North-East Atlantic Islands: The Macaronesian Archipelagos

Abstract

The archipelagos located at the central-eastern section of the North Atlantic (Azores, Madeira, Canary Islands and Cape Verde), known collectively as the Macaronesian islands, share many similarities and some significant differences. They are oceanic-island magmatic systems, believed to represent the activity of mantle plumes, with similar varieties in magma composition, being Ocean Island Basalt-type that may be evolving in some cases to more felsic magma compositions. Their most significant differences derive from their diverse geodynamic settings, allowing them to be separated into two contrasting groups: The Azores, situated in an active plate margin context, i.e., a region defined by major tectonic fractures, and the Madeira, Canary Islands and Cape Verde archipelagos, located adjacent to the African coastline in a passive margin setting, largely lacking the influence of active regional fracture tectonics. A significant consequence is a lack of internal age progression in the islands in the fracture-controlled settings (e.g., Azores islands), which is observed, however, in all three passive margin archipelagos. Other contrasting features are the island shapes, usually elongated and fracture parallel in the Azores, but more rounded and cluster-like in Madeira, the Canaries and the Cape Verde Islands. Finally, the fracture-controlled Azores islands are characterized by frequent and intense seismic activity, which is often associated with significant loss of life, while the other three Macaronesian island groups are far less seismically active, with generally lower magnitudes and no recorded fatalities from earthquakes in historical time.