Overprinting Hydrothermal Systems in the Taupo Volcanic Zone

Abstract

Numerical reservoir modelling point to geothermal systems in the Taupo Volcanic Zone (TVZ, New Zealand) having lifetimes similar to that of the TVZ itself, with heat fed from below the brittle-ductile transition in the TVZ crust (~8-10 km). The models suggest the geothermal systems are relatively fixed in geographic position, but are not positioned above a localised heat source. Recent work however, suggests localised magmatic intrusions playing a major role in providing heat to TVZ high-temperature hydrothermal systems, with individual hydrothermal systems active for tens of thousands of years. The study of hydrothermal processes and source fluids provides an indication of the evolution of heat source(s) associated with a geothermal system. Traditional petrological techniques, combined with hydrothermal alteration studies, stable isotopic tracers and geochronology can resolve the nature and composition of the fluids involved in the hydrothermal processes and how these might change through time. By mapping hydrothermal mineral occurrences and textural relationships at Kawerau geothermal system, we provide new insights into its thermal and chemical evolution and evidence of distinct hydrothermal events, including inferred input of magmatic-derived fluids and associated with thermal input, over the lifetime of the system.