The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at suprasolidus conditions,with variable concentrations of fluid-mobile incompatible trace elements.At ultrahigh-pressure(UHP) metamorphic conditions,supercritical fluids of intermediate compositions may occur with enhanced capability of dissolving and transporting incompatible trace elements.The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at high-pressure to UHP conditions.While breakdown of hydrous minerals such as phengite and lawsonite is a key to fluid activity in the subduction factory,water released from nominally anhydrous minerals provides an additional source for the fluid activity during exhumation of UHP crustal rocks.