Taupo Volcanic Zone

At the convergent plate boundaries, CO2 degasses not only from back-arc basins by hydrothermal solutions but also from terrestrial subduction zones by volcanic gases and hydrothermal solutions. However, the studies on CO2 degassing from terrestrial subduction zones are not many. Seward and Kerrich (1996) have shown that hydrothermal CO2 flux from terrestrial geothermal system (such as Taupo volcanic zone in New Zealand) exceeds lO mol/year which is comparable to that of midoceanic ridges (Table 3.4). 

Seward, T.M. and Kerrich, D.M. (1996) Hydrothermal emission from the Taupo volcanic zone. New Zealand. Earth Planet. Sci. Lett., 139, 105-113. 

In the Taupo volcanic zone of New Zealand, the 26.5 ka Oruanui eruption was studied by Charlier and Zellmer (2000). Three fractions of zircons (sub 63 pm 63-125 pm 125-250 pm) were extracted from the rhyolitic pumice, which together with the whole rock respectively define three ages from 5.5 to 12.3 ka before eruption (Fig. 12b). Microscopic observation of the zircons showed that they are composed of a core surrounded by euhedral rims, and the preferred explanation of the authors is that zircons represent mixtures in variable proportions of old crystal cores crystallized 27 ka before eruption and crystal rims crystallized just before eruption. 

Fig. 2. Au concentration in rock chip samples and location of four soil sampling grids. (CVR = Coromandel Volcanic Region TVZ = Taupo Volcanic Zone).

Stoffers P., Hannington M., Wright 1., Herzig P., and de Ronde C. (1999) Elemental mercury at submarine hydrothermal vents in the Bay of Plenty, Taupo volcanic zone. New Zealand. Geology 27(10), 931-934. 

This chapter reviews what is currently known of the source and mobility of As in geothermal systems, as weU as its fate and toxicity in the nearsurface environment. The discussion focuses on two of the most thoroughly studied geothermally active regions Yellowstone National Park in the US, which is mainly drained by the Madison and Yellowstone Rivers, and the Taupo Volcanic Zone in New Zealand, which is drained by the Waikato River (Fig. 1). 

Figure I. a) Yellowstone National Park (USA) and b) Taupo Volcanic Zone (NZ) and their surface drainage system.

Early analyses of As in hot springs of the Taupo Volcanic Zone in New Zealand by Ritchie (1961) revealed a positive correlation between As and Cl which has since been confirmed for most geothermal fields. However, the interpretation of trends in the As/Cl ratio requires caution (Ballantyne and Moore, 1988), as the association is more a function of common behaviour, than of a common source or direct chemical association. The source of the Cl ion may be gaseous HCl associated with magma intrusion, host rock... 

Figure 5. Arsenic mineral precipitates at the Waiotapu geothermal field, Taupo Volcanic Zone, NZ a) An As- and Sb-rich sulphide precipitate in Champagne Pool, b) Yellow orpiment in a small hot. spring.

Robinson, B. H., Brooks, R. R., Outred, H. A., and Kirkman, J. H., 1995, Mercury and arsenic in trout from the Taupo Volcanic Zone and Waikato River, North Island New Zealand Chem. Speciation Bioavad, v. 7, p. 27-32. 

Sarano F, Murphy RC, Houghton BF, Hedenquist JW (1989) Preliminary observations of submarine geothermal activity in the vicinity of White Island Volcano, Taupo Volcanic Zone, New Zealand. J Royal Soc New Zealand 19 449-459... 

Hooker PJ, Bertrami R, Lombardi S, O Nions RK, Oxburgh ER (1985b) Helium-3 anomalies and crast mantle interaction in Italy. Geochim Cosmochim Acta 49 2505-2513 Hulston JR, Lupton JE (1996) Helium isotope studies of geothermal fields in the Taupo volcanic zone, New Zealand. J Vole Geotherm Res 73 297-321... 

Fig. 1. Location of the Taranaki natural gas fields, Taupo Volcanic Zone (TVZ) and the subducting Pacific plate. WK, Wairakei RK, Rotokawa MK, Mokai NM, Ngatamariki BR, Ohaaki-Broadlands RO, Rotorua TT, Tikitere KA, Kawerau.

Table 2. Summary of results for geothermal CO2 and CH4 gases in Taupo Volcanic Zone... 

Christenson B. W., Mroczek E. K., Kennedy B. M., van Soest M. C., Stewart M. K. and Lyon G. (2002) Ohaaki reservoir chemistry characteristics of an arc-type hydrothermal system in the Taupo Volcanic Zone, New Zealand. J. Volcan. Geotherm. Res. 115, 53 -82. 

Giggenbach W. F. (1995) Variations in the chemical and isotopic composition of fluids discharged from the Taupo volcanic zone. New Zealand. J. Volcan. Geotherm Res. 68, 89 116. 

Hulston J. R. (1998) Correlations between B/Cl ratios and other chemical and isotopic components of Taupo Volcanic Zone, NZ geothermal fluids—evidence for water-rock interaction as a major source of boron and gas. In Proc. 9th Int. Symp. Water-Rock Interaction (eds. G. B. Arehart and J. R. Hulston), pp. 629-6 )2. Balkema, Rotterdam. 

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