CaSiO 3 and CaTiO 3 perovskite‐melt partitioning of trace elements: Implications for gross mantle differentiation

We report the results of CaSiO 3 perovskite‐melt partitioning experiments conducted at conditions relevant to the uppermost lower mantle. Partition coefficients, measured by LA‐ICPMS, show that CaSiO 3 perovskite has a strong affinity for REE, Y, Th and U, making CaSiO 3 the most likely host for these elements in the lower mantle. Comparison with the low‐pressure analogue CaTiO 3 shows that large ions partition similarly into the Ca‐sites of the two perovskites. Thus CaTiO 3 may be used as a model to investigate the factors controlling the partitioning of many trace ions into CaSiO 3 . Combined fractionation of MgSiO 3 and CaSiO 3 perovskites during an early magma ocean has been suggested as a means of enriching the lower mantle in silica. Our results show, however, that the chondritic upper mantle ratios of refractory lithophile elements would be lost after ∼17% of perovskite fractionation. A large perovskitic layer `hidden' in the lower mantle is therefore improbable.