HYDROGEN AND OXYGEN ISOTOPIC COMPOSITIONS OF WATERS FROM FUMAROLES ATKILAUEA SUMMIT, HAWAII

Condensate samples were collected in 1992 from a high-temperature (300 degrees C) fumarole on the floor of the Halemaumau Pit Crater at Kila uea. The emergence about two years earlier of such a hot fumarole was unprecedented at such a central location at Kilauea. The condensates h ave hydrogen and oxygen isotopic compositions which indicate that the waters emitted by the fumarole are composed largely of meteoric water, that any magmatic water component must be minor, and that the precipi tation that was the original source to the fumarole fell on a recharge area on the slopes of Mauna Loa Volcano to the west. However, the fum arole has no tritium, indicating that it taps a source of water that h as been isolated from atmospheric water for at least 40 years. It is n oteworthy, considering the unstable tectonic environment and abundant local rainfall of the Kilauea and Mauna Loa regions, that waters which are sources to the hot fumarole remain uncontaminated from atmospheri c sources over such long times and long transport distances. As for th e common, boiling point fumaroles of the Kilauea summit region, their O-18, D and tritium concentrations indicate that they are dominated by recycling of present day meteoric water. Though the waters of both ho t and boiling point fumaroles have dominantly meteoric sources, they s eem to be from separate hydrological regimes. Large concentrations of halogens and sulfur species in the condensates, together with the loca tion at the center of the Kilauea summit region and the high temperatu re, initially suggested that much of the total mass of the emissions o f the hot fumarole, including the H2O, might have come directly from a magma body. The results of the present study indicate that it is unre liable to infer a magmatic origin of volcanic waters based solely on h alogen or sulfur contents, or other aspects of chemical composition of total condensates.