Members of our team have demonstrated the first source-to-surface models of the central Taupō Volcanic Zone hydrothermal system in a 2D setting. And they have used these models to investigate the nature of the high-temperature geothermal systems and long-term fluid production and reinjection from them.
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The models represent a simplified geological setting with a 20 km-wide continental rift, based on observations from New Zealand’s Taupō Rift in the central North Island. This is the target zone for future supercritical and super-hot resource developments, and this model provides fundamental information about the shallow (2 km) locations of geothermal systems and the deeper (10 km) heat sources.
The model represents deeper magmatic intrusion into the lower crust with a 700°C to 900°C hotplate source at 10 km depth, but considers no other shallow magma bodies. The effective heat flux at the hotplate is 0.77 W/m2. In the model, low-permeability basement-like rocks define the rift margins and basement, which is then covered with volcanic infill. The permeability within the rift decreases with depth in such a way as to match the above-mentioned temperature range, and to respect geophysical constraints, from seismicity and magnetotellurics.
The models produce unsteady, irregular rift-scale hydrothermal circulation in the upper ~5 km of the crust. Plumes of hot water (see figure above) are interpreted as high-temperature geothermal systems, with temperatures of ca. 300°C at 2 km depth.
The shallow volcanics control the amount of cool surface water entering the rift scale hydrothermal system. Models with low permeability for the shallow volcanics produce longer lasting and higher temperature geothermal systems, and those with high permeability produce fewer and cooler geothermal systems.
These models and ongoing developments, such as extension to a 3-D setting, can be used as a basis for exploring the behaviour of the geothermal systems in response to long-term geothermal fluid extraction and addressing options for sustainable use of the geothermal resource.
This study and its authors were supported by our GNG programme, as well as GNS Science-led SSIF-funded geothermal research programmes, and the MBIE-funded the ECLIPSE project.