This proposal is to conduct: 1) an in depth study of the isotopic geochemistry of the Re-Os, Sm-Nd and Rb-Sr systems and of platinum group elements in basic and ultramafic rocks for the purpose of studying mantle sources, their differentiation products,and their evolution over the Phanerozoic; and 2) the application of 230Th and other intermediate daughters of the U and Th decay series to the dating of Holocene and late Pleistocene volcanics and the relationship of these volcanics to magma sources and the times of formation of phenocrysts. In addition to samples at hand, filed work will be conducted to obtain very fresh materials at key localities. These problems will be attacked over a three-year period, using newly developed mass spectrometric techniques of negative thermal ion mass spectrometry of the platinum group elements and a new generation high abundance sensitivity mass spectrometer (abundance sensitivity better than 5 x 10-10 for 2 amu) with high transmission. Recently developed analytical chemical procedures will be used to separate elements at ultra low level concentrations efficiently and with negligible contamination. This work should result in new scientific understanding on the origins of the rocks to be studied, as well as the development of improved analytical techniques.
