Ohaaki reservoir chemistry: Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand
B. W. Christenson, E. K. Mroczek, B. M. Kennedy, M. C. Van Soest, M. K. Stewart, G. Lyon
Situated along the eastern margin of the Taupo Volcanic Zone (TVZ), the high-gas and high-enthalpy production fluids from the Ohaaki geothermal field are chemically similar to other arc-type volcanic systems found along this part of the TVZ. Two thermal upwellings can be distinguished within the field, each apparently emanating from fault structures in the Mesozoic basement greywackes. Although both plumes have similar salinities and appear to be fully equilibrated with the reservoir rocks containing them, fluids associated with the eastern upflow zone are enriched in B and F compared to those in the western upflow zone. δ2H and δ18O signatures for water suggest that up to 20% of the water in the discharges may derive from a magmatic source, and a δ2H-Cl trend established by the East-Bank fluids indicate end-member mixing between a high-Cl fluid and Cl-deficient steam containing as much as 40% arc-type vapour. Gas signatures in fluids from the two production fields show compositional differences that cannot be explained by physical reservoir processes. The eastern fluids have higher N2/Ar and CO2/He ratios, and consistently higher CH4-CO2 13C fractionation temperatures than those in the western upflow zone. In addition, stark differences in 3He/4He and 40Ar/36Ar ratios for the two production fields suggest two-component mixing for the respective source components, with the eastern fluids having a significantly larger radiogenic gas content than those to the west. Collectively, these signatures suggest the presence of a relatively young and shallowly seated degassing intrusive beneath the eastern upflow zone, perhaps as shallow as 4 km beneath the surface.
Journal of Volcanology and Geothermal Research
Fluid chemistry
Magmatic degassing
Magmatic heat sources
Noble gas chemistry
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Christenson, B. W., Mroczek, E. K., Kennedy, B. M., Van Soest, M. C., Stewart, M. K., & Lyon, G. (2002). Ohaaki reservoir chemistry: Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand. Journal of Volcanology and Geothermal Research, 115(1-2), 53-82. https://doi.org/10.1016/S0377-0273(01)00309-2
Ohaaki reservoir chemistry : Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand. / Christenson, B. W.; Mroczek, E. K.; Kennedy, B. M.; Van Soest, M. C.; Stewart, M. K.; Lyon, G.
In: Journal of Volcanology and Geothermal Research, Vol. 115, No. 1-2, 15.06.2002, p. 53-82.
Christenson, BW, Mroczek, EK, Kennedy, BM, Van Soest, MC, Stewart, MK & Lyon, G 2002, 'Ohaaki reservoir chemistry: Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand', Journal of Volcanology and Geothermal Research, vol. 115, no. 1-2, pp. 53-82. https://doi.org/10.1016/S0377-0273(01)00309-2
Christenson BW, Mroczek EK, Kennedy BM, Van Soest MC, Stewart MK, Lyon G. Ohaaki reservoir chemistry: Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand. Journal of Volcanology and Geothermal Research. 2002 Jun 15;115(1-2):53-82. https://doi.org/10.1016/S0377-0273(01)00309-2
Christenson, B. W. ; Mroczek, E. K. ; Kennedy, B. M. ; Van Soest, M. C. ; Stewart, M. K. ; Lyon, G. / Ohaaki reservoir chemistry : Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand. In: Journal of Volcanology and Geothermal Research. 2002 ; Vol. 115, No. 1-2. pp. 53-82.
