Geochemical tracing of the source of water dissolved inorganic carbon and chloride in Banks Peninsula warm springs, New Zealand
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Determining the source, transport and fate or crustal fluids is an important problem in modern geoscience. Crustal fluids affect rheology and rock deformation through water-rock interaction at elevated temperatures and pressures. Geothermal resources are a globally significant source of low-carbon energy, and their associated hydrothermal systems are responsible for the formation of most of the world's precious metal deposits. Knowing where fluids originate in the crust, what flow paths they follow, and the conditions under which they discharge to the surface is essential to understanding how rocks, water and volatiles interact. This thesis explores the low-enthalpy warm springs present on Banks Peninsula, New Zealand, an anomalous and understudied example of upper-crustal fluid flow in one of the world's most active orogens. Geochemical tracing of the water in conjunction with soil-gas flux surveying has been applied to three selected localities, Motukarara, Rapaki Bay, and Hillsborough Valley to ascertain the warm spring’s origin and source of heat. This thesis shows the Banks Peninsula warm springs to be an eastward extension of the metamorphic-hydrothermal system associated with the Alpine Fault. Water δ18O, δD, δ13C and soil-gas δ13C values are consistent with a metamorphic hydrothermal system dominated by meteoric water, similar to the Alpine fault hot-springs system. Analyses of the warm springs’ gas and water isotopic and geochemical compositions reveal similar type waters to the Alpine Fault hydrothermal system that has mixed with local Canterbury Aquifer System (CAS) waters. Low temporal variance, combined with the elevated temperatures and localised nature of the Banks Peninsula warm springs suggests a strong structural control on the upper crust fluid flow of this system.