ABSTRACT

A basic question in geochemistry is whether or not there is chemical
exchange accompanying the transfer of heat from the core to the
mantle in the cooling cycle of the Earth. It has been previously
proposed that minor mass transfer from the outer core to a mantle
plume rising from the core-mantle boundary would be indicated if
certain, coupled variations in 186Os/188Os and 187Os/188Os ratios are
detected in lavas derived from the plume. To examine this issue,
186Os/188Os and 187Os/188Os ratios of rocks from two plume-derived,
ocean island basalt systems will be precisely measured. There is also
strong mass balance evidence that the core has a 182W/184W ratio that
is approximately 2 parts in 10,000 lower than the ambient mantle. A
portion of this signal could be transferred to a plume, as with the
Os isotopes. Consequently, techniques will be developed to examine
the same plume-derived rocks for W isotopes at the 5-15 parts per
million level that will likely be necessary to detect a core
component. The ability of Os and W isotopes to serve as tracers of
core input to mantle plumes require a good understanding of
metal/silicate partitioning behavior of these and allied elements,
under high-pressure conditions. Consequently, high-pressure
partitioning will be examined experimentally. Finally, a variety of
physical mechanisms of the transfer of core metal into the mantle
will be considered and evaluated.

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