Helium Isotopic Evidence for a Lower Mantle Component in Depleted
Archean Komatiite
Denis Richard,
Bernard Marty,
*
Marc Chaussidon,
Nicholas Arndt
Archean magnesium-rich komatiites require hot and presumably deep
mantle sources, but their trace-element composition and radiogenic
isotope composition are similar to those of modern mid-ocean ridge
basalts, which originate in the upper mantle. The isotopic composition
of helium extracted by sequential crushing of fresh olivines separated
from two Archean and one mid-Proterozoic komatiites varies over three
orders of magnitude, between a radiogenic end-member rich in helium-4
and a component rich in helium-3. Such helium-3 enrichment suggests the
presence of a lower mantle component in Archean komatiites.
D. Richard, B. Marty, M. Chaussidon, CNRS, Centre de Recherches
Pétrographiques et Géochimiques, Rue Notre-Dame des
Pauvres, B.P. 20, 54501 Vandoeuvre Cedex, and Ecole Nationale
Supérieure de Géologie, 94 Avenue De Lattre de Tassigny,
54001 Nancy Cedex, France.
N. Arndt, Géosciences, Unité Propre de Recherches 4661 CNRS, Université de Rennes, 35042 Rennes Cedex, France.
*
To whom correspondence should be addressed. E-mail:
bmarty{at}crpg.cnrs-nancy.fr
