Oxygen buffering of Kilauea volcanic gases and the oxygen fugacity of Kilauea basalt
- Geological Survey, Vancouver, WA (United States)
Volcanic gases collected during episode 1 of the Puu Oo eruption along the east rift zone of Kilauea Volcano, Hawaii, have uniform C-O-H-S-Cl-F compositions that are sharply depleted in CO[sub 2]. The CO[sub 2]-poor gases are typical of Type II volcanic gases (GERLACH and GRAEBER, 1985) and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing CO[sub 2]-rich gases during an earlier period of temporary residence in the summit magma chamber. The samples are remarkably free of contamination by atmospheric gases and meteoric water. Thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032[degrees]C. Open- and closed-system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling. These models indicate that the F[sub o[sub 2]] buffering process occurs by transfer of oxygen from the major species in the gas phase (H[sub 2]O, CO[sub 2], SO[sub 2]) to the lava during cooling and that the transfer of oxygen also controls the fugacities of several minor and trace species (H[sub 2], CO, H[sub 2]S, S[sub 2], Cl[sub 2], F[sub 2]), in addition to O[sub 2] during cooling. Gas/lava exchanges of other components are apparently insignificant and exert little influence, compared to oxygen exchange, during cooling. Oxygen transfer during cooling is variable, presumably reflecting short-term fluctuations in gas flow rates. Higher flow rates restrict the time available for gas/lava oxygen transfer and result in gases with higher equilibrium temperatures. Kilauea basalt either arrives in the crust with an oxygen fugacity between NNO and FMQ, or it develops an oxygen fugacity in this range immediately upon arrival in the summit chamber.
- OSTI ID:
- 6648149
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 57:4; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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