Rhenium-187 decays to form Osmium-187 through beta decay. Unlike the two systems previously discussed, Osmium is a compatible element. Rhenium is incompatible and partitions to the melt, but Osmium preferentially remains in the crystalline phase. Thus, over time, the crust is relatively enriched in Re relative to Os, and the mantle is relatively depleted in Re compared to Os.

(White, 2005)

One difficulty in the analysis of this system occurs because Os is compatible. This causes the Osmium levels to be extremely low in continental crust rocks. However, due to the extreme degree of fractionation, the measurements do not need to be as exact as in the previous two systems.

From White, 2005 and Dickin, 2002
neodymium

data for CRFB

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