K-Ar ages and magnetic stratigraphy of a hotspot-induced, fast grown oceanic island: El Hierro, Canary Islands

Abstract

The combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands. This method has been successfully applied on the island of El Hierro, the westernmost island of the Canaries Archipelago. For the emerged part of this island, built in the last 1.2 Ma, magnetic stratigraphy and mapping show the presence of four consecutive subchrons. K-Ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy. The ages show that the magnetic polarity zones correlate to the upper part of the Matuyama and to the Brunhes chrons. The Jaramillo normal polarity subchron of the upper part of the Matuyama reverse polarity Chron is recorded in one of the lava sequences. The lower limit of this event is constrained by two ages of 1.04 ± 0.02 Ma and one of 1.05 ± 0.02 Ma, close to the value deduced from the astronomically tuned magnetic polarity time scale (APTS). The volcanic history can be summarised by two consecutive main basaltic volcanic edifices: the El Tinor, active during the upper part of the Matuyama Chron and the El Golfo edifice, constructed during the Brunhes Chron.