The evolution of the upper mantle will be examined by analysis of compositional zonation of minerals of xenoliths. Electron and proton probe analysis will be combined to provide data both for major elements and for trace elements to levels of a few parts per million. The results will be related to numerical simulations and to models in order to understand both processes and their rates. Data on minerals in xenoliths with high equilibration temperatures will provide information on the movement of melts in the mantle and on the compositional evolution of "fertile" peridotite. The zonations of major and trace elements will be used to interpret substitution mechanism, partition coefficients, and interdiffusion effects in garnets. The temperature-composition histories of coarse-textured xenoliths with Cr-Al zoned garnets will be modeled, in order to learn how thermal events in the lithosphere are recorded by peridotite minerals at temperatures below 1100 C.
