Hotspot volcanism close to a passive continental margin: The Canary Islands

Abstract

The Canarian Archipelago is a group of volcanic islands on a slow-moving oceanic plate, close to a continental margin. The origins of the archipelago are controversial: a hotspot or mantle plume, a zone of lithospheric deformation, a region of compressional bock-faulting or a rupture propagating westwards, from the active Atlas Mountains fold belt have been proposed by different author. However, comparison of the Canarían Archipelago with the prototypical hotspot-related island group, the Hawaiian Archipelago, reveals that the differences between the two are not as great as had previously been supposed on the basis of older data. Quaternary igneous activity in the Canaries is concentrated at the western end of the archipelago, close to the present-day location of the inferred hotspot. This is the same relationship as seen in the Hawiian and Cape Verde islands. The latter archipelago, associated with a welldefined but slow-moving mantle plume, shows anomalies in a plot of island age against distance which are comparable to those seen in the Canary Islands: these anomalies cannot therefore be used to argue against a hotspot origin for the Canaries. Individual islands in both archipelagoes are characterized by initial rapid growth (the 'shieldbuilding' stages of activity), followed by a period of quiescence and deep erosion (erosion gap) which in turn is followed by a 'post-erosional' stage of activity. The absence of post-shield stage subsidence in the Canaries is in marked contrast with the major subsidence experienced by the Hawiian Islands, but is comparable with the lack of subsidence evident in other island group at slow-moving hotspots, such as the Cape Verdes. Comparison of the structure and structural evolution of the Canary Islands with other oceanic islands such as Hawii and Réunion reveals many similarities. These include the development af triple ('Mercedes Star`) rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones. The apparent absence of these features in the post-erosional islands may in part be a result of their- greater age and deeper- erosion, which has removed much of the evidence for their early volcanic architecture. We conclude that the many similarities between the Canary Islands and island groups whose hotspot origins are undisputed show that the Canaries have been produced in the same way.