McGovern, L.; Sanders, F.; Rosenberg, M.D.; Seward, A.M.; Chambefort, I; Funnell, R.H. 2021 Thermal properties of Matahina Ignimbrite. Lower Hutt, N.Z.: GNS Science. GNS Science report 2021/33. 36 p.; doi: 10.21420/271T-2T18
Abstract:
Thermal properties of a 140 m section of the Matahina Formation ignimbrite were determined from a rock core drilled near Rotorua, New Zealand. For this project, thermal conductivity, thermal diffusivity and specific heat capacity were determined using the divided-bar methodin order to investigate interrelationships with density/porosity and lithological variation throughout the unit. Thermal conductivity ranged from 0.25 to 1.44 W/(m.K) for dry samples and 1.06 to 2.18 W/(m.K) for water-saturated samples. Specific heat capacity ranged from 675 to 830 J/(K.kg) for dry samples and 800 to 1470 J/(K.kg) for the saturated samples. Thermal diffusivity was determined to range from 4.0 x 10-7 m2/s to 1.6 x 10-6 m2/s for water-saturated samples. Measurements established that both thermal conductivity and thermal diffusivity increasedwith increasing density and the degree of welding. Variations in lithology/minerology and welding were examined through the use of a binocular microscope and Scanning Electron Microscopy. Theoretical trends were calculated for thermal conductivity and specific heat capacity, based on appropriate mixing laws to account for porosity, and average matrix thermal rock properties were determined for this section of the ignimbrite. Measurement data are a good fit to those calculated trends, with some departure explained by variations in crystal content of the ignimbrite. (auth)
