Age of the volcanoes of the Columbretes Islands (Western Mediterranean)

The Columbretes Islands, compose the only volcanic archipelago in the western Mediterranean, and are located on the eastern edge of the Ebro continental shelf, 50 km to the east of the coast of the Iberian Peninsula, and constitute the emerging part of the Columbretes Volcanic Field. Only one volcanic structure is recognised on the surface, corresponding to Columbrete Grande, in which successive phases of hydromagmatic and strombolian volcanic activity are identified. The bathymetric analysis also identifies other monogenetic volcanoes, aligned according to two strikes: a main N170o E direction (formed by more than seven volcanic centres of phonolitic composition and which, at present, appears as small islets) and a second direction, N55o E (which belongs to the two volcanic centres of basic composition, one of which is Columbrete Grande). New K/Ar radiometric dating, along with the reinterpretation of the existing data and current volcanological criteria, allows two periods of main volcanic activity to be recognised: an older period with a basanitic composition (from 0.7 to 0.8 Ma) and a second period, of essentially phonolitic composition (from 0.2 to 0.3 Ma). The well-preserved morphology of submarine volcanoes indicates that volcanic activity has continued until much more recent times.