9725661 Sisson This project will address the metamorphic and structural processes associated with the development of gneissic banding in the migmatitic core of a low-pressure/high-temperature metamorphic belt in the eastern Chugach Mountains, southern Alaska. Two processes which may be responsible for formation of the gneissic banding are: (1) injection of felsic melts or (2) segregation by diffusive mass-transfer. These mechanisms are not mutually exclusive and may occur simultaneously. These two mechanisms predict very different crustal rheologies for the ductile regions in the middle and lower crust. This difference in rheological properties will influence large scale mechanics of the lithosphere. This research will attempt to distinguish between the two mechanisms for development of gneissic banding by looking at textural and compositional differences throughout the transition zone from schistose to gneissic fabrics. The PI will investigate several regions where the width of the metamorphic belt changes from 15-25 km. The proposed work includes detailed flied work to elucidate kinematics of the gneissic transition zone, detailed petrographic studies of both textural and compositional difference, and high resolution computed x-ray tomography.
