CSEDI: Collaborative Research:Development of Geochemical Tests for Detection of Core-Mantle Interaction

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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.