9628083 Zindler This proposal describes a detailed chemical and isotopic study of olivine tholeiites and picrites from three main localities in Iceland. It will focus on development of a quantitative understanding of the factors that cause variations in the degree of U-Th disequilibrium in these rocks. The principal goal of the project is to explore and quantify the effects of variations in the depth of melting and source composition on U-Th disequlibrium, absent the complications of age-uncertainty inherent in direct investigations of MORBs. Samples will be collected during field seasons early in the first and third years of the project. In addition, the study will make use of existing well-characterized sample suites. The main stage of data acquisition will occur during the first two years and result in detailed isotopic and geochemical characterization of approximately 75 samples. The second stage of data acquisition will occur during the third year of the project, and will focus on important targets identified by the earlier work. The results of this investigation are expected to lead to substantial improvement in the utility of the U-Th method as a tool for studying MORBs and other mantle-derived volcanics.
