Thermal properties of gneisses and amphibolites - high pressure and high temperature investigations of KTB-rock samples

The German Continental Deep Drilling Program (KTB) provided the opportunity to carry out a number of different investigations on the same rocks. So, factors influencing thermal transport properties could be quantified. Measurements of thermal diffusivity of amphibolites result in (0.8 +/- 0.2) x 10(-6) m(2) s(-1) under ambient conditions. New data are given for pressure and temperature dependence of thermal transport properties. The comparison of the effect of uniaxial and hydrostatic pressure yields a different behaviour in the lower pressure range up to 50 MPa. Linear relationships between thermal transport parameters and pressure are observed in the pressure range from 50 up to 1000 MPa with pressure coefficients (0.75 +/- 0.41) x 10(-1) GPa(-1) and (0.61 +/- 0.30) x 10(-1) GPa(-1) for the thermal conductivity and thermal diffusivity, respectively. Temperature has a stronger influence on the thermal conductivity than pressure with respect to depth. Thermal diffusivity decreases in the order of 30% from the Earth's surface up to 10 km depth. The anisotropy of the thermal parameters does not depend on pressure and water saturation but it strongly decreases at high temperature. (C) 1998 Elsevier Science B.V. All rights reserved.