Palaeomagnetism of the British Tertiary igneous province: Rhum and Canna

Palaeomagnetic measurements have been made on samples of lavas, dykes and plutonic rocks from Rhum, and of lavas and dykes from Canna. All the samples are reversely magnetized, except for three dykes cutting the Rhum lavas and two dykes cutting the Canna lavas. The magnetizations are believed to be primary, or to have been acquired only a short time after the units were formed. The simplest interpretation of the polarities is that the majority of the rocks were formed in a single reversed interval, with the normally magnetized dykes being intruded in the following normal interval. However, if the time during which the Rhum centre was eroded, prior to the extrusion of the lavas, was long, additional inversions of the Earth's magnetic field could have escaped detection. In this case the polarity sequence is extended from R—N to R… N … R—N, with the final R—N corresponding to the lavas and the normal dykes cutting them. Igneous activity began about 59 Ma ago, contemporary with activity elsewhere in the British Tertiary igneous province.