trend formed by previously analyzed Kerguelen Archipelago xenoliths (Valbracht et al. EPSL 1996). This well-defined trend (r$^{2} >$ 0.95) suggests that the Ne isotopic compositions of these basalts result from mixing between an air-like component and a primitive material characterized by $^{21}$Ne/$^{22}$Ne of 0.056 (calculated for a solar $^{20}$Ne/$^{22}$Ne = 13.8). This ratio appears to be a characteristic of the enriched source of the Kerguelen mantle plume. Alternatively, the Ne isotopic ratios of the studied samples may result from different amount of mixing between a MORB-like source end-member and a primitive source end-member subsequently contaminated by the air, an hypothesis that is apparently inconsistent with Sr-Nd isotopic systematics in these basalts (Doucet et al., EGS 2003).
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 5480 Volcanism (8450)
DE: 9340 Indian Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting