[¦jē·ō′presh·ə‚rīzd ¦jē·ō¦thər·məl ′sis·təm] (geology) A geothermal system dominated by the presence of hot fluids under high pressure (brine plus methane) and having higher-than-normal temperatures because of their low thermal conductivity, the presence of interbedded shale layers, or the existence of local, exothermic chemical reactions.