We have developed equations for the kinetics of 18O/16O exchange between minerals and hydrothermal fluids that can be used as an "oxygen isotope clock". The 18 values of coexisting minerals represent isochrons that can measure the "life-times" and water/rock ratios of fossil hydrothermal systems without doing lengthy computer simulations. We wish to apply these concepts to various rift-zone environments, where enhanced fracture permeability allows deep circulation of surface waters. Shallow, short-lived systems have been well studied, but deeper, longer-lived, and hotter systems transitional to crustal melting are poorly understood. We intend to study such "hydrothermal- anatetic" magmas in: (1) Hercynian-age Metamorphic Systems in Europe, including the classic area of migmatites in the Black Forest, West Germany. (2) Volcanism in Rift-Zone Environments, notably in Iceland, the Great Basin in Nevada, and the Snake River Plain, Idaho. (3) Spreading Centers in Arabia, including a 22 Ma subaerial hydrothermal system (opening of the Red Sea), and a 95 Ma submarine system (Oman ophiolite complex). Also, we need to improve our understanding of the 18O/16O geochemistry of the continental crust and upper mantle, notably in: (4) Detrital Sedimentary Rocks of different types and metamorphic grades to better define the geochemical cycles of 18O/16O and D/H during digeneses, metamorphism and melting. (5) The Ivrea Zone, Northern Italy, perhaps the best available section through the lowermost continental crust. (6) Quaternary- Age Igneous Rocks of Italy. (7) Eclogite and Periodotite Xenoliths to better define fluid-rock interactions in the upper mantle, and to try to identify ancient subducted oceanic crust in these sub-continental lithosphere.
