HR: 1330h
AN: V32A-1007    [PDF]
TI: He-Ne systematics in OIB and the nature of the source of mantle plumes
AU: * Moreira, M
EM: moreira@ipgp.jussieu.fr
AF: IPGP, 4 place jussieu, Paris, 75005 France
AU: Doucet, S
EM: doucet@ipgp.jussieu.fr
AF: IPGP, 4 place jussieu, Paris, 75005 France
AU: Madureira, P
AF: IPGP, 4 place jussieu, Paris, 75005 France
AU: Lecomte, A
AF: IPGP, 4 place jussieu, Paris, 75005 France
AU: Allegre, C
AF: IPGP, 4 place jussieu, Paris, 75005 France
AB: We have designed a new extraction and purification line, fully automated, coupled with our glass mass spectrometer ARESIBO I, equipped with a faraday cup and an ion counting system. The very low CO2 and 40Ar levels of the machine allow us to analyze the neon isotopic composition in very small samples. We have performed helium and neon analyses on olivine phenocrysts from different oceanic island basalts (St Helena, Gough, Tristan, Azores, Kerguelen, Hawaii). Most of the samples present anomalies compared to air for neon (with ratio 20Ne/22Ne up to 11.67) and all the data plot between the MORB line (e.g. Sarda et al. 1988) and the Iceland line (e.g. Moreira et al., 2001). Corrected for air 21Ne/22Ne ratios (assuming a solar 20Ne/22Ne) are between 0.036 and 0.081. In a diagram 21Ne/22Nec versus 4He/3He, all the OIB plot between a mean MORB composition and a solar like composition, and can be interpreted as a binary mixing with a r=(3He/22Ne)MORB/(3He/22Ne)solar parameter for the hyperbolae around 10 suggesting that mixing between the plume material and the MORB material occur in liquid condition. Another interpretation is that the 3He/22Ne of the MORB source is higher from the solar 3He/22Ne which appears in contradiction with previous estimates. Nevertheless, our conclusion is that the neon is a better tracer of primordial material than helium.
DE: 1010 Chemical evolution
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting