Structural model of El Hierro (Canary Islands) from aeromagnetic data: implications for the definition of rift zones in volcanic islands

Resumen

The subaerial part of the island of El Hierro shows the characteristic shape of three convergent ridges that has been interpreted as a triple-arm rift system. We analyzed an aeromagnetic anomaly data set acquired in 1993 by the Spanish National Geographic Institute. A digital elevation model of the volcanic edifice was divided into a mesh of prismatic cells and a three-dimensional magnetic inversion algorithm was applied. High magnetization values have been mainly interpreted as intrusive complexes on which rift zones are rooted. Their location confirms the hypothesis of a complex rift structure in the marine area. The inverse magnetization that characterizes the NE submarine rift area implies that this part of the volcanic edifice formed during the Matuyama and predates the W submarine rift zone, which is normally magnetized. The feeding system of the N-S rift zone extending southwards from the island seems to be shifted to the west with respect to the bathymetric ridge. This result suggests that the original rift zone was located in the area where the highest magnetizations presently occur so that the present morphology may reflect the westward collapse of the original ridge. In addition, very low magnetizations characterize the areas affected by giant landslides.