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Доповіді НАН України. – 2007. – N 8. – С. 110–115.
Крупномасштабное фракционирование редкоземельных элементов в мантии кратонов
О.В. Арясова, Я.М. Хазан
Abstract
Rare earth element (REE) abundances in clinopyroxene and garnet from
xenoliths entrained by kimberlites of the Kaapvaal craton, South Africa, and
the Somerset Island, Canada, show a strong and species-dependent variation
vs. pressure in a depth range of 70 to 200 km. As a result, the interelement
ratios of the REE vary across the upper mantle. This effect can be referred
to as a REE large-scale space fractionation. Based upon a strong correlation
between the activation energies of the REE diffusion in clinopyroxene,
and the logarithmic slopes Γ of the abundance vs. pressure
dependence, Γ = –d log C(P)/dP, we speculate that the space
fractionation had accompanied mantle melting events and was due to a
nonequilibrium REE partition between the melt and the solid residue.
A simplified model of the mantle partial melting, which takes into account a PT
dependent diffusive exchange between the melt and the multimineral solid
residue and a non-modal character of peridotite melting indicates that the
observed strong fractionation is resulted from a high degree (10–20%)
partial melting of a depleted peridotite (a few wt% of clinopyroxene).
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