9627324 Deines It is one of the aims of the planned work to examine whether it is possible to establish a chronological 18O record of mantle fluids through a combination of oxygen isotope measurements with other isotopic and geochemical investigations of kimberlitic zircons. From the Jagersfontein kimberlite, South Africa, a suite of xenoliths for which an origin in the transition zone and below can be postulated, has been collected by Dr. Haggerty, University of Massachusetts. These samples provide a unique opportunity to examine the, as yet unknown, oxygen isotope geochemistry of this part of the mantle. The P.I.s plan to carry out a systematic oxygen isotope study on these very deep mantle samples. Studies are planned in three different, but related, settings. The P.I.s will carry out: 1. An examination of the oxygen and radiogenic isotope record of zircons from the Jwaneng and Orapa kimberlites. Dr. N. Shimizu, Woods Hole Institute of Oceanography, who will carry out the geochronological work and trace element measurements on zircons. 2. An investigation of the oxygen isotopic composition of silicate inclusions in diamonds from Orapa. The measurements of the nitrogen content and aggregation state of the host will be coordinated with Dr. J. W. Harris, University of Glasgow. 3. A detailed oxygen isotope study on deep mantle xenoliths. This part will be coordinated with petrographic, mineralogical and geochemical studies by Dr. S. E. Haggerty, University of Massachusetts. All stable isotope studies will be carried out under the supervision of the principal investigator. The work will show whether it is possible to develop a tool for the study of the chronology of mantle fluids, and aid in the characterization of fluids present during diamond formation.
