Partitioning of rare earth elements between CaSiO3 perovskite and coexisting phases: constraints on the formation of CaSiO3 inclusions in diamonds

Minerals with CaSiO3 composition were found as inclusions in diamonds, and are considered to be originally of perovskite structure. To constrain their genesis and consequently the extent of circulation of mantle material, rar e earth element (REE) partitioning between CaSiO3 perovskite and coexisting majoritic garnet (20 GPa, 1520 degrees C) or MgSiO3 perovskite (25 GPa, 16 00 degrees C) was determined by combining the technologies of high-pressure synthesis and trace-element analysis using ion probe. It is consistent wit h previous experiments and confirms that CaSiO3 perovskite is the main REE depository, especially of the light-REE. K-Ce(CaPv/Gt) is similar to 1900, and decreases gradually to 18.5 of K-Yb(CaPv/Gt). For CaPv/MgPv, it decreas es gradually from 57.7 of K-Ce to about 10 of K-Yb. Estimated REE concentra tions in the source lithology of the CaSiO3 inclusions according to these p artitioning coefficients, either peridotitic or eclogitic paragenesis, show strong enrichment in light-REE (e.g. Ce-n 18-163), very different from nor mal mantle peridotite and subducted oceanic crust. It is proposed that inte raction with carbonatic melt in the deep mantle may have played an importan t role in the formation of these CaSiO3 inclusions in diamonds, as well as in their ascending transportation. (C) 2000 Elsevier Science B.V. All right s reserved.