Palaeomagnetic evidence for the origin of Madeira

The remanent magnetization of ‘basement’ volcanics from Madeira define three different axes of magnetization, each having a dual-polarity build-up. The suggested oldest of these components, with declination 302 and inclination +4, is assigned to the late Lower Cretaceous and is thought to reflect the age of the early volcanism of the island. Subsequent magnetization overprints seem to have occurred in the Late Cretaceous/Early Tertiary (minor) and in Neogene times, respectively. The latter magnetization, which is strongly developed, was most likely impressed during the extensive volcanism that swept the island in post-Late Miocene. The palaeomagnetic evidence for a Cretaceous origin of Madeira is supported by the finding of Lower-Middle Cretaceous tuff layers in DSDP site 136 which is located only 160 km north of the island. The inferred palaeomagnetic structure of the ‘basement’ rocks of Madeira is similar to that found in the old volcanic complexes of other east central Atlantic islands.