Heat Production and Thermal Conductivity in Mainland Portugal

Abstract

Temperature distribution within the Earth affects a great deal of phenomena and properties of earth materials. To understand the geophysical and geodynamic behaviour and evolution of the interior of the Earth is essential knowing its temperature distribution and thermal regime. One of the most important quantities to estimate the temperature distribution inside the Earth is heat flow density. In principle, with heat flow density values measured at the surface of the Earth and integrating the heat conduction equation, with the appropriate boundary conditions, it is possible to estimate the temperature distribution down to the Moho and deeper. However, temperature distribution in the lithosphere is highly dependent on the thermal conductivity and heat production of the geologic formations. In this contribution, a compilation of laboratory measurements of thermal conductivity and heat production for some geological formations that outcrop in Mainland Portugal are presented and are used to extrapolate measured surface temperatures to the crust and, in some cases, to the lithosphere. Heat flow density in Mainland Portugal varies from 42 to 115 mW/m2. These values are similar to heat flow densities obtained in other European Hercynian regions and allow inferring that temperatures at Moho depth should not be higher than about 700 ºC. One and two dimensional geothermal modelling suggests that in southern Portugal heat production in the crust must be as high as 4.8 μW/m3, which is higher than previously suspected for the area and higher than measured values for surface rocks.