A collaboration between petrologists and geochemists of the Carnegie Institution of Washington, Washington, D.C., and the Institute of Geology and Geophysics, Novosibirsk USSR, will be organized to carry out chemical and isotopic research on xenoliths of mantle rocks erupted in Siberian kimberlites. Soviet scientists will participate in the research performed in Washington in visits ranging from 2 to 8 weeks. Development of models for the origin of continental cratons with their massive mantle roots has been based in considerable part on investigations of xenoliths from southern Africa. Further progress requires comparative study. The Siberian craton is best suited because xenoliths are abundant and because extensive collections and basic research have been carried out by Soviet investigators. Attention will be focused on low-temperature, craton-forming peridotites and on megacrystalline dunites that sometimes contain diamonds. Bulk analyses will permit comparison of the Karpvaal and Siberian cratons. Analyses for Os, Sr, Nd and Pb will be virtually the first performed on SIberian mantle rocks and may provide records of craton evolution that have been obscured in African xenoliths by post-Archaean metasomatism. Insights to the timing and nature of diamond-forming processes and to the location and distribution of Re and Os in mantle minerals will be sought.
