| Title | Towards a national temperature model for New Zealand |
|---|---|
| Authors | A. Kirkby, R. Funnell, P. Scadden, M. Sagar, A. Seward |
| Year | 2023 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | temperature, thermal conductivity, heat production, numerical modelling |
| Abstract | Knowledge of crustal temperature is important in expanding geothermal energy use across New Zealand, including low temperature direct use applications. However, crustal temperature distribution across much of New Zealand is not well known, despite New Zealand’s extended history of developing geothermal resources. We are developing a national temperature map using a 1D transient heat flow model. To support the model, we have established thermal properties measurement capability and are using measurements from this in conjunction with geochemical and mineralogical data to estimate thermal properties. Development of other model inputs is ongoing. In this paper we discuss the thermal regime in three locations to demonstrate the impact of different processes occurring across the relatively young and tectonically active landmass of New Zealand. The Taupō Volcanic Zone is well known for extremely high heat output but the temperature gradient is strongly variable in this region due to fluid convection. Here, a conductive heat flow model will not be applicable, and so an alternative approach may be required. On the Alpine Fault, our transient 1D heat flow model estimates that the surface heat flow is enhanced by a factor of three due to Quaternary uplift and erosion; there are likely to be additional topographic and fluid flow effects for which the model does not account. In Wanganui, western North Island, our model predicts that the near surface heat flow is depressed by 20 mW/m2as a result of Plio–Pleistocene basin formation. In both regions, the effect of transient processes is present to depths of >20 km. Thus, Neogene processes leave a strong pervasive transient signal that extends to at least the mid crust. |