Thermal conductivity, density and porosity of sedimentary and metamorphic rocks from the Lower and Higher Himalaya, Western Himalaya, India

Abstract

SUMMARY Thermal conductivity at ambient conditions is a vital parameter in the determination of heat flow, thermal modelling and various geoengineering purposes. We have measured thermal conductivity in the laboratory at ambient conditions using a steady-state method on 69 samples of sedimentary and metamorphic rocks from the Western Himalaya, India, for the first time covering major lithologies of the region. Density and porosity measurements have been carried out along with petrographic and geochemical studies to characterize these rocks. The investigated rocks include sandstone, limestone, dolomitic limestone, quartzite, slate, phyllite and schist. The average thermal conductivity is found to be the highest (5.4 W m–1 K–1) for quartzite, moderate (ranges between 3.2 and 4.2 W m–1 K–1) for sandstone, limestone and dolomitic limestone and lowest (ranges between 2.6 and 2.9 W m–1 K–1) for the slate, phyllite and schist. The average values of the porosity for the rocks are less than 2 per cent. The variations in thermal conductivity within each rock type more or less reflect the compositional change, rather than the porosity. The measured thermal conductivity of the sandstone and limestone is found much higher than usually observed in such rocks, while it is on the lower side in the case of quartzite, phyllite and schist. Moreover, sedimentary rocks have higher density and lower porosity than usually found in such rocks. In fact, in this region, the sedimentary rocks show a similar density to that of the metamorphic rocks. The average density in sedimentary and metamorphic rocks varies from 2590 to 2780 kg m–3 and 2630 to 2740 kg m–3, respectively. The study region comes under the seismic gap, and several hot springs also exist here. Therefore, the obtained results will be useful in thermal modelling, which is critical for the understanding of earthquake nucleation.