Modeling of Cooling Plutons in the Taupo Volcanic Zone, New Zealand

Modeling carried out using a super-critical version of TOUGH2 has been used to investigate different source models for the geothermal fields in the Taupo Volcanic Zone (TVZ), New Zealand. The models describe the cooling, by groundwater circulation, of magmatic intrusions into the upper 8 km of the crust. By comparing the calculated surface heat flux from these intrusions with actual thermal outputs in the TVZ, limits can be placed on the size of such magma bodies. Typically, many intrusions are required to provide the heat for a geothermal field like Wairakei. An ‘entrainment’ mechanism is identified that can explain the apparent stability of the TVZ geothermal fields over timescales many times longer than the cooling time for an individual intrusion.