STRUCTURAL SETTINGS OF HYDROTHERMAL OUTFLOW - FRACTURE PERMEABILITY MAINTAINED BY FAULT-PROPAGATION AND INTERACTION

Hydrothermal outflow occurs most commonly at the terminations of indiv idual faults and where multiple faults interact. These areas of fault propagation and interaction are sites of elevated stress termed breakd own regions. Here, stress concentrations cause active fracturing and c ontinual re-opening of fluid-flow conduits, permitting long-lived hydr othermal flow despite potential clogging of fractures due to mineral p recipitation. As fault systems evolve, propagation, interaction, and l inkage of fault segments result in the migration and eventual localiza tion of breakdown regions in kinematically favorable sites such as fau lt bends or fault intersections. Concurrent migration of hydrothermal outflow sites along with these areas of elevated permeability leads to predictable patterns of hydrothermal deposition along fault zones. Th us, the distribution of active outflow sites and preserved deposits al ong fault zones can potentially provide a tool for studying fault-zone evolution. (C) 1997 Elsevier Science B.V.