Thermal properties of granulite facies rocks in the Precambrian basement of Finland and Estonia

We present results of heat production, thermal conductivity and P-wave velocity measurements of 252 rock samples from five granulite facies areas in Finland and Estonia. These compositionally mainly intermediate Archaean and Palaeoproterozoic metamorphic rocks have relatively high heat production values, Mean values averaged by areas range from 0.57 to 2.24 mu W m(-3). The lowest values are in the Varpaisjarvi area, which is the oldest and most mafic and where the highest metamorphic pressure occurred (8-11 kbar), whereas the highest heat production is found in the Turku granulite belt where the metamorphic pressure was 4-6 kbar. The heat production decreases with the increase of the metamorphic pressure. However, a general numerical relationship cannot be presented because of considerable variations in heat production data. There is no significant difference in the metamorphic temperatures of the studied granulites and therefore no dependence on temperature is found. Further, our data suggest no relationship between heat production and P-wave velocity. The mean thermal conductivity of granulites varies from 3.0 to 3.5 W m(-1) K(-1). Slightly elevated thermal conductivity values in the Varpaisjarvi and Lapland granulite areas can be attributed to higher sillimanite and quartz contents, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.