The proposed research will investigate the mechanism of isotopic and chemical interaction between metasomatic fluid and upper mantle assemblages. Xenolith samples from South African kimberlites and alkali basalts for the southwestern United States have been chosen for study. Neoblasts, porphyroclasts, and non-recrystallized phases will be analyzed for REE, LILE (Ba, Sr, Rb, Na, K) and HFSE (Ti, Nb, Zr, Hf, Ta) by a combination of electron microprobe and SIMS to discern the relationship of incompatible trace element geochemistry to recrystallization. Possible variations in oxidation state associated with textural variations will also be investigated. Isotopic measurements (87Sr/86Sr, and 143Nd/144ND) will be made on separates of porphyrocalsts and neoblasts of olivine and orthopyroxene to determine whether isotopic compositions vary systematically with grain size. In addition, isotopic measurements for garnet, clinopyroxene, and when possible minor phases (i.e. oxides or mica) will be determined so that the total data set can be combined with data for garnet and spinel lherzolites from basalts. This investigation will add to the understanding of the upper mantle processes which result in metasomatism.
