The Iceland Research Drilling Project Crustal Section: Physical properties of some basalts from the Reydarfjordur borehole, Iceland

Thermal, electrical, and other physical property data are reported for a suite of basalts from the core of a 1.9 km hole at Reydarfjordur, eastern Iceland. The principal aim is to add to the literature thermal diffusivity data on basalts. Both lava-flow and dyke-intrusion samples have been measured, in roughly the proportion of their abundances in the drilled section. Density and porosity measurements are in good agreement with values published previously by others. Thermal conductivity values are approximately 10% higher than those published by others, probably because of differences in measurement techniques. Porosity of the samples generally decreases with depth because of increasing infilling of voids and cracks with alteration products. Density, thermal conductivity, thermal diffusivity, and the derived properties grain density and grain conductivity increase with depth, whereas electrical resistivity decreases. Bulk properties of the section have been estimated. They are thermal diffusivity, 0.70 mm2/s (0.70 × 10−6 m2/s); thermal conductivity, 1.97 W/m∙K; bulk density, 2.82 Mg/m3; and porosity, 0.039 (3.9%). Curves modelling in situ electrical resistivity indicate values in the range 50–3000 ?∙m. The electrical structure of the crust in the Reydarfjordur area is apparently different from that in southwest Iceland, probably reflecting a different history of hydrothermal circulation and alteration.