The NE Rift of Tenerife: towards a model on the origin and evolution of ocean island rifts

The NE Rift of Tenerife is an excellent example of a persistent, recurrent rift, providing important evi-dence of the origin and dynamics of these major volcanic features. The rift developed in three successi-ve, intense and relatively short eruptive stages (a few hundred ka), separated by longer periods of quies-cence or reduced activity: A Miocene stage (7266 ± 156 ka), apparently extending the central Mioceneshield of Tenerife towards the Anaga massif; an Upper Pliocene stage (2710 ± 58 ka) and the lateststage, with the main eruptive phase in the Pleistocene.Detailed geological (GIS) mapping, geomagnetic reversal mapping and stratigraphic correlation, andradioisotopic (K/Ar) dating of volcanic formations allowed the reconstruction of the latest period of riftactivity. In the early phases of this stage the majority of the eruptions grouped tightly along the axis ofthe rift and show reverse polarity (corresponding to the Matuyama chron). Dykes are of normal andreverse polarities. In the final phase of activity, eruptions are more disperse and lavas and dykes areconsistently of normal polarity (Brunhes chron). Volcanic units of normal polarity crossed by dykes ofnormal and reverse polarities yield ages apparently compatible with normal subchrons (M-B Precursorand Jaramillo) in the Upper Matuyama chron. Three lateral collapses successively mass-wasted the rift:The Micheque collapse, completely concealed by subsequent nested volcanism, and the Güímar and LaOrotava collapses, that are only partially filled. Time occurrence of collapses in the NE rift apparentlycoincides with glacial stages, suggesting that giant landslides may be finally triggered by sea level chan-ges during glaciations. Pre-collapse and nested volcanism is predominantly basaltic, except in theMicheque collapse, where magmas evolved towards intermediate and felsic (trachytic) compositions.Rifts in the Canary Islands are long-lasting, recurrent features, probably related to primordial, plume-rela-ted fractures acting throughout the entire growth of the islands. Basaltic volcanism forms the bulk of theislands and rift zones. However, collapses of the flanks of the rifts disrupt their established fissural feedingsystem, frequently favouring magma accumulation and residence at shallow emplacements, leading to diffe-rentiation of magmas, and intermediate to felsic nested eruptions. Rifts and their collapse may therefore act asan important factor in providing petrological variability to oceanic vo