@article{d759436f2f634e7f9245986de8d60dc2,
title = "Ohaaki reservoir chemistry: Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand",
abstract = "Situated along the eastern margin of the Taupo Volcanic Zone (TVZ), the high-gas and high-enthalpy production fluids from the Ohaaki geothermal field are chemically similar to other arc-type volcanic systems found along this part of the TVZ. Two thermal upwellings can be distinguished within the field, each apparently emanating from fault structures in the Mesozoic basement greywackes. Although both plumes have similar salinities and appear to be fully equilibrated with the reservoir rocks containing them, fluids associated with the eastern upflow zone are enriched in B and F compared to those in the western upflow zone. δ2H and δ18O signatures for water suggest that up to 20% of the water in the discharges may derive from a magmatic source, and a δ2H-Cl trend established by the East-Bank fluids indicate end-member mixing between a high-Cl fluid and Cl-deficient steam containing as much as 40% arc-type vapour. Gas signatures in fluids from the two production fields show compositional differences that cannot be explained by physical reservoir processes. The eastern fluids have higher N2/Ar and CO2/He ratios, and consistently higher CH4-CO2 13C fractionation temperatures than those in the western upflow zone. In addition, stark differences in 3He/4He and 40Ar/36Ar ratios for the two production fields suggest two-component mixing for the respective source components, with the eastern fluids having a significantly larger radiogenic gas content than those to the west. Collectively, these signatures suggest the presence of a relatively young and shallowly seated degassing intrusive beneath the eastern upflow zone, perhaps as shallow as 4 km beneath the surface.",
keywords = "Fluid chemistry, Geothermal, Magmatic degassing, Magmatic heat sources, Noble gas chemistry",
author = "Christenson, {B. W.} and Mroczek, {E. K.} and Kennedy, {B. M.} and {Van Soest}, {M. C.} and Stewart, {M. K.} and G. Lyon",
journal = "Journal of Volcanology and Geothermal Research",
T1 - Ohaaki reservoir chemistry
T2 - Characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand
AU - Christenson, B. W.
AU - Mroczek, E. K.
AU - Kennedy, B. M.
AU - Van Soest, M. C.
AU - Stewart, M. K.
AU - Lyon, G.
N2 - Situated along the eastern margin of the Taupo Volcanic Zone (TVZ), the high-gas and high-enthalpy production fluids from the Ohaaki geothermal field are chemically similar to other arc-type volcanic systems found along this part of the TVZ. Two thermal upwellings can be distinguished within the field, each apparently emanating from fault structures in the Mesozoic basement greywackes. Although both plumes have similar salinities and appear to be fully equilibrated with the reservoir rocks containing them, fluids associated with the eastern upflow zone are enriched in B and F compared to those in the western upflow zone. δ2H and δ18O signatures for water suggest that up to 20% of the water in the discharges may derive from a magmatic source, and a δ2H-Cl trend established by the East-Bank fluids indicate end-member mixing between a high-Cl fluid and Cl-deficient steam containing as much as 40% arc-type vapour. Gas signatures in fluids from the two production fields show compositional differences that cannot be explained by physical reservoir processes. The eastern fluids have higher N2/Ar and CO2/He ratios, and consistently higher CH4-CO2 13C fractionation temperatures than those in the western upflow zone. In addition, stark differences in 3He/4He and 40Ar/36Ar ratios for the two production fields suggest two-component mixing for the respective source components, with the eastern fluids having a significantly larger radiogenic gas content than those to the west. Collectively, these signatures suggest the presence of a relatively young and shallowly seated degassing intrusive beneath the eastern upflow zone, perhaps as shallow as 4 km beneath the surface.
AB - Situated along the eastern margin of the Taupo Volcanic Zone (TVZ), the high-gas and high-enthalpy production fluids from the Ohaaki geothermal field are chemically similar to other arc-type volcanic systems found along this part of the TVZ. Two thermal upwellings can be distinguished within the field, each apparently emanating from fault structures in the Mesozoic basement greywackes. Although both plumes have similar salinities and appear to be fully equilibrated with the reservoir rocks containing them, fluids associated with the eastern upflow zone are enriched in B and F compared to those in the western upflow zone. δ2H and δ18O signatures for water suggest that up to 20% of the water in the discharges may derive from a magmatic source, and a δ2H-Cl trend established by the East-Bank fluids indicate end-member mixing between a high-Cl fluid and Cl-deficient steam containing as much as 40% arc-type vapour. Gas signatures in fluids from the two production fields show compositional differences that cannot be explained by physical reservoir processes. The eastern fluids have higher N2/Ar and CO2/He ratios, and consistently higher CH4-CO2 13C fractionation temperatures than those in the western upflow zone. In addition, stark differences in 3He/4He and 40Ar/36Ar ratios for the two production fields suggest two-component mixing for the respective source components, with the eastern fluids having a significantly larger radiogenic gas content than those to the west. Collectively, these signatures suggest the presence of a relatively young and shallowly seated degassing intrusive beneath the eastern upflow zone, perhaps as shallow as 4 km beneath the surface.
KW - Fluid chemistry
KW - Geothermal
KW - Magmatic degassing
KW - Magmatic heat sources
KW - Noble gas chemistry
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research