Helium isotopic systematics within the neovolcanic zones of Iceland

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Helium isotopic compositions have been measured in a suite of sub-glacial basaltic glasses from the neovolcanic zones of Iceland. The 3He/4He ratios vary between 8 and 26.2× atmospheric; the higher ratios are generally consistent with a relatively primitive undegassed mantle source for the helium. Several sampling tests indicate that sub-glacial basaltic glasses retain a representative sample of magmatic helium, much like mid-ocean ridge basalts. The overall variations, high observed helium concentrations (up to 1.6×10-6 cm3 STP/g), and young age of Icelandic crust argue strongly against crustal contamination as a primary control of helium isotopes in the basaltic lavas. Each volcanic zone has a distinctive basaltic 3He/4He isotopic signature: 18-26.2× atmospheric in the eastern volcanic zone and central Iceland, 12-16× atmospheric in the western volcanic zone, and 8-11 in the northeastern volcanic zone. The limited range of 3He/4He ratios within each zone, variability between volcanic zones in 3He/4He, and temporal aspects of Icelandic volcanism are interpreted within the framework of a plume model for the mantle beneath Iceland. The preferred model involves variable contributions from a plume source (i.e. undegassed) to each of the Icelandic volcanic zones. The fact that the highest 3He/4He ratios are observed in eastern and central Iceland suggests that volcanism in these areas has the greatest contribution from the plume. © 1985 Elsevier Science Publishers B.V.

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Earth and Planetary Science Letters