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20th Feb., 2009
Dear WM, An interesting piece of work was recently
published: Polyakov
V.B. Equilibrium iron isotope fractionation at core-mantle
boundary conditions. Science, 323,
912-914, 2009 on
the theory of stable isotope fractionation with implications
for iron isotopes in the Earth and other planets. It
appears that enrichment of the Earth and Moon by heavy
iron isotopes compared to Mars, Vesta and chondritic
meteorites can be explained by equilibrium fractionation
of iron isotopes at pressures of the Earth’s
core-mantle boundary.
This new model has two important
implications for Earth sciences. First, it suggests
that the separation of iron, which formed the Earth’s
core, happened at
high pressure and not in a shallow magma ocean.
Second, it suggests that plumes, if they originate
at the core-mantle boundary and feed ocean-island volcanism e.g.,
at Hawaii, could be distinguished from shallow-sourced
magmatism by iron isotope measurements in OIB and MORB
basalts.
The core contribution at Hawaii postulated
from earlier Re-Os isotope work was ruled out by a
later tungsten isotope work (Scherstén A., Elliott
T., Hawkesworth C., Norman M. Tungsten isotope
evidence that mantle plumes contain no contribution
from Earth’s core. Nature, 427,
234-237, 2004so this could provide a new investigative
approach–Alexei
Ivanov
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Cruises
