Mineral Chemistry of Mantle Eclogites

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This project will utilize various analytical and theoretical methods to better understand the origin of eclogite inclusions in kimberlites of southern Africa. The first objective is to characterize the major and trace element and stable and radiogenic isotopic relationships among primary phases. The P.I. will complete and publish the results of a preliminary study on a chemically diverse suite of samples, including data on major and trace elements, and oxygen and Sm-Nd and Rb-Sr isotopes. To do this he will require additional oxygen isotopic data on coesite and Sm-Nd and Rb-Sr data on garnet. In addition to completion of the preliminary study, he will undertake crystal chemical modeling of major and trace element and oxygen isotope fractionation in these rocks, based on compressibility measurements and additional structure refinements at room temperature and elevated temperature. A second objective is to characterize the major and trace-element chemistry of the secondary phases that have formed in small veins and grain boundaries in these samples, and appear to be the result of metasomatism at depth. This will be done by electron microprobe together with analytical SEM and TEM micropetrography of these phases which appear to be chemically related to the host eclogite. These studies should better define the causes of eclogite compositional variation which will yield a greater understanding of the chemical dynamics of the upper mantle. Funding of this proposal at a level reduced from the originally requested $123,603 will result in fewer analyses and reduced usage of the analytical TEM, which is the most expensive of the analytical techniques. We also will be unable to support a full- time graduate student in this study, although we do anticipate having student support from other sources which may be partly applied to this project. Also, support for T. McCormick is slightly reduced from 25% to 20% of full-time. The attached revised budget at approximately $78,400 over two years reflects these changes. At the funding level of the attached revised budget, we anticipate significant progress in understanding the chemical dynamics of the upper mantle over the next two years.