Kimberlites from the Kaapvaal craton have sampled numerous mantle garnet lherzolites in addition to garnet harzburgites. Trace element characteristics of constituent clinopyroxenes allow two groups of garnet lherzolites to be distinguished. Trace element compositions of all clinopyroxenes are characterized by enrichment in light rare earth elements (LREE) and large ion lithophile elements and by a relative depletion in Ti, Nb, Ta, and to a lesser extent Zr and Hf. However, the LREE enrichment and the depletion in Nb and Zr (Hf) are less in the Type 1 clinopyroxenes than in the Type 2 clinopyroxenes. Our study suggests that the two melts responsible for the metasomatic imprints observed in the two garnet lherzolite groups are highly alkaline mafic silicate melts. Type 1 clinopyroxenes that have trace element similarities to those of PIC (Phlogopite–Ilmenite–Clinopyroxene) rocks appear to have crystallized from, or been completely equilibrated with, the same melt related to Group I kimberlite magma. The Type 2 clinopyroxenes have trace element similarities to those of MARID (Mica– Amphibole–Rutile–Ilmenite–Diopside) rocks and are therefore probably linked to melt related to Group II kimberlite magma.

Mantle xenoliths in alkaline lavas of the Kerguelen Islands consist of: (1) protogranular, Cr-diopside-bearing harzburgite; (2) poikilitic, Mg-augite-bearing harzburgite and cpx-poor lherzolite; (3) dunite that contains clinopyroxene, spinel phlogopite, and rarely amphibole. Trace element data for rocks and minerals identify distinctive signatures for the different rock types and record upper-mantle processes. The harzburgites reflect an initial partial melting event followed by metasomatism by mafic alkaline to carbonatitic melts. The dunites were first formed by reaction of a harzburgite protolith with tholeiitic to transitional basaltic melts, and subsequently developed metasomatic assemblages of clinopyroxene + phlogopite ± amphibole by reaction with lamprophyric or carbonatitic melts. We measured two-mineral partition coefficients and calculated mineral–melt partition coefficients for 27 trace elements. In most samples, calculated budgets indicate that trace elements reside in the constituent minerals. Clinopyroxene is the major host for REE, Sr, Y, Zr and Th; spinel is important for V and Ti; orthopyroxene for Ti, Zr, HREE, Y, Sc and V; and olivine for Ni, Co and Sc.