| Abstract |
Low enthalpy geothermal resources are widely distributed in New Zealand and include (1) hot spring systems with <90oC discharge waters in the North and South Islands and offshore islands to the north of North Island, (2) peripheries of high-enthalpy geothermal systems within the Taupo Volcanic Zone, (3) 120-160oC waters at >3.5 km depth in abandoned hydrocarbon wells, (4) natural heat flow below 15-20 m from the surface. Hot spring systems in New Zealand are found in four major tectonic settings characterized by (1) subduction-related volcanism and rifting in the Taupo Volcanic Zone, (2) intraplate volcanism and associated hot mantle upwelling or deep-seated mantle upwelling in a continental rift zone, (3) rapid rise of heated waters along faults in the North Island forearc, and (4) rapid uplift and thrusting along the Alpine Fault Zone in South Island and parts of the North Island forearc. Most hot spring waters, outside the main high-enthalpy geothermal areas of the Taupo Volcanic Zone and Ngawha, are derived from deeply circulating meteoric waters that may sometimes bear imprints of mantle-derived volatiles, saline formation water or metamorphic water. Within the North Island forearc, saline reservoir waters originate from seawater and the dehydration of marine clays. New Zealand has an installed thermal power of 308 MWt. A conservative estimate, of the total annual extractable energy from all the low-enthalpy sources in the country, amounts to 55.7 PJ. Of these only 10% is being exploited at present, for direct utilization of heat. |