Previous investigation of the garnet granulite-eclogite facies transition exposed on Holsnoy Island, southwest Norway, suggests that seismic velocity and density increases across a sharp (<1 m thick) transition. The magnitude of the changes are postulated to be related to compositional changes (silica depletion and relative enrichment of Fe2O3, MgO, and CaO) caused by fluid transport during metamorphism plus fabric development during deformation. Detailed sampling, using paleomag drills, across the exposed reaction fronts will be carried out to test this idea. Resultant mineralogical and chemical compositional determinations will be compared to seismic velocity measurements at high confining pressure in order to understand the factors controlling the variations in velocity. Detailed petrofabric analysis of major mineral phases in eclogites and granulites will be made with standard U-stage methods. Seismic velocity will be calculated from the preferred orientation data and tested against velocities determined in the laboratory at high confining pressure.
