Abstract
The partitioning of La, Sm, Yb, Sc and major elements between majorite garnet and ultrabasic liquid has been studied experimentally at 16 GPa and 2000°C. Liquidus majorite possesses a Si/Mg ratio of 1.05 as compared to the Cl chondritic ratio of 0.95, so that extraction of more than 50% of majorite from a chondritic mantle composition would be required to obtain the pyrolite Si/Mg ratio of 0.78 in the upper mantle. Liquidus majorite is enriched in Al, Sc and Yb compared to the melt by almost a factor of two and is similarly depleted in Ca, Sm and Ti. Thus extensive majorite fractionation would necessarily imprint non‐chondritic Sm/Yb, Sm/Sc, Al/Ca and Al/Ti ratios on the coexisting liquid. These partition relationships demonstrate that the present upper mantle, which possesses these elements approximately in chondritic relative abundances, cannot have experienced prior separation of more than about 10% of a majorite garnet phase.
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