| Precambrian crystalline basement forms the core of an imbricated antiformal culmination within northern Utah. ;Estimated deformation conditions within the basement are T ;Distinct changes in strain, chemistry, mineralogy, and textures occur across DDZs. DDZs are characterized by phyllonitic cleavage, pervasive alteration, and large plastic strains. A bounding transition region is characterized by crack networks, variable alteration, and mixed cataclastic and plastic deformation. Basement between DDZs consists of relatively unaltered gneiss. Estimated axial ratios increase rapidly in the transition region and are ;A simple model for growth of deformation zones predicts strain profiles and width versus displacement relations that are consistent with natural examples. Fracture propagation favors instability, fluid circulation, and chemical alteration, whereas sealing and healing remove damage, increase strength, and reduce fluid flow. Representative times for these processes may be less than 10000 years for reasonable physical conditions, and are sensitive to stress, fluid composition, and temperature. |
