Paleomagnetic estimates of temperatures reached in contact metamorphism

A paleomagnetic study of some Silurian-Devonian lavas from the Lorne Plateau, Scotland, locally reheated by the intrusion of small Tertiary dikes, has shown that a laboratory equivalent of the actual peak temperature reached in the reheating can be accurately determined. Theoretically derived corrections are applied to the experimentally determined temperatures to obtain an estimate of the actual peak temperatures reached in a series of samples across the contact zones. These corrected experimental profiles can be compared with peak-temperature profiles calculated from heat-conduction models. The two profiles fit well when the temperatures of the lavas immediately prior to the intrusion are taken into account. Ambient-temperature estimates of 75 ± 25 °C and 150 ± 25 °C have been obtained for the lavas before intrusion by a normally magnetized dike and a reversely magnetized dike, respectively.